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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

Transequatorial propagation through equatorial plasma bubbles - Discrete events  

NASA Astrophysics Data System (ADS)

The discrete nature of VHF transequatorial propagation path openings is pointed out. These events are shown to be consistent with the concept of guided propagation inside equatorial plasma bubbles. The important prediction of this work is that observations on discrete transequatorial VHF links may be used to track the production and development of equatorial plasma bubbles.

Heron, M. L.

1980-08-01

3

Equatorial plasma bubbles with enhanced ion and electron temperatures  

Microsoft Academic Search

While the ion and electron temperatures inside equatorial plasma bubbles (EPBs) are normally lower than those in an ambient plasma, bubbles with enhanced temperatures (BETs) are found occasionally in the topside ionosphere. Here we report the characteristics of BETs identified from observations of the first Republic of China Satellite (ROCSAT-1), the first Korea Multi-purpose Satellite (KOMPSAT-1), and the Defense Meteorological

Kyoung Wook Min; Vitaly P. Kim; Hyosub Kil; Shin-Yi Su; Chi Kuang Chao; Jae-Jin Lee

2008-01-01

4

Zonal velocity of the equatorial plasma bubbles over Kolhapur, India  

NASA Astrophysics Data System (ADS)

This paper presents the observations of zonal drift velocities of equatorial ionospheric plasma bubbles and their comparison with model values. These velocities are determined by nightglow OI 630.0 nm images. The nightglow observations have been carried out from the low latitude station Kolhapur (16.8° N, 74.2° E; 10.6° N dip lat.) during clear moonless nights. Herein we have presented the drift velocities of equatorial plasma bubbles for the period of February-April 2011. Out of 80 nights, 39 showed the occurrence of equatorial plasma bubbles (49%). These 39 nights correspond to magnetically quiet days (?Kp < 26). The average eastward zonal velocities (112 ± 10 m s-1) of equatorial plasma bubbles increased from evening sector to 21:00 IST (Indian Standard Time = Universal Time + 05:30:00 h), reach maximum about 165 ± 30 m s-1 and then decreases with time. The calculated velocities are in good agreement with that of recently reported values obtained with models with occasional differences; possible mechanisms of which are discussed.

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

2013-11-01

5

Guest investigator program study: Physics of equatorial plasma bubbles  

NASA Technical Reports Server (NTRS)

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

Tsunoda, Roland T.

1994-01-01

6

Periodicity in the occurrence of equatorial plasma bubbles  

NASA Astrophysics Data System (ADS)

The observations of equatorial plasma bubbles by low-inclination orbit satellites show periodic occurrence of bubbles along satellite orbits. The periodicity in the bubble occurrence provides a useful tool for identifying the role of gravity waves in the creation of bubbles. In this study, we investigate the variability of the periodicity in the bubble occurrence by analyzing the observations of Communication/Navigation Outage Forecasting System (C/NOFS) and the first Republic of China satellite (ROCSAT-1). Here the periodicity indicates spatial periodicity and is derived by applying a Fourier analysis to the electron densities projected onto the magnetic apex height. Our preliminary results show an occurrence of significant amplitudes of periodicity peaks on the spatial scale range of 50-1000 km. The periodicity on small scales may be associated with the bifurcation of bubbles or to the creation of multiple bubbles for one wave seeding. The periodicity on larger scales is considered to be related with the scale size of a seeding mechanism. We present statistics of the periodicity and the coincident satellite observations of periodic bubbles with ground observations.

Choi, J.; Kim, Y.; Kil, H.; Kwak, Y.; Lee, W.

2013-12-01

7

Periodic spacing between consecutive equatorial plasma bubbles J. J. Makela,1  

E-print Network

Click Here for Full Article Periodic spacing between consecutive equatorial plasma bubbles J. J to determine the occurrence of equatorial plasma bubbles (EPBs). On 317 of the 552 predominately clear nights spacings were recorded with 88 nights showing 3 or more consecutive bubbles. We suggest that the periodic

Vadas, Sharon

8

Characteristics and solar activity dependence of equatorial plasma bubbles detected by the C/NOFS satellite  

NASA Astrophysics Data System (ADS)

Equatorial plasma bubbles are the primary disturbances in the night-time low-latitude ionosphere and cause significant radio scintillation. In this paper, we address the following outstanding problems: What is the threshold vertical plasma drift velocity necessary for the generation of plasma bubbles? How does the threshold plasma drift vary with longitude? How do the occurrence and characteristics of plasma bubbles depend on solar activity? We present observations of plasma bubbles by the C/NOFS satellite between solar minimum and solar maximum. During solar minimum, plasma bubbles often originate in the evening sector and become fully developed after midnight. The plasma flow inside the bubbles is always upward throughout the entire night time. A series of plasma bubbles merge and form broad plasma depletions over a very large longitudinal range (up to 3800 km) near dawn. During solar maximum, C/NOFS is often below the F peak, and this allows us to examine the early phase of irregularity formation. It is found that plasma bubbles are continuously generated near the sunset terminator over 12 hours and that the critical upward ion drift necessary for the generation of plasma bubbles determined from the C/NOFS measurements is 40-70 m/s. The plasma drift at the prereversal enhancement is large at the American-African longitudes but smaller at the Asian longitudes. Significant differences in the characteristics of plasma bubbles between solar minimum and solar maximum are identified. Large plasma bubbles occur in the midnight-dawn sector during solar minimum but in the evening sector during solar maximum. The lifetime of plasma bubbles is long (7 hours or longer) during solar minimum but is short (~3 hours) during solar maximum. The different behaviors of plasma bubbles between solar minimum and solar maximum are related to the F-peak height, the upward plasma drift, and the atmospheric profile that are controlled by solar activity.

Huang, C.; de la Beaujardiere, O.; Roddy, P.; Hunton, D.; Ballenthin, J.; Pfaff, R. F.; Hairston, M. R.

2012-12-01

9

Combined analysis of equatorial plasma bubbles using a multi-platform approach  

NASA Astrophysics Data System (ADS)

Owing to their impacts on geo-positioning and communications systems, understanding the formation and evolution of equatorial plasma bubbles and associated scintillations remains an important challenge for ionospheric physics. Significant prior efforts such as the C/NOFS mission have brought together a combination of ground- and space-based plasma observations to study these processes. The new missions ICON and GOLD will provide very different, primarily optical observations of the nighttime ionosphere and thermosphere that will allow for a new view of equatorial plasma bubbles. However, combining the data from these two spacecraft, along with existing and future ground-based observations, will require a fundamentally different approach than that used for C/NOFS. Here, the new approach required will be described and the new capabilities for such a coordinated effort to address new, as well as long-outstanding science questions related to equatorial plasma bubbles will be addressed.

England, S.

2013-12-01

10

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

11

Equatorial plasma bubbles studied using African slant total electron content observations  

NASA Astrophysics Data System (ADS)

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

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

2008-04-01

12

Equatorial plasma bubbles/range spread F irregularities and the QBO  

SciTech Connect

This paper reports on a study of plasma bubbles or spread F irregularities, observed at equatorial observation stations, looked at in conjunction with measures of the quasi biennial oscillation (QBO) of the mean lower stratospheric winds. Plasma bubbles and spread F irregularities are thought to be different manifestations of the same basic event, distinguished mainly by the observational method. For the case of range spread F events, ionosonde data has revealed in the past daily and seasonal variations, effects due to the solar cycle, and dependence upon the geomagnetic field and longitudinal location. These relationships have been shown to be statistical in nature, so the authors have looked for other relationships which might be more relational in nature. When correlation with QBO phase variations are investigated, there is an observed increase or decrease in the range spread F, dependent upon whether the QBO is in an easterly or westerly phase, and observed in the American sector or Indian/East African sector.

Chen, P.R. (Chinese Academy of Sciences, Beijing (China))

1993-11-05

13

Equatorial bubbles updrafting at supersonic speeds  

Microsoft Academic Search

Plasma and electric field observations from two satellite encounters with equatorial plasma bubbles updrafting at velocities of about 2 km\\/s are presented. These large, upward velocities are consistent with an adaptation of Chandrasekhar's model for the motion of plasma blobs supported against gravity by a magnetic field. Vector magnetic field measurements, available during one of the bubble encounters show a

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

1992-01-01

14

Geomagnetic control of equatorial plasma bubble activity modeled by the TIEGCM with Kp  

NASA Astrophysics Data System (ADS)

Describing the day-to-day variability of Equatorial Plasma Bubble (EPB) occurrence remains a significant challenge. In this study we use the Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIEGCM), driven by solar (F10.7) and geomagnetic (Kp) activity indices, to study daily variations of the linear Rayleigh-Taylor (R-T) instability growth rate in relation to the measured scintillation strength at five longitudinally distributed stations. For locations characterized by generally favorable conditions for EPB growth (i.e., within the scintillation season for that location), we find that the TIEGCM is capable of identifying days when EPB development, determined from the calculated R-T growth rate, is suppressed as a result of geomagnetic activity. Both observed and modeled upward plasma drifts indicate that the prereversal enhancement scales linearly with Kp from several hours prior, from which it is concluded that even small Kp changes cause significant variations in daily EPB growth.

Carter, B. A.; Retterer, J. M.; Yizengaw, E.; Groves, K.; Caton, R.; McNamara, L.; Bridgwood, C.; Francis, M.; Terkildsen, M.; Norman, R.; Zhang, K.

2014-08-01

15

Electric field observations of equatorial bubbles  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

16

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

17

Equatorial bubbles updrafting at supersonic speeds  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

18

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

19

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

20

Simultaneous optical measurements of equatorial plasma bubble (EPB) from Kolhapur (16.8°N, 74.2°E) and Gadanki (13.5°N, 79.2°E)  

NASA Astrophysics Data System (ADS)

In this paper, we study the Equatorial Plasma Bubble (EPB) features using All sky imager (ASI) observations of O(1D) 630.0 nm night airglow emission from Kolhapur (16.8°N, 74.2°E, 10.6°N dip lat.) and Gadanki (13.5°N, 79.2°E, 6.5°N dip lat.) during March 2012. The optical data was supported by the ionosonde measurements from Tirunelveli (8.7°N, 77.8°E, 0.5°N dip lat.) which revealed the occurrence of equatorial spread-F. The EPBs were monitored at both locations as nearly north-south aligned intensity depleted regions. We computed east-west plasma drift velocity over Kolhapur and Gadanki for the nights having coordinated measurements. Also, the observed plasma bubble drift velocities are compared with the zonal neutral wind velocities obtained from the HWM-07 model and the empirical drift model of England and Immel (2012). We observed that, generally, the mean zonal drift velocities of the plasma bubbles tend to decrease with local time (after midnight). Our results reveal the drift velocity noted in Kolhapur data varies from 124 m/s to 181.8 m/s, while from the Gadanki data show the drift velocity to range from 116.3 m/s to 160.3 m/s.

Ghodpage, R. N.; Taori, A.; Patil, P. T.; Gurubaran, S.; Sripathi, S.; Banola, S.; Sharma, A. K.

2014-12-01

21

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

22

In situ observations of bifurcation of equatorial ionospheric plasma depletions  

SciTech Connect

Vector electric field measurements from the San Marco D satellite are utilized to investigate the bifurcation of ionospheric plasma depletions (sometimes called {open_quotes}bubbles{close_quotes}) associated with nightside equatorial spread F. These depletions are identified by enhanced upward ExB convection in depleted plasma density channels in the nighttime equatorial ionosphere. The in situ determination of the bifurcation process is based on dc electric field measurements of the bipolar variation in the zonal flow, westward and eastward, as the eastbound satellite crosses isolated signatures of updrafting plasma depletion regions. The authors also present data in which more complicated regions of zonal velocity variations appear as the possible result of multiple bifurcations of updrafting equatorial plasma bubbles. 10 refs., 7 fig.

Aggson, T.L.; Pfaff, R.F. [NASA Goddard Space Flight Center, Greenbelt, MD (United States)] [NASA Goddard Space Flight Center, Greenbelt, MD (United States); Maynard, N.C. [Mission Research Corporation, Nashua, NH (United States)] [Mission Research Corporation, Nashua, NH (United States)

1996-03-01

23

Plasma bubble phenomenon in the topside ionosphere  

NASA Astrophysics Data System (ADS)

There are the indications that plasma bubbles/flux tube aligned plasma density depletions, produced by Rayleigh-Taylor instability at the bottomside of ionosphere, could rise up to the topside ionosphere and plasmasphere. Maruyama and Matuura [Maruyama, T., Matuura, N. Longitudinal variability of annual changes in activity of equatorial spread-F and plasma bubbles. J. Geophys. Res. 89(A12), 10903-10912, 1984.], using ISS-b satellite data for the high solar activity period, 1978-1979, have seen the plasma bubbles over equator at 1100 km altitudes in 46 cases in 1700 passes. That is ˜3% only. However, there is distinctly another picture in He + density depletions (subtroughs) according to the ISS-b data for the same period. He + density subtroughs were observed in the topside ionosphere over equatorial and low-latitudinal regions ( L ˜ 1.3-3) in 11% of the cases [Karpachev, A.T., Sidorova, L.N. Occurrence probability of the light ion trough and subtrough in He + density on season and local time. Adv. Space Res. 29, 999-108, 2002; Sidorova, L.N., He + density topside modeling based on ISS-b satellite data. Adv. Space Res. 33, 850-854, 2004.]. We have carried out a statistical study of the He + density subtrough characteristics. The subtrough depth (depletion value) as function of local time (evening-night hours) was compared with the vertical plasma drift velocity variations, obtained for the same periods from the AE-E satellite and IS radar (Jicamarca) data. Striking similarity in development dynamics is revealed for the different seasons. It is noted also that the He + density subtroughs are mostly observed in the evening-night sector (18-05 LT) from October till May, which is very similar to the peculiarities of the equatorial spread-F (ESF), usually associated with plasma bubbles. The monthly mean He + density subtrough occurrence probability, plotted in local time versus month, was compared with the similar plots for ESF occurrence probability derived by Abdu et al. [Abdu, M.A., Sobral, J.H.A., Batista, I.S. Equatorial spread-F statistics in the american longitudes: some problems relevant to ESF description in the IRI scheme. Adv. Space Res. 25, 113-124, 2000.] from ground-based ionograms obtained over Brazilian region for the same years. The comparison shows good enough correlation ( R ˜ 0.67). It is concluded that: (a) He + density subtroughs like ESF are controlled by pre-reversal enhancement electric field (vertical drift); (b) He + density subtroughs and ESF/bubble irregularities may be considered as phenomena of the same plasma bubble origin; (c) it seems, plasma bubbles, reaching the topside ionosphere altitudes, are most easily observable in He + density as depletions.

Sidorova, L. N.

24

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

25

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

26

Diagnostics of Microwave Bubble Plasma in Liquid  

NASA Astrophysics Data System (ADS)

Plasma production in the liquid phase has attracted much attention due to its potential applications such as biomedical or environmental processes. As a new technique, we have developed bubble plasma production in liquid with use of pulsed microwave from a slot antenna, and have succeeded in decomposing harmful chemicals such as trichloroethylene (TCE). In this work, optical emission and absorption spectroscopies were adopted to diagnose the microwave bubble plasma. OES result indicated strong OH emission from the plasma, suggesting production of reactive OH radical in the bubble plasma from water vapor. Furthermore, plasma density of the bubble plasma was investigated by time-resolved Stark broadening spectroscopy. To give insight into the reactive species in the liquid phase, plasma-treated water was investigated with UV/VIS optical absorption spectroscopy and a chemical reagent that is sensitive to hydrogen peroxide. From these measurements, existence of hydrogen peroxide in the liquid phase was confirmed.

Toyoda, Hirotaka; Sugiura, Hiroyasu; Saito, Ryota; Ishijima, Tatsuo

2008-10-01

27

Radio-tomographic images of postmidnight equatorial plasma depletions  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

28

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.

29

Plasma bubbles in the topside ionosphere: estimations of the survival possibilities  

NASA Astrophysics Data System (ADS)

The study deals with the evaluation of the survival possibilities of the plasma bubbles, seen as He+ density depletions in the topside ionosphere. He+ density depletions (or subtroughs) are usually observed during a high solar activity at the topside ionospheric altitudes ( 1000 km) deeply inside the plasmasphere (L 1.3-3). They are considered as originating from equatorial plasma bubbles phenomena or as possible fossil bubble signatures. The estimation of the characteristic times of a life, diffusion and vertical drift transport of helium ions (He+ ) at the topside ionosphere heights of the low-/mid-latitude region was made. It is revealed, that the diffusion transport process is the fastest one (some minutes). Since the ionosphere plasma is magnetized plasma at the topside ionosphere heights, the diffusion processes are field-aligned. Plasma bubbles spread (due to diffusion processes) along the magnetic tubes. Their spreading becomes more and more significant in process of their uplifting. So extended bubbles look like `banana' with the extremities reaching the ionosphere heights in both the hemispheres. This scheme is also correct if the separate components are under considerations, namely He+ . On the other hand, it is well known, that the magnetic tube, partially "devastated" by a plasma bubble, is replenished extremely slowly. The tube replenishment time is proportionally L4 (i.e. Badin, JATP, 1994). For example, it takes 10 hours for refilling the tube (L=2, 45o INVLAT), partially "devastated" or depleted by plasma bubble. It was concluded, that, if some plasma bubbles can reach the topside and plasmashere heights, they can exist here (may be as "dead" bubbles) during some hours. It was also concluded, that there is enough time to register the plasma bubbles at the topside ionosphere heights.

Sidorova, Larisa; Filippov, Sergey

30

Investigation of decaying phase of plasma bubbles showing a reduction in the apex altitude  

NASA Astrophysics Data System (ADS)

The formation of equatorial plasma bubbles (EPBs) associated with spread-F irregularities are fairly common and reasonably well understood phenomenon at the post sunset equatorial ionosphere. These bubbles grow as a result of Rayleigh-Taylor instability process initiated by a perturbation generating polarization electric field resulting in upward E x B drift. The electron density depletions arising from this phenomenon are often observed as airglow depletions in the images of OI 630 nm emission. On occasions the growth of the features over dip equator are observed as poleward extensions of the depletions in all-sky images. Herein, we present interesting observations of decrease in the latitudinal extent of the bubbles corresponding to reduction in their apex altitudes over dip equator. Such observations indicate that these bubbles not only grow but also ‘fall’ over magnetic equator on occasions. This appear to be a kind of decaying phase for the plasma bubbles. The observations discussed in this work are based on all-sky airglow imaging observations made from Panhala (11.1(°) N dip latitude) during the period of January and February 2008. Out of 12 nights of EPB observations, such decrease in apex altitude is identified on 5 nights. During these periods VHF scintillation measurements were made from Gadanki (6.5(°) N dip latitude). In addition, ionosonde observations and GPS scintillation measurements were made from dip equatorial site Tirunelveli (1.1(°) N dip latitude). Herein, we attempt to understand the events based on these coordinated observations.

Lakshmi Narayanan, Viswanathan; Shiokawa, Kazuo; Gurubaran, Subramanian; Emperumal, Kaliappan; Samireddipalle, Sripathi

31

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

32

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

33

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

34

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

35

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

36

Topside ionosphere plasma bubbles, seen in He+ density: longitudinal dependence and thermosphere meridional wind influence  

NASA Astrophysics Data System (ADS)

He+ density depletions, considered as originating from equatorial plasma bubbles, or as fossil bubble signatures, were involved in this study. He+ density depletions, obtained from ISS-b spacecraft data, were observed during a high solar activity (1978-80, F10.7=200) in the topside ionosphere (900-1100 km) deeply inside the plasmasphere (L=1.3-3) (Sidorova, 2004, 2007). (1) He+ density depletion statistics with respect to longitude is considered for the post-sunset hours under winter, summer and equinoctial conditions within of 35° invariant latitudes. The map of He+ density depletion distribution as function of latitude- and longitude was also derived. The statistics and the map were compared with Equatorial Spread-F statistics, plasma bubble distribution and Range Spread-F statistics, obtained by Maruyama and Matuura (1984, 1980) from ISS-b spacecraft data for the same period (1978-80). The longitudinal variations of the Equatorial F-region Irregularities probability, obtained from the AE-E spacecraft data (McClure et al., 1998) for the same period, were also taken. Comparison shows good conformity in statistics/spatial distributions of all mentioned irregularities. Their predominant occurrence area for all seasons and both hemispheres covers the region of Brasilia, Atlantic Ocean and Africa (270°-0°-30°), where the range of magnetic field declination angle varies from 0° to 20°. (2) It is also suggested, that the plasma bubbles, produced by Rayleigh-Taylor (R-T) instability at the bottomside of ionosphere and transported up to the topside ionosphere/plasmasphere, could be strong affected by meridional wind during a generation due to inhibiting the growth of R-T instability and flux tube integrated conductivity. For better understanding competing/complementary roles of thermosphere winds in the development of plasma bubbles, observed in He+ density, the evaluation of the possible influence of the thermosphere meridional winds was done. The diurnal He+ density depletion statistics, averaged for solstices and equinoxes, were compared with the model velocity variations of the thermosphere meridional wind, taken from (Maruyama, 1996). It was revealed that the meridional wind influence shows itself as modulation effect. The modulation has seasonal dependence and the best correlation in equinoxes (R=0.87). The best amplitude correlation was found for the longitudes of 270°-360° (Brasilia, Atlantic regions), where the declination angle of the magnetic meridional wind component is near 20°. It was concluded that the topside plasma bubbles, seen as He+ density depletions, are strong enough affected by thermosphere meridional wind. REFERENCE Maryama, T. and N. Matuura, Global distribution of occurrence probability of spread echoes based on ISS-b observation, RRL, vol.27, N 124, 201-216, 1980. 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. Maruyama, T., Modeling study of equatorial ionospheric height and spread F occurrence, J. Geophys. Res., vol. 101, A3, pp. 5157-5163, 1996. McClure, J. P., Singh S., Bamgboye D.K., Johnson F.S., Hyosub Kil. Occurrence of equatorial F region irregularities: Evidence for tropospheric seeding, J. Geophys. Res., 103(A12), 29,119-29,135, 1998. 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.

Sidorova, L.

2009-04-01

37

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

Microsoft Academic Search

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

I. Kostyukov; A. Pukhov; S. Kiselev

2004-01-01

38

Features of highly structured equatorial plasma irregularities deduced from CHAMP observations  

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

39

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

40

Plasma formation and temperature measurement during single-bubble cavitation  

Microsoft Academic Search

Single-bubble sonoluminescence (SBSL1-5) results from the extreme\\u000a temperatures and pressures achieved during bubble compression;\\u000a calculations have predicted(6,7) the existence of a hot, optically\\u000a opaque plasma core(8) with consequent bremsstrahlung radiation(9,10).\\u000a Recent controversial reports(11,12) claim the observation of neutrons\\u000a from deuterium - deuterium fusion during acoustic cavitation(11,12.)\\u000a However, there has been previously no strong experimental evidence for\\u000a the existence of a

David J. Flannigan; Kenneth S. Suslick

2005-01-01

41

On the Growth Phase of Large-Scale Wave Structure and Plasma Bubbles  

NASA Astrophysics Data System (ADS)

For those interested in understanding the day-to-day variability in the occurrence of equatorial plasma bubbles (EPBs), it is important to realize that (1) EPBs are spawned and launched from the crests of large-scale wave structure (LSWS) that develop in the bottomside of the equatorial F layer, and (2) LSWS appears to develop during the post-sunset rise (PSSR) of the F layer. The implication is strong that the process is not just a random seeding that occurs during the course of a night, as might be expected from atmospheric gravity waves. This behavior is consistent with observations that have shown that most EPBs are launched at the end of the PSSR, or soon thereafter. The focus should be, therefore, to determine how LSWS is excited and amplified during the PSSR, which includes E region sunset. The major obstacle, to date, has been the lack of diagnostic sensors that are capable of probing into the base of the F layer, where the plasma densities are low, and detecting (preferably describing) LSWS during its growth phase. Some progress toward this end has been made, however, through use of ALTAIR, a steerable incoherent-scatter radar, and newly found signatures of LSWS in ionograms. Results are also expected to be forthcoming from total electron content measurements that can be made using radio beacons on board the low-inclination-orbiting C/NOFS satellite. A brief review of this topic will be presented.

Tsunoda, R. T.

2009-05-01

42

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

43

New Evidence for Equatorially Trapped Thermal Plasma During Early Post-Storm Recovery  

NASA Technical Reports Server (NTRS)

Almost 20 years ago Olsen et al. [1987] reported Dynamics Explorer 1 Retarding Ion Mass Spectrometer observations of equatorially trapped, cold ions in the vicinity of the plasmapause. In that study the trapped population corresponded to a local minimum in density at the magnetic equator. During that time period observations were uncovered of a local maximum in plasma density at the equator. Until IMAGE there has been no good opportunity to experimentally revisit this topic, however until now no direct evidence of a relevant equatorial process has been recognized near the plasmapause during early recovery conditions. It appears that evidence has now been found in both the Extreme Ultraviolet Imager and Radio Plasma Imager observations. The observations, conditions, and properties of what appears to be an equatorially trapped and enhanced density near the magnetic equator will be presented and discussed.

Gallagher, D. L.; Green, J. L.

2005-01-01

44

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

Microsoft Academic Search

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

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

1994-01-01

45

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

E-print Network

bubbles using Thomson scattering and proton radiography M. J. Rosenberg,1,* J. S. Ross,2 C. K. Li,1 R. P-produced plasma bubbles or the interaction of bubble pairs, where reconnection of azimuthal magnetic fields occurs. Measurements of ion and electron temperatures agree with LASNEX simulations of single plasma bubbles, which

46

Equatorial electric field observations  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

47

Equatorial plasma irregularities: Solar cycle dependence and longitudinal variation of local time distribution  

NASA Astrophysics Data System (ADS)

Equatorial plasma irregularities represent important phenomena when steep ionospheric electron density gradients are concerned. During solar maximum conditions they cause the most severe radio wave scintillations in communications systems such as GPS. The understanding of their occurrence and evolution is therefore of high interest. The German CHAMP satellite orbiting at an altitude of about 400km is well suited for sampling the equatorial ionosphere, and equatorial plasma instabilities. This multi-years mission (July 2000 through present) provides an outstanding opportunity to investigate plasma irregularities in a climatological sense. Beside the observation of the electron density depletion it has been proven that the accompanying enhancement of magnetic field strength is a suitable signature for detecting these irregularities. The latter effect is caused by diamagnetic currents flowing along surfaces plasma pressure gradients. Based on the multi-years global climatology it is found that the seasonal/longitudinal occurrence distribution differs between solar maximum and minimum years. Also the latitude distribution of the events depends on solar activity. Another finding is that the local time distribution of the plasma irregularity occurrence rate varies with longitude. Events can be observed well after midnight in the Atlantic and African region, but its post-midnight probability is very low in the Pacific region. We suggest that atmospheric drivers altering the ionospheric conditions are responsible for such effects.

Stolle, C.; Luhr, H.; Park, J.; Fejer, B. G.; Rother, M.

2009-12-01

48

Combined in-situ and top-side remote observations of evolution of plasma bubbles  

NASA Astrophysics Data System (ADS)

Ionospheric plasma bubbles in the nighttime are known to cause interference with GPS navigation and trans-ionospheric RF propagation in general. The characteristics of these bubbles have been studied extensively through observations via TIMED GUVI instrument, ground-based imagers, and the C/NOFS mission, but the production and especially the evolution of the bubbles is not adequately understood. We present here a small satellite mission concept that attempts to do combined in-situ and top-side remote observations of the bubbles to better understand their evolution. The mission aims to specifically address key questions about ionospheric bubbles: What are the characteristics of bubbles and how do these characteristics evolve? Does bubble evolution vary with longitude and/or latitude? How do the bubble occurrence rates at the F-region peak and higher altitudes differ? The proposed mission will carry a 135.6 nm photometer to measure the recombination emission from oxygen ions and a Langmuir probe to measure in-situ plasma density. Topside remote sensing using the photometer allows for observations of bubbles near and below the F-region peak while the Langmuir probe gives in situ measurements necessary to characterize the plasma fluctuations and thereby infer the RF scintillation characteristics. Comparison of such coincident measurements will provide a unique insight into bubble formation and evolution.

Barjatya, A.; Eastes, R.; Dymond, K.

2010-12-01

49

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, many others. Ultimately, diffusive processes govern much of the physics, and the difference between the diffusivity of heat and dissolved gases in ordinary liquids holds the key to the striking differences between gas and vapor bubbles.

Prosperetti, Andrea

2002-11-01

50

Zonal drifts of plasma bubbles in South American sector during the extreme low solar activity 2008 - 2010  

NASA Astrophysics Data System (ADS)

Transequatorial F region plasma bubbles are large-scale ionospheric depleted regions that develop in the bottomside of equatorial F region due to plasma instability processes. All-sky imaging observations of the OI 630.0 nm nightglow emissions were done at low-latitude region (Sao Jose dos Campos 23.21(°) S, 45.86(°) W; dip latitude 17.6(°) S - hereafter SJC) and near equatorial region (Palmas 10.28(°) S, 48.33(°) W; dip latitude 6.7(°) S - hereafter PAL), Brazil, during the years 2008 and 2010, a period of extremely low solar activity (LSA). Because the OI 630.0 nm emission results from excitation mechanisms by dissociative recombination of O _{2} (+) + e rightarrow O + O (*) ( (1) D) and afterwards O (*) ( (1) D) rightarrow O( (3) P) + h?(630.0 nm) this emission is closely related with electronic density and consequently with the ionospheric electrodynamics. In this work we present and discuss the nighttime F region zonal plasma drift velocities inferred using OI 630.0 nm emissions imaging, during the occurrence of a plasma bubble. We investigated the nighttime zonal plasma drift variations using fixed emission peak altitudes at 280 km, used by earlier investigators, as well as emission peak altitudes based on simultaneous ionospheric sounding observations for both observatories. The nighttime pattern is similar to those observed during high solar activity (HSA). However, the maximum and minimum zonal plasma drift are lower than those observed during HSA. In addition, the zonal plasma drift was calculated using two different methodologies, fixed height (280 km) and variable height (based on ionosonde data measurements). The maximum and minimum average zonal plasma drift velocities using fixed emission peak altitudes for SJC are 119 ± 6 m/s and 58 ± 10 m/s and for PAL are 111 ± 5 m/s and 85 ± 10 m/s. The peak emission height based on simultaneous ionospheric observations for SJC are 116 ± 7 and 57 ± 15 m/s and for PAL are 119 ± 6 and 58 ± 10 m/s), respectively.

Abalde Guede, Jose Ricardo; Fagundes, Paulo Roberto; De Jesus, Rodolfo; De Abreu, Alessandro; Pillat, Valdir Gil; Coelho, Flavia Elaine

51

Formation of Optical Bullets in Laser-Driven Plasma Bubble Accelerators  

SciTech Connect

Electron density bubbles generated in plasma of density n{sub e{approx}10{sup 19}/cm{sup 3}} are shown to reshape copropagating probe pulses into optical 'bullets'. The bullets, reconstructed by frequency-domain interferometric techniques, are used to visualize bubble formation independently of relativistic electron generation.

Dong, P.; Reed, S. A.; Yi, S. A.; Shvets, G.; Downer, M. C. [Department of Physics, University of Texas at Austin, Austin, TX 78712 (United States); Kalmykov, S. [University of Nebraska, Lincoln, NE (United States); Matlis, N. H. [Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States); McGuffey, C.; Bulanov, S. S.; Chvykov, V.; Kalintchenko, G.; Krushelnick, K.; Maksimchuk, A.; Matsuoka, T.; Thomas, A. G. R.; Yanovsky, V. [Center for Ultrafast Optical Science, University of Michigan, 2200 Bonisteel Blvd, Ann Arbor, MI 48109 (United States)

2010-11-04

52

Equatorial Spacecraft-Plasma Interaction Phenomenon Observed With DE 2  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

53

Equatorial spacecraft-plasma interaction phenomenon observed with DE 2  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

54

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

55

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

56

Plasma Wave Irregularities in the Equatorial Upper E Region at Twilight  

NASA Astrophysics Data System (ADS)

A new class of plasma irregularities in the postsunset equatorial upper E region has been detected by radar experiments over Jicamarca, Peru [Chau and Hysell , 2004]. In comparison with daytime plasma irregularities, nighttime large-scale plasma waves are not well understood. These waves has been detected with the JULIA (Jicamarca Unattended Long-term Investigations of the Atmosphere) operation mode at Jicamarca. Despite the fact that observations of this new class of irregularities were made, there has been a lack of interest into the characterization of them. As stated by the work of Hysell and Chau [2002] and Chau and Hysell [2004], the source of these irregularities is related to gradient-drift (or interchange) instability process. This instability was firstly investigated for laboratory plasmas by Simon [1963]. It arises in the presence of an ionization gradient perpendicular to the current flow in a plasma [Sudan et al., 1973]. In the equatorial upper E region, the passage of the solar terminator generates an steep horizontal conductivity gradients which induce an upward current in the upper E region which is known to be present in the vicinity of the evening solar terminator and it is linked directly with the F-region overhead. This work focus on show experimental evidence, numerical simulation results and a theoretical discussion which attempts to describe the origin of these irregularities.

ILMA, R.; Hysell, D.

2013-12-01

57

Degradation of Perfluoro Compounds by Pulsed Plasmas within Bubbles in Water  

NASA Astrophysics Data System (ADS)

Perfluorooctanoic acid (PFOA) at a concentration of 500 mg/L in water was successfully degraded using pulsed plasmas generated inside oxygen or argon bubbles. 6 kV-200 ns pulsed voltages were applied to the water bubbles at repetition rates of 500?2000 Hz and pulse plasmas were generated along the inner surface of gas bubbles. After 120 min operation, almost half of the fluorine atoms were detached from PFOA molecules. The decomposition energy efficiency for PFOA obtained with oxygen was 140 mg/kWh which value was quite large as comparing to the values obtained with other chemical methods.

Sasaki, Keisuke; Hayashi, Ryuichi; Yasuoka, Koichi

58

Characteristics of the Plasma Distribution in Mercury's Equatorial Magnetosphere Derived from MESSENGER Magnetic Field and Plasma Observations  

NASA Astrophysics Data System (ADS)

Localized reductions in the magnetic field associated with plasma pressure in Mercury's plasma sheet have been routinely observed by the Magnetometer on the MErcury Surface, Space ENvironment, Geochemistry, and Ranging (MESSENGER) spacecraft. We present a statistical analysis of near-equatorial magnetic depressions to derive the structure of Mercury's plasma sheet pressure. Because the plasma pressure in the magnetosphere correlates with solar wind density, the pressures were normalized to a Mercury heliocentric distance of 0.39 AU. A model magnetic field was used to map observations obtained on the ascending and descending orbit nodes to the magnetic equator, and the mapped equatorial distribution revealed the presence of plasma in a toroidal section extending on the nightside from dusk to dawn. Mapping the data to invariant magnetic latitude shows that the pressure is symmetric about the magnetic equator. The average pressure normalized for heliocentric distance is 1.45 nPa and exhibits a weak, 0.05 nPa/h, dusk-to-dawn gradient with local time. The plasma sheet pressure can vary between successive orbits by an order of magnitude. Unlike the predictions of some global simulations of Mercury's magnetosphere but consistent with observations by MESSENGER's Fast Imaging Plasma Spectrometer, the plasma enhancements do not form a closed distribution around the planet. This difference may arise from the idealized solar wind and interplanetary magnetic field conditions used in the simulations, conditions that maximize the size and stability of the magnetosphere and thus promote the formation of drift paths that close around the planet. For typical plasma sheet energies, 5 keV, the first adiabatic invariant for protons fails to be conserved even within 500 km altitude at midnight, implying that stochastic processes must be considered in plasma sheet transport.

Korth, H.; Anderson, B. J.; Johnson, C. L.; Winslow, R. M.; Raines, J. M.; Slavin, J. A.; Purucker, M. E.; Zurbuchen, T.; Solomon, S. C.; McNutt, R. L.

2012-12-01

59

Global equatorial ionospheric vertical plasma drifts measured by the AE-E satellite  

NASA Technical Reports Server (NTRS)

Ion drift meter observations from the Atmosphere Explorer E (AE-E) satellite during the period of January 1977 to December 1979 are used to study the dependence of equatorial (dip latitudes less than or equal to 7.5 deg) F region vertical plasma drifts (east-west electric fields) on solar activity, season, and longitude. The satellite-observed ion drifts show large day-to-day and seasonal variations. Solar cycle effects are most pronounced near the dusk sector with a large increase of the prereversal velocity enhancement from solar minimum to maximum. The diuurnal, seasonal, and solar cycle dependence of the logitudinally averaged drifts are consistent with results from the Jicamarca radar except near the June solstice when the AE-E nighttime downward velocities are significantly smaller than those observed by the radar. Pronounced presunrise downward drift enhancements are often observed over a large longituudinal range but not in the Peruvian equatorial region. The satellite data indicate that longitudinal variations are largest near the June solstice, particularly near dawn and dusk but are virtually absent during equinox. The longitudinal dependence of the AE-E vertical drifts is consistent with results from ionosonde data. These measurements were also used to develop a description of equatorial F region vertical drifts in four longitudinal sectors.

Fejer, B. G.; De Paula, E. R.; Heelis, R. A.; Hanson, W. B.

1995-01-01

60

Plasma turbulence disc circulating the equatorial region of the plasmasphere identified by the plasma wave detector (PWS) onboard the Akebono (EXOS-D) satellite  

Microsoft Academic Search

For the observation data of the plasma wave turbulence detected by the PWS (Plasma Wave and Sounder Experiment) on board the EXOS-D (Akebono) satellite, the enhancements of the upper hybrid wave emission called equatorial enhancement of the plasma wave turbulence (EPWAT) that are characterized by the increasing level of the upper hybrid emissions are studied on their occurrence regions and

Hiroshi Oya; Masahide Iizima; Akira Morioka

1991-01-01

61

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

62

Plasma transport in the equatorial ionosphere during the great magnetic storm of March 1989  

NASA Technical Reports Server (NTRS)

We have modeled plasma transport in the low-latitude and equatorial ionosphere during the great magnetic storm of March 1989. Our goal was to provide a consistent explanation for the DMSP (Defense Meteorological Satellite Program) observations of dramatic decreases in ion density and rapid ion drifts in the low latitude ionosphere over South America during the storm. The modeling effort supports the hypothesis that abnormally large upward drifts lifted F region plasma above the satellite's altitude and created the density depletions observed by DMSP. Modeled O(+) densities at the satellite's altitude have a strong qualitative resemblance to DMSP observations. Both the model and the observations indicate a deep density trough with extremely sharp boundaries surrounding the equator. The widths of both the modeled and the observed equatorial troughs increase with time. Vertical ion drifts predicted by the model also have been compared with DMSP measurements. Like the observed vertical drifts, the modeled drifts reversed sign near the trough boundaries. The modeled vertical drifts are of the same order and direction as the vertical component of E x B convection near the equator, but of opposite direction (downward) near the trough boundaries and outside of the trough.

Rasmussen, C. E.; Greenspan, M. E.

1993-01-01

63

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

64

Effect of vertical plasma transport on ionospheric F2-region parameters at equatorial latitude  

NASA Astrophysics Data System (ADS)

The variability of the F2-layer even during magnetically quiet times are fairly complex owing to the effects of plasma transport. The vertical E × B drift velocities (estimated from simplified electron density continuity equation) were used to investigate the seasonal effects of the vertical ion drifts on the bottomside daytime ionospheric parameters over an equatorial latitude in West Africa, Ibadan, Nigeria (Geographic: 7.4°N, 3.9°E, dip angle: 6°S) using 1 year of ionsonde data during International Geophysical Year (IGY) of 1958, that correspond to a period of high solar activity for quiet conditions. The variation patterns between the changes of the vertical ion drifts and the ionospheric F2-layer parameters, especially; foF2 and hmF2 are seen remarkable. On the other hand, we observed strong anti-correlation between vertical drift velocities and h?F in all the seasons. We found no clear trend between NmF2 and hmF2 variations. The yearly average value of upward daytime drift at 300 km altitude was a little less than the generally reported magnitude of 20 ms-1 for equatorial F-region in published literature, and the largest upward velocity was roughly 32 ms-1. Our results indicate that vertical plasma drifts; ionospheric F2-layer peak height, and the critical frequency of F2-layer appear to be somewhat interconnected.

Oyekola, O. S.; Ojo, Akin

65

Equatorial 150-km echoes and daytime vertical plasma drifts in the Brazilian sector  

NASA Astrophysics Data System (ADS)

It has already been shown that the vertical component of the Doppler velocity of the so-called 150-km echoes is a good proxy of the F-region vertical plasma drift. These 150-km echoes have been observed at equatorial and low-latitude regions, but the origin of the irregularities producing the echoes is still subject of investigation. We present interesting observations of 150-km echoes made by the Sao Luis 30 MHz coherent backscatter radar interferometer in Brazil, and estimates of vertical plasma drifts from the observations. Results include abnormally large vertical drifts during daytime, and negative drifts in the early afternoon. Results of a comparison with independent measurements are also presented.

Rodrigues, F. S.; Paula, E. R.

2012-12-01

66

Characteristics of the plasma distribution in Mercury's equatorial magnetosphere derived from MESSENGER Magnetometer observations  

NASA Astrophysics Data System (ADS)

Localized reductions in the magnetic field associated with plasma pressure in Mercury's magnetospheric cusp and nightside plasma sheet have been routinely observed by the Magnetometer on the MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft. We present a statistical analysis of near-equatorial magnetic depressions to derive the structure of Mercury's plasma sheet pressure. Because the plasma pressure in the magnetosphere correlates with solar wind density, the pressures were normalized to a Mercury heliocentric distance of 0.39 AU. A model magnetic field was used to map observations obtained on the ascending and descending orbit nodes to the magnetic equator and revealed the presence of plasma in a toroidal section extending on the nightside from dusk to dawn. Mapping the data to invariant magnetic latitude shows that the pressure is symmetric about the magnetic equator. The average pressure normalized for heliocentric distance is 1.45 nPa and exhibits a weak, 0.05 nPa/h, dusk-to-dawn gradient with local time. The plasma sheet pressure can vary between successive orbits by an order of magnitude. Unlike the predictions of some global simulations of Mercury's magnetosphere, the plasma enhancements do not form a closed distribution around the planet. This difference may arise from the idealized solar wind and interplanetary magnetic field conditions used in the simulations, which maximize the size and stability of the magnetosphere, thus promoting the formation of drift paths that close around the planet. For typical plasma sheet energies, 5 keV, the first adiabatic invariant for protons fails to be conserved even within 500 km altitude at midnight, implying that stochastic processes must be considered in plasma sheet transport.

Korth, Haje; Anderson, Brian J.; Johnson, Catherine L.; Winslow, Reka M.; Slavin, James A.; Purucker, Michael E.; Solomon, Sean C.; McNutt, Ralph L., Jr.

2012-12-01

67

Topside ionosphere bubbles, seen as He+ density depletions: connection with ESF, vertical plasma drift, thermosphere wind and solar activity  

NASA Astrophysics Data System (ADS)

He+ density depletions, considered as originating from equatorial plasma bubbles (PB), or as possible fossil bubble signatures, were involved in this study. He+ density depletions were observed during a high solar activity (1978-79, F10.7 200) at the topside ionosphere altitudes deeply inside the plasmasphere (L 1.3-3) (Karpachev and Sidorova, ASR, 2002; Sidorova, ASR, 2004, 2007). It is suggested that the equatorial F region irregularities, their post sunset development, evolution, and decay processes are controlled by the sunset electrodynamics of the equatorial region. The He+ density depletion peculiarities were considered in connection with equatorial F-spread (ESF) and vertical plasma drift. The depletion values as function of local time (evening-night hours) were compared with the vertical plasma drift velocity variations, obtained for the same periods (1978-79, F10.7 200; AE-E, IS radar, Jicamarca). Striking similarity in development dynamics was revealed for the different seasons. The monthly mean PB occurrence probability, plotted in local time versus month, was compared with the similar plots for global ESF occurrence probability, derived from ISS-b data (1978-79). Good seasonal correlation (R=0.6) was obtained. Moreover, the comparison of the regional maps, derived from ground-based ionograms, obtained over Brazilian regions (Abdu et al., ASR, 2000) for period with the similar solar activity (1980-81, F10.7 230), shows very well correlation (R=0.67). It is also suggested, that the PBs, produced by Rayleigh-Taylor (R-T) instability at the bottomside of ionosphere and transported up to the topside ionosphere/plasmasphere, could be strong affected by meridional wind during a generation due to inhibiting the growth of R-T instability and flux tube integrated conductivity. For better understanding competing/complementary roles of thermospheric winds in the development of PBs, seen as He+ density depletions, the evaluation of the possible influence of the thermosphere meridional winds was done. The diurnal PB statistics, averaged for the periods around the solstices and equinoxes, was compared with the model velocity variations of the meridional thermosphere wind. The wind model calculation was taken from (Maruyama, JGR, 1996). The best amplitude correlation was found for the longitudes of 270-360° (Brazilia, Atlantic regions), where declination angle is near 20?. It was obtained that the topside PBs, seen as He+ density depletions, are strong enough affected by meridional wind. The modulation effect has a seasonal dependence and the best correlation in equinox (R=0.87). He+ density depletion occurrence in dependence on solar activity was also under consideration. It was revealed that there are many cases of the He+ density depletions in solar maxima on the OGO-4 (1968, 20th cycle), OGO-6 (1969, 20th cycle) and DE-2 (1981, 21th cycle) data. It was concluded that the topside PBs, seen as He+ density depletions, are rather typical phenomena for the topside ionosphere for high solar activity epoch. The possible reasons of topside PB occurrence as function of solar activity are discussed.

Sidorova, Larissa

68

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

NASA Astrophysics Data System (ADS)

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

Pai, C.-H.; Chang, Y.-Y.; Ha, L.-C.; Xie, Z.-H.; Lin, M.-W.; Lin, J.-M.; Chen, Y.-M.; Tsaur, G.; Chu, H.-H.; Chen, S.-H.; Lin, J.-Y.; Wang, J.; Chen, S.-Y.

2010-12-01

69

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

SciTech Connect

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

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

2010-12-15

70

Radio-Tomographic Images of Post-midnight Equatorial Plasma Depletions  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

71

Bubble regime for ion acceleration in a laser-driven plasma  

SciTech Connect

Proton trapping and acceleration by an electron bubble-channel structure in laser interaction with high-density plasma is investigated by using three-dimensional particle-in-cell simulations. It is shown that protons can be trapped, bunched, and efficiently accelerated for appropriate laser and plasma parameters, and the proton acceleration is enhanced if the plasma consists mainly of heavier ions such as tritium. The observed results are analyzed and discussed in terms of a one-dimensional analytical three-component-plasma wake model.

Shen Baifei [Shanghai Institute of Optics and Fine Mechanics, P.O. Box 800-211, Shanghai 201800 (China); Accelerator Systems Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Argonne Accelerator Institute, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Li Yuelin [Accelerator Systems Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Argonne Accelerator Institute, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Yu, M. Y. [Institut fuer Theoretische Physik I, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany); Cary, John [Tech-X Corporation, Boulder, Colorado 80303 (United States); Department of Physics, University of Colorado, Boulder, Colorado 80309 (United States)

2007-11-15

72

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

73

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

NASA Astrophysics Data System (ADS)

The development and dynamics of ionospheric plasma bubble (PB) irregularity during the super storm of 7-11 November 2004 are investigated using the data from a multi-instrument network operated in Southeast Asia. Analysis of fluctuations in Global Positioning System total electron content (GPS TEC), ionosonde, GPS scintillation, and in situ satellite density data indicates a series of intense PB-associated irregularities at equatorial, low, and middle latitudes in the Japanese longitude on 10 November. However, in the Chinese sector, the scintillations and PB irregularities are confined within the range of 20-50°N in geographic latitude and 110-125°E in geographic longitude. The absence of equatorial PB irregularities in this sector shows a major difference from that in the close-by longitude Japanese sector. In the Southern Hemisphere Australian sector, the irregularities occurrence is present as a symmetrical distribution at conjugate latitudes. Combined analysis of the data from Osan and Wuhan ionosondes illustrates that the middle-latitude spread F irregularities initially develop at the lower part of the F region and then distribute in the whole F region. This initiation of spread F at lower altitudes indicates that the middle-latitude PB-associated irregularities are locally generated. These results together with the irregularities occurrence sequence from higher to lower latitudes, and the onset time delay of several hours implies that the presence of PB-associated irregularities within a latitude range of 20-50°N in the Chinese sector cannot be attributed to the effects of prompt penetration electric fields (PPEFs), although the equatorial PBs in the close-by longitude are seen to be associated with PPEFs. The possible mechanism is the F region plasma instabilities triggered by wave structures, which act as an external driving force and seed active plasma dynamics and instability growth at middle latitude.

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

2009-07-01

74

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

NASA Astrophysics Data System (ADS)

This is the first study to compare plasma depletion drifts with the ambient plasma drifts and neutral winds in the post sunset equatorial ionosphere using global-scale satellite observations. 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 operated on the IMAGE satellite during 10 March to 7 June 2002. These depletion drift velocities are compared with the simultaneously measured ion drift velocities and 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 18:00-20:00 magnetic local time, and after 21:00, the variations of these velocities are similar. The difference of the plasma depletion drift with the background is found to be smaller at lower latitudes. Furthermore, the zonal drift velocity of the depletion is found 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 those studies use models and they only compare the depletion drifts with the modeled neutral winds. This study provides a measure of the difference that has never been studied before by any study using global observations. It has been suggested that polarization electric fields inside the plasma depletion structure drive the plasma to drift westward and thus the depletion structure moves to the east. The latitudinal gradient of the depletion drift velocity seen here in this study could also be explained by the polarization electric fields. For the C-shaped (reversed C) depletion, the polarization electric fields inside the depletion drive a westward drift of plasma and this drift velocity changes with increasing latitude. Consequently, the depletion drift has a latitudinal gradient becoming significant at higher latitudes.

Liu, Guiping; England, Scott L.; Frey, Harald U.; Immel, Thomas J.; Lin, Chin S.; Pacheco, Edgardo E.; Häusler, Kathrin; Doornbos, Eelco

2013-11-01

75

Equatorial Spread F Development\\/Disruption under Disturbance Electric Fields during Some Recent Intense Magnetic Storms  

Microsoft Academic Search

Equatorial spread F (ESF) and associated plasma bubble irregularity development can be initiated or inhibited under disturbance electric fields associated with magnetic storms. Case studies of ESF intensification\\/inhibition under intense storm conditions are rare, however. We have addressed this question using the data collected from the Brazilian network of Digisondes, a VHF radar and GPS scintillation receivers, complemented by Digisonde

M. A. Abdu; E. R. Paula; I. S. Batista; B. W. Reinisch; C. M. Denardini; J. H. Sobral

2006-01-01

76

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

77

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

E-print Network

-ray radiation from laser­plasma interactions (15­ 20), betatron radiation is straightforward and able to deliverConcurrence of monoenergetic electron beams and bright X-rays from an evolving laser-plasma bubble for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong

Wang, Wei Hua

78

Ponderomotive acceleration and the supra-bubble regime for electrons in tenuous plasmas  

NASA Astrophysics Data System (ADS)

In the present work, we study electron acceleration via interaction with ultraintense laser pulses in tenuous plasma. For electrons injected inside a pulse with arbitrary momenta, we demonstrate different regimes of ponderomotive acceleration and show that plasma dispersion affects this process at densities n/nc>a0-4, where nc is the critical plasma density, and a0=eA/mc^2 is the normalized laser amplitude, which we assume much larger than one. For a cold electron beam, the so-called supra-bubble acceleration is studied, when electrons are pushed by a moving ponderomotive potential ahead of the wakefield potential. In this case, the maximum energy gain, ?a0?g, is attained when the particle Lorentz factor ? is initially about ?g/a0, where ?g is the pulse group speed Lorentz factor. The supra-bubble acceleration scheme operates at ?g>=a0 and yields energies comparable to those attained through conventional wakefield acceleration for the same plasma and laser parameters.

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

2010-11-01

79

Formation and ascent of nonisothermal ionospheric and chromospheric bubbles  

SciTech Connect

The influences of nonisothermicity on the dynamics of ionospheric and chromospheric bubbles is discussed. The possibility of the existence in the ionosphere of a recombination-thermal instability, arising from the temperature dependence of the coefficient of charge exchange between molecules and atomic ions, is shown, and its influence on the formation and evolution of equatorial bubbles is analyzed. It is shown that the formation and dynamics of bubbles may depend on recombination processes and gravity, while plasma heating (predominantly by vertical electric fields) leads to the deepening and preservation of bubbles as they move to greater altitudes. The hypothesis is advanced that the formation of bubbles may be connected with the ascent of clumps of molecules in ionospheric tornados.

Genkin, L.G.; Erukhimov, L.M.; Myasnikov, E.N.; Shvarts, M.M.

1987-11-01

80

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

SciTech Connect

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

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

2008-09-15

81

Comment on 'Phenomenological theory of laser-plasma interaction in 'bubble' regime''[Phys. Plasmas 11, 5256 (2004)  

SciTech Connect

A reliable analytical expression for the maximum energy (gamma{sub max}) of the accelerated electrons in the bubble regime is derived. The presented equation is more consistent than the previous equation derived by Kostyukov et al. [Phys. Plasmas 11, 5256 (2004)]. The (gamma{sub max}) derived by I. Kostyukov et al. was two time larger than gamma{sub max} observed in the particle in the cell (PIC) simulations. This new equation explains the monoenergetic electron energy more accurately in the relativistic regime and is in consistence with the observed PIC simulations.

Rahmatollahpur, Sh. [Material School, 55515-196 Bonab (Iran, Islamic Republic of)

2010-05-15

82

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

83

Detection of localized, plasma-depleted flux tubes or bubbles in the midtail plasma sheet  

Microsoft Academic Search

Recent studies have shown that most Earthward transport in the midtail, high-beta plasma sheet takes place in the form of short-lived, high-speed plasma flow bursts. Bursty bulk flows are observed both when the plasma sheet ishin, such as during substorm expansion, and when it is thick, such as during substorm recovery. We present multi-instrument observations from the ISEE 1 and

V. A. Sergeev; V. Angelopoulos; J. T. Gosling; C. A. Cattell; C. T. Russell

1996-01-01

84

Equatorial distributions of the plasma sheet ions, their electric and magnetic drifts, and magnetic fields under different interplanetary magnetic field Bz conditions  

Microsoft Academic Search

To understand the nightside plasma sheet structure under different interplanetary magnetic field (IMF) Bz conditions, we have investigated statistically the equatorial distributions of ions and magnetic fields from Geotail when the IMF has been continuously northward or southward for shorter or longer than 1 hour. A dawn-dusk density (temperature) asymmetry with higher density (temperature) on the dawn (dusk) side is

Chih-Ping Wang; Larry R. Lyons; James M. Weygand; Tsugunobu Nagai; Richard W. McEntire

2006-01-01

85

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

NASA Astrophysics Data System (ADS)

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

Taori, A.; Sindhya, A.

2014-01-01

86

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

87

Trap Activation Energy and Transport Parameters of HgI$_2$ Crystals for Bubble-Plasma Diagnostics  

E-print Network

In recent data on neutron induced acoustic cavitation in deuterium--containing liquids obtained by neutron measurements it was shown that very high temperatures could arise in some special cases. To study temperature of so--called bubble plasma it is desirable to have micro--detectors of X-rays, which can be prepared on the basis of room--temperature semiconductor detectors, in particular on mercuric iodide ($\\alpha$--HgI$_2$) crystals. Having in view this aim, the properties of gel--grown ($\\alpha$--HgI$_2$) crystals was studied by means of isothermal currents, and trap parameters was estimated. Results are promising for special aim of preparing X-ray detectors with moderate energy resolution needed in bubble--plasma diagnostic, though improving of crystal growing technology is necessary. {\\it PACS:} 29.40.Wk; 52.70.La {\\it Keywords:} X-ray and gamma--ray measurements; semiconductor detectors; mercuric iodide; plasma diagnostics; cavitation

M. B. Miller; V. F. Kushniruk; A. V. Sermyagin

2003-01-13

88

Altitude-extended equatorial spread F observed near sunrise terminator over Indonesia  

Microsoft Academic Search

Spatial structure of a post-sunrise backscatter plume associated with a plasma bubble has been observed for the first time with the 47-MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (0.20°S, 100.32°E dip latitude 10.36°N). This plume is likely associated with a geomagnetic storm. It extended from what appears to be the base of the F layer into the topside

S. Fukao; Y. Ozawa; M. Yamamoto; R. T. Tsunoda

2003-01-01

89

Nature of axial tail instability and bubble-blob formation in near-Earth plasma sheet  

NASA Astrophysics Data System (ADS)

revious global magnetohydrodynamic (MHD) simulations of substorm events have identified the dynamic presence of an axial tail instability that is uniform in the dawn-dusk direction in the near-Earth plasma sheet. The axial tail instability is found to be a major cause of the initial growing MHD force imbalance on closed field lines prior to the subsequent magnetic reconnection and substorm expansion onset processes. In this work, energy principle analysis indicates that a two-dimensional thin current sheet configuration in the magnetotail is typically stable to the axial mode within the framework of ideal MHD model. However, linear resistive MHD calculations find axial tail instabilities on closed field lines in the generalized Harris sheet configurations. The properties of these instabilities are similar to the axial tail modes observed in the global MHD simulations. The axial tail mode is unstable in regimes of low Lundquist number and regions with small normal component of magnetic field. Such resistive axial tail instability would by many researchers be considered as tearing instability in a two-dimensional tail configuration. Unlike the conventional tearing mode of Harris sheet, the linear axial tail instability does not involve any reconnection process. Instead, the nature of the mode is dominantly a slippage process among neighboring flux tubes as facilitated by resistive dissipation. A natural consequence of the axial tail instability is shown to be the formation of bubble-blob pairs in the pressure and entropy profiles in the near-Earth plasma sheet.

Zhu, P.; Raeder, J.; Hegna, C. C.; Sovinec, C. R.

2013-02-01

90

The generation of azimuthal magnetic field in laser-induced plasma bubbles  

SciTech Connect

A two-dimensional (2D) analytical model for a laser-induced bubble is rebuilt by taking into account the generation of azimuthal magnetic field. It is shown that the azimuthal magnetic field surrounds the bubble transversely, whose amplitude peaks at the bubble edge and vanishes at laser axis. In a laser wakefield acceleration scheme, the longitudinal electric field accelerates the electrons injected from the rear of the bubble, while the azimuthal magnetic field makes the resulting energetic-electron beam converge. The analytical model is justified by a 2D Particle in Cell (PIC) simulation.

Zhou Suyun [Modern Institute of Optical Technologies, Soochow University, Suzhou 215006 (China); Communication and Electronic School, Jiangxi Science and Technology Normal University, Jiangxi 330013 (China); Yu Wei; Wang Xin; Ma Guangjing [Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Science, Shanghai 201800 (China); Yuan Xiao [Modern Institute of Optical Technologies, Soochow University, Suzhou 215006 (China); Xu Han [National Laboratory for Parallel and Distributed Processing, School of Computer Science, National University of Defense Technology, Changsha 410073 (China)

2010-11-15

91

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

92

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

93

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

94

Ionospheric bubbles detection algorithms: Analysis in low latitudes  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

95

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

96

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

97

Interchange Instability and "Bubbles" Gravitational Rayleigh-Taylor  

E-print Network

Interchange Instability and "Bubbles" Linear Nonlinear: Bubbles, fingers, vortices Magnetosphere #12;Jovian Magnetosphere #12;Interchange Bubbles should Propagate Inward through the Io Plasma al., JGR (1994) Jovian day is 11 hours! #12;Interchange Bubble seen in Jovian Magnetosphere? B. H

Mauel, Michael E.

98

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

99

Electron density and electric field fluctuations associated with developing plasma bubbles  

Microsoft Academic Search

In situ measurements of the height variation of the ionospheric electric field and electron density were made on 18 December, 1995 at 2117h (LT) from the equatorial station Alcantara (2.31°S44.4°W) in Brazil, with a rocket-borne electric field double probe and two different types of electron density probes. The main objective of the experiment was to study the characteristic features of

P. Muralikrishna; L. P. Vieira; M. A. Abdu

2003-01-01

100

Electron density and electric field fluctuations associated with developing plasma bubbles  

Microsoft Academic Search

In situ measurements of the height variation of the ionospheric electric field and electron density were made on 18 December, 1995 at 2117h (LT) from the equatorial station Alcantara (2.31°S;44.4°W) in Brazil, with a rocket-borne electric field double probe and two different types of electron density probes. The main objective of the experiment was to study the characteristic features of

P. Muralikrishna; L. P. Vieira; M. A. Abdu

2003-01-01

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

Equatorial Guinea.  

PubMed

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

1984-06-01

103

An axisymmetric magnetohydrodynamic model for the Crab pulsar wind bubble  

NASA Technical Reports Server (NTRS)

We extend Kennel and Coroniti's (1984) spherical magnetohydrodynamic models for the Crab Nebula to include the pinching effect of the toroidal magnetic field. Since the bulk nebular flow is likely to be very submagnetosonic, a quasi-static treatment is possible. We show that the pinching effect can be responsible for the observed elongation of the pulsar wind bubble, as indicated by the surface brightness contours of optical synchrotron radiation. From the observed elongation we estimate a value for sigma, the ratio of Poynting flux to plasma kinetic energy flux in the free pulsar wind, which is consistent with previous results from spherical models. Using the inferred magnetic field configuration inside the pulsar wind bubble, combined with the observed dimensions of the X-ray nebula, we are able to constrain the particle distribution function. We conclude that, for a power-law injection function, the maximum energy has to be much larger in the pulsar equatorial region than in the polar region.

Begelman, Mitchell C.; Li, Zhi-Yun

1992-01-01

104

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

E-print Network

, chiefly to relate these to the scale size and amplitude of electron density fluctuations in the ionosphere October 1996 Abstract. An important component of ionospheric plasma irregularity studies in the Indian low together with a higher order filter indicate a higher level of coherence for the plasma irregularities

Boyer, Edmond

105

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

106

Method for characterization of the equatorial anomaly using image subspace analysis of Global Ultraviolet Imager data  

NASA Astrophysics Data System (ADS)

We present a method for measuring equatorial anomaly (EA) morphology using nighttime 135.6 nm radiance observed by the Global Ultraviolet Imager (GUVI) on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) spacecraft. The method uses the singular value decomposition to estimate an along-track intensity profile as TIMED passes over the EA. The method is unique in that it removes intensity depletions due to equatorial plasma bubbles (EPBs) from the estimated intensity profile. Thus the profiles reflect plasma distribution in response to equatorial E × B drifts and neutral winds. A set of metrics including crest maximum intensity and its latitude are extracted from the intensity profiles. EPBs are also detected. Preliminary results from this method using GUVI equinox data from 2002 are compared with results from a ground-based ionosonde EA morphology study by Whalen (2001) in the western American sector. EPB occurrence rates are also compared with results from Huang et al. (2001), who used DMSP in situ density measurements to detect EPBs. General agreement was found in both studies with some localized differences. These results indicate that this method provides a valuable means of simultaneously studying EA morphology and EPB occurrence rates. Since the TIMED spacecraft precesses through all local times in 60 days, this method can be used to extend ground-based measurements to study the global relationship between E × B drifts and plasma distribution in the EA and how these relate to the occurrence of large-scale EPBs.

Henderson, S. B.; Swenson, C. M.; Gunther, J. H.; Christensen, A. B.; Paxton, L. J.

2005-08-01

107

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.

108

Measurements of the correlation between plasma bubble dynbamics and electron trapping in a laser wakefield accelerator  

Microsoft Academic Search

Summary form only given. Generation of conically emitted second harmonic radiation has recently been observed in a laser wakefield accelerator experiment at the U.S. Naval Research Laboratory. This second harmonic is the result of frequency mixing within the sheath surrounding a fully cavitated plasma region, \\

D. Kaganovich; M. Helle; D. Gordon; A. Ting

2010-01-01

109

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

110

PUBLISHED ONLINE: 27 JUNE 2010 | DOI: 10.1038/NPHYS1701 Inertially confined plasma in an imploding bubble  

E-print Network

. A bubble acoustically driven into nonlinear radial oscillation can focus the diffuse energy of the sound velocity to be greater than the speed of sound with enormous acceleration near maximum collapse10

Suslick, Kenneth S.

111

Bubble Puzzles  

NASA Astrophysics Data System (ADS)

Bubbles are fascinating. With their ubiquitous occurrence in a multitude of fluid systems bubbles occupy a very important place in contemporary science and technology. In many applications, bubble control is crucial. I will demonstrate that bubble nucleation at surfaces, which always has been associated with randomness, can be perfectly controlled both in space and time. This new technique allows to quantitatively study bubble-bubble and bubble-surface interaction and reveals a shielding effect in bubble clusters [1]. -- In a second example for the importance of bubble control I will discuss their disturbing effect in piezo-acoustic ink-jet printing: I will show how bubbles are entrained, grow by rectified diffusion, and finally seriously disturb the jetting process by counteracting the pressure build-up at the nozzle [2]. [1] N. Bremond, M. Arora, C. D. Ohl, and D. Lohse, Phys. Rev. Lett. 96, 224501 (2006). [2] J. de Jong, H. Reinten, M. van den Berg, H. Wijshoff, M. Versluis, G. de Bruin, and D. Lohse, J. Acoust. Soc. Am., (August 2006).

Lohse, Detlef

2006-11-01

112

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

Microsoft Academic Search

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

B. M. Ledvina; J. J. Makela

2005-01-01

113

Equatorial MU Radar project  

NASA Astrophysics Data System (ADS)

Research Institute for Sustainable Humanosphere, Kyoto University (RISH) has been studying the atmosphere by using radars. The first big facility was the MU (Middle and Upper atmosphere) radar installed in Shiga, Japan in 1984. This is one of the most powerful and multi-functional radar, and is successful of revealing importance of atmospheric waves for the dynamical vertical coupling processes. The next big radar was the Equatorial Atmosphere Radar (EAR) installed at Kototabang, West Sumatra, Indonesia in 2001. The EAR was operated under close collaboration with LAPAN (Indonesia National Institute for Aeronautics and Space), and conducted the long-term continuous observations of the equatorial atmosphere/ionosphere for more than 10 years. The MU radar and the EAR are both utilized for inter-university and international collaborative research program for long time. National Institute for Polar Research (NIPR) joined EISCAT Scientific Association together with Nagoya University, and developed the PANSY radar at Syowa base in Antarctica as a joint project with University of Tokyo. These are the efforts of radar study of the atmosphere/ionosphere in the polar region. Now we can find that Japan holds a global network of big atmospheric/ionospheric radars. The EAR has the limitation of lower sensitivity compared with the other big radars shown above. RISH now proposes a plan of Equatorial MU Radar (EMU) that is to establish the MU-radar class radar next to the EAR. The EMU will have an active phased array antenna with the 163m diameter and 1055 cross-element Yagis. Total output power of the EMU will be more than 500kW. The EMU can detect turbulent echoes from the mesosphere (60-80km). In the ionosphere incoherent-scatter observations of plasma density, drift, and temperature would be possible. Multi-channel receivers will realize radar-imaging observations. The EMU is one of the key facilities in the project "Study of coupling processes in the solar-terrestrial system" for Master Plan 2014 of the Science Council of Japan (SCJ). We show the EMU project and its science in the presentation.

Yamamoto, Mamoru; Hashiguchi, H.; Tsuda, Toshitaka; Yamamoto, Masayuki

114

Evidence of cell damages caused by circulating bubbles: high level of free mitochondrial DNA in plasma of rats.  

PubMed

Bubble formation can occur in the vascular system after diving, leading to decompression sickness (DCS). DCS signs and symptoms range from minor to death. Too often, patients are admitted to a hyperbaric center with atypical symptoms, as bubbles cannot be detected anymore. In the absence of a relevant biomarker for humans, the therapeutic management remains difficult. As circulating DNA was found in the blood of healthy humans and animals, our study was made to correlate the extracellular mitochondrial DNA (mDNA) concentration with the occurrence of clinical DCS symptoms resulting from initial bubble-induced damages. Therefore, 109 rats were subjected to decompression from a simulated 90-m sea water dive, after which, 78 rats survived (71.6%). Among the survivors, 15.6% exhibited typical DCS symptoms (DCS group), whereas the remaining 56% showed no detectable symptoms (noDCS group). Here, we report that the symptomatic rats displayed both a circulating mDNA level (DNADCS ? 2.99 ± 2.62) and a bubble grade (median Spencer score = 3) higher than rats from the noDCS group (DNAnoDCS ? 1.49 ± 1.27; Spencer score = 1). These higher levels could be correlated with the platelet and leukocyte consumption induced by the pathogenic decompression. Rats with no detectable bubble had lower circulating mDNA than those with higher bubble scores. We determined that in rats, a level of circulating mDNA >1.91 was highly predictive of DCS with a positive-predictive value of 87.3% and an odds ratio of 4.57. Thus circulating mDNA could become a relevant biomarker to diagnose DCS and should be investigated further to confirm its potential application in humans. PMID:24072411

Vallée, Nicolas; Gaillard, Sandrine; Peinnequin, André; Risso, Jean-Jacques; Blatteau, Jean-Eric

2013-11-01

115

Bubble Baryogenesis  

E-print Network

We propose an alternative mechanism of baryogenesis in which a scalar baryon undergoes a percolating first-order phase transition in the early Universe. The potential barrier that divides the phases contains explicit B and CP violation and the corresponding instanton that mediates decay is therefore asymmetric. The nucleation and growth of these asymmetric bubbles dynamically generates baryons, which thermalize after percolation; bubble collision dynamics can also add to the asymmetry yield. We present an explicit toy model that undergoes bubble baryogenesis, and numerically study the evolution of the baryon asymmetry through bubble nucleation and growth, bubble collisions, and washout. We discuss more realistic constructions, in which the scalar baryon and its potential arise amongst the color-breaking minima of the MSSM, or in the supersymmetric neutrino seesaw mechanism. Phenomenological consequences, such as gravitational waves, and possible applications to asymmetric dark-matter generation are also discussed.

Clifford Cheung; Alex Dahlen; Gilly Elor

2012-05-15

116

Session: Poster (Nov. 27 Dec. 1, 2006) Study of Equatorial Spread F using L-Band and VHF Radar (P1)  

NASA Astrophysics Data System (ADS)

An important component of ionospheric plasma irregularity studies in the Indian low latitudes involves the study of the plasma bubbles which produce intense scintillations of the transionospheric satellite signals. In order to investigate the dynamics of plasma density irregularities of different scale sizes, a campaign of observations was conducted during 11 to 15 September 2005 at Gadanki (geog.13.450N, 79.170E, geomag. Coor. 4.440N, 151.730E), an Indian station. A low latitude spread F event occurred over India during the campaign at the night of 15 September 2005. The observations using dual frequency GPS receiver, VHF coherent backscatter radar, and two ionosondes with some latitudinal separation has been made. Range type spread F on ionograms and radar plume signatures on range-time-intensity maps of the VHF radar on the same day was observed. Using the GPS receiver, the association of the fluctuations in the intensity (S4 ~ 0.36 and 0.39) with the depletions in total electron content ( 5 and 12 TECU) are seen on the same day which affect the positional accuracy of the GPS by 0.8m and 1.92m. The drift velocity is observed to be high (~30 m/s) and the plasma drift is maximum at 1915LT. The irregularities are observed first at Trivandrum (equatorial station) at 1915hrs, then is observed by GPS receiver and then by VHF radar (off- equatorial station) indicating that the observed bubble is drifting eastward.

Aggarwal, M.; Joshi, H. P.; Iyer, K. N.

2006-11-01

117

Recent results from CHAMP plasma parameter and magnetic field observations  

NASA Astrophysics Data System (ADS)

The multi-year data base of magnetic field and ionospheric measurements from the CHAMP satellite contains an enormous potential to investigate the behaviour and the origin of currents in the F region. Very prominent phenomena are the post-sunset equatorial plasma irregularities (commonly known as "bubbles", or "Equatorial Spread-F" (ESF)) which cause also signatures in the total magnetic field due to diamagnetic currents. The continuous magnetic observations, available at a 1Hz rate, have allowed for the compilation of a comprehensive climatology of the magnetic signatures due to ESF. It reveals a distinct seasonal/longitudinal (S/L) distribution, and the occurrence rate reduces considerably with decreasing solar flux. The (S/L) distribution of bubbles has been found to correlate very well, up to 90 percent, with the pre-reversal enhancement vertical plasma drift peak. This provides strong evidence for the close relation between these phenomena. Since the amplitude of the diamagnetic effect depends on the ambient magnetic field strength and on the background electron density, the global distribution shows also slight differences to the ESF climatology based on plasma depletions. Although electron density readings are only available every 15s, CHAMP data suggest that the plasma irregularities are less structured at places where the ambient magnetic field is strong (e.g. East Asia, Indonesia). In these regions the bubble statistic based on magnetic signatures is systematically lower than that from plasma measurements.

Stolle, Claudia; Luehr, Hermann; Park, Jaeheung; Xiong, Chao; Fejer, B. G.

118

Exploring Bubbles  

NASA Astrophysics Data System (ADS)

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

O'Geary, Melissa A.

119

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

120

Resent Status of ITER Equatorial Launcher Development  

Microsoft Academic Search

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

K. Takahashi; K. Kajiwara; A. Kasugai; Y. Oda; N. Kobayashi; K. Sakamoto

2009-01-01

121

The Coudé Equatorials  

NASA Astrophysics Data System (ADS)

Between 1884 and 1892, no fewer than seven coudé equatorials were installed in France, Algeria and Austria. Invented by Maurice Loewy, these equatorials allowed the observer to sit comfortably in a closed room, with all the controls and readings at hand. However they were expensive, they required two flat mirrors, which were a source of concern because of their thermal distortion, and their mechanics was complex and delicate, so that they did not succeed in replacing the conventional equatorials in spite of their advantages. Only two are preserved, in Lyons and in Algiers. We describe in detail these instruments, their history and their use.

Lequeux, James

2011-11-01

122

Specification of the occurrence of equatorial ionospheric scintillations during the main phase of large magnetic storms within solar cycle 23  

NASA Astrophysics Data System (ADS)

Satellite communication and navigation systems operating at low latitudes suffer outages due to ionospheric scintillations during large magnetic storms that are not currently specified by any model. This paper describes and demonstrates how in the framework of an eastward electric field penetration from high to low latitudes at dusk during the main phase of a large storm, for which the rate of change of Dst ? -50 nT/h and the Dst minimum index ? -100 nT, it is possible to specify the longitude interval within the low-latitude ionosphere where scintillations and plasma bubbles are most likely to occur. It is known that the eastward prompt penetration electric field becomes enhanced near sunset due to the day-to-night conductivity gradient. Such enhanced eastward electric fields generally set off the Rayleigh-Taylor plasma instability at F region heights and cause the formation of plasma bubbles and irregularities of electron density that give rise to scintillations of satellite signals. We first discuss two individual magnetic storms that satisfy the criterion of large magnetic storms mentioned above and for which the onsets of the main phase are about 15 h apart. We show that the dusk sectors corresponding to these two storms are such that irregularities and scintillations were observed in the Atlantic-Peruvian longitude sector for one storm and in the Pacific sector for the other. We then present a statistical study with 30 large magnetic storms during solar cycle 23 which satisfy the two criteria of large magnetic storms and we attempt to specify the longitude interval of irregularity and scintillation occurrence during the main phase of such storms. We have tracked globally the occurrence of equatorial scintillations during magnetic storms by the use of scintillation observations made by the Air Force Research Laboratory's Scintillation Network Decision Aid (SCINDA) network and the DMSP satellite in situ measurements of plasma bubbles at 840 km. The statistical study reveals that during large magnetic storms, scintillations and plasma bubbles occur over a specific longitude sector for which the local dusk corresponds to the time interval of the main phase of storms. The magnetic storm induced scintillations may enhance the general seasonal/longitudinal pattern of quiet time scintillations at the station but may also occur where it is least expected in accordance with climatology. The storm time response of the equatorial ionosphere discussed in this paper will be implemented in the SCINDA algorithm to enhance its capability to specify scintillations during large magnetic storms.

Basu, S.; Basu, Su.; MacKenzie, E.; Bridgwood, C.; Valladares, C. E.; Groves, K. M.; Carrano, C.

2010-10-01

123

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

124

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

125

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

126

Response of equatorial, low- and mid-latitude F-region in the American sector during the intense geomagnetic storm on 24-25 October 2011  

NASA Astrophysics Data System (ADS)

In this paper, we present and discuss the response of the ionospheric F-region in the American sector during the intense geomagnetic storm which occurred on 24-25 October 2011. In this investigation ionospheric sounding data obtained of 23, 24, 25, and 26 October 2011 at Puerto Rico (United States), Jicamarca (Peru), Palmas, São José dos Campos (Brazil), and Port Stanley, are presented. Also, the GPS observations obtained at 12 stations in the equatorial, low-, mid- and high-mid-latitude regions in the American sector are presented. During the fast decrease of Dst (about ˜54 nT/h between 23:00 and 01:00 UT) on the night of 24-25 October (main phase), there is a prompt penetration of electric field of magnetospheric origin resulting an unusual uplifting of the F region at equatorial stations. On the night of 24-25 October 2011 (recovery phase) equatorial, low- and mid-latitude stations show h'F variations much larger than the average variations possibly associated with traveling ionospheric disturbances (TIDs) caused by Joule heating at high latitudes. The foF2 variations at mid-latitude stations and the GPS-VTEC observations at mid- and low-latitude stations show a positive ionospheric storm on the night of 24-25 October, possibly due to changes in the large-scale wind circulation. The foF2 observations at mid-latitude station and the GPS-VTEC observations at mid- and high-mid-latitude stations show a negative ionospheric storm on the night of 24-25 October, probably associated with an increase in the density of molecular nitrogen. During the daytime on 25 October, the variations in foF2 at mid-latitude stations show large negative ionospheric storm, possibly due to changes in the O/N2 ratio. On the night of 24-25, ionospheric plasma bubbles (equatorial irregularities that extended to the low- and mid-latitude regions) are observed at equatorial, low- and mid-latitude stations. Also, on the night of 25-26, ionospheric plasma bubbles are observed at equatorial and low-latitude regions.

de Jesus, R.; Sahai, Y.; Fagundes, P. R.; de Abreu, A. J.; Brunini, C.; Gende, M.; Bittencourt, J. A.; Abalde, J. R.; Pillat, V. G.

2013-07-01

127

COLD BUBBLE FORMATION DURING TOKAMAK DENSITY LIMIT DISRUPTIONS  

E-print Network

COLD BUBBLE FORMATION DURING TOKAMAK DENSITY LIMIT DISRUPTIONS J. HOWARD, M. PERSSON* Plasma leading to the penetration of a cold bubble-like plasma volume to the centre. The role of mode coupling, With the energy mainly lost through radiation, the plasma becomes thermally detached from the wall, which leads

Howard, John

128

Steady bubble rise and deformation in Newtonian and viscoplastic fluids and conditions for bubble entrapment  

NASA Astrophysics Data System (ADS)

We examine the buoyancy-driven rise of a bubble in a Newtonian or a viscoplastic fluid assuming axial symmetry and steady flow. Bubble pressure and rise velocity are determined, respectively, by requiring that its volume remains constant and its centre of mass remains fixed at the centre of the coordinate system. The continuous constitutive model suggested by Papanastasiou is used to describe the viscoplastic behaviour of the material. The flow equations are solved numerically using the mixed finite-element/Galerkin method. The nodal points of the computational mesh are determined by solving a set of elliptic differential equations to follow the often large deformations of the bubble surface. The accuracy of solutions is ascertained by mesh refinement and predictions are in very good agreement with previous experimental and theoretical results for Newtonian fluids. We determine the bubble shape and velocity and the shape of the yield surfaces for a wide range of material properties, expressed in terms of the Bingham Bn=tau_y(*}/rho({*}g^{*)) R_b(*) Bond Bo =rho(*}g({*)) R_b({*) 2}/gamma(*) and Archimedes Ar=rho(*2}g({*)) R_b(*3}/mu_o({*2)) numbers, where *o the viscosity, *y the yield stress of the material, g* the gravitational acceleration and R*b the radius of a spherical bubble of the same volume. If the fluid is viscoplastic, the material will not be deforming outside a finite region around the bubble and, under certain conditions, it will not be deforming either behind it or around its equatorial plane in contact with the bubble. As Bn increases, the yield surfaces at the bubble equatorial plane and away from the bubble merge and the bubble becomes entrapped. When Bo is small and the bubble cannot deform from the spherical shape the critical Bn is 0.143, i.e. it is a factor of 3/2 higher than the critical Bn for the entrapment of a solid sphere in a Bingham fluid, in direct correspondence with the 3/2 higher terminal velocity of a bubble over that of a sphere under the same buoyancy force in Stokes flow. As Bo increases allowing the bubble to squeeze through the material more easily, the critical Bingham number increases as well, but eventually it reaches an asymptotic value. Ar affects the critical Bn value much less.

Tsamopoulos, J.; Dimakopoulos, Y.; Chatzidai, N.; Karapetsas, G.; Pavlidis, M.

129

Ionospheric Research with Miniaturized Plasma Sensors Aboard FalconSAT-3  

NASA Astrophysics Data System (ADS)

Investigations into a novel technique to measure ionosphere-thermosphere parameters have culminated in the Flat Plasma Spectrometer (FLAPS) experiment, presently under development through a collaboration between NASA Goddard Space Flight Center (GSFC) and the U. S. Air Force Academy (USAFA). FLAPS is capable of providing measurements of the full neutral wind vector, full ion-drift velocity vector, neutral and ion temperatures, and deviations from thermalization. In addition, coarse mass spectroscopy is possible using an energy analysis technique. The suite of instruments is comprised of a set of 16 individual neutral and ion analyzers, each of which is designed to perform a specific function. Advances in miniaturization technology have enabled a design in which the 16-sensor suite resides on a circular microchannel plate with an effective area of 25 cm2. The FLAPS electronics package, consisting of low voltage and high voltage power supplies, a microprocessor, and Application Specific Integrated Circuit (ASIC) amplifiers, requires a volume of 290 cm3, power of 1.5 W, and a mass of 500 g. The suite requires a +5V regulated power line from the spacecraft, and the telemetry interface is a 5.0 V TTL-compatible serial connection. Data collection rates vary from 1 to 1000 (192 Byte) spectra per second. The motivation for the FLAPS experiment is driven by objectives that fall into both basic science and technology demonstration categories. Scientifically, there is strong interest in the effects of ionosphere-thermosphere coupling and non-thermalized plasma on the processes associated with equatorial F-region ionospheric plasma bubbles. These bubbles have been known to scintillate transionospheric propagation of radio waves, often resulting in disruptions of space-based communication and navigation systems. FLAPS investigations will assist in quantifying the impact of various processes on the instigation or suppression of plasma bubbles; certain outstanding questions include 1) What is the relevance of meridional winds in suppression of plasma bubble growth? 2) What role does a velocity space instability driven by non-thermalized plasma play in the generation of small scale (<1 km) bubbles? 3) What process is responsible for turbulence in plasma beyond the edges of a bubble structure? Technologically, the need for small yet capable instruments arises from the desire to make multipoint in situ measurements of "microscopic" plasma parameters to provide insight into "macroscopic" phenomena. Examples include coherency of spatial boundaries of large-scale ( ˜100 km) plasma bubbles, three dimensional structure of the equatorial wind and temperature anomaly, and vertical velocity gradients in the low latitude ionosphere. This paper provides an overview of the experiment motivation and instrument design of the FLAPS experiment.

Habash Krause, L.; Herrero, F. A.; Chun, F. K.; McHarg, M. G.

2003-12-01

130

Equatorial and low latitude spread-F irregularity characteristics over the Indian region and their prediction possibilities  

NASA Astrophysics Data System (ADS)

To study the occurrence characteristics of equatorial spread-F irregularities and their latitudinal extent, simultaneous digital ionosonde data (January December 2001) from Trivandrum (8.2°N), Waltair (17.7°N) and Delhi (28.6°N) and 4 GHz scintillation data from Sikandarabad (26.8°N) and Chenglepet (10.4°N), and 250 MHz scintillation data from Bhopal (23.2°N) for equinoxes period are analysed. It is noted that except summer months, occurrence of spread F is always maximum at Trivandrum, minimum at Delhi and moderate at Waltair. During equinoxes and winter months. Their occurrences at higher latitude station are always conditional to their prior occurrences at lower latitudes indicating their association with the generation of equatorial plasma bubble and associated irregularities. Scintillation occurrences also follow the similar pattern. During the summer months, the spread-F occurrences are highest at equatorial location Trivandrum, moderate at Delhi and minimum at Waltair and seem to be caused by irregularities generated locally especially over Delhi. To gain forecasting capability, night-to-night occurrences of spread-F/scintillation at these locations are examined in relation to post sunset rise of h’F and upward ExB drift velocity over the magnetic equator using Trivandrum ionosonde data. It is noted that except the summer months, the spread-F at Trivandrum, Waltair and Delhi are observed only when equatorial ExB (h’F) is more than about 15 m/s (325 km), 20 m/s (350 km) and 25 m/s (375 km), respectively. With these threshold values their corresponding success rate of predictions are more than 90%, 50% and 15% at the respective locations. Whereas in the case of GHz scintillations near equator are observed only when ExB (h’F) is more than 15 m/s (325 km), whereas for low latitude, the same should be 30 m/s (400 km) and their success rate of prediction is about 90% and 30%, respectively. The intensity of 4 GHz scintillation at low latitude is also found to be positively correlated with equatorial upward ExB drift velocity values, whereas correlation is poor with that of equatorial scintillations. In conclusions, near magnetic equator threshold values of ExB or h’F can be successfully used for the night-to-night prediction of spread-F/scintillations occurrences, whereas these are necessary but not sufficient for their prediction at higher latitudes. For that some other controlling parameters like background electron density, neutral winds, gravity waves, etc. should also be examined.

Dabas, R. S.; Das, Rupesh M.; Sharma, Kavita; Garg, S. C.; Devasia, C. V.; Subbarao, K. S. V.; Niranjan, K.; Rama Rao, P. V. S.

2007-04-01

131

Acoustic bubble removal method  

NASA Technical Reports Server (NTRS)

A method is described for removing bubbles from a liquid bath such as a bath of molten glass to be used for optical elements. Larger bubbles are first removed by applying acoustic energy resonant to a bath dimension to drive the larger bubbles toward a pressure well where the bubbles can coalesce and then be more easily removed. Thereafter, submillimeter bubbles are removed by applying acoustic energy of frequencies resonant to the small bubbles to oscillate them and thereby stir liquid immediately about the bubbles to facilitate their breakup and absorption into the liquid.

Trinh, E. H.; Elleman, D. D.; Wang, T. G. (inventors)

1983-01-01

132

Bubbles and Superbubbles  

E-print Network

An isolated massive star can blow a bubble, while a group of massive stars can blow superbubbles. In this paper, we examine three intriguing questions regarding bubbles and superbubbles: (1) why don't we see interstellar bubbles around every O star? (2) how hot are the bubble interiors? and (3) what is going on at the hot/cold gas interface in a bubble?

Y. -H. Chu; M. A. Guerrero; R. A. Gruendl

2003-10-10

133

Buoyant Bubbles in a Cooling Intracluster Medium I. Hydrodynamic Bubbles  

E-print Network

Over the past several years, numerous examples of X-ray cavities coincident with radio sources have been observed in so-called "cool core" clusters of galaxies. Motivated by these observations, we explore the evolution and the effect of cavities on a cooling intracluster medium (ICM) numerically, adding relevant physics step by step. In this paper we present a first set of hydrodynamical, high resolution (1024^3 effective grid elements), three-dimensional simulations, together with two-dimensional test cases. The simulations follow the evolution of radio cavities, modeled as bubbles filled by relativistic plasma, in the cluster atmosphere while the ICM is subject to cooling. We find that the bubble rise retards the development of a cooling flow by inducing motions in the ICM which repeatedly displace the material in the core. Even bubbles initially set significantly far from the cluster center affect the cooling flow, although much later than the beginning of the simulation. The effect is, however, modest: the cooling time is increased by at most only 25%. As expected, the overall evolution of pure hydrodynamic bubbles is at odds with observations, showing that some additional physics has to be considered in order to match the data.

A. Gardini

2006-11-14

134

Characterization of transverse beam emittance of electrons from a laser-plasma wakefield accelerator in the bubble regime using betatron x-ray radiation  

NASA Astrophysics Data System (ADS)

We propose and use a technique to measure the transverse emittance of a laser-wakefield accelerated beam of relativistic electrons. The technique is based on the simultaneous measurements of the electron beam divergence given by v?/v?, the measured spectrum ?, and the transverse electron bunch size in the bubble r?. The latter is obtained via the measurement of the source size of the x rays emitted by the accelerating electron bunch in the bubble. We measure a normalized rms beam transverse emittance <0.5?mmmrad as an upper limit for a spatially Gaussian, spectrally quasimonoenergetic electron beam with 230 MeV energy in agreement with numerical modeling and analytic theory in the bubble regime.

Kneip, S.; McGuffey, C.; Martins, J. L.; Bloom, M. S.; Chvykov, V.; Dollar, F.; Fonseca, R.; Jolly, S.; Kalintchenko, G.; Krushelnick, K.; Maksimchuk, A.; Mangles, S. P. D.; Najmudin, Z.; Palmer, C. A. J.; Phuoc, K. Ta; Schumaker, W.; Silva, L. O.; Vieira, J.; Yanovsky, V.; Thomas, A. G. R.

2012-02-01

135

Atypical nighttime spread-F structure observed near the southern crest of the ionospheric equatorial ionization anomaly  

NASA Astrophysics Data System (ADS)

An atypical nighttime spread-F structure is observed on ionograms at or above the F2 trace, near the crest of the ionospheric equatorial ionization anomaly (EIA) region. This ionospheric atypical spread-F phenomenon was observed using two closed spaced (˜115 km) ionospheric soundings stations located in Sao Jose dos Campos (23.21°S, 45.97°W) and Cachoeira Paulista (22.70°S, 45.01°W), Brazil, in a low-latitude station (near the southern crest of the EIA region), during nighttime, low solar activity, and quiet geomagnetic conditions. This structure, in the initial phase, appears in the ionogram as a faint spread-F trace above or at the F2-layer peak height. After a few minutes, it develops into a strong spread-F trace, and afterwards, it moves to altitudes below the F2-layer peak heights. Finally, the atypical nighttime F-layer trace structure may remain for a while between the F-layer bottom side and peak height or can move to an altitude above the F-layer peak height, and then it disappears. In order to have a comprehensive view of the ionospheric environment characterizing the phenomenon under study, complementary data from six GPS station were used to investigate the ionosphere environment conditions, during both events. The six GPS stations used in this study are distributed from near the equatorial region to low latitudes and provide evidence that the atypical nighttime spread-F structures are not related with large scale equatorial irregularities (plasma bubbles).

Fagundes, P. R.; Bittencourt, J. A.; de Abreu, A. J.; Moor, L. P.; Muella, M. T. A. H.; Sahai, Y.; Abalde, J. R.; Pezzopane, M.; Sobral, J. H. A.; Abdu, M. A.; Pimenta, A. A.; Amorim, D. C. M.

2012-04-01

136

Soap-bubble growth  

Microsoft Academic Search

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

M. Marder

1987-01-01

137

Soap Bubbles and Logic.  

ERIC Educational Resources Information Center

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

Levine, Shellie-helane; And Others

1986-01-01

138

Lightning over Equatorial Africa  

NASA Technical Reports Server (NTRS)

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

2002-01-01

139

Brut: Automatic bubble classifier  

NASA Astrophysics Data System (ADS)

Brut, written in Python, identifies bubbles in infrared images of the Galactic midplane; it uses a database of known bubbles from the Milky Way Project and Spitzer images to build an automatic bubble classifier. The classifier is based on the Random Forest algorithm, and uses the WiseRF implementation of this algorithm.

Beaumont, Christopher; Goodman, Alyssa; Williams, Jonathan; Kendrew, Sarah; Simpson, Robert

2014-07-01

140

Oscillations of soap bubbles  

Microsoft Academic Search

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

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

2010-01-01

141

Soap Bubbles in Reverse  

Microsoft Academic Search

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

Leslie Rose

1946-01-01

142

Soap Films and Bubbles.  

ERIC Educational Resources Information Center

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

Rice, Karen

1986-01-01

143

Stable Coulomb bubbles ?  

E-print Network

Coulomb bubbles, though stable against monopole displacement, are unstable at least with respect to quadrupole and octupole distortions. We show that there exists a temperature at which the pressure of the vapor filling the bubble stabilizes all the radial modes. In extremely thin bubbles, the crispation modes become unstable due to the surface-surface interaction.

L. G. Moretto; K. Tso; G. J. Wozniak

1996-12-12

144

7, 1168511723, 2007 Equatorial wave  

E-print Network

EGU al., 2001). As a result of the interaction with the QBO winds tropical wave activity itself shows-called "tropical pipe", which is more stable during QBO easterly phases. Therefore equatorial waves play

Paris-Sud XI, Université de

145

Radio Bubbles in Clusters of Galaxies  

SciTech Connect

We extend our earlier work on cluster cores with distinct radio bubbles, adding more active bubbles, i.e. those with GHz radio emission, to our sample, and also investigating ''ghost bubbles'', i.e. those without GHz radio emission. We have determined k, which is the ratio of the total particle energy to that of the electrons radiating between 10MHz and 10GHz. Constraints on the ages of the active bubbles confirm that the ratio of the energy factor, k, to the volume filling factor, f lies within the range 1 {approx}< k/f {approx}< 1000. In the assumption that there is pressure equilibrium between the radio-emitting plasma and the surrounding thermal X-ray gas, none of the radio lobes has equipartition between the relativistic particles and the magnetic field. A Monte-Carlo simulation of the data led to the conclusion that there are not enough bubbles present in the current sample to be able to determine the shape of the population. An analysis of the ghost bubbles in our sample showed that on the whole they have higher upper limits on k/f than the active bubbles, especially when compared to those in the same cluster. A study of the Brightest 55 cluster sample shows that 17, possibly 20, clusters required some form of heating as they have a short central cooling time, t{sub cool} {approx}< 3 Gyr, and a large central temperature drop, T{sub centre}/T{sub outer} < 1/2. Of these between 12 (70 per cent) and 15 (75 per cent), contain bubbles. This indicates that the duty cycle of bubbles is large in such clusters and that they can play a major role in the heating process.

Dunn, Robert J.H.; Fabian, A.C.; /Cambridge U., Inst. of Astron.; Taylor, G.B.; /NRAO, Socorro /KIPAC, Menlo Park

2005-12-14

146

Bubble Colloidal AFM Probes Formed from Ultrasonically Generated Bubbles  

E-print Network

Letters Bubble Colloidal AFM Probes Formed from Ultrasonically Generated Bubbles Ivan U. Vakarelski forces between two small bubbles (80-140 µm) in aqueous solution during controlled collisions) was extended to measure interaction forces between a cantilever-attached bubble and surface-attached bubbles

Chan, Derek Y C

147

Chaotic bubbling and nonstagnant foams.  

PubMed

We present an experimental investigation of the agglomeration of bubbles obtained from a nozzle working in different bubbling regimes. This experiment consists of a continuous production of bubbles from a nozzle at the bottom of a liquid column, and these bubbles create a two-dimensional (2D) foam (or a bubble raft) at the top of this column. The bubbles can assemble in various dynamically stable arrangement, forming different kinds of foams in a liquid mixture of water and glycerol, with the effect that the bubble formation regimes influence the foam obtained from this agglomeration of bubbles. The average number of bubbles in the foam is related to the bubble formation frequency and the bubble mean lifetime. The periodic bubbling can generate regular or irregular foam, while a chaotic bubbling only generates irregular foam. PMID:17677349

Tufaile, Alberto; Sartorelli, José Carlos; Jeandet, Philippe; Liger-Belair, Gerard

2007-06-01

148

Electrowetting of soap bubbles  

NASA Astrophysics Data System (ADS)

A proof-of-concept demonstration of the electrowetting-on-dielectric of a sessile soap bubble is reported here. The bubbles are generated using a commercial soap bubble mixture—the surfaces are composed of highly doped, commercial silicon wafers covered with nanometer thick films of Teflon®. Voltages less than 40 V are sufficient to observe the modification of the bubble shape and the apparent bubble contact angle. Such observations open the way to inter alia the possibility of bubble-transport, as opposed to droplet-transport, in fluidic microsystems (e.g., laboratory-on-a-chip)—the potential gains in terms of volume, speed, and surface/volume ratio are non-negligible.

Arscott, Steve

2013-07-01

149

Ionospheric perturbations in the equatorial region during strong earthquakes observed by DEMETER satellite  

NASA Astrophysics Data System (ADS)

Ionospheric perturbations in the equatorial region during strong earthquakes observed by DEMETER satellite A.K. Gwala, Shivalika Sarkara and M. Parrotb (a) Space Science Laboratory, Department of Physics, Barkatullah University, Bhopal 462026, India (b) LPCE/CNRS, 3A Avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France Satellite data has proved to be very useful in studying the seismo-ionospheric effects in the equatorial latitudes. Some of the major seismic zones lie in the equatorial region. The equatorial ionosphere is highly dynamical and characterized by the existence of many irregularities. The attempts to understand the association between variations of the important plasma parameters (electron density, ion composition and temperature) and earthquakes in the equatorial region are discussed with help of some case studies in the equatorial region. Data from the Langmuir Probe instrument and Thermal Plasma Analyzer onboard DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions) satellite has been used for the study of the perturbations of the plasma parameters. The orbit of DEMETER is polar, circular with an altitude of 710 km. The considered examples show that during earthquake preparation the equatorial ionosphere has strong density zones in comparison with the ambient background level. A statistical analysis is also performed to confirm that the observed perturbations are due to seismic activity.

Gwal, Ashok Kumar; Shivalika, Shivalika; Parrot, Michel

150

Planar Soap Bubbles  

Microsoft Academic Search

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

RICHARD PAUL; DEVEREAUX VAUGHN

1998-01-01

151

Radio Bubbles in Clusters  

E-print Network

We extend our earlier work on cluster cores with distinct radio bubbles, adding more active bubbles, i.e. those with Ghz radio emission, to our sample, and also investigating ``ghost bubbles,'' i.e. those without GHz radio emission. We have determined k, which is the ratio of the total particle energy to that of the electrons radiating between 10 MHz and 10 GHz. Constraints on the ages of the active bubbles confirm that the ratio of the energy factor, k, to the volume filling factor, f lies within the range 1 bubbles present in the current sample to be able to determine the shape of the population. An analysis of the ghost bubbles in our sample showed that on the whole they have higher upper limits on k/f than the active bubbles, especially when compared to those in the same cluster. A study of the Brightest 55 cluster sample shows that 17, possibly 20, clusters required some form of heating as they have a short central cooling time, t_cool bubbles. This indicates that the duty cycle of bubbles is large in such clusters and that they can play a major role in the heating process.

R. J. H. Dunn; A. C. Fabian; G. B. Taylor

2005-10-06

152

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

153

Photon Bubbles and the Vertical Structure of Accretion Disks  

NASA Astrophysics Data System (ADS)

We consider the effects of ``photon bubble'' shock trains on the vertical structure of radiation pressure-dominated accretion disks. These density inhomogeneities are expected to develop spontaneously in radiation-dominated accretion disks where magnetic pressure exceeds gas pressure, even in the presence of magnetorotational instability (MRI). They increase the rate at which radiation escapes from the disk and may allow disks to exceed the Eddington limit by a substantial factor without blowing themselves apart. To refine our earlier analysis of photon bubble transport in accretion disks, we generalize the theory of photon bubbles to include the effects of finite optical depths and radiation damping. Modifications to the diffusion law at low ? tend to ``fill in'' the low-density regions of photon bubbles, while radiation damping inhibits the formation of photon bubbles at large radii, small accretion rates, and small heights above the equatorial plane. Accretion disks dominated by photon bubble transport may reach luminosities from 10 to >100 times the Eddington limit (LEdd), depending on the mass of the central object, while remaining geometrically thin. However, photon bubble-dominated disks with ?-viscosity are subject to the same thermal and viscous instabilities that plague standard radiation pressure-dominated disks, suggesting that they may be intrinsically unsteady. Photon bubbles can lead to a ``core-halo'' vertical disk structure. In super-Eddington disks the halo forms the base of a wind, which carries away substantial energy and mass, but not enough to prevent the luminosity from exceeding LEdd. Photon bubble-dominated disks may have smaller color corrections than standard accretion disks of the same luminosity. They remain viable contenders for some ultraluminous X-ray sources and may play a role in the rapid growth of supermassive black holes at high redshift.

Begelman, Mitchell C.

2006-06-01

154

Original paper Soap Bubble Clusters  

E-print Network

Original paper Soap Bubble Clusters Fred ALMGREN surface, soap bubbles Abstract. This article reviews the theorems from geometric measure theory which guarantee the existence and give the structure of mathematical models of soap bubble clusters. It also

Taylor, Jean

155

A Bubble Full of Sunshine  

NSF Publications Database

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

156

Prospects for bubble fusion  

SciTech Connect

In this paper a new method for the realization of fusion energy is presented. This method is based on the superhigh compression of a gas bubble (deuterium or deuterium/thritium) in heavy water or another liquid. The superhigh compression of a gas bubble in a liquid is achieved through forced non-linear, non-periodic resonance oscillations using moderate amplitudes of forcing pressure. The key feature of this new method is a coordination of the forced liquid pressure change with the change of bubble volume. The corresponding regime of the bubble oscillation has been called {open_quotes}basketball dribbling (BD) regime{close_quotes}. The analytical solution describing this process for spherically symmetric bubble oscillations, neglecting dissipation and compressibility of the liquid, has been obtained. This solution shown no limitation on the supercompression of the bubble and the corresponding maximum temperature. The various dissipation mechanisms, including viscous, conductive and radiation heat losses have been considered. It is shown that in spite of these losses it is possible to achieve very high gas bubble temperatures. This because the time duration of the gas bubble supercompression becomes very short when increasing the intensity of compression, thus limiting the energy losses. Significantly, the calculated maximum gas temperatures have shown that nuclear fusion may be possible. First estimations of the affect of liquid compressibility have been made to determine possible limitations on gas bubble compression. The next step will be to investigate the role of interfacial instability and breaking down of the bubble, shock wave phenomena around and in the bubble and mutual diffusion of the gas and the liquid.

Nigmatulin, R.I. [Tyumen Institute of Mechanics of Multiphase Systems (TIMMS), Marx (Russian Federation); Lahey, R.T. Jr. [Rensselaer Polytechnic Institute, Troy, NY (United States)

1995-09-01

157

Soap bubbles. 1  

Microsoft Academic Search

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

A. Glassner

2000-01-01

158

Let Them Blow Bubbles.  

ERIC Educational Resources Information Center

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

Korenic, Eileen

1988-01-01

159

Explosion of chaotic bubbling  

NASA Astrophysics Data System (ADS)

We have studied a saddle-node bifurcation/explosion of air bubble formation driven by a sound wave, whose amplitude is the control parameter. The bubbles are formed in a nozzle submerged in a water/glycerol solution inside a cylindrical tube, and the sound wave is tuned to the air column above the fluid. The nonlinear interaction between sound wave and the fluid oscillations, caused by the air bubbles passage through the liquid, results in a route to chaos via quasi-periodicity, with some resonant states characterized by the rational winding numbers W= fs/ fb, where fs is the sound wave frequency and fb is the bubbling rate. We also have shown that the bubble dynamics is similar to the one observed in the two-dimensional circle map.

Tufaile, A.; Reyes, M. B.; Sartorelli, J. C.

2002-05-01

160

The streaming-trapped ion interface in the equatorial inner magnetosphere  

NASA Technical Reports Server (NTRS)

Spacecraft measurements of core ions on L=4-7 field-lines typically show trapped ion distributions near the magnetic equator, and frequently indicate field-aligned ion streams at higher latitudes. The nature of the transition between them may indicate both the microphysics of hot-cold plasma interactions and overall consequences for core plasma evolution. We have undertaken a statistical analysis and characterization of this interface and its relation to the equatorial region of the inner magnetosphere. In this analysis, we have characterized such features as the equatorial ion flux anisotropy, the penetration of field-aligned ionospheric streams into the equatorial region, the scale of the transition into trapped ion populations, and the transition latitude. We found that most transition latitudes occur within 13 deg of the equator. The typical values of equatorial ion anisotropies are consistent with bi-Maxwellian temperature ratios of T(sub perpendicular)/T(sub parallel) in the range of 3-5. The latitudinal scales for the edges of the trapped ion populations display a rather strong peak in the 2-3 deg range. We also found that there is a trend for the penetration ratio, the anisotropy half width, and the transition scale length to decrease with a higher equatorial ion anisotropy. We may interpret these features in terms of Liouville mapping of equatorially trapped ions and the reflection of the incoming ionospheric ion streams from the equatorial potential peaks associated with such trapped ions.

Lin, J.; Horwitz, J. L.; Gallagher, D.; Pollock, C. J.

1994-01-01

161

Photon Bubbles and the Vertical Structure of Accretion Disks  

E-print Network

We consider the effects of "photon bubble" shock trains on the vertical structure of radiation pressure-dominated accretion disks. These density inhomogeneities are expected to develop spontaneously in radiation-dominated accretion disks where magnetic pressure exceeds gas pressure, even in the presence of magnetorotational instability. They increase the rate at which radiation escapes from the disk, and may allow disks to exceed the Eddington limit by a substantial factor. We first generalize the theory of photon bubbles to include the effects of finite optical depths and radiation damping. Modifications to the diffusion law at low optical depth tend to fill in the low-density regions of photon bubbles, while radiation damping inhibits the formation of photon bubbles at large radii, small accretion rates, and small heights above the equatorial plane. Accretion disks dominated by photon bubble transport may reach luminosities of 10 to >100 times the Eddington limit (L_E), depending on the mass of the central object, while remaining geometrically thin. However, photon bubble-dominated disks with alpha-viscosity are subject to the same thermal and viscous instabilities that plague standard radiation pressure-dominated disks, suggesting that they may be intrinsically unsteady. Photon bubbles can lead to a "core-halo" vertical disk structure. In super-Eddington disks the halo forms the base of a wind, which carries away substantial energy and mass, but not enough to prevent the luminosity from exceeding L_E. Photon bubble-dominated disks may have smaller color corrections than standard accretion disks of the same luminosity. They remain viable contenders for some ultraluminous X-ray sources and may play a role in the rapid growth of supermassive black holes at high redshift.

Mitchell C. Begelman

2006-02-01

162

Mounting and application of bubble display system: bubble cosmos  

Microsoft Academic Search

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

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

2006-01-01

163

Bubble core field modification by residual electrons inside the bubble  

SciTech Connect

Bubble core field modification due to the nondepleted electrons present inside the bubble is investigated theoretically. These residual electrons induce charge and current densities that can induce the bubble core field modification as well as the bubble shape change. It is found that the electrons entering into the bubble move backward at almost light speed and would weaken the transverse bubble fields. This reduces the ratio of longitudinal to transverse radius of the bubble. For the longitudinal bubble field, two effects compensate with each other because of their competition between the enhancement by the shortening of bubble shape and the reduction by the residual electrons. Therefore the longitudinal field is hardly changeable. As a comparison we perform particle-in-cell simulations and it is found that the results from theoretical consideration are consistent with simulation results. Implication of the modification of fields on bubble electron acceleration is also discussed briefly.

Wu Haicheng [College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); Center for Applied Physics and Technology, Peking University, Beijing 100084 (China); Xie Baisong; Zhao Xueyan [College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); Zhang Shan [College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); Department of Mathematics and Physics, Shijiazhuang Railway Institute, 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); Liu Mingping [School of Information Engineering, Nanchang University, Nanchang 330031 (China)

2010-11-15

164

Significance of viscoelastic effects on the rising of a bubble and bubble-to-bubble interaction  

NASA Astrophysics Data System (ADS)

Numerical results for the rising of a bubble and the interaction between two bubbles in non-Newtonian fluids will be discussed. The computations are carried out using a multiscale method combining front-tracking with Brownian dynamics simulations. The evaluation of the material properties for the non-Newtonian fluid will be discussed firstly. The results from the computations of a single bubble show how elastic effects modify the deformation and rising of the bubble by pulling the tail of it. The relationship between the strength of the elastic forces and the discontinuity in the bubble terminal velocity, when plotted versus bubble volume, is also observed in the computations. The bubble-to-bubble interaction is dominated not only by elastic effects but also by the shear-thinning caused by the leading bubble, which leads the trailing bubble to accelerate faster and coalesce with the leading bubble.

Fernandez, Arturo

2011-11-01

165

Viscosity destabilizes sonoluminescing bubbles.  

PubMed

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

Toegel, Ruediger; Luther, Stefan; Lohse, Detlef

2006-03-24

166

Charged vacuum bubble stability  

NASA Astrophysics Data System (ADS)

A type of scenario is considered where electrically charged vacuum bubbles, formed from degenerate or nearly degenerate vacua separated by a thin domain wall, are cosmologically produced due to the breaking of a discrete symmetry, with the bubble charge arising from fermions residing within the domain wall. Stability issues associated with wall tension, fermion gas, and Coulombic effects for such configurations are examined. The stability of a bubble depends upon parameters such as the symmetry breaking scale and the fermion coupling. A dominance of either the Fermi gas or the Coulomb contribution may be realized under certain conditions, depending upon parameter values.

Morris, J. R.

1999-01-01

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

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

169

Effects of magnetic storm phases on f-layer irregularities from auroral to equatorial latitudes. Quarterly report, 1 January-31 March 1993  

SciTech Connect

Equatorial ionospheric irregularities in the F layer have been the subject of intensive experimental and theoretical investigations during recent years. The class of irregularities which continues to receive much attention is characterized by large scale plasma depletions, generally referred to as ionospheric plumes and bubbles. The F-region nightglow emissions arising from recombination processes can be used to observe the dynamics of transequatorial ionospheric plasma bubbles and smaller scale plasma irregularities. In a collaborative project between the Center for Space Physics of Boston University and the Brazilian Institute for Space Research (INPE), an all-sky imaging system was operated at Cachoeira Paulista (22.7 deg S, 45.0 deg W, dip latitude 15.8 deg S), between March 1987 and October 1991. In addition to the imager, photometer and VHF polarimeter observations were conducted at Cachoeira Paulista with ionospheric soundings carried out at C. Paulista and Fortaleza, the latter at 3.9 deg S. 38.4 deg W, dip latitude 3.7 deg S. A VHF electronic polarimeter is in operation at C. Paulista. This long series of 01 630.0 nm imaging observations has permitted determination that when there are extended plumes, the altitudes affected over the magnetic equator often exceed 1500 km and probably exceed 2500 km at times, the maximum projection that can be seen from Cachoeira Paulista. This holds true even during years of low solar flux. For this longitude, the observed seasonal variation of the airglow depletions shows a maximum from October through March and a very low occurrence of airglow depletions from April through September.

Aarons, J.; Mendillo, M.

1993-03-31

170

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

171

Colloquium: Soap bubble clusters  

NASA Astrophysics Data System (ADS)

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

Morgan, Frank

2007-07-01

172

Bubble coalescence in magmas  

NASA Technical Reports Server (NTRS)

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

Herd, Richard A.; Pinkerton, Harry

1993-01-01

173

Prediction of the bubble-hole size of a cap bubble in a bubble swarm  

Microsoft Academic Search

A phenomenological, semi-theoretical model is proposed for predicting the size or thickness of the bubble-depleted region, or ‘bubble hole’, in the frontal vicinity of a larg cap bubble rising through a swarm of otherwise uniformly dispersed small bubbles. The model lays its theoretical basis on the axial pressure distribution in the very front of the cap nose which modifies the

Katsumi Tsuchiya; Kazutomo Ohsaki

1997-01-01

174

Collision of counterpropagating laser-excited wake bubbles  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

175

Experimental investigation of the mini-magnetospheric plasma propulsion prototype  

NASA Astrophysics Data System (ADS)

Mini-Magnetospheric Plasma Propulsion (M2P2) seeks the creation of a large-scale (10 km radius) magnetic wall or bubble (i.e. a magnetosphere) by the electromagnetic inflation of a small-scale (20 cm radius) dipole magnet. The inflated magnetosphere will intercept the, solar wind and thereby provide high-speed propulsion with modest power and fuel requirements due to the gain provided by the ambient medium. Magnetic field inflation is produced by the injection of plasma onto the dipole magnetic field eliminating the need for large mechanical structures and added material weight at launch. For successful inflation of the magnetic bubble a beta near unity must be achieved along the imposed dipole field. This is dependent of the plasma parameters that can be achieved with a plasma source that provide continuous operation at the desired power levels of 1 to 2 kilowatts. Over the last two years I have been developing a laboratory prototype to demonstrate the inflation of the magnetic field under space-like conditions. In this thesis I will present some of the latest results from the prototype development at the University of Washington and show that the prototype can produce high ionization efficiencies while operating in near space-like neutral background pressures producing electron temperatures of a few tens of electron volts. Plasma characteristics from the helicon source region and in the dipole equator show a beam like plasma that is generated from the helicon source. Some magnetic inflation dynamics are noted, but magnitudes are much lower than modeling predicts. It is believed that the helicon source is generating a field-aligned electron current, which adds to the plasma confinement and possibly hampering inflation. Additionally, the experimental results indicate that wall interactions with the vacuum chamber also have a negative effect. Possible solutions to overcome low plasma betas in the equatorial region are discussed.

Ziemba, Timothy Martin

176

Long Term Evolution of Magnetized Bubbles in Galaxy Clusters  

E-print Network

We have performed nonlinear ideal magnetohydrodynamic simulations of the long term evolution of a magnetized low-density "bubble" plasma formed by a radio galaxy in a stratified cluster medium. It is found that about 3.5% of the initial magnetic energy remains in the bubble after $\\sim 8 \\times 10^{9}$ years, and the initial magnetic bubble expansion is adiabatic. The bubble can survive for at least $8 \\times 10^9$ years due to the stabilizing effect of the bubble magnetic field on Rayleigh-Taylor and Kelvin-Holmholtz instabilities, possibly accounting for "ghost cavities" as observed in Perseus-A\\@. A filament structure spanning about 500 kpc is formed along the path of bubble motion. The mean value of the magnetic field inside this structure is $\\sim 0.88$ $\\mu$G at $\\sim8\\times10^9$ years. Finally, the initial bubble momentum and rotation have limited influence on the long term evolution of the bubble.

Wei Liu; Hui Li; Shengtai Li; Scott C. Hsu

2008-06-23

177

Evidence for hydrogen generation in laser- or spark-induced cavitation bubbles  

NASA Astrophysics Data System (ADS)

The growing use of focused lasers or electric sparks to generate cavitation bubbles raises concerns about the possible alteration of gas content during the initiation process and its effect on bubble dynamics. We provide experimental evidence that hydrogen molecules are produced for such plasma-induced bubbles. We performed spectral analysis of the light emitted by the plasma and monitored the dissolved hydrogen concentration in water. The mass of dissolved hydrogen was found proportional to the potential energy of the rebound bubble for both laser and spark methods. Nevertheless, hydrogen concentration was found 2.7 times larger with the spark.

Sato, Takehiko; Tinguely, Marc; Oizumi, Masanobu; Farhat, Mohamed

2013-02-01

178

The dynamics of histotripsy bubbles  

NASA Astrophysics Data System (ADS)

Histotripsy describes treatments in which high-amplitude acoustic pulses are used to excite bubbles and erode tissue. Though tissue erosion can be directly attributed to bubble activity, the genesis and dynamics of bubbles remain unclear. Histotripsy lesions that show no signs of thermal coagulative damage have been generated with two different acoustic protocols: relatively long acoustic pulses that produce local boiling within milliseconds and relatively short pulses that are higher in amplitude but likely do not produce boiling. While these two approaches are often distinguished as `boiling' versus `cavitation', such labels can obscure similarities. In both cases, a bubble undergoes large changes in radius and vapor is transported into and out of the bubble as it oscillates. Moreover, observations from both approaches suggest that bubbles grow to a size at which they cease to collapse violently. In order to better understand the dynamics of histotripsy bubbles, a single-bubble model has been developed that couples acoustically excited bubble motions to the thermodynamic state of the surrounding liquid. Using this model for bubbles exposed to histotripsy sound fields, simulations suggest that two mechanisms can act separately or in concert to lead to the typically observed bubble growth. First, nonlinear acoustic propagation leads to the evolution of shocks and an asymmetry in the positive and negative pressures that drive bubble motion. This asymmetry can have a rectifying effect on bubble oscillations whereby the bubble grows on average during each acoustic cycle. Second, vapor transport to/from the bubble tends to produce larger bubbles, especially at elevated temperatures. Vapor transport by itself can lead to rectified bubble growth when the ambient temperature exceeds 100 °C (`boiling') or local heating in the vicinity of the bubble leads to a superheated boundary layer.

Kreider, Wayne; Bailey, Michael R.; Sapozhnikov, Oleg A.; Khokhlova, Vera A.; Crum, Lawrence A.

2011-09-01

179

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

180

Bubble convection within magma reservoirs  

NASA Astrophysics Data System (ADS)

Volcanoes are gas-rich hence small bubbles slowly rise in magma reservoirs. Under certain condition of gas flux, bubble size and reservoir height, the bubble rise is no more homogeneous: the collective buoyancy of the bubbles produces instabilities and the bubble motion becomes driven by convection. If such a convection occurs, the residence time of bubbles in the reservoir is reduced and thus eruptive activity is modified. By analogy with thermal convection, we define Rayleigh (Rab) and Prandtl (Prb) numbers for bubble convection. However, the critical Rab for bubble convection is hardly known from previous studies and its dependence to Prb is ignored. Laboratory experiments are performed with small bubbles rising in a cylindrical tank filled with viscous oils in order to quantify bubble convection and apply it to real volcanoes. Rab and Prb are acurately determined from measurement, via two hydrophones, of bubble size and gas volume fraction. Bubble velocity is obtained by PIV. Experiments show two main regimes: a steady cellular regime at low Rab and a bubble plume regime when Rab is higher. The critical Rab depends on the critical Prb for the two transitions.

Bouche, Emmanuella; Vergniolle, Sylvie; Gamblin, Yves; Vieira, Antonio

2008-11-01

181

Microfluidic Actuation Using Electrochemically Generated Bubbles  

E-print Network

Microfluidic Actuation Using Electrochemically Generated Bubbles Susan Z. Hua,*, Frederick Sachs, Buffalo, New York 14260 Bubble-based actuation in microfluidic applications is attractive owing of electrochemically generated bubble valves were studied. By generating electrochemical bubbles as valves directly

Sachs, Frederick

182

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

183

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

184

Large and small bubble interaction patterns in a bubble column  

Microsoft Academic Search

A visual analysis is made on the fate of a large (or “cap”) bubble injected into a swarm of otherwise uniformly dispersed small bubbles; experiments, covering gas holdups for the swarm bubbles as high as 6%, are conducted in a two-dimensional column to ensure the distinct appearance of a single cap throughout its rise in the swarm. Specific focus is

K. Tsuchiya; K. Ohsaki; K. Taguchi

1996-01-01

185

Equatorial refuge amid tropical warming  

NASA Astrophysics Data System (ADS)

Upwelling across the tropical Pacific Ocean is projected to weaken in accordance with a reduction of the atmospheric overturning circulation, enhancing the increase in sea surface temperature relative to other regions in response to greenhouse-gas forcing. In the central Pacific, home to one of the largest marine protected areas and fishery regions in the global tropics, sea surface temperatures are projected to increase by 2.8°C by the end of this century. Of critical concern is that marine protected areas may not provide refuge from the anticipated rate of large-scale warming, which could exceed the evolutionary capacity of coral and their symbionts to adapt. Combining high-resolution satellite measurements, an ensemble of global climate models and an eddy-resolving regional ocean circulation model, we show that warming and productivity decline around select Pacific islands will be mitigated by enhanced upwelling associated with a strengthening of the equatorial undercurrent. Enhanced topographic upwelling will act as a negative feedback, locally mitigating the surface warming. At the Gilbert Islands, the rate of warming will be reduced by 0.7+/-0.3°C or 25+/-9% per century, or an overall cooling effect comparable to the local anomaly for a typical El Niño, by the end of this century. As the equatorial undercurrent is dynamically constrained to the Equator, only a handful of coral reefs stand to benefit from this equatorial island effect. Nevertheless, those that do face a lower rate of warming, conferring a significant advantage over neighbouring reef systems. If realized, these predictions help to identify potential refuges for coral reef communities from anticipated climate changes of the twenty-first century.

Karnauskas, Kristopher B.; Cohen, Anne L.

2012-07-01

186

Bubbles and Biosensors  

NSDL National Science Digital Library

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

Vu Bioengineering Ret Program

187

Magnetic-bubble conservative logic  

Microsoft Academic Search

Among integrated-circuit devices, magnetic bubbles are a particularly interesting candidate to implement the Fredkin gate and conservative logic. The magnetostatic repulsion of magnetic bubbles simulates the bouncing-ball model of conservative logic.

Hsu Chang

1982-01-01

188

Unsteady forces on spherical bubbles  

Microsoft Academic Search

An experimental investigation of freely rising spherical bubbles through a quiescent liquid is presented. The objective of the experiments is to examine the validity of a recently proposed history force expression for clean, spherical bubbles at finite Reynolds number (Mei et al. 1994). Excellent agreement between the measured and predicted bubble trajectory is obtained when using the proposed history force

W. C. Park; J. F. Klausner; R. Mei

1995-01-01

189

The Home Zone: Bubble Shapes  

NSDL National Science Digital Library

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

Damonte, Kathleen

2003-05-01

190

Bubbles Unbound: Bubbles of Nothing Without Kaluza-Klein  

E-print Network

I present analytic time symmetric initial data for five dimensions describing ``bubbles of nothing'' which are asymptotically flat in the higher dimensional sense, i.e. there is no Kaluza-Klein circle asymptotically. The mass and size of these bubbles may be chosen arbitrarily and in particular the solutions contain bubbles of any size which are arbitrarily light. This suggests the solutions may be important phenomenologically and in particular I show that at low energy there are bubbles which expand outwards, suggesting a new possible instability in higher dimensions. Further, one may find bubbles of any size where the only region of high curvature is confined to an arbitrarily small volume.

Keith Copsey

2006-10-05

191

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

192

The Bubble N10  

NASA Astrophysics Data System (ADS)

We studied the environment surrounding the infrared bubble N10 in molecular and infrared emission. There is an HII region at the center of this bubble. We investigated J=1-0 transitions of molecules ^{12}CO, ^{13}CO and C^{18}O towards N10. This object was detected by GLIMPSE, a survey carried out between 3.6 and 8.0 ? m. We also analyzed the emission at 24 ? m, corresponding to the emission of hot dust, with a contribution of small grains heated by nearby O stars. Besides, the contribution at 8 ? m is dominated by PAHs (polycyclic aromatic hydrocarbons) excited by radiation from the PDRs of bubbles. In the case of N10, it is proposed that the excess at 4.5 ? m IRAC band indicate an outflow, a signature of early stages of massive star formation. This object was the target of observations at the PMO 13.7 m radio telescope. The bubble N10 presents clumps, from which we can derive physical features through the observed parameters. We also intended to discuss the evolutionary stage of the clumps and their distribution. It can lead us to understand the triggered star formation scenario in this region.

Gama, D.; Lepine, J.; Wu, Y.; Yuan, J.

2014-10-01

193

Soap bubbles and crystals  

Microsoft Academic Search

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

Jean E. Taylor

2006-01-01

194

Oscillations of soap bubbles  

NASA Astrophysics Data System (ADS)

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

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

2010-07-01

195

Colloquium: Soap bubble clusters  

Microsoft Academic Search

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

Frank Morgan

2007-01-01

196

Bubble fusion: Preliminary estimates  

SciTech Connect

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

Krakowski, R.A.

1995-02-01

197

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

198

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

199

Resent Status of ITER Equatorial Launcher Development  

NASA Astrophysics Data System (ADS)

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.

2009-11-01

200

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

201

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

202

G amma-Ray Burst Phenomenon as Collapse of QED Magnetized Vacuum Bubble: Analogy with Sonoluminescence  

Microsoft Academic Search

process of the bubble shape instability in a resonant MHD field of an accreting plasma. The QED effect of vacuum polarizability by a strong magnetic fie ld is taken into a consideration. We develop the analogy with the phenomenon of sonoluminescence (SL) when the gas bubble i s located in surrounding l iquid w ith a driven sound intensity. We

Yu. N. Gnedin; S. O. Kiikov

203

Disturbance Equatorial Electric Fields and Ionospheric Responses During Some Recent Intense Magnetic Storms  

Microsoft Academic Search

Outstanding features of the equatorial disturbance electric fields during some intense magnetic storms that occurred in recent times (2003-05 period) are investigated using ground-based ionosonde and magnetometer data. During the October 2003 storm which was the most intense one, very strong prompt penetrating eastward electric field in the dusk sector caused giant plasma fountain with rapid uplift of the F

M. A. Abdu; I. S. Batista; B. W. Reinisch; J. H. Sobral; C. G. Brum

2005-01-01

204

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

205

Ionization instability as a generation mechanism of electron density irregularities in the equatorial electrojet  

Microsoft Academic Search

A system of equations describing plasma behavior in the equatorial electrojet (equations of motion for electrons and ions, equations of continuity for electrons and ions, an equation of energy for electrons, and the Maxwell equation) in the quasihydrodynamic approximation are used to demonstrate that ionization instability is a mechanism that can effectively produce small scale electron density irregularities in the

J. Blecki

1975-01-01

206

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

207

Bubble dynamics in drinks  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

208

Sonoluminescence, sonochemistry and bubble dynamics of single bubble cavitation  

NASA Astrophysics Data System (ADS)

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

Hatanaka, Shin-ichi

2012-09-01

209

EQUATORIAL SUPERROTATION ON TIDALLY LOCKED EXOPLANETS  

SciTech Connect

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. [Department of Planetary Sciences and Lunar and Planetary Laboratory, University of Arizona, 1629 University Blvd., Tucson, AZ 85721 (United States); Polvani, Lorenzo M., E-mail: showman@lpl.arizona.edu [Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY (United States)

2011-09-01

210

Fermi gamma-ray "bubbles" from stochastic acceleration of electrons.  

PubMed

Gamma-ray data from Fermi Large Area Telescope reveal a bilobular structure extending up to ?50° above and below the Galactic Center. It has been argued that the gamma rays arise from hadronic interactions of high-energy cosmic rays which are advected out by a strong wind, or from inverse-Compton scattering of relativistic electrons accelerated at plasma shocks present in the bubbles. We explore the alternative possibility that the relativistic electrons are undergoing stochastic 2nd-order Fermi acceleration by plasma wave turbulence through the entire volume of the bubbles. The observed gamma-ray spectral shape is then explained naturally by the resulting hard electron spectrum modulated by inverse-Compton energy losses. Rather than a constant volume emissivity as in other models, we predict a nearly constant surface brightness, and reproduce the observed sharp edges of the bubbles. PMID:21929220

Mertsch, Philipp; Sarkar, Subir

2011-08-26

211

On the hierarchy of processes contributing to equatorial spread F  

SciTech Connect

Unstable plasma stratification in the twilight equatorial F region ionosphere is subject to plasma instabilities known collectively as equatorial spread F. Small-scale irregularities in electron density give rise to coherent VHF and UHF radio scatter during spread F while in situ spacecraft detect intermediate- and large-scale plasma structures. The authors present data from observations made over three years at the Jicamarca Radio Observatory and from the summer 1990 CRRES/EQUIS campaign which involved the Cornell 50 MHz radar interferometer (CUPRI) and the Altair UHF radar at Kwajalein, MI. Radar findings are correlated with spread F data from sounding rockets launched during the EQUIS project and from the Atmospheric Explorer E satellite. A review of fundamental fluid theory for the ionospheric interchange instability emphasizes dissipative and non-local effects that restrict linear instability to intermediate-scale wavelengths. A nonlinear fluid theory incorporating three wave interactions extends the range of instability to transitional and small scales, and renormalization group analysis offers a way to evaluate enhanced transport due to these nonlinearly excited modes. At large scales, circumstantial evidence suggests that internal gravity waves seed plasma upwellings and initiate topside spread F. Density and electric field spectra measured by the spread F sounding rockets exhibit inertial-convective and inertial-diffusive subranges. A model of quasi one-dimensional plasma turbulence reproduces the spectral indices and breaking scales observed by the rockets. Density power spectra from 30 AE-E orbits also possess convective and diffusive subranges, but their characteristic scale sizes are about 10 times larger than the rocket's. One-dimensional rocket and satellite power spectra combine to form a two-dimensional spectral model of F region irregularities which predicts VHF radar scattering cross-sections.

Hysell, D.L,.

1992-01-01

212

THEMIS analysis of observed equatorial electron distributions responsible for the chorus excitation  

Microsoft Academic Search

A statistical survey of plasma densities and electron distributions (0.5–100 keV) is performed using data obtained from the Time History of Events and Macroscale Interactions During Substorms spacecraft in near-equatorial orbits from 1 July 2007 to 1 May 2009 in order to investigate optimum conditions for whistler mode chorus excitation. The plasma density calculated from the spacecraft potential, together with

W. Li; R. M. Thorne; Y. Nishimura; J. Bortnik; V. Angelopoulos; J. P. McFadden; D. E. Larson; J. W. Bonnell; O. Le Contel; A. Roux; U. Auster

2010-01-01

213

Electrowetting of a soap bubble  

E-print Network

A proof-of-concept demonstration of the electrowetting-on-dielectric of a sessile soap bubble is reported here. The bubbles are generated using a commercial soap bubble mixture - the surfaces are composed of highly doped, commercial silicon wafers covered with nanometre thick films of Teflon. Voltages less than 40V are sufficient to observe the modification of the bubble shape and the apparent bubble contact angle. Such observations open the way to inter alia the possibility of bubble-transport, as opposed to droplet-transport, in fluidic microsystems (e.g. laboratory-on-a-chip) - the potential gains in terms of volume, speed and surface/volume ratio are non-negligible.

Arscott, Steve

2013-01-01

214

Electrowetting of a soap bubble  

E-print Network

A proof-of-concept demonstration of the electrowetting-on-dielectric of a sessile soap bubble is reported here. The bubbles are generated using a commercial soap bubble mixture - the surfaces are composed of highly doped, commercial silicon wafers covered with nanometre thick films of Teflon. Voltages less than 40V are sufficient to observe the modification of the bubble shape and the apparent bubble contact angle. Such observations open the way to inter alia the possibility of bubble-transport, as opposed to droplet-transport, in fluidic microsystems (e.g. laboratory-on-a-chip) - the potential gains in terms of volume, speed and surface/volume ratio are non-negligible.

Steve Arscott

2013-04-25

215

Collapse of large vapor bubbles  

NASA Technical Reports Server (NTRS)

The refilling of propellant tanks while in a low-gravity environment requires that entrapped vapor bubbles be collapsed by increasing the system pressure. Tests were performed to verify the mechanism of collapse for these large vapor bubbles with the thermodynamic conditions, geometry, and boundary conditions being those applicable to propellant storage systems. For these conditions it was found that conduction heat transfer determined the collapse rate, with the specific bubble geometry having a significant influence.

Tegart, J.; Dominick, S.

1982-01-01

216

Colliding Kaluza-Klein Bubbles  

E-print Network

We construct an exact solution describing the collision of two Kaluza-Klein "bubbles of nothing" in 3+1 dimensions. When the bubbles collide, a curvature singularity forms which is hidden inside an event horizon. However, unlike the formation of ordinary black holes, in this case the spacetime resembles the entire maximally extended Schwarzschild solution. We also point out that there are inequivalent bubbles that can be constructed from Kerr black holes.

Gary T. Horowitz; Kengo Maeda

2002-07-30

217

Electron Bubbles in Liquid Helium  

E-print Network

When an electron (or positronium atom) is injected into liquid helium with nearly zero energy, a bubble quickly forms around it. This phenomenon (which also occurs in liquid hydrogen, liquid neon and possibly in solid helium) lowers the mobility of the electron to a value similar to that for a positive ion. We estimate the radius of the bubble at zero pressure and temperature based on the zero point energy of the electron. If the liquid is held in a state of negative pressure, the bubble will expand beyond the radius at zero pressure. We also estimate the negative pressure such that a bubble once formed will grow without limit.

Kirk T. McDonald

2003-12-03

218

Detecting bubbles in exotic nuclei  

E-print Network

The occurrence of a bubble, due to an inversion of s$_{1/2}$ state with the state usually located above, is investigated. Proton bubbles in neutron-rich Argon isotopes are optimal candidates. Pairing effects which can play against the bubble formation are evaluated. They cannot prevent bubble formation in very neutron-rich argon isotopes such as $^{68}$Ar. This pleads for a measurement of the charge density of neutron-rich argon isotopes in the forthcoming years, with the advent of electron scattering experiments in next generation exotic beam facilities such as FAIR or RIBF.

E. Khan; M. Grasso; J. Margueron; N. Van Giai

2007-07-03

219

When sound slows down bubbles  

E-print Network

We present experimental evidence that a bubble moving in a fluid in which a well-chosen acoustic noise is superimposed can be significantly slowed down for moderate acoustic pressures. Through mean velocity measurements, we show that a condition for this effect to occur is for the acoustic noise spectrum to match or overlap the bubble's fundamental resonant mode. By rendering the bubble's oscillations and translational movements using high speed video, we evidence that radial oscillations have no effect on the mean velocity, while above a critical sound pressure threshold, Faraday waves are triggered and are responsible for the bubble's drag increase.

Remi Dangla; Cedric Poulain

2010-01-21

220

Domain Walls and Double Bubbles  

E-print Network

We study configurations of intersecting domain walls in a Wess-Zumino model with three vacua. We introduce a volume-preserving flow and show that its static solutions are configurations of intersecting domain walls that form double bubbles, that is, minimal area surfaces which enclose and separate two prescribed volumes. To illustrate this field theory approach to double bubbles, we use domain walls to reconstruct the phase diagram for double bubbles in the flat square two-torus and also construct all known examples of double bubbles in the flat cubic three-torus.

Mike Gillard; Paul Sutcliffe

2009-03-30

221

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

222

Decadal changes in the equatorial Pacific circulation  

E-print Network

An ocean general circulation model with data assimilation is used to analyze the decadal changes in the tropical Pacific Ocean circulation. Results indicate that the variability in the Equatorial Undercurrent (EUC) and subtropical cells (STC) have...

Urizar, S. Cristina

2012-06-07

223

Planetary waves in Jupiter's equatorial atmosphere  

NASA Astrophysics Data System (ADS)

Planetary-scale waves which have been latitudinally trapped within the equatorial jet of Jupiter are attested to by Voyager IR, radio occultation, and imaging data. An effort is presently made to identify a distinguishing class of planetary wave modes in the course of interpreting these data, with special attention being given to the equatorial plume features observed. A comparative evaluation of horizontal dispersion properties for linear wave modes on an equatorial beta plane suggests that the Rossby modes with a meridional structure index of 1 and an equivalent depth of 2-4 km are the interpretation most nearly consistent with all of the observational data for an equatorially trapped, wavenumber 12 pattern.

Allison, M.

1990-02-01

224

Modeling of bubble coalescence in bubbly co-current flows restricted by confined geometry  

Microsoft Academic Search

Principles of kinetic theory are used to model the coalescence of bubbles in horizontal and vertical upflows where bubble movements are restricted by channel geometry. There are four critical variables that determine the rate at which a swarm of small bubbles will coalesce: the initial bubble population, the average initial bubble diameter, the average relative velocity of the bubbles, and

Michael D. Lundin; Mark J. McCready

2009-01-01

225

Effect of bubble size on micro-bubble drag reduction  

NASA Astrophysics Data System (ADS)

The effect of bubble size on micro-bubble drag reduction was investigated experimentally in a high-speed turbulent channel flow of water. A variety of near-wall injection techniques were used to create a bubbly turbulent boundary layer. The resulting wall friction force was measured directly by a floating element force balance. The bubble size was determined from photographic imaging. Using compressed nitrogen to force flow through a slot injector located in the plate beneath the boundary layer of the tunnel test section, a surfactant solution (Triton X-100, 19ppm) and salt water solution (35ppt) generated bubbles of average size between ˜500 microns and ˜200 microns and ˜100 microns, respectively (40 < d^+ < 200). In addition hollow spherical glass beads (˜75 microns (d^+ = 30) and specific gravity 0.18) and previously prepared lipid stabilized gas bubbles of ˜ 30 micron (d^+ =12) were injected. The results indicate that the drag reduction is related strongly to the injected gas volume flux and the static pressure in the boundary layer. Changing bubble size had essentially no influence on the measured friction drag, suggesting that friction drag is not a strong function of bubble size. [Sponsored by the Office of Naval Research.

Shen, Xiaochun

2005-11-01

226

The colour of bubbles  

NASA Astrophysics Data System (ADS)

Students of General Physics often complain that the course is too abstract and remote from daily life. As teachers, we emphasize that the abstract concepts of physics are indispensable for understanding our daily experiences, and we try to give the impression that quantitative descriptions can be achieved by adopting concrete mathematical expressions. Thus the abstract formulation is not to make physics more difficult, but to make it easier to grasp. We expect the students to learn to describe phenomena qualitatively using the concepts of physics, and to provide a quantitative description by manipulating the mathematical formulation. Here we supply one such example to calculate the colour of bubble films.

Huang, Ding-wei; Huang, Wei-neng; Tseng, Hsiang-chi

2005-11-01

227

A bubbling bolt  

E-print Network

We present a new solvable system, solving the equations of five-dimensional ungauged N=1 supergravity coupled to vector multiplets, that allows for non-extremal solutions and reduces to a known system when restricted to the floating brane Ansatz. A two-centre globally hyperbolic smooth geometry is obtained as a solution to this system, describing a bubble linking a Gibbons--Hawking centre to a charged bolt. However this solution turns out to violate the BPS bound, and we show that its generalisation to an arbitrary number of Gibbons--Hawking centres never admits a spin structure.

Guillaume Bossard; Stefanos Katmadas

2014-05-16

228

A bubbling bolt  

NASA Astrophysics Data System (ADS)

We present a new solvable system, solving the equations of five-dimensional ungauged = 1 supergravity coupled to vector multiplets, that allows for non-extremal solutions and reduces to a known system when restricted to the floating brane Ansatz. A two-centre globally hyperbolic smooth geometry is obtained as a solution to this system, describing a bubble linking a Gibbons-Hawking centre to a charged bolt. However this solution turns out to violate the BPS bound, and we show that its generalisation to an arbitrary number of Gibbons-Hawking centres never admits a spin structure.

Bossard, Guillaume; Katmadas, Stefanos

2014-07-01

229

Latitudinal comparisons of equatorial Pacific zooplankton  

NASA Astrophysics Data System (ADS)

Zooplankton biomass and rates of ingestion, egestion and production in the equatorial Pacific Ocean along 140°W and 180° exhibit maximum values in the High-Nutrient Low-Chlorophyll (HNLC) zone associated with equatorial upwelling (5°S-5°N) as compared to the more oligotrophic regions to the north and south. Zooplankton biomass and rates are not usually highest on the equator, but increase "downstream" of the upwelling center as the zooplankton populations exhibit a delayed response to enhanced phytoplankton production. The vertical distribution of zooplankton biomass in the equatorial HNLC area tends to be concentrated in surface waters and is more uniform with depth in oligotrophic regions to the north and south of the equatorial upwelling zone. In general, the amount of mesozooplankton (>200 ?m) carbon biomass is approximately 25% of estimated phytoplankton biomass and 30% of bacterial biomass in the HNLC area of the equatorial Pacific Ocean. Zooplankton grazing on phytoplankton is low in the equatorial Pacific Ocean, generally <5% of the total chlorophyll-a standing stock grazed per day. Based on estimates of metabolic demand, it is apparent that zooplankton in the equatorial Pacific Ocean are omnivores, consuming primarily microzooplankton and detritus. Estimated zooplankton growth rates in the warm waters of the HNLC equatorial Pacific Ocean are high, ranging from 0.58 d -1 for 64-200 ?m zooplankton to 0.08 d -1 for 1000-2000 ?m zooplankton. Thus, the numerical and functional response of equatorial zooplankton to increases in phytoplankton production are more rapid than normally occurs in sub-tropical and temperate waters. Potential zooplankton fecal pellet production, estimated from metabolic demand, is approximately 1.6 times the estimated gravitational carbon flux at 150 m in the zone of equatorial upwelling (5°S-5°N) and 1.1 times the export flux in the more oligotrophic regions to the north and south. The active flux of carbon by diel migrant zooplankton in the HNLC zone is a minor fraction of the gravitational flux (2% at 140°W, 4% at 180°) but increases in the more oligotrophic regions to the north and south where there is a deeper mixed layer and a greater relative proportion of diel migrant zooplankton.

Roman, M. R.; Dam, H. G.; Le Borgne, R.; Zhang, X.

230

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; Juttler, Bert

2011-01-01

231

Bubbles under stress.  

PubMed

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

Bohn, S

2003-06-01

232

Radiolytic Bubble Gas Hydrogen Compositions  

SciTech Connect

Radioactive waste solids can trap bubbles containing hydrogen that may pose a flammability risk if they are disturbed and hydrogen is released. Whether a release is a problem or not depends, among other things, on the hydrogen composition of the gas. This report develops a method for estimating the hydrogen composition of trapped bubbles based on waste properties.

Hester, J.R.

2003-02-05

233

Radiolytic Bubble Gas Hydrogen Compositions  

SciTech Connect

Radioactive waste solids can trap bubbles containing hydrogen that may pose a flammability risk if they are disturbed and hydrogen is released. Whether a release is a problem or not depends, among other things, on the hydrogen composition of the gas. This report develops a method for estimating the hydrogen composition of trapped bubbles based on waste properties.

Hester, J.R.

2001-08-28

234

Gas bubbles in shaped sapphire  

Microsoft Academic Search

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

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

2010-01-01

235

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

236

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

237

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

2007-06-02

238

Constrained Vapor Bubble  

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

239

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

240

Steady-state Hadronic Gamma-Ray Emission from 100-Myr-Old Fermi Bubbles  

NASA Astrophysics Data System (ADS)

Fermi Bubbles are enigmatic ?-ray features of the Galactic bulge. Both putative activity (within few × Myr) connected to the Galactic center super-massive black hole and, alternatively, nuclear star formation have been claimed as the energizing source of the Bubbles. Likewise, both inverse-Compton emission by non-thermal electrons ("leptonic" models) and collisions between non-thermal protons and gas ("hadronic" models) have been advanced as the process supplying the Bubbles' ?-ray emission. An issue for any steady state hadronic model is that the very low density of the Bubbles' plasma seems to require that they accumulate protons over a multi-gigayear timescale, much longer than other natural timescales occurring in the problem. Here we present a mechanism wherein the timescale for generating the Bubbles' ?-ray emission via hadronic processes is ~few × 108 yr. Our model invokes the collapse of the Bubbles' thermally unstable plasma, leading to an accumulation of cosmic rays and magnetic field into localized, warm (~104 K), and likely filamentary condensations of higher-density gas. Under the condition that these filaments are supported by non-thermal pressure, the hadronic emission from the Bubbles is L ? ~= 2 × 1037 erg s-1 \\dot{M}_{in}/(0.1 \\, {M_\\odot } yr-1 ) \\ T_{FB}^2/(3.5 \\times 10^7 K)2 M fil/M pls, equal to their observed luminosity (normalizing to the star-formation-driven mass flux into the Bubbles and their measured plasma temperature and adopting the further result that the mass in the filaments, M fil is approximately equal to the that of the Bubbles' plasma, M pls).

Crocker, Roland M.; Bicknell, Geoffrey V.; Carretti, Ettore; Hill, Alex S.; Sutherland, Ralph S.

2014-08-01

241

Bubble Growth in Lunar Basalts  

NASA Astrophysics Data System (ADS)

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

Zhang, Y.

2009-05-01

242

Bubbles and Wormholes: Analytic Models  

E-print Network

The first junction conditions of spherically symmetric bubbles are solved for some cases, and whereby analytic models to the Einstein field equations are constructed. The effects of bubbles on the spacetime structure are studied and it is found that in some cases bubbles can close the spatial sector of the spacetime and turn it into a compact one, while in other cases they can give rise to wormholes. One of the most remarkable features of these wormholes is that they do not necessarily violate the weak and dominant energy condition even at the classical level.

Anzhong Wang; Patricio S. Letelier

1995-05-31

243

On Charged Mesoscopic Metallic Bubbles  

E-print Network

We investigate the existence of stable charged metallic bubbles using the shell correction method. We find that for a given mesoscopic system of n atoms of a given metal and q less n (positive) elementary charges, a metallic bubble turns out to have a lower total energy than a compact spherical cluster, whenever the charge number q is larger than acritical charge number q_c. For a magic number (n-q) of free electrons, the spherical metallic bubble may become stable against fission.

Krzysztof Pomorski; Klaus Dietrich

1997-11-14

244

Terminating marine methane bubbles by superhydrophobic sponges.  

PubMed

Marine methane bubbles are absorbed, steadily stored, and continuously transported based on the employment of superhydrophobic sponges. Antiwetting sponges are water-repellent in the atmosphere and absorb gas bubbles under water. Their capacity to store methane bubbles increases with enhanced submerged depth. Significantly, trapped methane bubbles can be continuously transported driven by differential pressure. PMID:22945667

Chen, Xiao; Wu, Yuchen; Su, Bin; Wang, Jingming; Song, Yanlin; Jiang, Lei

2012-11-14

245

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

246

Assessing model representations of stratospheric equatorial waves  

NASA Astrophysics Data System (ADS)

Some westward-propagating Rossby-gravity waves and eastward Kelvin waves can travel up through the atmosphere following their formation in the tropical troposphere. Once they reach the stratosphere, these waves dissipate, releasing their energy. Known as stratospheric equatorial waves, these Rossby-gravity and Kelvin waves are an important aspect driving the quasi-biennial oscillation (QBO), a roughly monthly reversal, in the direction of the equatorial stratospheric winds. Similar to other atmospheric systems, such as the El Niño-Southern Oscillation or the North Atlantic Oscillation, the phase of the QBO affects global weather patterns, particularly in North America and western Europe.

Schultz, Colin

2014-07-01

247

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

248

Statistical equilibrium of bubble oscillations in dilute bubbly flows Tim Colonius,1  

E-print Network

of bubbles with a given radius and radial velocity.2 For spherical bubbles ini- tially in static equilibriumStatistical equilibrium of bubble oscillations in dilute bubbly flows Tim Colonius,1 Rob Hagmeijer statistical equilibrium, whereby phase cancellations among bubbles with different sizes lead to time

Dabiri, John O.

249

Oceanic Gas Bubble Measurements Using an Acoustic Bubble Spectrometer  

NASA Astrophysics Data System (ADS)

Gas bubble injection by breaking waves contributes significantly to the exchange of gases between atmosphere and ocean at high wind speeds. In this respect, CO2 is primarily important for the global ocean and climate, while O2 is especially relevant for ecosystems in the coastal ocean. For measuring oceanic gas bubble size distributions, a commercially available Dynaflow Acoustic Bubble Spectrometer (ABS) has been modified. Two hydrophones transmit and receive selected frequencies, measuring attenuation and absorption. Algorithms are then used to derive bubble size distributions. Tank test were carried out in order to test the instrument performance.The software algorithms were compared with Commander and Prosperetti's method (1989) of calculating sound speed ratio and attenuation for a known bubble distribution. Additional comparisons with micro-photography were carried out in the lab and will be continued during the SPACE '08 experiment in October 2008 at Martha's Vineyard Coastal Observatory. The measurements of gas bubbles will be compared to additional parameters, such as wind speed, wave height, white cap coverage, or dissolved gases.

Wilson, S. J.; Baschek, B.; Deane, G.

2008-12-01

250

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

251

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

252

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

253

Bubbles created from vacuum fluctuation  

E-print Network

We show that the bubbles $S^2\\times S^2$can be created from vacuum fluctuation in certain De Sitter universe, so the space-time foam-like structure might really be constructed from bubbles of $S^2\\times S^2$ in the very early inflating phase of our universe. But whether such foam-like structure persisted during the later evolution of the universe is a problem unsolved now.

Liao Liu; Feng He

2001-01-05

254

Slowing down bubbles with sound  

NASA Astrophysics Data System (ADS)

We present experimental evidence that a bubble moving in a fluid in which a well-chosen acoustic noise is superimposed can be significantly slowed down even for moderate acoustic pressure. Through mean velocity measurements, we show that a condition for this effect to occur is for the acoustic noise spectrum to match or overlap the bubble's fundamental resonant mode. We render the bubble's oscillations and translational movements using high speed video. We show that radial oscillations (Rayleigh-Plesset type) have no effect on the mean velocity, while above a critical pressure, a parametric type instability (Faraday waves) is triggered and gives rise to nonlinear surface oscillations. We evidence that these surface waves are subharmonic and responsible for the bubble's drag increase. When the acoustic intensity is increased, Faraday modes interact and the strongly nonlinear oscillations behave randomly, leading to a random behavior of the bubble's trajectory and consequently to a higher slow down. Our observations may suggest new strategies for bubbly flow control, or two-phase microfluidic devices. It might also be applicable to other elastic objects, such as globules, cells or vesicles, for medical applications such as elasticity-based sorting.

Poulain, Cedric; Dangla, Remie; Guinard, Marion

2009-11-01

255

Holographic description of vacuum bubbles  

E-print Network

We discuss a holographic description of vacuum bubbles, with possible implications for a consistent description of the multiverse. In particular, we elaborate on the recent observation by Maldacena, that the interior of AdS bubbles can be described in terms of CFT degrees of freedom living on the worldsheet of the bubble wall. We consider the scattering of bulk gravitons in the ambient parent vacuum, off the bubble wall. In the dual description, the transmission coefficient is interpreted as the probability that a graviton is absorbed by the worldsheet CFT degrees of freedom. The result is in agreement with intuitive expectations. Conformal invariance is not exact in this setup, and the leading corrections due to the IR and UV cut-offs are displayed. Aside from bulk scattering states, we find that when a bubble nucleates within a parent dS vacuum, there is a zero mode of the graviton which describes lower dimensional gravity with a finite Newton's constant. This massless graviton lives within one Hubble radius away from the bubble wall. Possible implications for a fully holographic description of the inflating multiverse are briefly discussed.

Jaume Garriga

2010-12-29

256

Gradient drift eigenmodes in the equatorial electrojet  

Microsoft Academic Search

The problem of kilometer-scale irregularities in the daytime equatorial electrojet is revisited by means of an eigenmode analysis of the gradient drift instability. Realistic physical parameters are used, including the modeled altitude variations of ion and electron collision frequencies and mobilities. The full fourth-order system of two coupled differential equations (each of second order) for the denisty and electrostatic potential

X.-H. Wang; A. Bhattacharjee

1994-01-01

257

Mapping Magnetospheric Equatorial Regions at Saturn from Cassini Prime Mission Observations  

NASA Astrophysics Data System (ADS)

Saturn's rich magnetospheric environment is unique in the solar system, with a large number of active magnetospheric processes and phenomena. Observations of this environment from the Cassini spacecraft has enabled the study of a magnetospheric system which strongly interacts with other components of the saturnian system: the planet, its rings, numerous satellites (icy moons and Titan) and various dust, neutral and plasma populations. Understanding these regions, their dynamics and equilibria, and how they interact with the rest of the system via the exchange of mass, momentum and energy is important in understanding the system as a whole. Such an understanding represents a challenge to theorists, modellers and observers. Studies of Saturn's magnetosphere based on Cassini data have revealed a system which is highly variable which has made understanding the physics of Saturn's magnetosphere all the more difficult. Cassini's combination of a comprehensive suite of magnetospheric fields and particles instruments with excellent orbital coverage of the saturnian system offers a unique opportunity for an in-depth study of the saturnian plasma and fields environment. In this paper knowledge of Saturn's equatorial magnetosphere will be presented and synthesised into a global picture. Data from the Cassini magnetometer, low-energy plasma spectrometers, energetic particle detectors, radio and plasma wave instrumentation, cosmic dust detectors, and the results of theory and modelling are combined to provide a multi-instrumental identification and characterisation of equatorial magnetospheric regions at Saturn. This work emphasises the physical processes at work in each region and at their boundaries. The result of this study is a map of Saturn's near equatorial magnetosphere, which represents a synthesis of our current understanding at the end of the Cassini Prime Mission of the global configuration of the equatorial magnetosphere.

Arridge, C. S.; André, N.; McAndrews, H. J.; Bunce, E. J.; Burger, M. H.; Hansen, K. C.; Hsu, H.-W.; Johnson, R. E.; Jones, G. H.; Kempf, S.; Khurana, K. K.; Krupp, N.; Kurth, W. S.; Leisner, J. S.; Paranicas, C.; Roussos, E.; Russell, C. T.; Schippers, P.; Sittler, E. C.; Smith, H. T.; Thomsen, M. F.; Dougherty, M. K.

2011-12-01

258

Ionospheric effects of the March 13, 1989, magnetic storm at low and equatorial latitudes  

Microsoft Academic Search

The great geomagnetic storm of March 13, 1989 caused severely anomalous behavior in the equatorial and low latitude ionosphere in the Brazilian longitude sector. The ionograms over Fortaleza indicated F region upward plasma drifts exceeding 200 m s⁻¹ at 1,830 LT as compared to normal values of 40 m s⁻¹ for this epoch. Large negative phases were observed in foF2

Inez S. Batista; E.R. De Paula; M. A. Abdu; N. B. Trivedi; M. E. Greenspan

1991-01-01

259

Intraseasonal vertical velocity variation caused by the equatorial wave in the central equatorial Indian Ocean  

Microsoft Academic Search

Intraseasonal vertical velocity variation investigated using observation dataUpwelling event in the central equatorial Indian OceanStructure of the quasi-biweekly mixed Rossby-gravity wave in the ocean

Takanori Horii; Yukio Masumoto; Iwao Ueki; S. Prasanna Kumar; Keisuke Mizuno

2011-01-01

260

Equatorial deep jets in the Atlantic Ocean  

NASA Astrophysics Data System (ADS)

Vertically alternating deep zonal jets of short vertical wavelength were discovered in the equatorial oceans more than 35 years ago. These jets that are observed to be coherent across the equatorial basins are characterized by vertically alternating eastward and westward currents lying within 1° of the equator, with amplitudes of 0.1-0.2 ms-1 and vertical wavelengths between 300 and 700 m. In the Atlantic, equatorial deep jets oscillate with a period of about 4.5 years, while their energy propagates upward. The 4.5 year signal can be seen in sea surface temperature as well as atmospheric data (e.g. surface wind and rainfall) indicating the significance of the deep jets for climate. Here we analyse velocity data from more than 7 years of moored observations at the equator, 23°W as well as shipboard hydrographic and current observations along the 23°W repeat section. Our focus is on intermediate depth levels (300-700 m), where the deep jets are superimposed on a mean flow composed of the westward flowing Equatorial Intermediate Current centred on the equator and the eastward Southern and Northern Intermediate Countercurrents located at 2°S and 2°N, respectively. The large zonal oxygen gradient from the well ventilated western boundary toward low-oxygen values near the eastern boundary makes the meridional oxygen distribution in the central equatorial Atlantic sensitive to zonal flow variations in time and latitude. We compare the observed meridional structures of the mean and anomalous oxygen and zonal velocity distributions as well as their temporal evolution with results of an advection-diffusion model driven by a prescribed velocity field, restoring to high oxygen values at the western boundary, and otherwise constant oxygen consumption. The prescribed velocity field is composed of a high order baroclinic vertical normal mode aimed at representing the 4.5-year cycle and a mean velocity field resembling the observed mean zonal current structure. Similarities between observed and simulated tracer distribution are used to discuss the equatorial deep jet's nature in the light of normal mode oscillations and their role in the ventilation of the equatorial Atlantic at intermediate depths.

Brandt, P.; Greatbatch, R. J.; Didwischus, S.-H.; Claus, M.; Hormann, V.; Funk, A.; Dengler, M.

2012-04-01

261

On large-scale wave structure and equatorial spread F without a post-sunset rise of the F layer  

Microsoft Academic Search

Large-scale wave structure (LSWS) and the plasma structure, referred to as equatorial spread F (ESF), are shown, for the first time, to develop on a night, when the post-sunset rise (PSSR) of the F layer was absent. Using ionograms from two nearby locations, together with measurements of total electron content, LSWS and ESF are also shown to coexist in regions

Roland T. Tsunoda; David M. Bubenik; Smitha V. Thampi; Mamoru Yamamoto

2010-01-01

262

Shabansky Mechanism as a Source for Off-Equatorial Chorus Wave Growth  

NASA Astrophysics Data System (ADS)

Recent observations show presence of chorus wave activity in off-equatorial regions of the dayside magnetosphere. It is thought that temperature anisotropies in energetic electron populations can lead to chorus wave growth. In the presence of off-equatorial magnetic field minima, trapped energetic electrons undergo Shabansky orbits, which lead to temperature anisotropies off the equator. Additionally, drift shell splitting (DSS) can produce anisotropies in a compressed dipole. We used a 3D particle tracing code in an analytic compressed-dipole field to study the role of Shabansky orbits on off-equatorial chorus wave growth. By adjusting the dependence on L of the phase space density, we have determined Shabansky orbits play a definite role. We have used the computed anisotropy for both cases along with a cold plasma model to compute a linear convective wave growth rate for dayside waves, including off-equatorial regions. We will use MHD fields to simulate a specific wave activity event and compare the spectral and spatial characteristics with observations from the Polar spacecraft wave data.

McCollough, J. P.; Elkington, S. R.; Bunch, N. L.; Spasojevic, M.

2012-12-01

263

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

264

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

265

Holographic description of vacuum bubbles  

E-print Network

We discuss a holographic description of vacuum bubbles, with possible implications for a consistent description of the multiverse. In particular, we elaborate on the recent observation by Maldacena, that the interior of AdS bubbles can be described in terms of CFT degrees of freedom living on the worldsheet of the bubble wall. We consider the scattering of bulk gravitons in the ambient parent vacuum, off the bubble wall. In the dual description, the transmission coefficient is interpreted as the probability that a graviton is absorbed by the worldsheet CFT degrees of freedom. The result is in agreement with intuitive expectations. Conformal invariance is not exact in this setup, and the leading corrections due to the IR and UV cut-offs are displayed. Aside from bulk scattering states, we find that when a bubble nucleates within a parent dS vacuum, there is a zero mode of the graviton which describes lower dimensional gravity with a finite Newton's constant. This massless graviton lives within one Hubble radiu...

Garriga, Jaume

2010-01-01

266

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. Time-resolved experimental photographs and simulations of large aspect ratio (length:diameter {approximately}20) cylindrical bubble dynamics are presented. The experiments and calculations exhibit similar dynamics. A small high-pressure cylindrical bubble initially expands radially with hardly any axial motion. Then, after reaching its maximum volume, a cylindrical bubble collapses along its long axis with relatively little radial motion. The growth-collapse period of these very aspherical bubbles differs only sightly 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 energy even for aspherical bubbles. The prolongation of the oscillation period of bubbles near solid boundaries relative to that of isolated spherical bubbles is also discussed.

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

1999-03-01

267

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, Michal; Schmitz, Georg; Lewin, Peter A.

2012-01-01

268

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

269

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

270

VISUALIZATION OF SOAP BUBBLE GEOMETRIES Fred Almgren (mathematician)  

E-print Network

VISUALIZATION OF SOAP BUBBLE GEOMETRIES Fred Almgren (mathematician) Department of Mathematics ABSTRACT The authors discuss mathematical soap bubble problems and a new technique for generating computer soap bubble possesses an exquisite perfection of form. Soap bubbles are lovely physical manifestations

Sullivan, John M.

271

From rational bubbles to crashes  

NASA Astrophysics Data System (ADS)

We study and generalize in various ways the model of rational expectation (RE) bubbles introduced by Blanchard and Watson in the economic literature. Bubbles are argued to be the equivalent of Goldstone modes of the fundamental rational pricing equation, associated with the symmetry-breaking introduced by non-vanishing dividends. Generalizing bubbles in terms of multiplicative stochastic maps, we summarize the result of Lux and Sornette that the no-arbitrage condition imposes that the tail of the return distribution is hyperbolic with an exponent ?<1. We then outline the main results of Malevergne and Sornette, who extend the RE bubble model to arbitrary dimensions d: a number d of market time series are made linearly interdependent via d× d stochastic coupling coefficients. We derive the no-arbitrage condition in this context and, with the renewal theory for products of random matrices applied to stochastic recurrence equations, we extend the theorem of Lux and Sornette to demonstrate that the tails of the unconditional distributions associated with such d-dimensional bubble processes follow power laws, with the same asymptotic tail exponent ?<1 for all assets. The distribution of price differences and of returns is dominated by the same power-law over an extended range of large returns. Although power-law tails are a pervasive feature of empirical data, the numerical value ?<1 is in disagreement with the usual empirical estimates ??3. We then discuss two extensions (the crash hazard rate model and the non-stationary growth rate model) of the RE bubble model that provide two ways of reconciliation with the stylized facts of financial data.

Sornette, D.; Malevergne, Y.

2001-10-01

272

Initial thermal plasma observations from ISEE-1  

Microsoft Academic Search

The initial measurements of magnetospheric thermal ions by the Plasma Composition Experiment on ISEE-1 are presented to demonstrate the surprising variety in this plasma population. The data provide evidence that the adiabatic mapping of the high latitude ionosphere to the equatorial plasma trough provides an insufficient description of the origin, transport, and accumulation processes which supply low energy ions to

C. R. Baugher; C. R. Chappell; J. L. Horwitz; E. G. Shelley; D. T. Young

1980-01-01

273

Plasma observations at the Earth's magnetic equator  

Microsoft Academic Search

The magnetic equator provides a unique location for thermal plasma and plasma wave measurements. Plasma populations are found to be confined within a few degrees latitude of the equator, particularly the ions. The equatorially trapped ion population is found to be primarily hydrogen, and the authors find little evidence for preferential heating of heavier ions. Helium is occasionally found to

R. C. Olsen; S. D. Shawhan; D. L. Gallagher; J. L. Green; C. R. Chappell; R. R. Anderson

1987-01-01

274

Collapsing Sub-Critical Bubbles  

E-print Network

In the standard scenario, the electroweak phase transition is a first order phase transition which completes by the nucleation of critical bubbles. Recently, there has been speculation that the standard picture of the electroweak phase transition is incorrect. Instead, it has been proposed that throughout the phase transition appreciable amounts of both broken and unbroken phases of $SU(2)$ coexist in equilibrium. I argue that this can not be the case. General principles insure that the universe will remain in a homogenous state of unbroken $SU(2)$ until the onset of critical bubble production.

Greg W. Anderson

1992-09-20

275

Time variability of Indian Ocean equatorial currents  

NASA Astrophysics Data System (ADS)

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

Knox, R. A.

1981-03-01

276

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

277

Soap Bubbles on a Cold Day.  

ERIC Educational Resources Information Center

Discusses the effects of blowing bubbles in extremely cold weather. Describes the freezing conditions of the bubbles and some physical properties. Suggests using the activity with all ages of students. (MVL)

Waiveris, Charles

1994-01-01

278

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

279

TECHNOLOGY ASSESSMENT OF FINE BUBBLE AERATORS  

EPA Science Inventory

This technology assessment addresses design and evaluation of fine bubble aeration equipment. It discusses the associated gas transfer theory used as the basis for measuring water and wastewater oxygenation efficiency. Mixing requirements are also discussed. While bubble aeration...

280

Experimental characterisation of bubbly flow using MRI  

E-print Network

This thesis describes the first application of ultra-fast magnetic resonance imaging (MRI) towards the characterisation of bubbly flow systems. The principle goal of this study is to provide a hydrodynamic characterisation of a model bubble column...

Tayler, Alexander B.

2011-11-08

281

Global Specification of the Post-Sunset Equatorial Ionization Anomaly  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

282

Detonation wave phenomena in bubbled liquid  

Microsoft Academic Search

Shock wave propagation was investigated in two phase media consisting of diluted glycerin (85%) and reactive gas bubbles. To understand these complex phenomena, we first performed a numerical analysis and experimental studies of single bubbles containing a reactive gas-mixture. For the two-phase mixtures, a needle matrix bubble-generator enabled us to produce a homogeneous bubble distribution with a size dispersion less

A. E. Beylich

1990-01-01

283

Detonation wave phenomena in bubbled liquid  

Microsoft Academic Search

Shock wave propagation was investigated in two phase media consisting of diluted glycerin (85%) and reactive gas bubbles. To understand these complex phenomena, we first performed a numerical analysis and experimental studies of single bubbles containing a reactive gas-mixture. For the two-phase mixtures, a needle matrix bubble-generator enabled us to produce a homogeneous bubble distribution with a size dispersion less

A. Gülhan; A. E. Beylich

1990-01-01

284

Lifetime expectancy for a soap bubble  

NASA Astrophysics Data System (ADS)

Soap bubbles are metastable : drainage and evaporation cause their soapy water skin to thin and eventually to rupture. We have investigated experimentally the maximum lifetime of bubbles as a function of their size. For a large range of sizes, this lifetime is proportional to the bubble radius : small bubbles last shorter than large ones, but their lifetime is more predictable. A model based on lubrication theory is proposed : evaporation is shown to be the key process in determining the maximum lifetime.

Gilet, Tristan; Scheller, Tom; Vandewalle, Nicolas; Dorbolo, Stephane

2007-11-01

285

Period-adding route in sparkling bubbles.  

PubMed

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 periods known as the period-adding route. PMID:16241621

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

2005-09-01

286

Improved design of an ITER equatorial EC launcher  

NASA Astrophysics Data System (ADS)

New design improvements for an ITER equatorial EC launcher are described. A design of the front shield modules was evaluated analytically. The results indicate that these modules can withstand the electromagnetic forces induced by plasma disruption and vertical plasma motion. The steering mirror mock-up including the spiral cooling tubes was fabricated based on the present design with application of the hot isostatic pressing technique to bond the copper alloy mirror body and the embedded stainless steel cooling tubes. The test of water flow was carried out and the expected flow rate was successfully obtained. A quasi-optical (QO) transmission layout has been proposed instead of the waveguide lines. The advantage of this option is possibly to increase the reliability in terms of fabrication and refurbishment. According to the beam propagation analysis, it is verified that transmission loss at the QO region is 1.1%-2.2%, which is comparable to the reference design. The peak heat load on the steering mirror surface could be reduced by 55%, which relaxes the mirror design.

Takahashi, K.; Kajiwara, K.; Kobayashi, N.; Kasugai, A.; Sakamoto, K.

2008-05-01

287

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

288

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

289

HIGH QUALITY ANISOTROPIC TETRAHEDRAL MESH GENERATION VIA ELLIPSOIDAL BUBBLE PACKING  

E-print Network

the behavior of soap bubbles in nature. If we pack soap bubbles in a volumetric domain, the bubblesHIGH QUALITY ANISOTROPIC TETRAHEDRAL MESH GENERATION VIA ELLIPSOIDAL BUBBLE PACKING Soji Yamakawa1 through a physically based particle simulation, which we call 'bubble packing.' Ellipsoidal bubbles

Shimada, Kenji

290

Black hole formation from colliding bubbles  

E-print Network

Some indication of conditions that are necessary for the formation of black holes from the collision of bubbles during a supercooled phase transition in the the early universe are explored. Two colliding bubbles can never form a black hole. Three colliding bubbles can refocus the energy in their walls to the extent that it becomes infinite.

Ian G. Moss

1994-05-21

291

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

292

Inverted Soap Bubbles-A Surface Phenomenon  

Microsoft Academic Search

By pouring soap water onto a surface of soap water it is possible to produce thin spherical shells of air in the water (inverted soap bubbles). The largest diameter observed is about 20 mm. Interference colors indicate shell thickness of the order 0.001 mm. Lifetimes of the bubbles of 4-5 minutes have been observed. A connection between the inverted bubbles

N. Skogen

1956-01-01

293

A User's Guide to Bubbles Frdric Gosselin  

E-print Network

A User's Guide to Bubbles Frédéric Gosselin Philippe G. Schyns Correspondence concerning;Abstract This article provides a user's guide to Bubbles, a technique that reveals the information Effect and discuss the six basic decisions that must be made to set up a Bubbles experiment (i

Gosselin, Frédéric

294

Dynamic removal of oral biofilms by bubbles  

Microsoft Academic Search

A novel approach to the removal of biofilms from solid surfaces is to pass large numbers of air bubbles over the surfaces. Such a phenomenon occurs when teeth are brushed with some types of powered toothbrushes that accelerate bubbly fluid against or across teeth surfaces. Video recordings of air bubbles propelled against a mature biofilm of Streptococcus mutans showed that

Michael R. Parini; William G. Pitt

2006-01-01

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

Multifractal properties of large bubble paths in a single bubble column  

NASA Astrophysics Data System (ADS)

In the paper the paths of bubbles emitted from the brass nozzle with inner diameter equal to 1.6 mm have been analyzed. The mean frequency of bubble departure was in the range from 2 to 65.1 Hz. Bubble paths have been recorded using a high speed camera. The image analysis technique has been used to obtain the bubble paths for different mean frequencies of bubble departures. The multifractal analysis (WTMM - wavelet transform modulus maxima methodology) has been used to investigate the properties of bubble paths. It has been shown that bubble paths are the multifractals and the influence of previously departing bubbles on bubble trajectory is significant for bubble departure frequency fb > 30 Hz.

Mosdorf, Romuald; Wyszkowski, Tomasz; D?browski, Kamil

2011-04-01

298

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

NASA Astrophysics Data System (ADS)

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 by an equatorial minimum of zero-age topography, a maximum in mantle shear waves seismic velocity and a minimum in the degree of melting, indicated by the chemistry of MAR basalts and peridotites. This thermal minimum has probably been a stable feature since before the Cretaceous separation of Africa from South America; it caused a pre-opening equatorial continental lithosphere thicker and colder than normal. The Cretaceous Benue Trough in western Africa and the Amazon depression in South America are interpreted as morphostructural depressions created or rejuvenated by strike-slip, transpressional and transtensional tectonics ducing extension of the cold/thick equatorial lithosphere. The oceanic rift propagating northward from the South Atlantic impinged against the equatorial thicker, colder and, therefore, stronger than normal continental, lithosphere that consequently acted as a 'locked zone'. This, and a low magmatic budget due to the cold upper mantle, caused a lower than normal rate of propagation of the oceanic rift into the equatorial belt, with diffuse deformation during mostly amagmatic extension. The thick/cold lithosphere prevented major Cretaceous igneous activity from the St. Helena plume. Eventually initial 'weak' isolated nuclei oceanic lithosphere were emplaced, separated by E-W continent/continent transforms. Opening occurred largely by strike-slip motion along these initial transforms. The consequences were that the Equatorial Atlantic opened prevalently along an E-W direction, in contrast to the N-S opening of the North and South Atlantic, and that sheared continental margins are particularly well developed in the Equatorial Atlantic. After further continental separation the cold equatorial mantle caused a low degree of melting (with Na-rich MORB and alkali basalt rather than normal MORB and with undepleted mantle peridotities), thin crust, depressed ridge segments and a prevalence of amagmatic extension. Similar conditions still exist today. Long transforms offsetting short ridge segments kept sea floor spreading unstable and dominated by transform tectonics, with transform migration, transpression, and transtension causing strong vertical motion, emersion and subsidence of lithospheric blocks, development of deep pull-apart basins, and preservation of relict slivers of old lithosphere (occasionally even of continental lithosphere) within younger crust. The equatorial transforms are caused ultimately by a long lived thermal minimum in the upper mantle and not vice versa; however, they then create second-order 'rebound' thermal effects that help maintain the thermal minimum in the upper mantle. It can be speculated that mantle thermal minima at the Earth's equator might be related to true polar wander triggered by subduction of dense masses into the mantle.

Bonatti, Enrico

1996-09-01

299

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

300

A Campaign to Study Equatorial Ionospheric Phenomena over Guam  

NASA Astrophysics Data System (ADS)

With the development of a series of ground-based and space-based experiments, the United States Air Force Academy (USAFA) is in the process of planning a campaign to investigate the relationship between equatorial ionospheric plasma dynamics and a variety of space weather effects, including: 1) ionospheric plasma turbulence in the F region, and 2) scintillation of radio signals at low latitudes. A Digisonde Portable Sounder DPS-4 will operate from the island of Guam (with a magnetic latitude of 5.6° N) and will provide measurements of ionospheric total electron content (TEC), vertical drifts of the bulk ionospheric plasma, and electron density profiles. Additionally, a dual-frequency GPS TEC/scintillation monitor will be located along the Guam magnetic meridian at a magnetic latitude of approximately 15° N. In campaign mode, we will combine these ground-based observations with those collected from space during USAFA's FalconSAT-3 and FalconSAT-5 low-earth orbit satellite missions, the first of which is scheduled to be active over a period of several months beginning in the 2007 calendar year. The satellite experiments are designed to characterize in situ irregularities in plasma density, and include measurements of bulk ion density and temperature, minority-to- majority ion mixing ratios, small scale (10 cm to 1 m) plasma turbulence, and ion distribution spectra in energy with sufficient resolution for observations of non-thermalized distributions that may be associated with velocity- space instabilities. Specific targets of investigation include: a) a comparison of plasma turbulence observed on- orbit with spread F on ionograms as measured with the Digisonde, b) a correlation between the vertical lifting of the ionospheric layer over Guam and the onset of radio scintillation activity along the Guam meridian at 15° N magnetic latitude, and c) a correlation between on-orbit turbulence and ionospheric scintillation at 15° N magnetic latitude. These relationships may provide further clues into understanding the trigger mechanisms responsible for instigating disturbances in the ionospheric plasma, thus resulting in a turbulent radio propagation medium that may cause outages of radio based communication and navigation systems.

Habash Krause, L.; Balthazor, R.; Dearborn, M.; Enloe, L.; Lawrence, T.; McHarg, M.; Petrash, D.; Reinisch, B. W.; Stuart, T.

2007-05-01

301

The longitudinal variability of equatorial electrojet and vertical drift velocity in the African and American sectors  

NASA Astrophysics Data System (ADS)

While the formation of equatorial electrojet (EEJ) and its temporal variation is believed to be fairly well understood, the longitudinal variability at all local times is still unknown. This paper presents a case and statistical study of the longitudinal variability of dayside EEJ for all local times using ground-based observations. We found EEJ is stronger in the west American sector and decreases from west to east longitudinal sectors. We also confirm the presence of significant longitudinal difference in the dusk sector pre-reversal drift, using the ion velocity meter (IVM) instrument onboard the C/NOFS satellite, with stronger pre-reversal drift in the west American sector compared to the African sector. Previous satellite observations have shown that the African sector is home to stronger and year-round ionospheric bubbles/irregularities compared to the American and Asian sectors. This study's results raises the question if the vertical drift, which is believed to be the main cause for the enhancement of Rayleigh-Taylor (RT) instability growth rate, is stronger in the American sector and weaker in the African sector - why are the occurrence and amplitude of equatorial irregularities stronger in the African sector?

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

2014-03-01

302

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

Konicek-Moran, Richard

2010-03-12

303

Soap bubbles. 2 [Computer graphics  

Microsoft Academic Search

For pt.1 see ibid., previous issue. Soap bubbles are fragile, beautiful phenomena. They're fun to make and play with, and their geometry is as clean and elegant as anything in nature, which makes them particularly suited to computer graphics. In pt.1 I discussed the nature of soap films. These thin sheets of soapy water have less surface tension than water

A. Glassner

2000-01-01

304

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

305

Pulling bubbles from a bath  

E-print Network

Deposition of bubbles on a wall withdrawn from a liquid bath is a phenomenon observed in many everyday situations—the foam lacing left behind in an emptied glass of beer, for instance. It is also of importance to the many ...

Kao, Justin C. T.

306

Electrino bubbles and relational entanglement  

E-print Network

We argue that the phenomena exhibited by bubbles forming around free electrons in liquid helium and examined by Maris in his controversial 2000 paper point to the experimental relevance of relational entanglement. An experiment to verify/disprove the relevant argument is suggested.

Italo Vecchi

2007-03-26

307

Models of cylindrical bubble pulsation  

PubMed Central

Three models are considered for describing the dynamics of a pulsating cylindrical bubble. A linear solution is derived for a cylindrical bubble in an infinite compressible liquid. The solution accounts for losses due to viscosity, heat conduction, and acoustic radiation. It reveals that radiation is the dominant loss mechanism, and that it is 22 times greater than for a spherical bubble of the same radius. The predicted resonance frequency provides a basis of comparison for limiting forms of other models. The second model considered is a commonly used equation in Rayleigh-Plesset form that requires an incompressible liquid to be finite in extent in order for bubble pulsation to occur. The radial extent of the liquid becomes a fitting parameter, and it is found that considerably different values of the parameter are required for modeling inertial motion versus acoustical oscillations. The third model was developed by V. K. Kedrinskii [Hydrodynamics of Explosion (Springer, New York, 2005), pp. 23–26] in the form of the Gilmore equation for compressible liquids of infinite extent. While the correct resonance frequency and loss factor are not recovered from this model in the linear approximation, it provides reasonable agreement with observations of inertial motion. PMID:22978863

Ilinskii, Yurii A.; Zabolotskaya, Evgenia A.; Hay, Todd A.; Hamilton, Mark F.

2012-01-01

308

Mechanisms of bubble coalescence in silicic magmas  

NASA Astrophysics Data System (ADS)

Bubble coalescence is an important process that strongly affects magmatic degassing. Without coalescence, bubbles remain isolated from one another in the melt, severely limiting gas release. Despite this fact, very little has been done to identify coalescence mechanisms from textures of magmatic rocks or to quantify the dynamics of bubble coalescence in melts. In this paper, we present a systematic study of bubble-coalescence mechanisms and dynamics in natural and experimentally produced bubbly rhyolite magma. We have used a combination of natural observations aided by high-resolution X-ray computed tomography, petrological experiments, and physical models to identify different types of bubble-bubble interaction that lead to coalescence on the timescales of magma ascent and eruption. Our observations and calculations suggest that bubbles most efficiently coalesce when inter-bubble melt walls thin by stretching rather than by melt drainage from between converging bubble walls. Orders of magnitude are more rapid than melt drainage, bubble wall stretching produces walls thin enough that inter-bubble pressure gradients may cause the melt wall to dimple, further enhancing coalescence. To put these results into volcanogical context, we have identified magma ascent conditions where each coalescence mechanism should act, and discuss the physical conditions for preserving coalescence structures in natural pumice. The timescales we propose could improve volcanic eruption models, which currently do not account for bubble coalescence. Although we do not address the effect of shear strain on bubble coalescence, the processes discussed here may operate in several different eruption regimes, including vesiculation of lava domes, post-fragmentation frothing of vulcanian bombs, and bubbling of pyroclasts in conduits.

Castro, Jonathan M.; Burgisser, Alain; Schipper, C. Ian; Mancini, Simona

2012-12-01

309

Serendipitous Chandra X-Ray Detection of a Hot Bubble within the Planetary Nebula NGC 5315  

NASA Astrophysics Data System (ADS)

We report the serendipitous detection of the planetary nebula NGC 5315 by the Chandra X-Ray Observatory. The Chandra imaging spectroscopy results indicate that the X-rays from this PN, which harbors a Wolf-Rayet (W-R) central star, emanate from a TX~2.5×106 K plasma generated via the same wind-wind collisions that have cleared a compact (<~8000 AU radius) central cavity within the nebula. The inferred X-ray luminosity of NGC 5315 is ~2.5×1032 ergs s-1 (0.3-2.0 keV), placing this object among the most luminous such ``hot bubble'' X-ray sources yet detected within PNe. With the X-ray detection of NGC 5315, objects with W-R-type central stars now constitute a clear majority of known examples of diffuse X-ray sources among PNe; all such ``hot bubble'' PN X-ray sources display well-defined, quasi-continuous optical rims. We therefore assert that X-ray-luminous hot bubbles are characteristic of young PNe with large central star wind kinetic energies and closed bubble morphologies. However, the evidence at hand also suggests that processes such as wind and bubble temporal evolution, as well as heat conduction and/or mixing of hot bubble and nebular gas, ultimately govern the luminosity and temperature of superheated plasma within PNe.

Kastner, Joel H.; Montez, Rodolfo, Jr.; Balick, Bruce; De Marco, Orsola

2008-01-01

310

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

2013-10-22

311

How long will a bubble be ?  

E-print Network

A soap bubble is a metastable object that eventually breaks. Indeed, the soapy water film thins until rupture, due to drainage and evaporation. In our experimental investigations, floating bubbles at the surface of a liquid bath have been considered. Their lifetime has been measured and reported with respect to their radius. Large bubbles last longer than small ones. Moreover, small bubbles have more predictable lifetimes than large ones. We propose a general equation for that lifetime, based on the lubrication theory. The evaporation is shown to be an essential process which determines the bubble lifetime.

Gilet, T; Reyssat, E; Vandewalle, N; Dorbolo, S

2007-01-01

312

Mesoporous hollow spheres from soap bubbling.  

PubMed

The smaller and more stable bubbles can be generated from the large parent bubbles by rupture. In the presence of a bubble blowing agent, hollow spheres can be prepared by bubbling a silica sol. Herein, the trapped gas inside the bubble acts as a template. When the porogen, i.e., other surfactant, is introduced, a mesostructured shell forms by the co-assembly with the silica sol during sol-gel process. Morphological evolution emphasizes the prerequisite of an intermediate interior gas flow rate and high exterior gas flow rate for hollow spheres. The method is valid for many compositions from inorganic, polymer to their composites. PMID:22078340

Yu, Xianglin; Liang, Fuxin; Liu, Jiguang; Lu, Yunfeng; Yang, Zhenzhong

2012-02-01

313

Bubbles in Anti-de Sitter Space  

E-print Network

We explore the bubble spacetimes which can be obtained from double analytic continuations of static and rotating black holes in anti-de Sitter space. In particular, we find that rotating black holes with elliptic horizon lead to bubble spacetimes only in dimension greater than five. For dimension greater than seven, the topology of the bubble can be non-spherical. However, a bubble spacetime is shown to arise from a rotating de Sitter black hole in four dimensions. In all cases, the evolution of the bubble is of de Sitter type. Double analytic continuations of hyperbolic black holes and branes are also discussed.

Danny Birmingham; Massimiliano Rinaldi

2002-05-23

314

Asymmetric interface temperature during vapor bubble growth  

NASA Astrophysics Data System (ADS)

We investigate the nucleation, growth, and detachment of single vapor bubbles at the interface microscale. Shear flow is used to investigate pool and convective boiling situations using visible and infrared visualizations. We determine a threshold Reynolds number for the onset of asymmetric interfacial temperatures. Below this threshold, bubble growth is geometrically and thermally symmetric, while above, bubbles no longer grow thermally symmetrically. This is explained by the dominance of convective heat transfer removal over viscous effects at the bubble interface. We experimentally demonstrate asymmetric interfacial temperature profiles that should be taken into account for future bubble growth modeling.

Diana, A.; Castillo, M.; Steinberg, T.; Brutin, D.

2013-07-01

315

Response of the Equatorial Ionosphere to Major Magnetic Storms During the Current Solar Maximum Phase  

NASA Astrophysics Data System (ADS)

The generalized response of the equatorial ionosphere to major magnetic storms is discussed in the context of recently observed storm induced effects on VHF/UHF scintillation, total electron content (TEC) of the ionosphere and satellite insitu measurements of ion density and ion drifts. The scintillation data are obtained from AFRL's network of ground stations that monitor geostationary satellite signals and TEC and TEC fluctuation data are from the global network of the International Geodynamic Service that monitors GPS satellites. The satellite insitu measurements of ion density and ion drifts are obtained from DMSP and the Republic of China Satellite-1 (ROCSAT-1). It is found that prompt penetration of eastward electric field leading to a destabilization of ionospheric plasma in the equatorial region occurs over a longitude sector for which the early evening period corresponds to the time of rapid SYM-H (1-min resolution Dst) variations. A few examples of such longitudinally confined response are given for storms with different times of rapid SYM-H variations. It is shown that at some longitudes the eastward electric field can be intense enough to cause total plasma depletions dur to large upward plasma drift and field aligned plasma diffusion. It is also observed that IMF Bz northward turning and ionospheric disturbance dynamo can lead to fresh irregularity generation in the post-midnight period.

Basu, S.; Sultan, P.; Valladares, C.; Yeh, H.; Su, S.

2001-12-01

316

Coronal equatorial rotation during solar cycle 23: radial variation and connections with helioseismology  

NASA Astrophysics Data System (ADS)

Time-series observations of the O vi 1032 Å spectral line intensity provided by the UltraViolet Coronagraph Spectrometer (UVCS) telescope aboard the Solar and Heliospheric Observatory (SOHO) spacecraft have been analyzed to establish the rotational characteristics of the equatorial solar corona as a function of height and time during solar cycle 23. Overall, the coronal rotation period is observed to vary considerably from 1996 to 2006, with episodes of sudden acceleration and deceleration. On average, the rotation period in the equatorial corona tends to increase radially by ~0.2 days/R? from 1.6 to 3.0 R?. An anticorrelation throughout the solar cycle is observed between the radial gradients in the inner corona (?2.2 R?), where the magnetic pressure dominates and the plasma is more rigidly connected, and the outer corona (?2.4 R?), where the field lines open up. Around the equator, the extended corona is found to rotate faster than the underlying photosphere, but its rotation rate is comparable to that estimated within the subphotospheric layers in the outer 5% of the Sun. Moreover, a striking significant positive correlation (r = 0.629 at the 0.99 R? level) has been discovered between the variations in the residual rotation rates of the coronal and subphotospheric equatorial plasma, at least down to 0.95 R?. This correlation suggests that the observed variations in the coronal rotation rate reflect the dynamic changes inferred within the near-surface shear layer, where the tracer structures responsible for the observed coronal emission are thus most probably anchored. These results raise the possibility that the plasma in the upper layers of the solar convection zone, at least around the equator, may be tightly connected to the plasma in the extended corona and that the deeper layers in the Sun might thus directly influence the dynamic evolution of the solar wind.

Mancuso, S.; Giordano, S.

2012-03-01

317

Simulations of Rising Hydrodynamic and Magnetohydrodynamic Bubbles  

NASA Astrophysics Data System (ADS)

Motivated by recent Chandra and XMM-Newton observations of X-ray emission voids in galaxy cluster cooling flows, we have investigated the behavior of rising bubbles in stratified atmospheres using the FLASH adaptive-mesh simulation code. We present results from two-dimensional simulations with and without the effects of magnetic fields, and with varying bubble sizes and background stratifications. We find purely hydrodynamic bubbles to be unstable; a dynamically important magnetic field is required to maintain a bubble's integrity. This suggests that, even absent thermal conduction, for bubbles to be persistent enough to be regularly observed, they must be supported in large part by magnetic fields. We also observe that magnetically supported bubbles leave a tail as they rise. The structure of these tails may provide clues to the bubble's dynamical history.

Ricker, P. M.; Robinson, K.; Dursi, L. J.; Rosner, R.; Calder, A. C.; Zingale, M.; Truran, J. W.; Linde, T.; Caceres, A.; Fryxell, B.; Olson, K.; Riley, K.; Siegel, A.; Vladimirova, N.

318

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

319

The stability of buoyant bubbles in the atmospheres of galaxy clusters  

E-print Network

The buoyant rise of hot plasma bubbles inflated by AGN outflows in galaxy clusters can heat the cluster gas and thereby compensate radiative energy losses of this material. Numerical simulations of this effect often show the complete disruption of the bubbles followed by the mixing of the bubble material with the surrounding cluster gas due to fluid instabilities on the bubble surface. This prediction is inconsistent with the observations of apparently coherent bubble structures in clusters. We derive a general description in the linear regime of the growth of instabilities on the surface between two fluids under the influence of a gravitational field, viscosity, surface tension provided by a magnetic field and relative motion of the two fluids with respect to each other. We demonstrate that Kelvin-Helmholtz instabilities are always suppressed, if the fluids are viscous. They are also suppressed in the inviscid case for fluids of very different mass densities. We show that the effects of shear viscosity as well as a magnetic fields in the cluster gas can prevent the growth of Rayleigh-Taylor instabilities on relevant scale lengths. R-T instabilities on pc-scales are suppressed even if the kinematic viscosity of the cluster gas is reduced by two orders of magnitude compared to the value given by Spitzer for a fully ionised, unmagnetised gas. Similarly, magnetic fields exceeding a few microG result in an effective surface tension preventing the disruption of bubbles. For more massive clusters, instabilities on the bubble surface grow faster. This may explain the absence of thermal gas in the north-west bubble observed in the Perseus cluster compared to the apparently more disrupted bubbles in the Virgo cluster.

C. R. Kaiser; G. Pavlovski; E. C. D. Pope; H. Fangohr

2005-02-08

320

Low Latitude Ionospheric Zonal Plasma Drifts Measured by C/NOFS During the 2008-2011 Solar Minimum  

NASA Astrophysics Data System (ADS)

We use the measurements by Vector Electric Field Instrument (VEFI) on board the C/NOFS satellite to study seasonal, longitudinal, and latitudinal dependence of low latitude ionospheric zonal plasma drifts during 2008-2011. Over Jicamarca, these measurements are in good agreement with incoherent scatter radar F-region zonal drifts. Our data show strong longitudinal variations on both the daytime westward and nighttime eastward drifts at all seasons, particularly in the South American sector during the solstices. The daytime data indicate the occurrence of largely enhanced and short-lived westward drifts near sunrise, and strong longitude dependent peaks close to noon that resemble those observed on the equatorial vertical drift data. The nighttime eastward drifts have largest values near the western American sector at all seasons. Near midnight during June solstice, there is a sharp decrease in the magnitude of the eastward drifts at about 45 west and much smaller values in the entire eastern hemisphere. We also compare the satellite nighttime drifts with zonal winds and equatorial bubble drift velocities.

Fejer, B. G.; Tracy, B. D.; Pfaff, R. F.

2012-12-01

321

Bubbling the False Vacuum Away  

E-print Network

We investigate the role of nonperturbative, bubble-like inhomogeneities on the decay rate of false-vacuum states in two and three-dimensional scalar field theories. The inhomogeneities are induced by setting up large-amplitude oscillations of the field about the false vacuum as, for example, after a rapid quench or in certain models of cosmological inflation. We show that, for a wide range of parameters, the presence of large-amplitude bubble-like inhomogeneities greatly accelerates the decay rate, changing it from the well-known exponential suppression of homogeneous nucleation to a power-law suppression. It is argued that this fast, power-law vacuum decay -- known as resonant nucleation -- is promoted by the presence of long-lived oscillons among the nonperturbative fluctuations about the false vacuum. A phase diagram is obtained distinguishing three possible mechanisms for vacuum decay: homogeneous nucleation, resonant nucleation, and cross-over. Possible applications are briefly discussed.

Marcelo Gleiser; Barrett Rogers; Joel Thorarinson

2007-08-28

322

Sonoporation from jetting cavitation bubbles.  

PubMed

The fluid dynamic interaction of cavitation bubbles with adherent cells on a substrate is experimentally investigated. We find that the nonspherical collapse of bubbles near to the boundary is responsible for cell detachment. High-speed photography reveals that a wall bounded flow leads to the detachment of cells. Cells at the edge of the circular area of detachment are found to be permanently porated, whereas cells at some distance from the detachment area undergo viable cell membrane poration (sonoporation). The wall flow field leading to cell detachment is modeled with a self-similar solution for a wall jet, together with a kinetic ansatz of adhesive bond rupture. The self-similar solution for the delta-type wall jet compares very well with the full solution of the Navier-Stokes equation for a jet of finite thickness. Apart from annular sites of sonoporation we also find more homogenous patterns of molecule delivery with no cell detachment. PMID:16950843

Ohl, Claus-Dieter; Arora, Manish; Ikink, Roy; de Jong, Nico; Versluis, Michel; Delius, Michael; Lohse, Detlef

2006-12-01

323

An Expanding Bubble in Space  

NASA Technical Reports Server (NTRS)

Astronomers, using the Wide Field Planetary Camera 2 on board NASA's Hubble Space Telescope in October and November 1997 and April 1999, imaged the Bubble Nebula (NGC 7635) with unprecedented clarity. For the first time, they are able to understand the geometry and dynamics of this very complicated system. Earlier pictures taken of the nebula with the Wide Field Planetary Camera 1 left many issues unanswered, as the data could not be fully calibrated for scientific use. In addition, those data never imaged the enigmatic inner structure presented here. The remarkably spherical 'Bubble' marks the boundary between an intense wind of particles from the star and the more quiescent interior of the nebula. Research Team: Donald Walter (South Carolina State University), Paul Scowen, Jeff Hester, Brian Moore (Arizona State University), Reggie Dufour, Patrick Hartigan and Brent Buckalew (Rice University).

2000-01-01

324

On the long-wave equatorial dynamics  

NASA Astrophysics Data System (ADS)

Long-wave non-linear equatorial dynamics is examined in the framework of a rotating shallow water model on the equatorial beta-plane. For analysis we use an asymptotic multiple time-scale theory based on the assumption that the Rossby number Ro and the ratio d = Ly/Lx of the typical across- and along-equator space scales of the motion are small parameters. Like the f-plane case (Reznik, Zeitlin, Ben Jelloul, 2001) an arbitrary initial perturbation is split in a unique way into slow and fast components evolving with typical times 1/(bLy) and 1/(RobLy), respectively, where b is the meridional derivative of the Coriolis parameter. The slow component consisting of the Rossby and Kelvin waves and a zonal flow, in the leading order is not influenced by the fast component and remains close to geostrophic balance in the across-equator direction. The fast component includes the inertia-gravity and Yanai waves with phases slowly changing under the influence of the slow component. The equations governing the evolution of the each component depend strongly on the relationship between the parameters d and Ro. Classification of typical regimes depending on this relationship is given.

Reznik, G. M.; Zeitlin, V.

2003-04-01

325

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

326

Bioinspired bubble design for particle generation  

PubMed Central

In this study, we devise a method to generate homogeneous particles from a bubble suspension, with the capability to control loading and the structure of bubbles. Ideally, a process such as this would occur at the interface between daughter bubble formation (instant) and gaseous diffusion (gradual). Interestingly, the budding mechanism in micro-organisms is one that demonstrates features of the desired phenomena (although at a much slower rate), as viruses can eject and evolve structures from their membranes. With these natural concepts, a bubble's surface can also be made to serve as a platform for particle generation, which transfers significant elements from the initial bubble coating to the newly generated structures. Here, we illustrate this by preparing coated bubbles (approx. 150 µm in diameter) using a hydrophobic polymer, which may be comparable to naturally occurring bubble coatings (e.g. organic matter forming part of bubble coatings in the sea), and dye (which can demonstrate entrapment of smaller quantities of a desired moiety) and then observe particle generation (approx. 500 nm). The process, which may be driven by a polymerosome-forming mechanism, also illustrates how additional uniform sub-micrometre-scale structures may form from a bubble's surface, which may have also previously been attributed to gas diffusion. In addition, such methods of particle formation from a bubble structure, the incorporation of chemical or biological media via an in situ process and subsequent release technologies have several areas of interest across the broad scientific community. PMID:22112651

Gunduz, Oguzhan; Ahmad, Zeeshan; Stride, Eleanor; Tamerler, Candan; Edirisinghe, Mohan

2012-01-01

327

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

328

Unsteady thermocapillary migration of bubbles  

NASA Technical Reports Server (NTRS)

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.

1988-01-01

329

Forced Kelvin Waves on an Equatorial Beta Plane  

NASA Astrophysics Data System (ADS)

Equatorial Waves forced by a surface zonal wind stress acting on a continuously stratified ocean on an equatorial beta plane will be explored. For a uniformly stratified (constant N) ocean the time evolution of the lowest meridional mode (Kelvin Wave) part of the solution will be explored in detail.

Moore, D. W.; Kloosterziel, R.

2012-12-01

330

On the local equatorial characterization of zonoids and intersection bodies  

Microsoft Academic Search

In this paper we show that there is no local equatorial characterization of zonoids in odd dimensions. This gives a negative answer to the conjecture posed by W. Weil in 1977 and shows that the local equatorial characterization of zonoids may be given only in even dimensions. In addition we prove a similar result for intersection bodies and show that

Fedor Nazarov; Dmitry Ryabogin; Artem Zvavitch

2008-01-01

331

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...

332

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

333

Interaction of interannual and diurnal variations over equatorial Africa  

NASA Astrophysics Data System (ADS)

This paper shows evidence of interannual variation of the local diurnal variability over equatorial Africa. The dry season of December-February over the equatorial African region of the eastern Democratic Republic of Congo (formerly Zaire) typically experiences wetter (drier) than normal seasonal anomalies during warm (cold) El Niño-Southern Oscillation (ENSO) events. This study finds that from the additive influence or phase locking of the seasonal cycle, the interannual signal from ENSO, and the local diurnal cycle, there is a tendency for local amplification of the remote ENSO signal over this region of equatorial Africa. This additive influence of the three temporal scales over the equatorial African region is established from the analysis of a multidecadal coupled ocean-atmosphere model integration that simulates the observed seasonal cycle and its interannual variations over equatorial Africa reasonably well.

Misra, Vasubandhu

2010-01-01

334

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

335

Collapse of Kaluza-Klein Bubbles  

E-print Network

Kaluza-Klein theory admits ``bubble" configurations, in which the circumference of the fifth dimension shrinks to zero on some compact surface. A three parameter family of such bubble initial data at a moment of time-symmetry (some including a magnetic field) has been found by Brill and Horowitz, generalizing the (zero-energy) ``Witten bubble" solution. Some of these data have negative total energy. We show here that all the negative energy bubble solutions start out expanding away from the moment of time symmetry, while the positive energy bubbles can start out either expanding or contracting. Thus it is unlikely that the negative energy bubbles would collapse and produce a naked singularity.

Steven Corley; Ted Jacobson

1994-03-09

336

Collapse of cavitation bubbles in blood  

NASA Astrophysics Data System (ADS)

The behaviour of a single bubble in blood and in water is studied by using a non-Newtonian model of spherical bubble dynamics. This model considers the compressibility of the liquid surrounding the bubble, the shear-thinning characteristic of liquid viscosity, liquid density and surface tension. It was found that, for values of the maximum bubble radius larger than 10-1 mm, the collapse of a bubble in a constant pressure field in blood is more violent than in water. It suggests that the amount of collateral damage of the biological tissue induced by bubble collapse during high-speed rotational angioplasty and laser-induced angioplasty can be underestimated by experiments in vitro using water as ambient liquid.

Brujan, E.-A.

2000-04-01

337

Data-driven numerical simulations of equatorial spread F in the Peruvian sector: 2. Autumnal equinox  

NASA Astrophysics Data System (ADS)

An ongoing effort to simulate plasma instability in the equatorial ionosphere leading to equatorial spread F (ESF) in the American sector is described. Ionospheric state parameters including plasma number density and vector drift velocity profiles were measured at the Jicamarca Radio Observatory in the period between 20 September and 3 October 2013. Coherent radar backscatter from plasma irregularities was recorded simultaneously, and images of the irregularities were calculated using aperture synthesis methods. Neutral winds were measured by the red line Fabry-Perot interferometers at Jicamarca and Arequipa, Peru. A fully 3-D numerical simulation of ionospheric irregularities, initialized and forced using parameterizations derived from measurements and empirical models, was used to reproduce the ESF activity observed. Simulations were able to recover many of the features of the irregularities, although some important anomalies can be noted. ESF events in which the first appearance of radar plumes occurred either very early or very late were not reproduced in simulation and may be indicative of nonlocal influence.

Hysell, D. L.; Milla, M. A.; Condori, L.; Meriwether, J. W.

2014-08-01

338

Radiation Characteristics of Glass Containing Gas Bubbles Laurent Pilon*  

E-print Network

Radiation Characteristics of Glass Containing Gas Bubbles Laurent Pilon* Mechanical and Aerospace, ceramics, and glass, gas bubbles can form in liquid and solid phases. The presence of such bubbles affects media containing large gas bubbles (bubble radius is much larger than the wavelength of radiation

Pilon, Laurent

339

Thermocapillary migration of long bubbles in polygonal tubes. II. Experiments  

E-print Network

Thermocapillary migration of long bubbles in polygonal tubes. II. Experiments E. Lajeunesse experimentally the thermocapillary migration of a long gas bubble in a horizontal pipe of rectangular cross migration of the bubble towards the hotter region. The bubble velocity is found to be independent of bubble

Lajeunesse, Eric

340

Decay of equatorial ring current ions and associated aeronomical consequences  

NASA Technical Reports Server (NTRS)

The decay of the major ion species which constitute the ring current is studied by solving the time evolution of their distribution functions during the recovery phase of a moderate geomagnetic storm. In this work, only equatorially mirroring particles are considered. Particles are assumed to move subject to E x B and gradient drifts. They also experience loses along their drift paths. Two loss mechanisms are considered: charge exchange with neutral hydrogen atoms and Coulomb collisions with thermal plasma in the plasmasphere. Thermal plasma densities are calculated with a plasmaspheric model employing a time-dependent convection electric field model. The drift-loss model successfully reproduces a number of important and observable features in the distribution function. Charge exchange is found to be the major loss mechanism for the ring current ions; however the important effects of Coulomb collisions on both the ring current and thermal populations are also presented. The model predicts the formation of a low-energy (less than 500 eV) ion population as a result of energy degradation caused by Coulomb collision of the ring current ions with the plasmaspheric electrons; this population may be one source of the low-energy ions observed during active and quiet periods in the inner magnetosphere. The energy transferred to plasmaspheric electrons through Coulomb collisions with ring current ions is believed to be the energy source for the electron temperature enhancement and the associated 6300 A (stable auroral red (SAR) arc) emission in the subauroral region. The calculated energy deposition rate is sufficient to produce a subauroral electron temperature enhancement and SAR arc emissions that are consistent with observations of these quantities during moderate magnetic activity levels.

Fok, M.-C.; Kozyra, J. U.; Nagy, A. F.; Rasmussen, C. E.; Khazanov, G. V.

1993-01-01

341

Equatorially generated ULF waves as a source for the turbulence associated with ion conics  

NASA Technical Reports Server (NTRS)

Consideration is given to the possible source of low frequency turbulence on closed field lines in the central plasma sheet, which is used to explain ion heating and conic formation. Observations show that ion distributions in the equatorial region are often anisotropic and that these distributions excite ion cyclotron waves below the proton gyrofrequency and near the harmonics of the hydrogen cyclotron frequency. It is suggested that downcoming right-hand circularly polarized waves acquire a left-hand circularly polarized component at the crossover frequency and may tunnel through a stop zone to altitudes where they contribute to ion heating.

Johnson, Jay R.; Chang, Tom; Crew, G. B.; Andre, Mats

1989-01-01

342

Dynamics of a Single Reactive Gas Bubble  

Microsoft Academic Search

\\u000a The dynamics of a single combustible stoichiometric oxyacetylene gas bubble immersed in glycerine subjected to an impulsive\\u000a pressure wave has been studied experimentally and theoretically. Emphasis is placed on determining the range of bubble sizes\\u000a over which ignition of the gas occurs after the passage of a pressure pulse generated by the impact of a projectile with a\\u000a piston. Bubbles

B. Bruckert; D. L. Frost; A. N. Meidani; R. Chue; M. Brouillette

343

Bubble kinematics in a sheared foam  

E-print Network

We characterize the kinematics of bubbles in a sheared two-dimensional foam using statistical measures. We consider the distributions of both bubble velocities and displacements. The results are discussed in the context of the expected behavior for a thermal system and simulations of the bubble model. There is general agreement between the experiments and the simulation, but notable differences in the velocity distributions point to interesting elements of the sheared foam not captured by prevalent models.

Yuhong Wang; Kapilanjan Krishan; Michael Dennin

2006-07-05

344

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

2008-10-04

345

Bremsstrahlung Radiation At a Vacuum Bubble Wall  

E-print Network

When charged particles collide with a vacuum bubble, they can radiate strong electromagnetic waves due to rapid deceleration. Owing to the energy loss of the particles by this bremsstrahlung radiation, there is a non-negligible damping pressure acting on the bubble wall even when thermal equilibrium is maintained. In the non-relativistic region, this pressure is proportional to the velocity of the wall and could have influenced the bubble dynamics in the early universe.

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

2007-04-06

346

Constraining bubbling of methane from thermokarst lakes  

NASA Astrophysics Data System (ADS)

In northern thermokarst lakes, which form in depressions left as permafrost thaws, methane, a greenhouse gas, can be released from lake sediments to the atmosphere through bubbling, or ebullition. Constraining the amount of methane released through bubbling would help scientists understand the role of thawing permafrost in the carbon cycle and global climate change. However, bubbling is highly variable in both space and time and thus difficult to measure accurately, so there are large uncertainties in estimates of methane emissions from northern ecosystems.

Balcerak, Ernie

2013-08-01

347

Draping of Cluster Magnetic Fields over Bullets and Bubbles-Morphology and Dynamic Effects  

Microsoft Academic Search

High-resolution X-ray observations have revealed cavities and ``cold fronts'' with sharp edges in temperature and density within galaxy clusters. Their presence poses a puzzle, since these features are not expected to be hydrodynamically stable or to remain sharp in the presence of diffusion. However, a moving core or bubble in even a very weakly magnetized plasma necessarily sweeps up enough

L. J. Dursi; C. Pfrommer

2008-01-01

348

Some problems of the theory of bubble growth and condensation in bubble chambers  

NASA Technical Reports Server (NTRS)

This work is an attempt to explain the reasons for the discrepancies between the theoretical and experimental values of bubble growth rate in an overheated liquid, and to provide a brief formulation of the main premises of the theory on bubble growth in liquid before making a critical analysis. To simplify the problem, the floating upward of bubbles is not discussed; moreover, the study is based on the results of the theory of the behavior of fixed bubbles.

Tkachev, L. G.

1988-01-01

349

Initial thermal plasma observations from ISEE-1  

NASA Technical Reports Server (NTRS)

The initial measurements of magnetospheric thermal ions by the Plasma Composition Experiment on ISEE-1 are presented to demonstrate the surprising variety in this plasma population. The data provide evidence that the adiabatic mapping of the high latitude ionosphere to the equatorial plasma trough provides an insufficient description of the origin, transport, and accumulation processes which supply low energy ions to the outer plasmasphere and plasma trough.

Baugher, C. R.; Chappell, C. R.; Horwitz, J. L.; Shelley, E. G.; Young, D. T.

1980-01-01

350

Anomalies in H at Indian equatorial stations and their effect on equatorial enhancements  

NASA Astrophysics Data System (ADS)

The nature of anomalies at Indian equatorial stations has been studied through the use of transfer functions for anomalous horizontal and vertical fields. These functions are calculated for Annamalainagar (ANR) and Trivandrum (TRV) taking Kodaikanal (KOD) as a reference normal station. The period covered is 3-100 min. It is found that for periods below 10 min local induction starts playing a dominant role and anomalies are largely manifestations of a coastal effect. This effect causes a large suppression of H at TRV. At this station the source field effect is quite pronounced. Anomalies in the latitudinal profile of equatorial enhancement seen in the Indian sector are discussed in terms of source field geometry.

Singh, B. P.; Agarwal, A. K.; Carlo, L.

1982-03-01

351

Marangoni bubble motion in zero gravity  

NASA Technical Reports Server (NTRS)

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 media, as a result of which the bubble begins to move. A mathematical model consisting of the Navier-Stokes equations and the thermal energy equations, along with the appropriate boundary conditions for both media, is proposed.

Thompson, R. L.; De Witt, K. J.

1979-01-01

352

Multiple Spark-Generated Bubble Interactions  

NASA Astrophysics Data System (ADS)

The complex interactions of two and three spark-generated bubbles are studied using high speed photography. The corresponding simulations are performed using a 3D Boundary Element Method (BEM) code. The bubbles generated are between 3 to 5 mm in radius, and they are either in-phase or out-of-phase with one another. The possible interaction phenomena between two identically sized bubbles are summarized. Depending on their relative distances and phase differences, they can coalesce, jet towards or away from one another, split into smaller bubbles, or 'catapult' away from one another. The 'catapult' effect can be utilized to generated high speed jet in the absence of a solid boundary or shockwave. Also three bubble interactions are highlighted. Complicated phenomena such as bubble forming an elliptical shape and bubble splitting are observed. The BEM simulations provide insight into the physics of the phenomena by providing details such as detailed bubble shape changes (experimental observations are limited by the temporal and spatial resolution), and jet velocity. It is noted that the well-tested BEM code [1,2] utilized here is computationally very efficient as compared to other full-domain methods since only the bubble surface is meshed.

Khoo, Boo Cheong; Adikhari, Deepak; Fong, Siew Wan; Klaseboer, Evert

353

Bubble dynamics in an acoustic flow field  

NASA Astrophysics Data System (ADS)

Dynamics of interaction between cavitational bubbles is investigated when a complex of a compression and a rarefaction pulse passes through a liquid with pre-existing micro bubbles. Cavitation was generated experimentally with the help of electromagnetic generator of a flat and a convergent acoustic pulse (2-mus duration, 1-20 MPa) having the form of a hollow sphere segment. A modeling was performed within the frame of two-dimensional axisymmetric nonstationary approach on the basis of conservation laws for a model of an ideal compressible liquid. A thermodynamic flow field was computed both in liquid and inside bubbles. Behind the rarefaction wave the microbubbles begin to grow and generate secondary compression shocks, the amplitude of which may exceed that of the incident pulse under certain conditions. It is shown that the process of bubble interaction within a cluster is accompanied by bubble coalescence, fragmentation, and collapse of the initial bubble or its fragments. Simultaneously, high temperature spots appear in the bubble compressing by the secondary wave. Adiabatic heating of gas either inside a bubble or near the neck between a bubble and its fragment may result in sonoluminescence, also observed in experiments. [Work supported by ASA, DAAD, and RFBR.

Voronin, Dmitry V.; Sankin, Georgij N.; Mettin, Robert; Teslenko, Vyacheslav S.; Lauterborn, Werner

2002-11-01

354

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

355

Analysis of a deflating soap bubble  

NASA Astrophysics Data System (ADS)

A soap bubble on the end of a cylindrical tube is seen to deflate as the higher pressure air inside the bubble escapes through a tube. We perform an experiment to measure the radius of the slowly deflating bubble and observe that the radius decreases to a minimum before quickly increasing. This behavior reflects the fact that the bubble ends up as a flat surface over the end of the tube. A theoretical analysis reproduces this behavior and compares favorably with the experimental data.

Jackson, David P.; Sleyman, Sarah

2010-10-01

356

Instability and Subsequent Evolution of Electroweak Bubbles  

E-print Network

Bubbles in a first-order electroweak phase transition are nucleated with radii $R_0$ and expand with velocity $v$. If $v$ is subsonic, a bubble becomes unstable to non-spherical perturbations when its radius is roughly $10^4\\, R_0$. These perturbations accelerate the transition, and the effective velocity of bubble growth rapidly becomes supersonic. The transition should subsequently proceed spherically via detonation. If for some reason the onset of detonation is postponed, the surface area of the bubbles may be enhanced by $10^5$. We discuss consequences for electroweak baryogenesis.

Marc Kamionkowski; Katherine Freese

1992-08-04

357

Measurements of Equatorial Thermospheric Dynamics - Quo Vadis?  

NASA Astrophysics Data System (ADS)

Observations of equatorial thermospheric winds and temperatures at Arequipa, Peru, have been carried out over two decades with a pressure scanning Fabry-Perot interferometer. The results from this long series of measurements will be summarized, and new plans for the future presented. The work for the future will be based upon the upgrade of the instrument sensitivity to be obtained through the replacement of the photomultiplier detector with a CCD camera producing an expected increase of sensitiivty by a factor of 15 and decreasing measurement errors to less than 5 ms-1 and 20 K in 2 to 5 minutes of signal collection. The new plans include the initiation of twilight studies of the 732 nm airglow emission, which is generated by radiative ionization of [O]. This will enable the study of atomic oxygen concentration variations combined with ion drift measurements during the evening and morning twilight periods. Results from the first series of measurements with this new capability will be presented.

Meriwether, J. W.

2004-05-01

358

The equatorial aurora in the extreme ultraviolet  

NASA Technical Reports Server (NTRS)

The extreme ultraviolet telescope on the Apollo-Soyuz mission observed the equatorial aurora from an altitude of 220 km on four separate occasions in July 1975, in quiet geomagnetic conditions (Ap = 6). In all cases signals well above ambient background in the 50-150, 114-150, 170-600, and 500-780 A bands were recorded as the spacecraft moved across the equator and the instrument viewed the atmosphere below it. The observed emissions are confined to a band roughly 10 to 20 deg in width with the peak emission occurring in the range -15 to +2 deg magnetic latitude. No enhancement on the 1350-1550 A channel was noted. The observed signals are interpreted as recombination radiation of energetic helium and, possibly, oxygen ions originating in the terrestrial ring current.

Paresce, F.; Chakrabarti, S.

1980-01-01

359

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

360

Magnetar Driven Bubbles and the Origin of Collimated Outflows from GRBs  

E-print Network

We model the interaction between the wind from a newly formed rapidly rotating magnetar and the surrounding progenitor. In the first few seconds after core collapse the magnetar inflates a bubble of plasma and magnetic fields behind the supernova shock, which expands asymmetrically because of the pinching effect of the toroidal magnetic field, as in PWNe, even if the host star is spherically symmetric. The degree of asymmetry depends on the ratio of the magnetic energy to the total energy in the bubble. We assume that the wind by newly formed magnetars inflating these bubbles is more magnetized than for PWNe. We show that for a magnetic to total power supplied by the central magnetar $\\sim 0.1$ the bubble expands relatively spherically while for values greater than 0.3, most of the pressure in the bubble is exerted close to the rotation axis, driving a collimated outflow out through the host star. This can account for the collimation inferred from observations of long-duration gamma-ray bursts (GRBs). Given that the wind magnetization increases in time, we thus suggest that the magnetar-driven bubble initially expands relatively spherically (enhancing the energy of the associated supernova) while at late times it becomes progressivelymore collimated (producing the GRB). Similar processes may operate in more modestly rotating neutron stars to produce asymmetric supernovae and lower energy transients such as X-ray flashes.

N. Bucciantini; E. Quataert; J. Arons; B. D. Metzger; Todd A. Thompson

2007-10-05

361

The potential and force law between different-size bubbles in soap bubble rafts  

Microsoft Academic Search

Since the Bragg bubble model continues to be a powerful tool for modelling interatomic binding and inelastic processes in close-packed metals with particularly attractive applications to the mechanism of plastic flow in metallic glasses, the inter-bubble potential previously developed by Nicolson and Lomer has been generalized to cover interactions between bubbles of unequal size. Fitting the binding energy between pairs

L. T. Shi; A. S. Argon

1982-01-01

362

Opposed bubbly jets at different impact angles: Jet structure and bubble properties  

Microsoft Academic Search

The structure of two colliding water jets containing small gas bubbles is studied experimentally. The effects of the separation distance between jets, as well as the orientation angle, on the spatial distribution of bubbles have been considered. Results on the global structure of the final jet and bubble properties have been obtained using a high-speed video camera, and measurements of

Francesc Suñol; Ricard González-Cinca

2010-01-01

363

Bubble-wall interactions in a vertical gas–liquid flow: Bouncing, sliding and bubble deformations  

Microsoft Academic Search

The paper presents the results of a study on the motion of single (individual) bubbles rising in upward shear liquid flow in the vicinity of a vertical wall. Bubbles were found to slide along the wall when their diameter is small. Bubbles could also experience multiple collisions with the wall at certain experimental parameters (geometry of a channel, range of

Alexander Zaruba; Dirk Lucas; Horst-Michael Prasser; Thomas Höhne

2007-01-01

364

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

365

DGP with bubble of nothing  

E-print Network

We construct exact solutions with the bubble of nothing in the Dvali-Gabadadze-Porrati braneworld model. The configuration with a single brane can be constructed, unlike in the Randall-Sundrum braneworld model. The geometry on the single brane looks like the Einstein-Rosen bridge. We also discuss the junction of multibranes. Surprisingly, even without any artificial matter fields on the branes such as three-dimensional tension of the codimension-two objects, two branes can be connected in certain configurations. We investigate solutions of multibranes too. The presence of solutions may indicate the semiclassical instability of the models.

Keisuke Izumi; Tetsuya Shiromizu

2014-02-12

366

THE GEOMETRY OF BUBBLES AND FOAMS JOHN M. SULLIVAN  

E-print Network

, while the second covered the combinatorics of foams. Soap films, bubble clusters, and foams THE GEOMETRY OF BUBBLES AND FOAMS JOHN M. SULLIVAN University consider mathematical models of bubbles, foams and froths, as collections of surfaces which minimize area

Sullivan, John M.

367

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

368

The incorporation of bubbles into a computer graphics fluid simulation  

E-print Network

We present methods for incorporating bubbles into a photorealistc fluid simulation. Previous methods of fluid simulation in computer graphics do not include bubbles. Our system automatically creates bubbles, which are simulated on top of the fluid...

Greenwood, Shannon Thomas

2005-08-29

369

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

370

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

371

Bubbles, Gating, and Anesthetics in Ion Channels  

PubMed Central

We suggest that bubbles are the bistable hydrophobic gates responsible for the on-off transitions of single channel currents. In this view, many types of channels gate by the same physical mechanism—dewetting by capillary evaporation—but different types of channels use different sensors to modulate hydrophobic properties of the channel wall and thereby trigger and control bubbles and gating. Spontaneous emptying of channels has been seen in many simulations. Because of the physics involved, such phase transitions are inherently sensitive, unstable threshold phenomena that are difficult to simulate reproducibly and thus convincingly. We present a thermodynamic analysis of a bubble gate using morphometric density functional theory of classical (not quantum) mechanics. Thermodynamic analysis of phase transitions is generally more reproducible and less sensitive to details than simulations. Anesthetic actions of inert gases—and their interactions with hydrostatic pressure (e.g., nitrogen narcosis)—can be easily understood by actions on bubbles. A general theory of gas anesthesia may involve bubbles in channels. Only experiments can show whether, or when, or which channels actually use bubbles as hydrophobic gates: direct observation of bubbles in channels is needed. Existing experiments show thin gas layers on hydrophobic surfaces in water and suggest that bubbles nearly exist in bulk water. PMID:18234836

Roth, Roland; Gillespie, Dirk; Nonner, Wolfgang; Eisenberg, Robert E.

2008-01-01

372

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

373

The Physics of Foams, Droplets and Bubbles  

ERIC Educational Resources Information Center

Foams or bubble dispersions are common to milkshakes, bread, champagne froth, shaving mousse, shampoo, crude oil extraction systems, upholstery packing and bubble wrap, whereas the term droplet is often synonymous with either a small drop of water or a drop of oil--a type of coarse dispersion. The latter are seen in butter and milk, household…

Sarker, Dipak K.

2013-01-01

374

Steady Detonation in a Bubbly Medium  

Microsoft Academic Search

It is shown that the Iordanskii–Kogarko model contains a steady-state solution for a detonation wave in chemically active bubbly media under the following minimum requirements to the model: compressibility of the liquid and allowance for acoustic losses. The rule for choosing the velocity is formulated. The wave structure of the reaction zone and the velocity of steady bubble detonation are

S. A. Zhdan

2002-01-01

375

Chaotic behavior in bubble formation dynamics  

Microsoft Academic Search

We constructed an experimental apparatus to study the dynamics of the formation of air bubbles in a submerged nozzle in a water\\/glycerin solution inside a cylindrical tube. The delay time between successive bubbles was measured with a laser-photodiode system. It was observed bifurcations, chaotic behavior, and sudden changes in a periodic regime as a function of the decreasing air pressure

A. Tufaile; J. C Sartorelli

2000-01-01

376

Acoustic emissions associated with single bubble sonoluminescence  

Microsoft Academic Search

Acoustic emission (AE) from a single bubble trapped in a water\\/glycerine mixture by an acoustic standing wave is reported. The AE has been measured by a calibrated needle hydrophone in different regimes of bubble dynamics. The hydrophone response shows a large amplitude AE pulse which corresponds to the principal collapse along with smaller amplitude pulses which can be associated with

M. Dan; J. D. N. Cheeke

1997-01-01

377

The rheology of gravity driven bubbly liquids  

Microsoft Academic Search

Experiments on a vertical channel were performed to to study the behavior of a monodispersed bubble suspension. Using water and water-glycerin mixtures, we were able to obtain measurements for a range of Reynolds and Weber numbers. To generate a uniform stream of bubbles an array of identical capillaries was used. To avoid the coalescence effects, a small amount of salt

Julian Martinez-Mercado; Roberto Zenit

2002-01-01

378

Soap Films and the Joy of Bubbles  

NASA Astrophysics Data System (ADS)

As a celebration of this year's National Chemistry Week theme, the cover of this issue tries to capture the joy of playing with bubbles. There is nothing quite like the kaleidoscopic rainbow of colors and wetly wild elastic behavior of soap films and bubbles for experiencing the pure joy of a "toy".

Saecker, Mary E.

2005-10-01

379

Measuring soap bubble thickness with color matching  

Microsoft Academic Search

This paper describes a laboratory experiment designed to measure thickness variations across a soap bubble. The experiment uses the phenomenon of thin film interference and the principles of color perception to measure the thickness of the soap film at various points across the surface of the bubble. The students review the classical theory of interference and use a digital camera

Y. D. Afanasyev; G. T. Andrews; C. G. Deacon

2011-01-01

380

Videotaping the Lifespan of a Soap Bubble.  

ERIC Educational Resources Information Center

Describes how the use of a videotape to record the history of a soap bubble allows a study of many interesting events in considerable detail including interference fringes, convection and turbulence patterns on the surface, formation of black film, and the ultimate explosion of the bubble. (JRH)

Ramme, Goran

1995-01-01

381

GK Batchelor When bubbles are spikes,  

E-print Network

GK Batchelor Laboratory When bubbles are spikes, it can matter how the heavy stuff falls Explorations into the behaviour of Rayleigh-Taylor instability CAMBRIDGE UNIVERSITY OF #12;GK Batchelor Laboratory what is a spike? Benjamin St Venant St Venant #12;GK Batchelor Laboratory bubbles = spikes

Dalziel, Stuart

382

Bubble nucleation from gas cavities — a review  

Microsoft Academic Search

This review is concerned with the nucleation of bubbles in solutions supersaturated with a gas, in particular the bubble nucleation that occurs at specific sites, as a cycle. A classification system for the kinds of nucleation that occur is defined and discussed in order to place this specific form of nucleation into a better defined context. It is noted that

S. F. Jones; G. M. Evans; K. P. Galvin

1999-01-01

383

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

384

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

385

Gamma-Ray Burst Phenomenon as Collapse of QED Magnetized Vacuum Bubble: Analogy with Sonoluminescence  

E-print Network

We consider the phenomenon of a gamma-ray burst as a nonlinear collapse of a magnetic cavity surrounding a neutron star with very strong magnetic field B = 10^15 - 10^16 G due to the process of the bubble shape instability in a resonant MHD field of the accreting plasma. The QED effect of vacuum polarizability by the strong magnetic field is taken into account. We develop an analogy with the phenomenon of sonoluminescence (SL) when the gas bubble is located in the surrounding liquid with a driven sound intensity. We show that this analogy between GRB and SL phenomena really exists.

Yu. N. Gnedin; S. O. Kiikov

1999-08-11

386

Simulations of shock waves and cavitation bubbles produced in water by picosecond and nanosecond laser pulses  

SciTech Connect

The authors compare numerical simulations of bubble dynamics in water with experiments performed at the Medizinisches Laserzentrum Luebeck. Spatial and temporal features of the laser beam were modeled. Plasma growth was predicted using a moving breakdown model. The authors compare the measured and calculated positions of the shock front and the bubble wall as a function of time after optical breakdown in water. Nd:YAG laser pulses of 30-ps 1-mJ and 6-ns 10-mJ were simulated. The authors have extended previous work in which picosecond deposition was modeled as temporally instantaneous and spatially uniform.

Scammon, R.J.; Chapyak, E.J.; Godwin, R.P. [Los Alamos National Lab., NM (United States); Vogel, A. [Medizinisches Laserzentrum Lueebeck GmbH (Germany)

1998-12-01

387

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

388

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

389

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

390

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

391

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

392

Dynamics of charged hemispherical soap bubbles  

NASA Astrophysics Data System (ADS)

Raising the potential of a charged hemispherical soap bubble over a critical limit causes deformation of the bubble into a cone and ejection of a charged liquid jet. This is followed by a mode which has not previously been observed in bubbles, in which a long cylindrical liquid film column is created and collapses due to a Rayleigh-Plateau instability creating child bubbles. We show that the formation of the column and subsequent creation of child bubbles is due to a drop in potential caused by the ejection of charge from the system via the jet. Similar dynamics may occur in microscopic charged liquid droplets (electrospray processes), causing the creation of daughter droplets and long liquid spindles.

Hilton, J. E.; van der Net, A.

2009-04-01

393

Interaction mechanism of double bubbles in hydrodynamic cavitation  

NASA Astrophysics Data System (ADS)

Bubble-bubble interaction is an important factor in cavitation bubble dynamics. In this paper, the dynamic behaviors of double cavitation bubbles driven by varying pressure field downstream of an orifice plate in hydrodynamic cavitation reactor are examined. The bubble-bubble interaction between two bubbles with different radii is considered. We have shown the different dynamic behaviors between double cavitation bubbles and a single bubble by solving two coupling nonlinear equations using the Runge-Kutta fourth order method with adaptive step size control. The simulation results indicate that, when considering the role of the neighbor smaller bubble, the oscillation of the bigger bubble gradually exhibits a lag in comparison with the single-bubble case, and the extent of the lag becomes much more obvious as time goes by. This phenomenon is more easily observed with the increase of the initial radius of the smaller bubble. In comparison with the single-bubble case, the oscillation of the bigger bubble is enhanced by the neighbor smaller bubble. Especially, the pressure pulse of the bigger bubble rises intensely when the sizes of two bubbles approach, and a series of peak values for different initial radii are acquired when the initial radius ratio of two bubbles is in the range of 0.9˜1.0. Although the increase of the center distance between two bubbles can weaken the mutual interaction, it has no significant influence on the enhancement trend. On the one hand, the interaction between two bubbles with different radii can suppress the growth of the smaller bubble; on the other hand, it also can enhance the growth of the bigger one at the same time. The significant enhancement effect due to the interaction of multi-bubbles should be paid more attention because it can be used to reinforce the cavitation intensity for various potential applications in future.

Li, Fengchao; Cai, Jun; Huai, Xiulan; Liu, Bin

2013-06-01

394

Primary Particles from different bubble generation techniques  

NASA Astrophysics Data System (ADS)

Sea spray aerosols (SSA) are of major interest to global climate models due to large uncertainty in their emissions and ability to form Cloud Condensation Nuclei (CCN). In general, SSA are produced from wind breaking waves that entrain air and cause bubble bursting on the ocean surface. Preliminary results are presented for bubble generation, bubble size distribution, and CCN activity for laboratory generated SSA. In this study, the major processes of bubble formation are examined with respect to particle emissions. It has been suggested that a plunging jet closely resembles breaking wave bubble entrainment processes and subsequent bubble size distributions (Fuentes, Coe et al. 2010). Figure 1 shows the different particle size distributions obtained from the various bubble generation techniques. In general, frits produce a higher concentration of particles with a stronger bimodal particle size distribution than the various jet configurations used. The experiments consist of a stainless steel cylinder closed at both ends with fittings for aerosol sampling, flow connections for the recirculating jet, and air supply. Bubble generation included a recirculating jet with 16 mm or 4 mm nozzles, a stainless steel frit, or a ceramic frit. The chemical composition of the particles produced via bubble bursting processes has been probed using particle CCN activity. The CCN activity of sodium chloride, artificial sea salt purchased from Tropic Marin, and laboratory grade artificial sea salt (Kester, Duedall et al. 1967) has been compared. Considering the the limits of the shape factor as rough error bars for sodium chloride and bubbled sea salt, the CCN activity of artificial sea salt, Tropic Marin sea salt, and sodium chloride are not significantly different. This work has been supported by the Carlsberg Foundation.

Butcher, A. C.; King, S. M.; Rosenoern, T.; Nilsson, E. D.; Bilde, M.

2011-12-01

395

Interstellar Bubbles in Two Young HII Regions  

E-print Network

Massive stars are expected to produce wind-blown bubbles in the interstellar medium; however, ring nebulae, suggesting the existence of bubbles, are rarely seen around main-sequence O stars. To search for wind-blown bubbles around main-sequence O stars, we have obtained high-resolution Hubble Space Telescope WFPC2 images and high-dispersion echelle spectra of two pristine HII regions, N11B and N180B, in the Large Magellanic Cloud. These HII regions are ionized by OB associations that still contain O3 stars, suggesting that the HII regions are young and have not hosted any supernova explosions. Our observations show that wind-blown bubbles in these HII regions can be detected kinematically but not morphologically because their expansion velocities are comparable to or only slightly higher than the isothermal sound velocity in the HII regions. Bubbles are detected around concentrations of massive stars, individual O stars, and even an evolved red supergiant (a fossil bubble). Comparisons between the observed bubble dynamics and model predictions show a large discrepancy (1--2 orders of magnitude) between the stellar wind luminosity derived from bubble observations and models and that derived from observations of stellar winds. The number and distribution of bubbles in N11B differ from those in N180B, which can be explained by the difference in the richness of stellar content between these two HII regions. Most of the bubbles observed in N11B and N180B show a blister-structure, indicating that the stars were formed on the surfaces of dense clouds. Numerous small dust clouds, similar to Bok globules or elephant trunks, are detected in these HII regions and at least one of them hosts on-going star formation.

Yael Naze; You-Hua Chu; Sean D. Points; Charles W. Danforth; Margarita Rosado; C. -H. Rosie Chen

2001-04-25

396

Satellite observations of zonal electric fields near sunrise in the equatorial ionosphere  

NASA Technical Reports Server (NTRS)

We report here on a number of examples of anomalous enhancements of eastward electric fields near sunrise in the equatorial ionospheric F-region. These examples were selected from the data base of the equatorial satellite, San Marco D (1988), which measured ionospheric electric fields during a period of solar minimum. The eastward electric fields reported correspond to vertical plasma drifts. The examples studied here are similar in signature and polarity to the pre-reversal electric field enhancements seen near sunset from ground-based radar systems. The morphology of these sunrise events, which are observed on about 14% of the morning-side satellite passes, are studied as a function of local zonal velocity, magnetic activity, geographic longitude and altitude. The nine events studied occur at locations where the zonal plasma flow is generally measured to be eastward, but reducing as a function of local time and at satellite longitudes where the magnetic declination has the opposite polarity as the declination of the sunrise terminator.

Aggson, T. L.; Herrero, F. A.; Johnson, J. A.; Pfaff, R. F.; Laakso, H.; Maynard, N. C.; Moses, J. J.

1995-01-01

397

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

398

Country Reports on Human Rights Practices, 2006: Equatorial Guinea.  

National Technical Information Service (NTIS)

Equatorial Guinea is nominally a multiparty constitutional republic, with a population estimated at between 540,000 and over one million. All branches of government are dominated by President Teodoro Obiang Nguema Mbasogo and his inner circle, mostly of t...

2007-01-01

399

Numerical investigation of electron self-injection in the nonlinear bubble regime  

SciTech Connect

The process of electron self-injection in the nonlinear bubble wake generated by a short and intense laser pulse propagating in a uniform underdense plasma is studied by means of fully self-consistent particle-in-cell simulations and test-particle simulations. We consider a wake generated by a non-evolving laser driver traveling with a prescribed velocity, which then sets the structure and the velocity of the wake, so the injection dynamics is decoupled from driver evolution, but a realistic structure for the wakefield is retained. We show that a threshold for self-injection into a non-evolving bubble wake exists, and we characterize the dependence of the self-injection threshold on laser intensity, wake velocity, and plasma temperature for a range of parameters of interest for current and future laser-plasma accelerators.

Benedetti, C.; Schroeder, C. B.; Esarey, E.; Leemans, W. P. [Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)] [Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Rossi, F. [Department of Physics and Astronomy, University of Bologna and INFN, Via Irnerio 46, 40126 Bologna (Italy)] [Department of Physics and Astronomy, University of Bologna and INFN, Via Irnerio 46, 40126 Bologna (Italy)

2013-10-15

400

Electron inertial effects on ULF wave absorption near the equatorial region: A simulation study  

NASA Astrophysics Data System (ADS)

We investigate the role of electron inertia on ULF wave absorption in the magnetosphere. Recently, wave simulations and numerical calculations show that resonant absorption at the ion-ion hybrid (IIH) resonance occurs in multi-ion plasmas at Earth and Mercury. The IIH resonance is believed to have an important role for electromagnetic ion cyclotron wave generation near the equatorial region and energy transfer at the magnetopause. By adopting a multi-fluid wave model that can fully include effects of electrons and multi-ions, we show how resonant absorptions occur in electron-proton-helium/oxygen plasmas when electron inertial effect is considered. Our results show that (a) resonant absorption occur at both IIH and Bushsbaum (BB) resonances, (b) IIH resonant waves are electronmagentic while (c) BB resonance has electrostatic, and (d) the frequency drift from IIH to BB resonance in the dynamics spectra.

Kim, E.; Lee, D.; Johnson, J.

2011-12-01

401

Observations of the relationship between solar wind parameters and equatorial noise  

NASA Astrophysics Data System (ADS)

The interplanetary magnetic field (IMF) and solar wind plasma can substantially influence processes in the Earth's magnetosphere. This especially concerns processes in the outer radiation belt, where electrons can be accelerated to relativistic energies. According to recent results equatorial noise (EN) emissions might be responsible for the acceleration of electrons with energies above 10 keV. We focus on possible connection between the IMF and the flow speed of the solar wind to the characteristics of EN. We use data from the STAFF-SA instrument located on board the Cluster spacecraft for EN emissions and data from OMNIWeb (mainly from spacecraft ACE, WIND, IMP 8 and Geotail) for the flow speed of plasma and IMF. We study the occurrence of EN as a function of the magnetic local time, McIlwain's L parameter, and the magnetic latitude, parameterized by the flow speed and IMF.

Hrbackova, Z.; Santolik, O.; Nemec, F.; Cornilleau-Wehrlin, N.

2012-12-01

402

Ancient El Nino may have warmed equatorial Pacific  

NSDL National Science Digital Library

Sediment records were used to report the sea surface temperatures in the equatorial Sulu Sea. These results were compared to ice core records in Greenland, specifically examining the size and timing of climate change shifts between the equatorial Pacific and the rest of the world. Results indicate that modern sea surface temperatures, combined with larger weather patterns like El Nino, significantly affect atmospheric circulation patterns and global climate conditions.

Rosenthal, Yair; Oppo, Delia; Linsley, Braddock K.; Agu

403

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

2014-09-01

404

Mesospheric planetary wave signatures in the equatorial electrojet  

Microsoft Academic Search

Using five years (1994–1998) of simultaneous and collocated measurements of horizontal winds associated with mesosphere and lower thermosphere (MLT) region and geomagnetic field measurements in the Indian geomagnetic dip equatorial region, an extensive experimental study has been made on the influences of mesospheric planetary waves on the equatorial electrojet (EEJ). The winds are measured using medium-frequency (MF) radar (1.98 MHz)

T. K. Ramkumar; S. Gurubaran; R. Rajaram

2009-01-01

405

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

406

Nanoplankton mixotrophy in the eastern equatorial Pacific  

NASA Astrophysics Data System (ADS)

Heterotrophic bacteria, cyanobacteria, and picoeukaryotic algae dominate the plankton community of high nutrient-low chlorophyll (HNLC) areas of the eastern equatorial Pacific (EEP). While grazing on these picoplankton is often attributed to aplastidic zooflagellates, mixotrophic nanoflagellates (phagotrophic phototrophs) may also exert a large grazing pressure. We assessed the relative contributions of mixotrophic nanoplankton and obligate heterotrophs to picoplankton phagotrophy in mixed-layer water of the EEP using 0.8-?m Fluorescently-Labeled Bacteria (FLB). Obligate heterotrophs and phototrophs were distinguished from their ratios of microscopically measured red (chlorophyll a) to green (proflavin-stained protein) fluorescence. Sampling sites were located along a nutrient gradient formed by a tropical instability wave at 0.5°N between 123.5°W and 128°W and at 1.75°N, 125°W. The majority of ingested particles were found within 3-5 ?m flagellates, with 54% of the demonstrated phagotrophs belonging to the high-pigment putatively phototrophic population and obligate heterotrophs responsible for 51% of the demonstrated phagotrophy due to their greater propensity to ingest multiple prey. The importance of mixotrophy as a means of alleviating nutrient stress is indicated by a strong inverse relationship between the proportion of community FLB uptake by mixotrophs and ambient nutrient concentration. Low ambient Fe concentration and a demonstrated community response to Fe-addition in shipboard grow-out experiments suggest that mixotrophs were primarily engaging in phagotrophy to offset Fe-deficiencies.

Stukel, Michael R.; Landry, Michael R.; Selph, Karen E.

2011-03-01

407

Lunar modulations of the equatorial electrojet  

NASA Astrophysics Data System (ADS)

An attempt has been made to reproduce the counter electrojet (CE) in the equatorial dynamo by considering neutral winds with solar (1, -2), (2, 4), (2, 2) and lunar (2, 2) tidal modes as well as a constant electrostatic field. The daily variation of conductivity is assumed to consist of steady (average), diurnal and semi-diurnal components. An equation governing the relationship between the jet current, electrostatic field, conductivity and wind is given, and this equation is then used to describe diurnal, semi- and ter-diurnal variations of the jet current separately. It is found that: (1) the lunar tide is relatively powerful in affecting semi- and ter-diurnal components of the jet current; (2) such a possibility is a maximum for the afternoon CE near new and full moon and (3) the morning CE is likely to occur at lunar age between the new and full moons. From this theory, the seasonal characteristics and the solar activity dependence of CE are demonstrated to be predictable.

Maeda, K.-I.

1983-04-01

408

Gradient drift eigenmodes in the equatorial electrojet  

NASA Technical Reports Server (NTRS)

The problem of kilometer-scale irregularities in the daytime equatorial electrojet is revisited by means of an eigenmode analysis of the gradient drift instability. Realistic physical parameters are used, including the modeled altitude variations of ion and electron collision frequencies and mobilities. The full fourth-order system of two coupled differential equations (each of second order) for the denisty and electrostatic potential perturbations is solved numerically by a relaxation technique. Under some approximations, the fourth-order system can be shown to reduce to a second-order differential equation for the perturbed potential or density. The latter is solved using a shooting technique and provides initial guesses for numerical solutions to the full problem. It is shown that the linear growth rate peaks for kilometer-scale waves, contrary to the findings of recent initial-value studies. This occurs because the equilibrium velocity shear is much more effective as a damping mechanism for short-wavelength modes than it is for the longer, kilometer-scale modes. These results provide a natural qualitative explanation for the observed dominance of kilometer-scale structures in the daytime electrojet spectrum.

Wang, X.-H.; Bhattacharjee, A.

1994-01-01

409

POGO observations of the equatorial electrojet  

NASA Technical Reports Server (NTRS)

During intervals in 1967 to 1970, the OGO-4 and 6 spacecraft made over 2000 traversals over the equatorial electrojet in the altitude range 400-800 km when local times were between 9 and 15 hours. These spacecraft carried total field magnetometers making measurements to an accuracy of 2 gamma with a sample rate greater than once a second. Delta F values, the deviations from these observations, were formed from an internal reference model. The results were plotted for a 30 deg band about the equator, and the characteristics of the electrojet effect in the data were investigated. This effect was characterized by a sharp negative V-signature of some 16-19 deg in width and a variable amplitude. The position of this minimum was found to lie within 0.5 deg of the dip equator. A slight northward shift was noted at the longitude of Huancayo. The jet amplitudes were normalized to 400 km amplitudes and observed to be highly variable in time. Amplitudes over the longitude range 50 to 90 deg W averaged 60% higher than elsewhere, as expected, due to the weaker main field. However, though the scatter of amplitudes is high, the expected minima in east Asia was not evident. It was speculated that this could be due to a less conducting upper mantle in this area.

Cain, J. C.; Sweeney, R. E.

1972-01-01

410

Vertical motions in the equatorial middle atmosphere  

NASA Technical Reports Server (NTRS)

A single station vertical velocity equation which considers ageostrophic and diabatic effects derived from the first law of thermodynamics and a generalized thermal wind relation is presented. An analysis and verification procedure which accounts for measurement and calculation errors as well as time and space continuity arguments and theoretical predictions are described. Vertical velocities are calculated at every kilometer between 25 and 60 km and for approximately every three hours for the above diurnal period at Kourou (French Guiana), Fort Sherman (Panama Canal Zone), Ascension Island, Antigua (British West Indies) and Natal (Brazil). The results, plotted as time series cross sections, suggest vertical motions ranging in magnitude from 1 or 2 cm/sec at 30 km to as much as 15 cm/sec at 60 km. Many of the general features of the results agree well with atmospheric tidal predictions but many particular features suggest that both smaller time scale gravity waves (periods less than 6 hours) and synoptic type waves (periods greater than 1 day) may be interacting significantly with the tidal fields. The results suggest that vertical motions can be calculated for the equatorial middle atmosphere and must be considered a significant part of the motion for time scales from 8 to 24 hours.

Weisman, M. L.

1979-01-01

411

Sources of frontogenesis in the Equatorial Atlantic Front  

NASA Astrophysics Data System (ADS)

The Equatorial Atlantic front is located along 1°N in the eastern equatorial Atlantic basin, at the northern boundary of the cold tongue. It separates the cold waters of the southern cold tongue from the warmest, tropical waters circulating in the Gulf of Guinea. This seasonal front appears every year from May to August, and is characterized by meridional SST gradients up to 2 to 3°C/20 km. It is thought to play an important role for the circulation in the marine atmospheric boundary layer and influence the coastal precipitation and the western African monsoon onset. In this presentation the processes at the origin of the equatorial front were investigated. For that, diagnosis of the frontogenesis forcings were applied on a realis