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Sample records for equatorial plasma bubbles

  1. Gravity Wave Seeding of Equatorial Plasma Bubbles

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

    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.

  2. Guest investigator program study: Physics of equatorial plasma bubbles

    NASA Technical Reports Server (NTRS)

    Tsunoda, Roland T.

    1994-01-01

    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.

  3. GPS Observations of Plasma Bubbles and Scintillations over Equatorial Africa

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  4. Measuring the equatorial plasma bubble drift velocities over Morroco

    NASA Astrophysics Data System (ADS)

    Lagheryeb, Amine; Benkhaldoun, Zouhair; Makela, Jonathan J.; Harding, Brian; Kaab, Mohamed; Lazrek, Mohamed; Fisher, Daniel J.; Duly, Timothy M.; Bounhir, Aziza; Daassou, Ahmed

    2015-08-01

    In this work, we present a method to measure the drift velocities of equatorial plasma bubbles (EPBs) in the low latitude ionosphere. To calculate the EPB drift velocity, we use 630.0-nm airglow images collected by the Portable Ionospheric Camera and Small Scale Observatory (PICASSO) system deployed at the Oukkaimden observatory in Morocco. To extract the drift velocity, the individual images were processed by first spatially registering the images using the star field. After this, the stars were removed from the images using a point suppression methodology, the images were projected into geographic coordinates assuming an airglow emission altitude of 250 km. Once the images were projected into geographic coordinates, the intensities of the airglow along a line of constant geomagnetic latitude (31°) are used to detect the presence of an EPB, which shows up as a depletion in airglow intensity. To calculate the EPB drift velocity, we divide the spatial lag between depletions found in two images (found by the application of correlation analysis) by the time difference between these two images. With multiple images, we will have several velocity values and consequently we can draw the EPB drift velocity curve. Future analysis will compare the estimates of the plasma drift velocity with the thermospheric neutral wind velocity estimated by a collocated Fabry-Perot interferometer (FPI) at the observatory.

  5. Equatorial plasma bubbles studied using African slant total electron content observations

    NASA Astrophysics Data System (ADS)

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

    2008-04-01

    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.

  6. Magnetospheric disturbance induced equatorial plasma bubble development and dynamics: A case study in Brazilian sector

    NASA Astrophysics Data System (ADS)

    Abdu, M. A.; Batista, I. S.; Takahashi, H.; MacDougall, J.; Sobral, J. H.; Medeiros, A. F.; Trivedi, N. B.

    2003-12-01

    Equatorial ionospheric plasma bubble irregularity development and dynamics during the major magnetospheric storm of 26 August 1998 are investigated using the data collected by a multistation and multi-instrument diagnostic network operated at equatorial and low latitude sites in Brazil, and auroral electrojet activity (AU/AL), IMF, and Dst indices. A magnetospheric disturbance onset in the morning of 26 August 1998 was initiated by a solar wind shock and associated IMF Bz polarity reversals and ssc that were soon followed by a succession of substorm-like auroral electrojet (AE) intensifications and Dst development. An IMF Bz southward turning and associated AE intensifications in the Brazilian dusk sector produced intense prompt penetration eastward electric field that caused large F region vertical drift and consequently the developments of intense postsunset equatorial anomaly and a series of intense plasma bubbles, the latter event lasting the entire night, as observed by digital ionosondes at São Luís (2.33°S, 315.8°E, dip angle: -.5°) and Fortaleza (3.9°S, 321.55°W, dip angle: -9°) and an all-sky imager, two scanning photometers, and a Digisonde at the low-latitude site Cachoeira Paulista (22.6°S, 315°E dip angle: -28°). A notable aspect of the dynamics of the bubbles was their initially very low eastward drift velocity which turned into steadily increasing westward velocity that lasted till early morning hours. The results show for the first time a relationship between the zonal drift velocities of optically observed large-scale bubbles (tens to hundreds of kilometers) and that of the smaller scale (kilometer sizes) structures as observed by a digital ionosonde. The results point to the dominant role of a disturbance dynamo associated westward thermospheric wind to maintain the plasma irregularity drift increasingly westward going into postmidnight hours. As an important finding, the results further show that significant contribution to the westward plasma bubble irregularity drift, normally attributed to disturbance dynamo effect, could arise from prompt penetration disturbance zonal electric field, in the course of a disturbance sequence lasting several hours. Such effect is attributed to Hall electric field arising from the primary disturbance zonal electric field, under enhanced nighttime ionospheric conductivities produced possibly by storm associated particle precipitation, in the Brazilian longitude sector in agreement with recent evidences [Abdu et al., 1998b].

  7. Ray-tracing Calculation of VHF Radio Waves Scattered by Field-aligned Irregularities Associated with Equatorial Plasma Bubbles

    NASA Astrophysics Data System (ADS)

    Nakata, Hiroyuki; Akaike, Yoshiaki; Otsuka, Yuichi; Takano, Toshiaki; Ujigawa, Satoshi; Nagashima, Ikuo

    In order to explain the propagation of VHF radio waves for TV broadcasting transmitted from Southeast Asia associated with equatorial plasma bubbles, we have examined ray paths of the radio waves scattered by field-aligned irregularities in equatorial plasma bubbles. In determining the ray paths of the radio waves, a ray tracing calculation combined with a model of the scattering by field-aligned irregularities is used. It is found that VHF radio waves transmitted from Philippines can propagate to Japan due to scattering by field-aligned irregularities located above the East China Sea.

  8. Medium Scale Gravity Waves and Plasma Bubbles Depletions Observations over the Brazilian Equatorial Region

    NASA Astrophysics Data System (ADS)

    Wrasse, Cristiano M.; Takahashi, Hisao; Buriti, Ricardo; Medeiros, Amauri; Paulino, Igo; Cosme Alexandre Figueiredo, M.; Gomes, Vitor C. F.

    Medium Scale Gravity Waves (MSGW) were observed simultaneously with Equatorial Plasma Bubbles (EPB) by using an all-sky airglow imager at São João do Cariri (7.4(°) S, 36(°) W, geomag. 11(°) S) A total of 39 nights of simultaneous observation of MSGW and EPB were identified during 2012. Keogram image analyses were applied in the data set in order to find out the main MSGW characteristics: horizontal wavelength’s between 75 and 200 km, observed period of 20-40 minutes, phase velocity between 25-150 m/s propagating mainly to NE and SE. The distance between the EPB were also computed, 50-300 km, and compared with the MSGW horizontal wavelengths, showing a good correlation coefficient, indicating a possible relation between these phenomena.

  9. The Postsunset Vertical Plasma Drift and Its Effects on the Generation of Equatorial Plasma Bubbles Observed by the C/NOFS Satellite

    NASA Astrophysics Data System (ADS)

    Huang, C.; Hairston, M. R.

    2014-12-01

    The prereversal enhancement of the vertical plasma drift in the postsunset sector is an important factor that controls the generation of equatorial plasma bubbles. In this study, we use the measurements of the ion velocity meter (IVM) on board the Communication/Navigation Outage Forecasting System (C/NOFS) satellite to identify the postsunset ion vertical drift and its effects on the occurrence of plasma bubbles. We only include the events when C/NOFS is located within ±5o from the magnetic equator during the interval of 1800-1900 LT and lower than 500 km in altitude. In total, we identified 886 events in which plasma bubbles were detected by C/NOFS between 1900 and 2100 LT and 1170 events in which no plasma bubbles were detected during May 2008-June 2013. The ion vertical drift is almost always upward for the 886 cases of occurrence of plasma bubbles, with a mean value of ~40 m/s. The mean ion vertical drift for bubble occurrence increases with the solar radio flux and varies with longitude. The mean ion vertical drift for the cases without plasma bubbles is smaller than 20 m/s, with minimum values near 60o and 300o longitude, respectively. There is some overlap in the ion vertical drift between the two categories, with plasma bubbles and without plasma bubbles. The occurrence probability of plasma bubbles increases with the ion upward drift when the ion drift is within 0 and 40 m/s.

  10. Geographical analysis of equatorial plasma bubbles by GPS and nightglow measurements

    NASA Astrophysics Data System (ADS)

    Nade, D. P.; Shetti, D. J.; Sharma, A. K.; Taori, A.; Chavan, G. A.; Patil, P. T.; Ghodpage, R. N.; Gurav, O. B.; Nikte, S. S.

    2015-11-01

    This work about the zonal drift velocity and signature of equatorial plasma bubbles (EPBs) by measurements of global positioning system (GPS) receiver and all sky imager (ASI) operating in India, at the low latitude region. The optical and radio observations have been made from Kolhapur (16.8° N, 74.2° E) and Hyderabad (17.37°N, 78.48°E), respectively. The zonal drift velocity of EPBs has estimated using images of nightglow OI 630.0 nm emission recorded by ASI at Kolhapur. The measurements of total electron content (TEC) using the GPS have carried from the nearby station, Hyderabad. When depletions occurred about 00:37 h (IST) in TEC, the EPBs were found to occur about 5:30 h in optical data of OI 630.0 nm emission. This work focuses on simultaneous measurements of TEC and intensity of OI 630.0 nm emissions for EPBs during nighttime. The occurrence period of EPBs in TEC and OI 630.0 nm has found to be different. To study this difference, the zonal drift velocity of EPBs has established. The averaged eastward velocity of EPBs was found to be 138 m/s. The calculated values of zonal drift velocities are well correlated with that of the empirical model values. This work may be helpful in finding the growth of EPBs over low latitude.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

  12. Remote detection of the maximum altitude of equatorial ionospheric plasma bubbles

    NASA Technical Reports Server (NTRS)

    Benson, R. F.

    1981-01-01

    Nearly 200 post-sunset low-altitude passes of the Alouette 2 and ISIS 1 satellites near the dip equator are studied in order to find the maximum ionospheric plasma bubble altitudes, which are determined by calculating the apex altitude of the magnetic field line passing through the satellite when it is immersed in a bubble. The calculations are made only upon the observation of conjugate hemisphere ionospheric echoes, which result from ducted HF sounder signals that are guided along field-aligned irregularities within the plasma depletion. The maximum bubble altitudes corresponding to the three longitude sectors centered on zero deg, 75 deg W, and 105 deg E, are found to often exceed 1000 km, but seldom 3000 km. The electron density depletions within these field-aligned bubbles, as measured at the point of satellite encounter with the topside ionosphere, are generally less than a factor of two but may exceed a factor of ten.

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  14. Topside sounder observations of equatorial bubbles

    NASA Technical Reports Server (NTRS)

    Dyson, P. L.; Benson, R. F.

    1978-01-01

    Large scale regions of depleted equatorial ionospheric plasma, called equatorial bubbles, are investigated using topside sounder data. The sounder's unique remote measuring capability enables the magnetic field-aligned nature of the bubbles to be investigated. A search of all available Alouette 2 and ISIS 1 ionograms during nighttime perigee passes near the magnetic equator has revealed a variety of echo signatures associated with bubbles. In addition to a sudden drop in electron density, these signatures usually include in situ spread F and ducted traces. The ducted traces have been used to determine the electron density distribution and to infer changes in ion composition along the magnetic field line within the duct associated with the bubble. In some cases it can be determined that the bubble is asymmetric with respect to the magnetic equator. Even though such features require 3 dimensional models for their explanation, the great field-aligned extent of the bubbles (relative to their cross section) suggests that current theories, which ignore variations along the magnetic field, are still applicable.

  15. Modeling the Climatology of Equatorial Plasma Bubbles at Solar Minimum Using Plasma Drifts Observed by C/NOFS

    NASA Astrophysics Data System (ADS)

    Retterer, J. M.; Su, Y.; Gentile, L. C.; de La Beaujardiere, O.; Stoneback, R. A.; Pfaff, R. F.

    2010-12-01

    The goal of the C/NOFS (Communication and Navigation Outage Forecast System) project is to further our understanding of the processes in the low-latitude ionosphere that lead to radio scintillation that can interfere with operational systems. Because the height of the F-layer of the ionospheric plasma at night largely controls whether scintillation occurs, the vertical plasma drift is a key parameter among the several quantities the C/NOFS satellite was instrumented to measure in predicting whether scintillation occurs or not. Based on the operation of the C/NOFS IVM Ion Driftmeter and VEFI Electric Field Instrument over the two years since its launch, a climatological model of the vertical plasma drift has been obtained using long-term averages of the measurements. These drifts have been used in PBMOD, the first-principles model of the low-latitude ionosphere, bubble formation, and scintillation developed for the C/NOFS program, to see whether these drifts are in accord with observations of these phenomena. The DMSP satellites, in circular near-polar orbits around 840 km altitude, occasionally observe depletions in plasma density when they cross the geomagnetic equator in the evening and dawn sectors. Statistics for the frequency of observation of these depletions have been collected over the period of the C/NOFS mission. Recall that this period was a remarkably low and extended solar minimum, and the pattern of scintillation occurrence then is notably different from the standard paradigm of post-sunset occurrence. We will present maps of the frequency of occurrence of depletions, calculated with the models using the C/NOFS drift climatology, as a function of season and longitude, and compare the results with DMSP and other observations.

  16. Characteristics of equatorial plasma bubble zonal drift velocity and tilt based on Hong Kong GPS CORS network: From 2001 to 2012

    NASA Astrophysics Data System (ADS)

    Ji, Shengyue; Chen, Wu; Weng, Duojie; Wang, Zhenjie

    2015-08-01

    Hong Kong (22.3°N, 114.2°E, dip: 30.5°N; geomagnetic 15.7°N, 173.4°W, declination: 2.7°W) is a low-latitude area, and the Hong Kong Continuously Operating Reference Station (CORS) network has been developed and maintained by Lands Department of Hong Kong government since 2001. Based on the collected GPS observations of a whole solar cycle from 2001 to 2012, a method is proposed to estimate the zonal drift velocity as well as the tilt of the observed plasma bubbles, and the estimated results are statistically analyzed. It is found that although the plasma bubbles are basically vertical within the equatorial plane, the tilt can be as big as more than 60° eastward or westward sometimes. And, the tilt and the zonal drift velocity are correlated. When the velocity is large, the tilt is also large generally. Another finding is that large velocity and tilt generally occur in spring and autumn and in solar active years.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  18. Explicit characteristics of evolutionary-type plasma bubbles observed from Equatorial Atmosphere Radar during the low to moderate solar activity years 2010-2012

    NASA Astrophysics Data System (ADS)

    Ajith, K. K.; Ram, S. Tulasi; Yamamoto, M.; Yokoyama, T.; Gowtam, V. Sai; Otsuka, Y.; Tsugawa, T.; Niranjan, K.

    2015-02-01

    Using the fan sector backscatter maps of 47 MHz Equatorial Atmosphere Radar (EAR) at Kototabang (0.2°S geographic latitude, 100.3°E geographic longitude, and 10.4°S geomagnetic latitude), Indonesia, the spatial and temporal evolution of equatorial plasma bubbles (EPBs) were examined to classify the evolutionary-type EPBs from those which formed elsewhere and drifted into the field of view of radar. A total of 535 EPBs were observed during the low to moderate solar activity years 2010-2012, out of which about 210 (~39%) are of evolving type and the remaining 325 (~61%) are drifting-in EPBs. In general, both the evolving-type and drifting-in EPBs exhibit predominance during the postsunset hours of equinoxes and December solstices. Interestingly, a large number of EPBs were found to develop even a few minutes prior to the apex sunset during equinoxes. Further, the occurrence of evolving-type EPBs exhibits a clear secondary peak around midnight (2300-0100 LT), primarily, due to higher rate of occurrence during the postmidnight hours of June solstices. A significant number (~33%) of postmidnight EPBs generated during June solstices did not exhibited any clear zonal drift, while about 14% of EPBs drifted westward. Also, the westward drifting EPBs are confined only to June solstices. The responsible mechanisms for the genesis of fresh EPBs during postmidnight hours were discussed in light of equatorward meridional winds in the presence of weak westward electric fields.

  19. Disruption of Equatorial Spread-F Leading to a Fossil Bubble and Airglow Enhancement

    NASA Astrophysics Data System (ADS)

    Krall, J.; Martinis, C.; Huba, J. D.

    2008-12-01

    The NRL SAMI3/ESF ionosphere model[1] is used to show that, when equatorial spread-F (ESF) occurs in the presence of a steady, mild (20 m/s) meridional wind, the electron density in downwind "leg" of the geomagnetic field-aligned ESF bubble can exceed the background density. Further, a mild (10 m/s) converging zonal wind pattern can disrupt the upward motion of an ESF bubble, thereby creating a "fossil" ESF bubble. The fossil bubble occurs, not because of a lack of buoyancy as previously thought, but because the driving mechanism of the ESF instability has been interrupted. The cessation of ESF-related plasma uplift allows the downwind leg of the bubble to fill in, further enhancing the density in the downwind leg of the newly-fossilized bubble. A sequence of 630.0 nm images obtained with the Boston University all-sky imaging system at Arecibo (18.3 N, 66.7 W, 28 N mag) show ESF-related airglow depletions changing their pattern and becoming airglow enhancements. The results from the NRL SAMI3/ESF model provide an explanation for this enhancement as well as satellite observations of ESF-related ion density enhancements. [1] Huba, J.D., G. Joyce, and J. Krall, GRL, 35, L10102, doi:10.1029/2008GL033509, 2008

  20. Theory for modeling the equatorial evening ionosphere and the origin of the shear in the horizontal plasma flow

    SciTech Connect

    Haerendel, G.; Eccles, J.V.; Cakir, S. )

    1992-02-01

    Companion papers in this series present (1) the role of equatorial E region postsunset ionosphere, (2) the origin of horizontal plasma shear flow in the postsunset equatorial ionosphere (this paper), (3) the Colored Bubbles experiments results, and (4) computer simulations of artificial initiation of plasma density depletions (bubbles) in the equatorial ionosphere. Within this paper, equations describing the time evolution of the equatorial ionosphere are developed using flux tube integrated and flux tube weighted quantities which model the chemistry, dynamics, and electrodynamics of the equatorial ionosphere. The resulting two-dimensional set of equations can be used to investigate equatorial ionosphere. The resulting two-dimensional set of equations can be used to investigate equatorial electric fields neglecting small-scale phenomena ({lambda} < 1 km). An immediate result derived from the integrated current equations is an equation describing the physics of the shear in the horizontal flow of the equatorial plasma during the evening hours. The profile of the horizontal flow has three important contributing terms relating to the neutral wind dynamo, Hall conduction, and the equatorial electrojet current divergence. Using a one-dimensional model of the velocity shear equation and the integrated ionosphere transport equations, a time history of the development of the shear feature during postsunset hours is presented. The one-dimensional model results are compared to the velocity shear measurements from the Colored Bubbles experiments.

  1. Occurrence of large scale equatorial F-region plasma depletions during geo-magnetic disturbances

    NASA Astrophysics Data System (ADS)

    Sahai, Y.; Fagundes, P. R.; Bittencourt, J. a.; Abdu, M. a.

    1998-11-01

    During the period March 1987 to October 1991, a wide-angle imaging system to observe the OI 630 nm nightglow emission was operational at Cachoeira Paulista (22.7°S, 45.0°W dip latitude 15.8°S), Brazil. The OI 630 nm wide-angle imaging observations detect optical signatures of large scale equatorial F-region ionospheric plasma depletions or bubbles and the large data-base (about 4.5 years) permitted studies of their occurrence characteristics in the Brazilian sector. It has been observed that between the months of May and August the occurrence of large scale F-region plasma bubbles is at its minimum. However, during this period on several occasions at times of magnetic disturbances, the presence of large scale plasma bubbles was noted. In this paper we present and discuss several cases of the generation (or absence of generation) of plasma depleted regions during these months with magnetic disturbances. The imaging observations are complemented with ionospheric parameters obtained at Fortaleza (3.9°S, 38.4°W dip latitude 3.7°S), Brazil. The possible influence of magnetic disturbance effects on equatorial ionospheric fields during the events studied is analysed and presented. It has been observed that on no plasma bubble nights with magnetic disturbances, possibly the storm induced high latitude electric field could not penetrate to the equatorial region due to the shielding charges in the inner magnetosphere, whereas on the nights with plasma bubbles, disturbance drifts result from the prompt penetration of high latitude electric fields.

  2. Plasma turbulence in the equatorial electrojet

    SciTech Connect

    Kudeki, E.

    1983-01-01

    Plasma turbulence in the daytime and nighttime equatorial electrojet is studied with a highly sophisticated radar interferometer technique. It is shown that the outer scale of the plasma turbulence scales with the zero order plasma density gradient length, and is smaller during the day because of increased recombinational damping. Observations indicate that the horizontally propagating coherent waves at the other scale dominate the electrojet turbulence and give rise to vertically propagating type 1 waves during strong electrojet conditions. According to the linear theory extended to the long wavelength regime the large scale primary modes are dispersive and have phase velocities considerably smaller than the mean driving electron velocity, in agreement with the interferometer observations. Vertical electron transport, a quasi-linear effect due to large scale wave action, is shown to give rise to a vertical dc current which has the right direction and magnitude to explain the up-down and possibly the east-west asymmetries observed at Jicamarca. These quasi-linear considerations also show that the first order perturbed vertical electron velocity associated with the primary mode is limited to a maximum value on the order of the mean horizontal electron velocity, which might explain why vertically propagating type 1 waves are only observed during strong electrojet conditions.

  3. Plasma bubble monitoring by TEC map and 630 nm airglow image

    NASA Astrophysics Data System (ADS)

    Takahashi, H.; Wrasse, C. M.; Otsuka, Y.; Ivo, A.; Gomes, V.; Paulino, I.; Medeiros, A. F.; Denardini, C. M.; Sant'Anna, N.; Shiokawa, K.

    2015-08-01

    Equatorial ionosphere plasma bubbles over the South American continent were successfully observed by mapping the total electron content (TECMAP) using data provided by ground-based GNSS receiver networks. The TECMAP could cover almost all of the continent within ~4000 km distance in longitude and latitude, monitoring TEC variability continuously with a time resolution of 10 min. Simultaneous observations of OI 630 nm all-sky image at Cachoeira Paulista (22.7°S, 45.0°W) and Cariri (7.4°S, 36.5°W) were used to compare the bubble structures. The spatial resolution of the TECMAP varied from 50 km to 1000 km, depending on the density of the observation sites. On the other hand, optical imaging has a spatial resolution better than 15 km, depicting the fine structure of the bubbles but covering a limited area (~1600 km diameter). TECMAP has an advantage in its spatial coverage and the continuous monitoring (day and night) form. The initial phase of plasma depletion in the post-sunset equatorial ionization anomaly (PS-EIA) trough region, followed by development of plasma bubbles in the crest region, could be monitored in a progressive way over the magnetic equator. In December 2013 to January 2014, periodically spaced bubble structures were frequently observed. The longitudinal spacing between the bubbles was around 600-800 km depending on the day. The periodic form of plasma bubbles may suggest a seeding process related to the solar terminator passage in the ionosphere.

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

    NASA Technical Reports Server (NTRS)

    Johnson, Francis S.; Coley, William R.

    1995-01-01

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

  5. Plasma bubbles in the topside ionosphere: solar activity dependence

    NASA Astrophysics Data System (ADS)

    Sidorova, L.

    2009-04-01

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

  6. Oscillating plasma bubbles. I. Basic properties and instabilities

    SciTech Connect

    Stenzel, R. L.; Urrutia, J. M.

    2012-08-15

    Plasma bubbles are created in an ambient discharge plasma. A bubble is a plasma volume of typically spherical shape, which is separated from the ambient plasma by a negatively biased grid of high transparency. Ions and electrons from the ambient plasma flow into the bubble volume. In steady state the flow of particles and currents is divergence-free, which is established by the plasma potential inside the bubble. The grid has two sheaths, one facing the ambient plasma, the other the bubble plasma. The inner sheath is observed to become unstable, causing the plasma potential in the bubble to oscillate. The instability arises from an excess of ions and a deficiency of electrons. Its frequency is in the range of the ion plasma frequency but depends on all parameters which influence the charge density in the sheath. When the grid voltage is very negative, electrons cannot enter the outer sheath, and the inner sheath becomes a virtual anode which reflects ions such that the bubble interior is empty. When an electron source is placed into the bubble it can neutralize the ions and the bubble refills. Without plasma sources or sinks the bubble plasma is extremely sensitive to perturbations by probes. Modified current-voltage characteristics of Langmuir and emissive probes are demonstrated. A sequence of papers first describes the basic steady-state properties, then the time evolution of bubbles, the effects of electron sources in bubbles, and the role of the grid and bubble geometry. The physics of plasma bubbles is important to several fields of basic plasma physics such as sheaths, sheath instabilities, diagnostic probes, electrostatic confinement, and current and space charge neutralization of beams.

  7. Broad plasma depletions detected in the bottomside of the equatorial F region: Simultaneous ROCSAT-1 and JULIA observations

    NASA Astrophysics Data System (ADS)

    Kil, Hyosub; Kwak, Young-Sil; Lee, Woo Kyoung; Oh, Seung-Jun; Milla, Marco; Galkin, Ivan

    2014-07-01

    We investigated the association of broad plasma depletions (BPDs) with plasma bubbles and ionospheric uplift in the equatorial F region using the coincident satellite and radar observations over Jicamarca in Peru. BPDs were detected by the first Republic of China satellite (ROCSAT-1) on the nights of 21 and 22 December 2002 during the period of moderate geomagnetic activity. The observations of the Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere radar and an ionosonde showed that the F peak height was lifted above the ROCSAT-1 altitude (600 km) at the times of the BPD detection. The fraction of NO+ was substantial at the locations of BPDs. These observations support the association of the BPDs with the ionospheric uplift. However, the absence of large backscatter plumes at the times of the BPD detection indicates that the BPDs were not produced by a single large bubble or a merger of bubbles.

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

    NASA Astrophysics Data System (ADS)

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

    2011-07-01

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

  9. Planetary/Kelvin wave modulation of the equatorial ionospheric evening vertical plasma drift and the post sunset spread F developments

    NASA Astrophysics Data System (ADS)

    Abdu, Mangalathayil A.; Sobral, José; Gurubaran, Subramanian; Brum, Christiano Marques Garnett; Batista, Inez S.; Valentin Bageston, José; Batista, Paulo

    2012-07-01

    Recent studies have shown that the evening prereversal enhancement in the equatorial ionospheric zonal electric field /vertical plasma drift (PRE) and hence post sunset spread F irregularity (ESF) generation are significantly modified by Planetary waves of a few-day (2-, 5-, 7-day) periodicity, although many specific details of which remain to be investigated. Thus the widely observed day to day/short terms variability in the PRE and ESF developments originate not only from the variable forcing (in the form of disturbance electric fields) from magnetosphere, as is well known, but a large part of it arises also from forcing by upward propagating wave from lower atmosphere. In this paper we have analyzed the PRE vertical drifts measured by an equatorial Digisonde (Fortaleza), and the mesospheric zonal and meridional winds as measured by two meteor radars operated at an equatorial site (Sao Joao de Cariri) and a low latitude sites (Cachoeira Paulista), in Brazil, together with mesospheric winds as measured by MF radar at an equatorial site (Tirunelveli) in India. The comparison of these results show the presence of oscillations of around 3 and 5-7 days of periodicities in the evening vertical drift as well as in the mesospheric wind field simultaneously in the Brazilian and Indian longitudes, which are shown to be produced by eastward propagating Equatorial Kelvin wave as well as by westward propagating planetary waves. The effects of these waves on the development of the ESF/plasma bubble irregularities are also studied.

  10. Scalings for radiation from plasma bubbles

    SciTech Connect

    Thomas, A. G. R.

    2010-05-15

    In this paper, electron trajectories are studied analytically in the rest frame of a plasma bubble using nonevolving, linear, radial electric and azimuthal magnetic fields in a spherical structure. The electron motion is broken into two distinct periods; one where it orbits around the periphery to the rear of the bubble, and one where it performs oscillations within the bubble interior. By using the first period as an initial condition for the second, general scalings are developed for the x-ray radiation produced by the electron oscillations. The equations are also analyzed to give self-trapping conditions for the electron and to examine the sensitivity of the transverse momentum to small variations from an orbit that is a circular arc. The scalings are in reasonable agreement with recent experiments on x-ray generation and predict a peak spectral brightness of S{approx_equal}6x10{sup 27} photons/s mrad mm 0.1%BW of radiation with a critical energy of 300 MeV using a single stage accelerator driven by a 120 PW laser.

  11. Equatorial broad plasma depletions associated with the enhanced fountain effect

    NASA Astrophysics Data System (ADS)

    Lee, Woo Kyoung; Kil, Hyosub; Kwak, Young-Sil; Paxton, Larry J.; Zhang, Yongliang; Galkin, Ivan; Batista, Inez S.

    2014-01-01

    plasma depletions (BPDs), plasma depletions whose longitudinal width is over several hundred kilometers, have been detected in the equatorial F region by low-earth-orbit satellites during both magnetically quiet and magnetically disturbed periods. A few hypotheses were suggested to explain the creation of BPDs, but the underlying mechanism of this phenomenon is still under debate. We investigate the origin of BPDs by analyzing the simultaneous in situ and optical observations of the ionosphere on 30 May 2003 (Kp = 8+), 24 April 2012 (Kp = 7-), and 31 October 2012 (Kp = 0+). BPDs on 30 May 2003 were detected by the Republic of China Satellite-1 at an altitude of 600 km, and BPDs on the other days were detected by the Communication/Navigation Outage Forecasting System satellite near an altitude of 400 km. Our results show that the detection of BPDs is closely associated with background ionospheric morphology; BPDs are detected on the days when the equatorial ionization anomaly (EIA) is intense and the crests of the EIA have moved poleward. Measurements of upward plasma motion support the existence of ionospheric uplift at BPD locations. These observations and the detection of BPDs near the magnetic equator lead to the interpretation that the satellite detection of BPDs during those 3 days is likely related to the uplift of the F peak height above the satellite orbits.

  12. Stabilizing effect of plasma discharge on bubbling fluidized granular bed

    NASA Astrophysics Data System (ADS)

    Hu, Mao-Bin; Dang, Sai-Chao; Ma, Qiang; Xia, Wei-Dong

    2015-07-01

    Fluidized beds have been widely used for processing granular materials. In this paper, we study the effect of plasma on the fluidization behavior of a bubbling fluidized bed with an atmospheric pressure plasma discharger. Experiment results show that the bubbling fluidized bed is stabilized with the discharge of plasma. When the discharge current reaches a minimum stabilization current Cms, air bubbles in the bed will disappear and the surface fluctuation is completely suppressed. A simplified model is proposed to consider the effect of electric Coulomb force generated by the plasma. It is found that the Coulomb force will propel the particles to move towards the void area, so that the bubbling fluidized bed is stabilized with a high enough plasma discharge. Project supported by the National Natural Science Foundation of China (Grant Nos. 11035005 and 11034010).

  13. Plasma core at the center of a sonoluminescing bubble

    NASA Astrophysics Data System (ADS)

    Bemani, F.; Sadighi-Bonabi, R.

    2013-01-01

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

  14. Simultaneous observations of equatorial F-region plasma depletions over Brazil during the Spread-F Experiment (SpreadFEx)

    NASA Astrophysics Data System (ADS)

    Pautet, P.-D.; Taylor, M. J.; Chapagain, N. P.; Takahashi, H.; Medeiros, A. F.; São Sabbas, F. T.; Fritts, D. C.

    2009-06-01

    From September to November 2005, the NASA Living with a Star program supported the Spread-F Experiment campaign (SpreadFEx) in Brazil to study the effects of convectively generated gravity waves on the ionosphere and their role in seeding Rayleigh-Taylor instabilities, and associated equatorial plasma bubbles. Several US and Brazilian institutes deployed a broad range of instruments (all-sky imagers, digisondes, photometers, meteor/VHF radars, GPS receivers) covering a large area of Brazil. The campaign was divided in two observational phases centered on the September and October new moon periods. During these periods, an Utah State University (USU) all-sky CCD imager operated at São João d'Aliança (14.8° S, 47.6° W), near Brasilia, and a Brazilian all-sky CCD imager located at Cariri (7.4° S, 36° W), observed simultaneously the evolution of the ionospheric bubbles in the OI (630 nm) emission and the mesospheric gravity wave field. The two sites had approximately the same magnetic latitude (9-10° S) but were separated in longitude by ~1500 km. Plasma bubbles were observed on every clear night (17 from Brasilia and 19 from Cariri, with 8 coincident nights). These joint datasets provided important information for characterizing the ionospheric depletions during the campaign and to perform a novel longitudinal investigation of their variability. Measurements of the drift velocities at both sites are in good agreement with previous studies, however, the overlapping fields of view revealed significant differences in the occurrence and structure of the plasma bubbles, providing new evidence for localized generation. This paper summarizes the observed bubble characteristics important for related investigations of their seeding mechanisms associated with gravity wave activity.

  15. Oscillating plasma bubbles. III. Internal electron sources and sinks

    SciTech Connect

    Stenzel, R. L.; Urrutia, J. M.

    2012-08-15

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

  16. Effects of pre-reversal enhancement of E × B drift on the latitudinal extension of plasma bubble in Southeast Asia

    NASA Astrophysics Data System (ADS)

    Abadi, Prayitno; Otsuka, Yuichi; Tsugawa, Takuya

    2015-12-01

    We investigated the effects of the F region bottomside altitude ( h'F), maximum upward E × B drift velocity, duration of pre-reversal enhancement and the integral of upward E × B drift on the latitudinal extension of equatorial plasma bubbles in the Southeast Asian sector using the observations recorded by three GPS receivers and two ionosondes. The GPS receivers are installed at Kototabang (0.2°S, 100.3°E; 9.9°S magnetic latitude), Pontianak (0.02°S, 109.3°E; 9.8°S magnetic latitude) and Bandung (6.9°S, 107.6°E; 16.7°S magnetic latitude) in Indonesia. The ionosondes are installed at magnetically equatorial stations, Chumphon (10.7°N, 99.4°E; 0.86°N magnetic latitude) in Thailand and Bac Lieu (9.3°N, 105.7°E; 0.62°N magnetic latitude) in Vietnam. We analysed those observations acquired in the equinoctial months (March, April, September and October) in 2010-2012, when the solar activity index F 10.7 was in the range from 75 to 150. Assuming that plasma bubbles are the major source of scintillations, the latitudinal extension of the bubbles was determined according to the S4 index. We have found that the peak of h'F, maximum upward E × B drift and the integral of upward E × B drift during the pre-reversal enhancement period are positively correlated with the maximum latitude extension of plasma bubbles, but that duration of pre-reversal enhancement does not show correlation. The plasma bubbles reached magnetic latitudes of 10°-20° in the following conditions: (1) the peak value of h'F is greater than 250-450 km, (2) the maximum upward E × B drift is greater than 10-70 m/s and (3) the integral of upward E × B drift is greater than 50-250 m/s. These results suggest that the latitudinal extension of plasma bubbles is controlled mainly by the magnitude of pre-reversal enhancement and the peak value of h'F at the initial phase of development of plasma bubbles (or equatorial spread F) rather than by the duration of pre-reversal enhancement.

  17. Laboratory Experiments on Propagating Plasma Bubbles into Vacuum, Vacuum Magnetic Field, and Background Plasmas

    NASA Astrophysics Data System (ADS)

    Lynn, Alan G.; Zhang, Yue; Gilmore, Mark; Hsu, Scott

    2014-10-01

    We discuss the dynamics of plasma ``bubbles'' as they propagate through a variety of background media. These bubbles are formed by a pulsed coaxial gun with an externally applied magnetic field. Bubble parameters are typically ne ~1020 m-3, Te ~ 5 - 10 eV, and Ti ~ 10 - 15 eV. The structure of the bubbles can range from unmagnetized jet-like structures to spheromak-like structures with complex magnetic flux surfaces. Some of the background media the bubbles interact with are vacuum, vacuum with magnetic field, and other magnetized plasmas. These bubbles exhibit different qualitative behavior depending on coaxial gun parameters such as gas species, gun current, and gun bias magnetic field. Their behavior also depends on the parameters of the background they propagate through. Multi-frame fast camera imaging and magnetic probe data are used to characterize the bubble evolution under various conditions.

  18. Equatorial F region zonal plasma irregularity drifts under magnetospheric disturbances

    NASA Astrophysics Data System (ADS)

    Abdu, M. A.; Jayachandran, P. T.; MacDougall, J.; Cecile, J. F.; Sobral, J. H. A.

    Equatorial F region plasma drift velocities measured by a digital ionosonde (CADI) that was recently installed in Fortaleza, Brazil, are used to investigate magnetospheric disturbance effects in the vertical (zonal) and zonal (vertical) velocities (electric fields). For the first time we report evidence of large fluctuations in irregularity zonal drift velocities (˜50-180 m/s) associated with magnetospheric disturbances. The fluctuations in the zonal velocity, anti correlated with those in vertical velocity, are unlikely to be produced by prompt penetration of disturbance meridional electric field of high latitude/magnetospheric origin. A mechanism is proposed to explain the velocity fluctuations that involves: (1) Hall polarization vertical electric field in the E-layer that is field line mapped on to F-layer, and (2) electric field caused by vertical current arising from divergence in field line integrated zonal Pedersen current; both produced by the primary disturbance zonal electric field. Enhanced nighttime E region conductivity with possible spatial gradients, a requirement for the functioning of this mechanism, is observed to be present from other simultaneous measurements, whose source is suggested to be particle induced ionization in the south Atlantic Magnetic Anomaly (SAMA) zone, as known also from previous studies.

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

    SciTech Connect

    Stenzel, R. L.; Urrutia, J. M.

    2012-08-15

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

  20. Interaction of field-aligned cold plasma flows with an equatorially-trapped hot plasma - Electrostatic shock formation

    NASA Technical Reports Server (NTRS)

    Singh, Nagendra

    1993-01-01

    Effects of equatorially trapped hot plasma on the highly supersonic cold-plasma flow occurring during early stage plasmaspheric refilling are studied by means of numerical simulations. It is shown that the equatorially trapped hot ions set up a potential barrier for the cold ion beams and facilitate formation of electrostatic shocks by reflecting them from the equatorial region. Simulations with and without the hot plasma show different flow properties; the formation of electrostatic shocks occur only in the former case. The simulation with the hot plasma also reveals that the magnetic trapping in conjunction with the evolution of the electrostatic potential barrier produces ion velocity distribution functions consisting of a cold core and a hot ring in the perpendicular velocity. Such a distribution function provides a source of free energy for equatorial waves. The corresponding electron population is warm and field-aligned.

  1. Theoretical study of the ionospheric plasma cave in the equatorial ionization anomaly region

    NASA Astrophysics Data System (ADS)

    Chen, Yu-Tsung; Lin, C. H.; Chen, C. H.; Liu, J. Y.; Huba, J. D.; Chang, L. C.; Liu, H.-L.; Lin, J. T.; Rajesh, P. K.

    2014-12-01

    This paper investigates the physical mechanism of an unusual equatorial electron density structure, plasma cave, located underneath the equatorial ionization anomaly by using theoretical simulations. The simulation results provide important new understanding of the dynamics of the equatorial ionosphere. It has been suggested previously that unusual E>?×B>? drifts might be responsible for the observed plasma cave structure, but model simulations in this paper suggest that the more likely cause is latitudinal meridional neutral wind variations. The neutral winds are featured by two divergent wind regions at off-equator latitudes and a convergent wind region around the magnetic equator, resulting in plasma divergences and convergence, respectively, to form the plasma caves structure. The tidal-decomposition analysis further suggests that the cave related meridional neutral winds and the intensity of plasma cave are highly associated with the migrating terdiurnal tidal component of the neutral winds.

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

    NASA Astrophysics Data System (ADS)

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

    2007-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

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

  4. Variation of type I plasma wave phase velocity with electron drift velocity in the equatorial electrojet

    SciTech Connect

    Ravindran, S.; Reddy, C.A.

    1993-12-01

    The authors report the use of VHF coherent backscatter radar to detect the phase velocity variations of type I and type II plasma waves coming from the equatorial electrojet in conjunction with substorm and magnetic storm events. These plasma waves are generated by two-stream type instabilities. The authors observe a correlation between the phase velocity of the type I plasma waves and the electron drift velocity, which is consistent with present models which explain the generation of such waves.

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

    SciTech Connect

    Li, X. F.; Yu, Q.; Huang, S.; Zhang, F.; Kong, Q.; Gu, Y. J.; Kawata, S.

    2014-07-15

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

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

    SciTech Connect

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

    1995-02-01

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

  7. Micro Dynamics of Pulsed Laser Induced Bubbles in Dusty Plasma Liquids

    SciTech Connect

    Teng, L.-W.; Tsai, C.-Y.; Tseng, Y.-P.; I Lin

    2008-09-07

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

  8. The Study of the origin of broad plasma depletions in the equatorial F region

    NASA Astrophysics Data System (ADS)

    Oh, S.; Lee, W.; Kil, H.; Kwak, Y.; Paxton, L.; Zhang, Y.

    2013-12-01

    Broad plasma depletions (BPDs), plasma depletions broader than regular plasma bubbles, are occasionally detected by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. The BPD phenomenon is understood in association with either plasma bubbles or modulation of the F region height. This study presents the BPD events that are considered to be associated with the latter. The coincident observations of the ionosphere from space (C/NOFS and the first Republic of China satellite) and on the ground (radars and ionosondes) showed that significant fountain process or uplift of the ionosphere occurred in the regions where BPDs were detected. The coincident ionosonde observations in the American sector showed the rapid increase of the F region height and, eventually, the disappearance of the ionosphere at the time of the BPD detection. Some BPDs showed the association with large scale wave structures and storm-induced electric fields. Our observation results indicate that the satellite detection of BPDs can be understood in terms of the uplift of the F region height above the satellite altitude. The coincidence of bubbles often with BPDs is explained by the promotion of the bubble activity by the uplift of the ionosphere.

  9. Bubbles

    NASA Astrophysics Data System (ADS)

    Prosperetti, Andrea

    2004-06-01

    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.

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

    SciTech Connect

    Thomas, A. G. R.

    2011-03-15

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

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

    SciTech Connect

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

    2013-01-15

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

  12. Electromagnetic Analysis of ITER Diagnostic Equatorial Port Plugs During Plasma Disruptions

    SciTech Connect

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

    2012-08-27

    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.

  13. Geomagnetically conjugate observation of plasma bubbles and thermospheric neutral winds at low latitudes

    NASA Astrophysics Data System (ADS)

    Fukushima, D.; Shiokawa, K.; Otsuka, Y.; Nishioka, M.; Kubota, M.; Tsugawa, T.; Nagatsuma, T.; Komonjinda, S.; Yatini, C. Y.

    2015-03-01

    This is the first paper that reports simultaneous observations of zonal drift of plasma bubbles and the thermospheric neutral winds at geomagnetically conjugate points in both hemispheres. The plasma bubbles were observed in the 630 nm nighttime airglow images taken by using highly sensitive all-sky airglow imagers at Kototabang, Indonesia (geomagnetic latitude (MLAT): 10.0°S), and Chiang Mai, Thailand (MLAT: 8.9°N), which are nearly geomagnetically conjugate stations, for 7 h from 13 to 20 UT (from 20 to 03 LT) on 5 April 2011. The bubbles continuously propagated eastward with velocities of 100-125 m/s. The 630 nm images at Chiang Mai and those mapped to the conjugate point of Kototabang fit very well, which indicates that the observed plasma bubbles were geomagnetically connected. The eastward thermospheric neutral winds measured by two Fabry-Perot interferometers were 70-130 m/s at Kototabang and 50-90 m/s at Chiang Mai. We compared the observed plasma bubble drift velocity with the velocity calculated from the observed neutral winds and the model conductivity, to investigate the F region dynamo contribution to the bubble drift velocity. The estimated drift velocities were 60-90% of the observed velocities of the plasma bubbles, suggesting that most of the plasma bubble velocity can be explained by the F region dynamo effect.

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

    SciTech Connect

    Cremaschini, Claudio; Ková?, Ji?í; Slaný, Petr; Stuchlík, Zden?k; Karas, Vladimír

    2013-11-01

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

  15. Electron trajectories and betatron oscillation in the wake bubble in laser-plasma interaction

    SciTech Connect

    Wu Haicheng; Xie Baisong; Liu Mingping; Hong Xueren; Zhangshan; Yu, M. Y.

    2009-07-15

    The trajectories of electrons originating from different initial locations in the unperturbed plasma during the interaction of an ultraintense laser with underdense plasma in the bubble regime are followed by particle-in-cell simulation. It is found that plasma electrons initially aligned with the rim of the laser focal spot contribute most to the bow wave in front of the bubble and those aligned with the lateral bubble sheath edge contribute most to the self-injection at the back of the bubble. A scaling law between the transverse electric and magnetic fields for the case where there are many electrons in the bubble is given and discussed in terms of betatron oscillations of the injected electrons.

  16. THEMIS observations of plasma bubbles associated with energetic electron acceleration in the inner magnetosphere

    NASA Astrophysics Data System (ADS)

    Tang, C. L.

    2014-12-01

    Using Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations, we study the plasma bubbles associated with a transient increase of the magnetic field Bz component in the inner magnetosphere during the substorm expansion phase. Except small electric field, the main characteristics of these plasma bubbles are similar with those associated with dipolarization front (DF) in the mid-tail and near-Earth tail. Based on the different dipolarization of the magnetic field, we defined the plasma bubble with no dipolarization phenomenon as "no dipolarization bubble" (NDB), the plasma bubble with dipolarization phenomenon as "dipolarization bubble" (DB). We find that these plasma bubbles in the inner magnetosphere accompany the energetic electron acceleration. Some pancake-type distributions of energetic electrons inside the NDB in the inner magnetosphere are caused by drift betatron acceleration, other pancake-type distributions of energetic electrons inside the NDB are caused by gyrobetatron acceleration. For the DB in the inner magnetosphere, the cigar-type distributions of energetic electrons are attributed to Fermi acceleration. Our observations suggest that the inner magnetosphere may be a very important source region for energetic electrons, except for a reconnection site in the mid-tail and the plasma sheet in the near-Earth tail.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  18. Electrons trajectories around a bubble regime in intense laser plasma interaction

    SciTech Connect

    Lu, Ding; Xie, Bai-Song; Ali Bake, Muhammad; Sang, Hai-Bo; Zhao, Xue-Yan; Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 ; Wu, Hai-Cheng

    2013-06-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

    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.

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

    SciTech Connect

    Kushner, Mark Jay

    2014-07-10

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-11-01

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

  2. Understanding the plasma and power characteristics of a self-generated steam bubble discharge

    NASA Astrophysics Data System (ADS)

    Garcia, Maria C.; Gucker, Sarah N.; Foster, John E.

    2015-09-01

    Plasma formation in a self-generated steam bubble is studied using a coaxial discharge tube with an axial powered electrode (nominal peak operating voltage 2000?V) and an external ground lead without any gas flow. The discharge is potentially attractive for water purification applications in that the production of reactive nitrogen species and the associated water acidification is avoided. The discharge was found to form after a finite delay, which is attributed to the vapor bubble formation necessary for plasma ignition. Steam bubble composition was confirmed using emission spectra. Plasma properties and power dissipated in the self-generated steam bubble were characterized using emission spectroscopy and Lissajous methods. Discharge density and gas temperature were found to vary significantly over the applied ac voltage cycle. The power dissipated as inferred from the Lissajous method was found to scale inversely with frequency over the low frequency range investigated (4?kHz and 5?kHz).

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

    PubMed

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

    2014-12-12

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

  4. Generation of Shock-Wave Disturbances at Plasma-Vapor Bubble Oscillation

    NASA Astrophysics Data System (ADS)

    Kuznetsova, N. S.; Yudin, A. S.; Voitenko, N. V.

    2015-11-01

    The complex physical and mathematical model describing all steps of plasma-vapor bubble evolution in the system of the water-ground condensed media is presented. Discharge circuit operation, discharge plasma channel expansion, its transformation into the vapor-plasma bubble and its pulsation, pressure wave generation and propagation of the mechanical stress waves in the ground are self-consistently considered in the model. The model allows investigation of the basic laws of stored energy transformation into the discharge plasma channel, next to the plasma-vapor bubble and transformation of this energy to the energy of pressure wave compressing the surrounding ground. Power characteristics of wave disturbances generated by gas-vapor bubble oscillation in liquid depending on the circuit parameters are analyzed for the prediction of the ground boundary displacement. The dynamics of the shock-wave propagation in water-ground condensed media depending on the rate of the plasma channel energy release is investigated. Simulation of the shock-wave phenomena at a plasma-vapor bubble oscillation in condensed media consecutively describes the physical processes underlying technology for producing piles by electro-discharge stuffing. The quantitative model verified by physical experimental tests will allow optimization of pulse generator parameters and electrode system construction of high-voltage equipment.

  5. A simulation study on the impact of altitudinal dependent vertical plasma drift on the equatorial ionosphere in the evening

    NASA Astrophysics Data System (ADS)

    Qian, Cheng; Lei, Jiuhou; Wang, Wenbin

    2015-04-01

    We carry out a simulation study on the impact of altitudinal dependent plasma drift on the equatorial ionosphere in the evening, under geomagnetically quiet conditions. Our study used the vertical plasma drift velocity data measured by an incoherent scatter radar at Jicamarca (11.95°S, 76.87°W). The data covered the local sunset period on 15 and 16 November 2004. The plasma drift had significant altitudinal variations in the vertical component, which is perpendicular to the magnetic field. We employed SAMI2 (SAMI2 is another model of the ionosphere) to evaluate the effect of the altitude-dependent ion drift on the equatorial ionosphere. Three types of plasma drift velocity inputs were used in our simulations. The first input is calculated from an empirical model, the second is a height-averaged drift obtained from the observed drift velocity, and the third one corresponds to the observed altitudinal dependent drift data. A strong equatorial ionization anomaly occurred in the results of all numerical experiments. Additional layers (F3 layers) in electron densities over the equatorial F region and "arch" latitudinal structures extending to lower middle latitudes were seen in the simulations driven by the observed altitudinal dependent drift. We further show that neutral winds do not have a significant effect on the simulated F3 layers. The results of our numerical experiments suggest that the simulated additional ionospheric layers and arch structures are associated with the altitudinal gradients in the vertical plasma drift velocity.

  6. On the contribution of plasma sheet bubbles to the storm time ring current

    NASA Astrophysics Data System (ADS)

    Yang, Jian; Toffoletto, Frank R.; Wolf, Richard A.; Sazykin, Stanislav

    2015-09-01

    Particle injections occur frequently inside 10 Re during geomagnetic storms. They are commonly associated with bursty bulk flows or plasma sheet bubbles transported from the tail to the inner magnetosphere. Although observations and theoretical arguments have suggested that they may have an important role in storm time dynamics, this assertion has not been addressed quantitatively. In this paper, we investigate which process is dominant for the storm time ring current buildup: large-scale enhanced convection or localized bubble injections. We use the Rice Convection Model-Equilibrium (RCM-E) to model a series of idealized storm main phases. The boundary conditions at 14-15 Re on the nightside are adjusted to randomly inject bubbles to a degree roughly consistent with observed statistical properties. A test particle tracing technique is then used to identify the source of the ring current plasma. We find that the contribution of plasma sheet bubbles to the ring current energy increases from ~20% for weak storms to ~50% for moderate storms and levels off at ~61% for intense storms, while the contribution of trapped particles decreases from ~60% for weak storms to ~30% for moderate and ~21% for intense storms. The contribution of nonbubble plasma sheet flux tubes remains ~20% on average regardless of the storm intensity. Consistent with previous RCM and RCM-E simulations, our results show that the mechanisms for plasma sheet bubbles enhancing the ring current energy are (1) the deep penetration of bubbles and (2) the bulk plasma pushed ahead of bubbles. Both the bubbles and the plasma pushed ahead typically contain larger distribution functions than those in the inner magnetosphere at quiet times. An integrated effect of those individual bubble injections is the gradual enhancement of the storm time ring current. We also make two predictions testable against observations. First, fluctuations over a time scale of 5-20 min in the plasma distributions and electric field can be seen in the central ring current region for the storm main phase. We find that the plasma pressure and the electric field EY there vary over about 10%-30% and 50%-300% of the background values, respectively. Second, the maximum plasma pressure and magnetic field depression in the central ring current region during the main phase are well correlated with the Dst index.

  7. Electron self-injection into an evolving plasma bubble: Quasi-monoenergetic laser-plasma acceleration in the blowout regimea)

    E-print Network

    Umstadter, Donald

    Electron self-injection into an evolving plasma bubble: Quasi-monoenergetic laser (Received 26 November 2010; accepted 27 January 2011; published online 12 April 2011) An electron density quiescent plasma electrons, whereas stabilization and contraction terminate self-injection thus limiting

  8. Radio-Tomographic Images of Post-midnight Equatorial Plasma Depletions

    NASA Astrophysics Data System (ADS)

    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

    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.

  9. Modelling chemical reactions in dc plasma inside oxygen bubbles in water

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

  10. On the Contribution of Plasma Sheet Bubbles to the Storm-Time Ring Current Injection

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Plasma sheet transport is bimodal, consisting of both large-scale adiabatic convection and bursty flows. The bursty flows are associated with plasma sheet bubbles, containing lower entropy parameter PV5/3 than their neighbors. Although bubbles are major contributors to plasma sheet transport, it is still unclear whether they play a critical role in the formation of the storm-time ring current, since bubbles are much more frequently observed tailward of 10 Re in the magnetotail than inside geosynchronous orbit. In this paper, we use RCM-E, which combines the Rice Convection Model (RCM) with the magnetic field in force balance with particle pressure, to simulate an idealized geomagnetic storm. In the simulation, random bubble injections through the high latitude boundary are superimposed on a background of large-scale enhanced convection. We use the RCM-E solutions with the test particle approach to determine the relative roles of the three mechanisms of formation of the storm-time ring current: (1) energization of particles already trapped on closed drift trajectories; (2) localized injection of plasma sheet particles in flow channels associated with bubbles; (3) large-scale cross-tail particle transport from the tail into the inner magnetosphere under enhanced convection. We will discuss the fractional contribution of each of the three sources to the storm-time ring current and provide a picture of how each mechanism works.

  11. Phase Transition to an Opaque Plasma in a Sonoluminescing Bubble

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

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

  12. Simultaneous observation of nascent plasma and bubble induced by laser ablation in water with various pulse durations

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    We investigate the effects of pulse duration on the dynamics of the nascent plasma and bubble induced by laser ablation in water. To examine the relationship between the nascent plasma and the bubble without disturbed by shot-to-shot fluctuation, we observe the images of the plasma and the bubble simultaneously by using two intensified charge coupled device detectors. We successfully observe the images of the plasma and bubble during the pulsed-irradiation, when the bubble size is as small as 20 ?m. The light-emitting region of the plasma during the laser irradiation seems to exceed the bubble boundary in the case of the short-pulse (30-ns pulse) irradiation, while the size of the plasma is significantly smaller than that of the bubble in the case of the long-pulse (100-ns pulse) irradiation. The results suggest that the extent of the plasma quenching in the initial stage significantly depends on the pulse duration. Also, we investigate how the plasma-bubble relationship in the very early stage affects the shape of the atomic spectral lines observed at the later delay time of 600 ns. The present work gives important information to obtain high quality spectra in the application of underwater laser-induced breakdown spectroscopy, as well as to clarify the mechanism of liquid-phase laser ablation.

  13. Simultaneous observation of nascent plasma and bubble induced by laser ablation in water with various pulse durations

    SciTech Connect

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

    2015-05-07

    We investigate the effects of pulse duration on the dynamics of the nascent plasma and bubble induced by laser ablation in water. To examine the relationship between the nascent plasma and the bubble without disturbed by shot-to-shot fluctuation, we observe the images of the plasma and the bubble simultaneously by using two intensified charge coupled device detectors. We successfully observe the images of the plasma and bubble during the pulsed-irradiation, when the bubble size is as small as 20??m. The light-emitting region of the plasma during the laser irradiation seems to exceed the bubble boundary in the case of the short-pulse (30-ns pulse) irradiation, while the size of the plasma is significantly smaller than that of the bubble in the case of the long-pulse (100-ns pulse) irradiation. The results suggest that the extent of the plasma quenching in the initial stage significantly depends on the pulse duration. Also, we investigate how the plasma-bubble relationship in the very early stage affects the shape of the atomic spectral lines observed at the later delay time of 600?ns. The present work gives important information to obtain high quality spectra in the application of underwater laser-induced breakdown spectroscopy, as well as to clarify the mechanism of liquid-phase laser ablation.

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

    SciTech Connect

    FISHER,RK

    2002-10-01

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

  15. Cluster observations of kinetic structures and electron acceleration within a dynamic plasma bubble

    NASA Astrophysics Data System (ADS)

    Zhou, Meng; Deng, Xiaohua; Ashour-Abdalla, Maha; Walker, Raymond; Pang, Ye; Tang, Chaoling; Huang, Shiyong; El-Alaoui, Mostafa; Yuan, Zhigang; Li, Huimin

    2013-02-01

    Fast plasma flows are believed to play important roles in transporting mass, momentum, and energy in the magnetotail during active periods, such as the magnetospheric substorms. In this paper, we present Cluster observations of a plasma-depleted flux tube, i.e., a plasma bubble associated with fast plasma flow before the onset of a substorm in the near-Earth tail around X = -18 RE. The bubble is bounded by both sharp leading (?bz/?x < 0) and trailing (?bz/?x > 0) edges. The two edges are thin current layers (approximately ion inertial length) that carry not only intense perpendicular current but also field-aligned current. The leading edge is a dipolarization front (DF) within a slow plasma flow, while the trailing edge is embedded in a super-Alfvénic convective ion jet. The electron jet speed exceeds the ion flow speed thus producing a large tangential current at the trailing edge. The electron drift is primarily given by the E × B drift. Interestingly, the trailing edge moves faster than the leading edge, which causes shrinking of the bubble and local flux pileup inside the bubble. This resulted in a further intensification of Bz, or a secondary dipolarization. Both the leading and trailing edges are tangential discontinuities that confine the electrons inside the bubble. Strong electron acceleration occurred corresponding to the secondary dipolarization, with perpendicular fluxes dominating the field-aligned fluxes. We suggest that betatron acceleration is responsible for the electron energization. Whistler waves and lower hybrid drift waves were identified inside the bubble. Their generation mechanisms and potential roles in electron dynamics are discussed.

  16. Nucleation Rate of Hadron Bubbles in Baryon-Free Quark-Gluon Plasma

    E-print Network

    Franco Ruggeri; William Friedman

    1995-11-30

    We evaluate the factor $\\kappa$ appearing in Langer's expression for the nucleation rate extended to the case of hadron bubbles forming in zero baryon number cooled quark-gluon plasma. We consider both the absence and presence of viscosity and show that viscous effects introduce only small changes in the value of $\\kappa$

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  18. X-ray imaging of an X-pinch plasma with a bubble compound refractive lens

    NASA Astrophysics Data System (ADS)

    Gary, C. K.; Pikuz, S. A.; Mitchell, M. D.; Chandler, K. M.; Shelkovenko, T. A.; Hammer, D. A.; Dudchik, Yu. I.

    2004-10-01

    We present diagnostic images taken of an X-pinch plasma x-ray source driven by the XP pulser (100 ns, 500 kA) at Cornell University using an x-ray bubble compound refractive lens. The lens consists of a 200 ?m inside diameter glass capillary that contains about 100 biconcave microlenses formed by a string of bubbles in epoxy. A precise system for lens alignment with of 3-5 arcmin accuracy is described. X-ray images of four-wire X pinches were obtained with a spatial resolution of approximately 2 ?m.

  19. Airglow-imaging observation of plasma bubble disappearance at geomagnetically conjugate points

    NASA Astrophysics Data System (ADS)

    Shiokawa, Kazuo; Otsuka, Yuichi; Lynn, Kenneth JW; Wilkinson, Philip; Tsugawa, Takuya

    2015-12-01

    We report the first observation of the disappearance of a plasma bubble over geomagnetically conjugate points. It was observed by airglow imagers at Darwin, Australia (magnetic latitude: -22°N) and Sata, Japan (21°N) on 8 August 2002. The plasma bubble was observed in 630-nm airglow images from 1530 (0030 LT) to 1800 UT (0300 LT) and disappeared equatorward at 1800 to 1900 UT (0300 to 0400 LT) in the field of view. The ionograms at Darwin and Yamagawa (20 km north of Sata) show strong spread-F signatures at approximately 16 to 21 UT. At Darwin, the F-layer virtual height suddenly increased from approximately 200 to approximately 260 km at the time of bubble disappearance. However, a similar F-layer height increase was not observed over the conjugate point at Yamagawa, indicating that this F-layer rise was caused not by an eastward electric field but by enhancement of the equatorward thermospheric wind over Darwin. We think that this enhancement of the equatorward neutral wind was caused by an equatorward-propagating large-scale traveling ionospheric disturbance, which was identified in the north-south keogram of 630-nm airglow images. We speculate that polarization electric field associated with this equatorward neutral wind drive plasma drift across the magnetic field line to cause the observed bubble disappearance.

  20. The ESPERIA equatorial, electromagnetic, plasma, and particle mission concerned with detecting preseismic related signals.

    NASA Astrophysics Data System (ADS)

    Sgrigna, V.; Esperia Team

    ESPERIA is an equatorial mission planned with a LEO small-satellite and a multi-instrument payload. The project has been ideally conceived to define the near-Earth electromagnetic, plasma, and particle environment, both in steady-state and perturbed-state conditions. In recent times has been observed that either Earth's interior processes or near-Earth space phenomena have a privileged and sensitive zone of investigation constituted by the ionosphere-magnetosphere transition region, at altitudes ranging around 500(1000 km. In fact, sun and cosmic rays as well as, seismic, anthropogenic and thunderstorm activities, influence the structure and dynamics of the zone. These external and internal contributions play an important role in defining the particle and electromagnetic field character of the region, both in steady-state and perturbed-state conditions. So, a suitable monitoring of the topside ionosphere may give an help in studying many important physical phenomena as pre-earthquake and anthropogenic electromagnetic emissions, solar wind and flares, as well as in mapping the geomagnetic field. The ESPERIA Phase A Study has been performed by an International Consortium lead by the University Roma Tre, within the Earth observation program for small scientific missions of the Italian Space Agency (ASI). The scientific objectives of the study are to plan an EM, plasma, and particle mission concerned with detecting tectonic, anthropogenic, and preseismic related EM signals. The primary aim of the mission is to study ionospheric and magnetospheric effects caused by seismicity to develop methods for the evaluation of seismic risk (providing for disaster assessment) and give contribution in earthquake forecasting studies. A secondary objective is the study of electromagnetic emissions of anthropogenic origin (power line harmonic radiation, VLF and HF transmitters) and their influence in the ionosphere and magnetosphere. To achieve the objectives with maximum reliability, ESPERIA is based with strong emphasis on coordinated, simultaneous, and continuous ground-based and space observations, as well as on mutual data comparison with other missions of similar quality. On board the satellite ULF(HF electromagnetic fields, fluxes of charged particle (200 keV(GeV), and ionospheric plasma temperature and density will be detected. Ground-based measurements of mechanical (tilt and strain) and electromagnetic fields will be carried out in several test areas of the Earth's surface.

  1. Searching for Quark-Gluon Plasma(QGP) Bubble effects at RHIC/LHC

    E-print Network

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

    2003-04-30

    Since the early eighties, we have shared with Leon Van Hove the following view. That if a QGP were produced in high energy heavy ion colliders, that its hadronization products would likely come from small localized in phase space bubbles of plasma. We develop a model based on HIJING, to which we added a ring of adjoining multiple bubbles in the central rapidity region. Our simulations were designed to be tested by the forthcoming RHIC STAR detector data for 65 GeV/n Au colliding with 65 GeV/n Au. We took into account background and resonance effects to allow a direct comparison with the data. Later 100 GeV/n Au colliding with 100 GeV/n Au and LHC data could also test these ideas. We used two charged particle correlation's as a sensitive method to test for bubbles.

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

    SciTech Connect

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

    2012-12-21

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

  3. Automated Detection and Tracking of Equatorial Plasma Depletions Using Ground-Based Optical Imagers

    NASA Astrophysics Data System (ADS)

    Pedersen, T.; Carrano, C.; Griffin, J.

    2004-12-01

    Optical imaging is one of the few means available for determining space weather parameters simultaneously over large areas, but tropospheric cloud cover presents a significant barrier to operational use of data from ground-based optical instruments. Distributed sensors experiencing different tropospheric conditions but with overlapping fields of view in the upper atmosphere are one possible solution to the cloud cover difficulty, while intelligent processing of imager data to discriminate between clouds and upper atmospheric features is another potential means of providing reliable data output from only a single instrument. We evaluate and discuss a variety of processing algorithms developed or adapted for the purpose of detecting and tracking equatorial plasma depletions in all-sky imager data under realistic conditions including significant cloud cover. Our most successful technique thus far relies on discrimination between depletions and other image features based on their signatures in velocity and correlation space rather than physical coordinates. In addition to allowing identification and tracking of the depletions, accurate knowledge of the velocity allows multiple frames of image data to be processed coherently in the reference frame moving with the depletions. This processing can virtually eliminate cloud effects up to 50 percent cloud cover. With externally provided velocity information (such as from a spaced-antenna scintillation system, for example) or an improved velocity algorithm, useful data can be obtained at even greater cloud cover fractions. A similar motion-based technique can also be applied to the background star field, allowing stars to be easily distinguished from pixel noise and hot pixels for rapid automatic identification of image regions affected by clouds without the need to identify, locate, or track any specific stars.

  4. Instabilities observed at the bubble edge of a laser produced plasma during its expansion in an ambient tenuous plasma

    NASA Astrophysics Data System (ADS)

    Lee, Bo Ram; Clark, S. E.; Hoffmann, D. H. H.; Niemann, C.

    2014-10-01

    The Raptor kJ class 1053 nm Nd:Glass laser in the Phoenix laser laboratory at University of California, Los Angeles, is used to ablate a dense debris plasma from a graphite or plastic target embedded in a tenuous, uniform, and quiescent ambient magnetized plasma in the Large Plasma Device (LAPD) which provides a peak plasma density of ni ~ 1013 cm-3. Its background magnetic field can vary between 200 and 1200 G. Debris ions from laser produced plasma expand out conically with super-Alfvénic speed (MA ~ 2) and expel the background magnetic field and ambient ions to form a diamagnetic bubble. The debris plasma interacts with the ambient plasma and the magnetic field and acts as a piston which can create collisionless shocks. Flute-type instabilities, which are probably large Larmor radius Rayleigh Taylor instabilities or lower hybrid drift instabilities, are developed at the bubble edge and also observed in the experiment. The amplitude and wavelength dependence of the instabilities, which might be a strong function of debris to ambient mass to charge ratio, is studied and the experimental results are compared to the two dimensional hybrid simulations. the Deutsche Forschungsgemeinschaft in the framework of the Excellence Initiative Darmstadt Graduate School of Energy Science and Engineering (GSC1070).

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

    NASA Astrophysics Data System (ADS)

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

    2008-04-01

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

  6. Evolution of Plasma-Exposed Tungsten Surfaces Due to Helium Diffusion and Bubble Growth

    NASA Astrophysics Data System (ADS)

    Hammond, Karl; Hu, Lin; Maroudas, Dimitrios; Wirth, Brian; PSI-SciDAC Team

    2013-10-01

    Helium from linear plasma devices and tokamak plasmas causes the formation of microscopic features, termed ``fuzz'' or ``coral,'' on the surface of plasma-exposed materials after only a few hours of plasma exposure. The details of such surface modifications are only beginning to be understood. This study examines the initial and intermediate stages of fuzz formation by large-length-scale molecular dynamics (MD) simulations of helium-implanted tungsten over time scales of up to microseconds using single-crystalline and polycrystalline supercell models of tungsten. The large-scale MD simulations employ state-of-the-art many-body interatomic potentials and implantation depth distributions for the insertion of helium atoms into the tungsten matrix constructed based on MD simulations of helium-atom impingement onto tungsten surfaces under prescribed thermal and implantation conditions. The large-scale MD simulations reveal surface features formed via the sequence of helium implantation, diffusion of helium atoms and their aggregation to form bubbles, growth of bubbles and consequent production of tungsten self-interstitial atoms, organization of those atoms into prismatic loops, glide of those loops to the surface, and bubble rupture.

  7. Multi-wavelength emission from the Fermi bubbles. I. Stochastic acceleration from background plasma

    SciTech Connect

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

    2014-07-20

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2008-11-01

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

  9. The causal relationship between plasma bubbles and blobs in the low-latitude F region during a solar minimum

    NASA Astrophysics Data System (ADS)

    Kil, Hyosub; Kwak, Young-Sil; Lee, Woo Kyoung; Miller, Ethan S.; Oh, Seung-Jun; Choi, Ho-Sung

    2015-05-01

    Plasma density depletions (bubbles) and enhancements (blobs) with respect to the background ionosphere occur at night in the low-latitude F region. Those phenomena are understood to be either causally linked or independent. The idea of the causal relationship between bubbles and blobs is on the basis of the observations of them in the same longitude. However, the occurrence of bubbles and blobs in the same longitude can also be just a coincidence. We investigate causal linkage of bubbles and blobs using the measurements of the ion density on 5 days in June 2008 and April 2009 by the Communication/Navigation Outage Forecasting System and CHAllenging Minisatellite Payload satellites. The observations during the solar minimum show that blobs occur in broader longitudes than do bubbles and occur in any longitudes regardless of the existence of bubbles. These observations indicate that a significant portion of blobs are not associated with bubbles. Even if some blobs are associated with bubbles, those blobs are indistinguishable from those produced by other sources. Therefore, the observations of bubbles and blobs at the same longitudes do not warrant their causal relationship. The independent behavior of bubbles and blobs rather indicates that their occurrences in the same longitudes are mostly coincidences. Considering the frequent occurrence of blobs near midnight, June solstice, and the solar minimum, medium-scale traveling ionospheric disturbances are likely the major source of blobs. This idea is supported by the observations of blobs with the ionospheric disturbances in broad longitudes and latitudes.

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

    SciTech Connect

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

    2003-03-01

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

  11. Electric field and plasma density measurements in the strongly driven daytime equatorial electrojet. 2. Two-stream waves

    SciTech Connect

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

    1987-12-01

    Both primary and secondary two-stream (Farley-Buneman) waves have been detected by in situ electric field and plasma density probes in the strongly driven daytime equatorial electrojet over Peru. Simultaneous Jicamarca radar observations showed strong vertical and oblique 3-m type 1 echoes, also indicative of the two-stream mechanism. The rocket data show the two-stream region on the topside of the unstable layer to be situated between 103 and 111 km where the electron current was the strongest.

  12. Upwelling: a unit of disturbance in equatorial spread F

    NASA Astrophysics Data System (ADS)

    Tsunoda, Roland T.

    2015-12-01

    Plasma structure in the nighttime equatorial F layer, often referred to as equatorial spread F (ESF), is not uniformly distributed, either in time or in space. Observations indicate that ESF in the bottomside F layer takes the form of patches; plasma structure within the F layer takes the form of localized plasma depletions, called equatorial plasma bubbles (EPBs), which tend to occur in clusters. Another observed feature is an upwelling, which has been described as a localized, upward modulation of isodensity contours in the bottomside F layer. Interestingly, zonal widths of ESF patches, EPB clusters, and upwellings are similar. Moreover, all display an east-west asymmetry. The objective of this paper is to show, for the first time, that an ESF patch is the bottomside counterpart of an EPB cluster, and that both are products of the electrodynamical process that takes place within an upwelling. The process can be described as having three phases: (1) amplification of upwelling amplitude during the post-sunset rise of the F layer, (2) launching of the first EPB of the evening, from crest of the upwelling, and (3) structuring of plasma within the upwelling. Hence, an upwelling, whose presence is responsible for the formation of ESF patches and EPB clusters, can be envisioned as a unit of disturbance that occurs in the nighttime equatorial ionosphere.

  13. On the Current System and Electric Field Associated with the Boundary of Plasma Bubble

    NASA Astrophysics Data System (ADS)

    Sun, W.; Fu, S.; Parks, G. K.; Pu, Z.; Slavin, J. A.

    2014-12-01

    The current and electric fields associated with the dipolarization fronts (DFs, the leading edge of plasma bubble) have been investigated in the magnetotail plasma sheet using Cluster multi-point observations. We have studied each term in the generalized Ohm's law and showed that electric fields are directed normal to the DF in the magnetic dip region ahead of the DF as well as in the DF layer but in opposite directions in the plasma flow frame. The ions decouple from the magnetic field in the DF layer and dip region, whereas electrons remain frozen-in [Sun et al., 2014]. The field-aligned current on the DFs is similar to region-1-sense and is similar to region-2-sense just earthward of the boundary [Sun et al., 2013]. Further study has revealed a full picture of current system associated with the boundary of plasma bubble. Sun, W. J., et al. (2013), Field-aligned currents associated with dipolarization fronts, Geophys. Res. Lett., 40, 4503-4508, doi:10.1002/grl.50902. Sun, W.-J., et al. (2014), Electric fields associated with dipolarization fronts, J. Geophys. Res. Space Physics, 119, doi:10.1002/2014JA020045.

  14. Observations of day-to-day variability in precursor signatures to equatorial F-region plasma depletions

    NASA Astrophysics Data System (ADS)

    Fagundes, P. R.; Sahai, Y.; Batista, I. S.; Abdu, M. A.; Bittencourt, J. A.; Takahashi, H.

    1999-08-01

    In December 1995, a campaign was carried out to study the day-to-day variability in precursor signatures to large-scale ionospheric F-region plasma irregularities, using optical diagnostic techniques, near the magnetic equator in the Brazilian sector. Three instruments were operated simultaneously: (a) an all-sky (180° field of view) imaging system for observing the OI 630 nm nightglow emission at Alcântara (2.5°S, 44.4°W); (b) a digisonde (256-Lowell) at São Luis (2.6°S, 44.2°W); and (c) a multi-channel tilting filter-type zenith photometer for observing the OI 630 nm and mesospheric nightglow emissions at Fortaleza (3.9°S, 38.4°W). During the period December 14-18, 1995 (summer in the southern hemisphere), a good sequence of the OI 630 nm imaging observations on five consecutive nights were obtained, which are presented and discussed in this study. The observing period was geomagnetically quiet to moderate (Kp = 0+ to 5+; Dst = 18 nT to -37 nT). On four nights, out of the five observation nights, the OI 630 nm imaging pictures showed formations of transequatorial north-south aligned intensity depletions, which are the optical signatures of large-scale ionospheric F-region plasma bubbles. However, considerable day-to-day variability in the onset and development of the plasma depleted bands was observed. On one of the nights it appears that the rapid uplifting of the F-layer in the post-sunset period, in conjunction with gravity wave activity at mesospheric heights, resulted in generation of very strong plasma bubble irregularities. One of the nights showed an unusual formation of north-south depleted band in the western sector of the imaging system field of view, but the structure did not show any eastward movement, which is a normal characteristic of plasma bubbles. This type of irregularity structure, which probably can be observed only by wide-angle imaging system, needs more investigations for a better understanding of its behaviour.

  15. Relationships between plasma lipids, proteins, surface tension and post-dive bubbles.

    PubMed

    Schellart, Nico A M; Rozložník, Miroslav; Balestra, Costantino

    2015-01-01

    Decompression sickness (DCS) in divers is caused by bubbles of inert gas. When DCS occurs, most bubbles can be found in the venous circulation: venous gas emboli (VGE). Bubbles are thought to be stabilized by low molecular weight surfactant reducing the plasma-air surface tension (?). Proteins may play a role as well. We studied the interrelations between these substances, ? and VGE, measured before and after a dry dive simulation. VGE of 63 dive simulations (21-msw/40-minute profile) of 52 divers was examined 40, 80, 120 and 160 minutes after surfacing (precordial Doppler method) and albumin, total protein, triglycerides, total cholesterol and free fatty acids were determined pre- and post-exposure. To manipulate blood plasma composition, half of the subjects obtained a fat-rich breakfast, while the other half got a fat-poor breakfast pre-dive. Eleven subjects obtained both. VGE scores measured with the precordial Doppler method were transformed to the logarithm of Kisman Integrated Severity Scores. With statistical analysis, including (partial) correlations, it could not be established whether ? as well as VGE scores are related to albumin, total protein or total cholesterol. With triglycerides and fatty acids correlations were also lacking, despite the fact that these compounds varied substantially. The same holds true for the paired differences between the two exposures of the 11 subjects. Moreover, no correlation between surface tension and VGE could be shown. From these findings and some theoretical considerations it seems likely that proteins lower surface tension rather than lipids. Since the findings are not in concordance with the classical surfactant hypothesis, reconsideration seems necessary. PMID:26094288

  16. Waves in Space Plasmas Program

    NASA Technical Reports Server (NTRS)

    Fredricks, R. W.; Taylor, W. W. L.

    1981-01-01

    The Waves in Space Plasmas (WISP) program is a joint international effort involving instrumentation to be designed and fabricated by funding from NASA and the National Research Council of Canada. The instrumentation, with a tentatively planned payload for 1986, can be used to perturb the plasma with radio waves to solve problems in ionospheric, atmospheric, magnetospheric, and plasma physics. Among the ionospheric and plasma phenomena to be investigated using WISP instrumentation are VLF wave-particle interactions; ELF/VLF propagation; traveling ionospheric disturbances and gravity wave coupling; equatorial plasma bubble phenomena; plasma wave physics such as mode-coupling, dispersion, and instabilities; and plasma physics of the antenna-plasma interactions.

  17. 5-50-m wavelength plasma instabilities in the equatorial electrojet 2. Two-stream conditions

    SciTech Connect

    Hanuise, C.; Crochet, M.

    1981-05-01

    New multifrequency measurements with a HF radar in the equatorial electrojet have extended the range of wavelengths investigated during high drift velocity conditions to 50 m. It is shown that the socalled type 1 spectra can be detected at all wavelengths. Their phase velocity has a value given by the threshold for instability in the full dispersion equation and is constant with elevation angle and time when corrected for neutral wind effect. Spectral width increases with wave number, following a law K/sup n/, napprox.0.7, but is constant with elevation angle. Ratio of spectral width to mean Doppler shift is of the order of unity at the lowest wave number and decrease as K/sup -n/, napprox.0.6. These results are compared to the existing numerical simulations and theoretical works.

  18. The Longitudinal Variation of Equatorial Electrodynamics Observations

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  19. 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)

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

    2013-04-01

    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.

  20. Ionospheric vertical plasma drift and electron density response during total solar eclipses at equatorial/low latitude

    NASA Astrophysics Data System (ADS)

    Adekoya, B. J.; Chukwuma, V. U.; Reinisch, B. W.

    2015-09-01

    The response of the vertical plasma drift (Vz) and the electron density (NmF2) during different solar eclipses was investigated. The diurnal values of the direct scaled measurement of F2 peak height and the one derived from M(3000) F2 data, acquired over an equatorial/low-latitude stations, have been used to determine the vertical plasma drift. The ionosphere during a solar eclipse is significantly affected by the E × B vertical drift; the large depletion of electron density at low altitudes can be transported to high altitudes through the plasma vertical drift. The loss in ionization density during the eclipse phase decreases the electron density, which was accompanied by rapid increase in hmF2. This deviation in the NmF2 during eclipse compared to control days can be related to the increase in the loss rate due to recombination, as a result of reduction in thermal energy. However, the maximum reduction in NmF2 is not synchronous with the time of maximum totality but some minutes later. The differences in the solar epochs may contribute to the observed relative changes in the ionospheric F2 region behavior during the eclipse window. Lastly, it is very difficult to separate the influence of magnetic disturbances from solar eclipse. The deviation in NmF2 is higher during magnetic disturbed days than the quiet day. The reverse is the case for hmF2 observation. However, the NmF2 variation increases with an increase in solar activity.

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

    E-print Network

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

    2003-01-13

    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

  2. The dependence of pulsating auroral events on energetic electrons and cold plasma near the equatorial plane

    SciTech Connect

    Nemzek, R.J.; Belian, R.D.; McComas, D.J.; Thomsen, M.F. ); Nakamura, R.; Baker, D.N. . Goddard Space Flight Center); Yamamoto, T. )

    1992-01-01

    Pulsating auroras are a substorm recovery phase phenomenon, occurring shortly after an auroral breakup. The current theory of the pulsating aurora involves a relaxation oscillator'' mechanism requiring a population of high-energy (10's of keV) electrons and a low-energy plasma number density on the order of a few particles per cm{sup 3}. We investigated this relationship by comparing energetic electron and plasma data from a geosynchronous satellite to pulsating auroras recorded by an all-sky video camera which contained the satellite's ionospheric conjugate point in its field of view. Pulsating auroral events were generally closely connected to substorm injections on the satellite, but there was no clear correlation with changes in plasma density. During all of the events the density was in an acceptable range for the relaxation oscillator mechanism to function. The relationship to substorm injections impiles that the pulsating aurora can be used to map the substorm injection region down to the ionosphere. An unusual diminishing of the pulsating aurora during the growth phase of a subsequent substorm was also discovered.

  3. The dependence of pulsating auroral events on energetic electrons and cold plasma near the equatorial plane

    SciTech Connect

    Nemzek, R.J.; Belian, R.D.; McComas, D.J.; Thomsen, M.F.; Nakamura, R.; Baker, D.N.; Yamamoto, T.

    1992-10-01

    Pulsating auroras are a substorm recovery phase phenomenon, occurring shortly after an auroral breakup. The current theory of the pulsating aurora involves a ``relaxation oscillator`` mechanism requiring a population of high-energy (10`s of keV) electrons and a low-energy plasma number density on the order of a few particles per cm{sup 3}. We investigated this relationship by comparing energetic electron and plasma data from a geosynchronous satellite to pulsating auroras recorded by an all-sky video camera which contained the satellite`s ionospheric conjugate point in its field of view. Pulsating auroral events were generally closely connected to substorm injections on the satellite, but there was no clear correlation with changes in plasma density. During all of the events the density was in an acceptable range for the relaxation oscillator mechanism to function. The relationship to substorm injections impiles that the pulsating aurora can be used to map the substorm injection region down to the ionosphere. An unusual diminishing of the pulsating aurora during the growth phase of a subsequent substorm was also discovered.

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

    NASA Technical Reports Server (NTRS)

    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

    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.

  5. On the Azimuthal Variation of Core Plasma in the Equatorial Magnetosphere

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    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.

  6. On the height variation of the equatorial F region vertical plasma drifts

    SciTech Connect

    Pingree, J.E.; Fejer, B.G. )

    1987-05-01

    The authors have used improved incoherent scatter radar measurements at the Jicamarca Radio Observatory to study the height variation of the F region vertical plasma drift velocity (driven by the zonal electric field) during moderately quiet conditions. Preliminary results indicate a nearly linear change of the vertical drift velocity with altitude between 200 and 700 km, but with considerable day-to-day variations in the value of the slope. On the average, the velocity gradients are positive in the late night and morning periods and negative during the afternoon and evening hours. Simultaneous vertical and zonal drift measurements confirm that the measured height variation of the vertical drift is consistent with the existence of a curl free electric field in the low latitude ionosphere. The time dependence of the Jicamarca vertical drifts extrapolated to higher altitudes closely resembles the diurnal variation of the drift component due to the zonal electric field observed at F region heights over Arecibo.

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

    PubMed

    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

    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

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

    PubMed Central

    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

    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

  9. Variability of the ionospheric plasma density, NmF2, and of Total Electron Content, TEC, over equatorial and low latitude region in Brazil during solar minimum activity

    NASA Astrophysics Data System (ADS)

    Candido, Claudia; Batista, Inez S.; Negreti, Patricia M. S.; Klausner, Virginia

    The recent solar minimum period was unusually deep and prolonged, which opened a window to observe the ionospheric behavior under unprecedented low solar activity conditions. This work is part of a multi-instrumental effort to investigate the equatorial and low latitude ionosphere over Brazilian sector during low solar activity. We present a study of the ionospheric plasma densities variations through ionosondes measurements and dual frequency GPS receivers (L1= 1275.4 MHz, L2 = 1227.6 MHz) for two equatorial stations, Sao Luis (3° S, 45º W) e Fortaleza (4° S, 39.5° W), and for a station close to the south crest of the equatorial ionization anomaly region, Cachoeira Paulista (23º S, 45º W). From ionosondes we extract the plasma critical frequency foF2 which is related to F2 region peak electron density, NmF2, by the relationship: NmF2 = 1.24 x 104 (foF2)2, and the F2 layer peak height, hmF2. From GPS receivers we used the quantity VTEC (Vertical total electron content). We analyzed the seasonal and local time variations of NmF2 and VTEC, as well as the differences between two solar minima, 2008-2009 and 1996. We observe that the ionospheric plasma densities were lower in 2008-2009 than in 1996 for both regions. In addition, we observe that the lowest plasma densities persisted longer during 2008/2009 than in 1996, especially for nighttime periods. Finally, we applied the wavelet technique to investigate the impact of some distinct time scales drivers on the ionosphere, such as the wave activity from below that seems have been better observed and appreciated during this unusual solar quiescence.

  10. Hot bubbles of planetary nebulae with hydrogen-deficient winds I. Heat conduction in a chemically stratified plasma

    E-print Network

    Sandin, Christer; Schönberner, Detlef; Rühling, Ute

    2015-01-01

    Heat conduction has been found a plausible solution to explain discrepancies between expected and measured temperatures in hot bubbles of planetary nebulae (PNe). While the heat conduction process depends on the chemical composition, to date it has been exclusively studied for pure hydrogen plasmas in PNe. A smaller population of PNe show hydrogen-deficient and helium- and carbon-enriched surfaces surrounded by bubbles of the same composition; considerable differences are expected in physical properties of these objects in comparison to the pure hydrogen case. The aim of this study is to explore how a chemistry-dependent formulation of the heat conduction affects physical properties and how it affects the X-ray emission from PN bubbles of hydrogen-deficient stars. We extend the description of heat conduction in our radiation hydrodynamics code to work with any chemical composition. We then compare the bubble-formation process with a representative PN model using both the new and the old descriptions. We also ...

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

    SciTech Connect

    FISHER,RK

    2003-02-01

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

  12. Equatorial Guinea.

    PubMed

    1989-03-01

    Equatorial Guinea is situated on the Gulf of Guinea along the west African coast between Cameroon and Gabon. The people are predominantly of Bantu origin. The country's ties with Spain are significant; in 1959, it became the Spanish Equatorial region ruled by Spain's commissioner general. Recent political developments in Equatorial Guinea include the formation of the Democratic Party for Equatorial Guinea in July of 1987 and the formation of a 60-member unicameral Chamber of Representatives of the People in 1983. Concerning the population, 83% of the people are Catholic and the official language is Spanish. Poverty and serious health, education and sanitary problems exist. There is no adequate hospital and few trained physicians, no dentists, and no opticians. Malaria is endemic and immunization for yellow fever is required for entrance into the country. The water is not potable and many visitors to the country bring bottled water. The tropical climate of Equatorial Guinea provides the climate for the country's largest exports and source of economy; cacao, wood and coffee. Although the country, as a whole, has progressed towards developing a participatory political system, there are still problems of governmental corruption in the face of grave health and welfare conditions. In recent years, the country has received assistance from the World Bank and the United States to aid in its development. PMID:12177983

  13. 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)

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

    1987-01-01

    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.

  14. Determination of dynamical changes in sputtering and retention on bubble-growing tungsten under helium plasma irradiation by binary-collision-approximation-based simulation

    NASA Astrophysics Data System (ADS)

    Saito, Seiki; Nakamura, Hiroaki; Tokitani, Masayuki; Sakaue, Ryota; Yoshida, Kenta

    2016-01-01

    Binary-collision-approximation-based (BCA) simulation is performed for the investigation of bubble formation and the influence of the growth of bubbles on the characteristics of tungsten as a plasma-facing material. The BCA simulation provides the time evolution of the surface modification, the sputtering yield of tungsten atoms, and the absorption rate and retention of helium atoms for incident energies from 100 to 1000 eV and fluences up to 1.0 × 1022 He/m2. The following results are obtained: the tungsten material is eroded by repeated swelling and exfoliation near the surface, the sputtering yield of the bubble-formimg tungsten is lower than that of a material without bubbles, and the absorption rate increases as bubbles grow.

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  16. Electric field and plasma density measurements in the strongly driven daytime equatorial electroject. 1. The unstable layer and gradient drift waves

    SciTech Connect

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

    1987-12-01

    Electric field and plasma density instrumentation on board a sounding rocket launched from Punta Lobos, Peru, detected intense electrostatic waves indicative of plasma instabilities in the daytime equatorial electrojet. Simultaneous measurements taken by the Jicamarca radar showed strong 3-m type 1 electrojet echoes as well as evidence of kilometer scale horizontally propagating waves. The in situ electric field wave spectra displayed three markedly different height regions within the unstable layer: (1) a two-stream region on the topside between 103 and 111 km where the electron current was considered to be strongest, (2) a gradient drift region between 90 and 106.5 km wher the upward directed, zero-order electron density gradient was unstable, and (3) an ''interaction'' region between 103 and 106.5 km where both of these instabilities were linearly unstable. The unstable altitudes and differentiation showed good agreement with the simultaneous 3-m Jicamarca backscatter radar observations.

  17. Synchrotron Radiation from a Laser Plasma Accelerator in the Bubble Regime

    SciTech Connect

    Kneip, S.; McGuffey, C.; Chvykov, V.; Dollar, F.; Kalintchenko, G.; Maksimchuk, T.; Matsuoka, T.; Thomas, A. G. R.; Krushelnick, K.; Mangles, S. P. D.; Nagel, S. R.; Palmer, C. A. J.; Schreiber, J.; Najmudin, Z.; Ta Phuoc, K.

    2010-11-04

    A laser wakefield accelerator is shown to operate in the highly non-linear bubble regime, following the characteristic scaling of energy gain with density and leading to monoenergetic electron beams with up to 400 MeV and hundreds of pC charge. The bubble acts at the same time as a miniature undulator, causing the electrons to give off a beam of betatron x-rays with milliradian divergence, {mu}m source size, 1-100 keV photon energy and 10{sup 22} ph/mm{sup 2}/mrad{sup 2}s/0.1% BW.

  18. Equatorial Guinea.

    PubMed

    1984-06-01

    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

  19. A Modeling Study of the Latitudinal Variations in the Nighttime Plasma Temperatures of the Equatorial Topside Ionosphere During Northern Winter at Solar Maximum

    NASA Technical Reports Server (NTRS)

    Bailey, G. J.; Denton, M. H.; Heelis, R. A.; Venkatraman, S.

    2000-01-01

    Latitudinal variations in the nighttime plasma temperatures of the equatorial topside ionosphere during northern winter at solar maximum have been examined by using values modelled by SUPIM (Sheffield University Plasmasphere Ionosphere Model) and observations made by the DMSP F10 satellite at 21.00 LT near 800 km altitude. The modelled values confirm that the crests observed near 15 deg latitude in the winter hemisphere are due to adiabatic heating and the troughs observed near the magnetic equator are due to adiabatic cooling as plasma is transported along the magnetic field lines from the summer hemisphere to the winter hemisphere. The modelled values also confirm that the interhemispheric plasma transport needed to produce the required adiabatic heating/cooling can be induced by F-region neutral winds. It is shown that the longitudinal variations in the observed troughs and crests arise mainly from the longitudinal variations in the magnetic meridional wind. At longitudes where the magnetic declination angle is positive the eastward geographic zonal wind combines with the northward (summer hemisphere to winter hemisphere) geographic meridional wind to enhance the northward magnetic meridional wind. This leads to deeper troughs and enhanced crests. At longitudes where the magnetic declination angle is negative the eastward geographic zonal wind opposes the northward geographic meridional wind and the trough depth and crest values are reduced. The characteristic features of the troughs and crests depend, in a complicated manner, on the field-aligned flow of plasma, thermal conduction, and inter-gas heat transfer. At the latitudes of the troughs/crests, the low/high plasma temperatures lead to increased/decreased plasma concentrations.

  20. Automatically identification of Equatorial Spread-F occurrence on ionograms

    NASA Astrophysics Data System (ADS)

    Pillat, Valdir Gil; Fagundes, Paulo Roberto; Guimarães, Lamartine Nogueira Frutuoso

    2015-12-01

    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 in 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. With advancement of digital ionosonde, it is now possible to carry out an ionospheric sounding with a cadence of 5 min or even with 1-minute cadence. To analyse a large amount of ionograms, more sophisticated tools are needed. Thus, development of algorithms to identify and analyse different aspects of ionograms has become very important to space science researchers. 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 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 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 of Spread-F occurrence was compared with those obtained manually and good agreement was found.

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

    NASA Astrophysics Data System (ADS)

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

    2005-08-01

    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.

  2. Proposal for a Longitudinal Network of Upper Atmosphere Diagnostics for the Dip Equatorial Region: Scientific need and Expected Outcome (P41)

    NASA Astrophysics Data System (ADS)

    Sastri, J. H.

    2006-11-01

    It is increasingly being realized that the unique characteristics of the plasma and neutral domains of the equatorial upper atmosphere exhibit significant longitudinal dependence both during geomagnetically quiet and disturbed periods. The spatial variability of the diurnal development of the equatorial electrojet (EEJ) and of the equatorial ionization anomaly (EIA), post-sunset generation and non-linear development of equatorial F region plasma density irregularities (plasma bubbles) and forenoon bite-out in F-layer peak density at the EIA rest location and the equatorial midnight temperature maximum (MTM) typifies the longitudinal dependence of the equatorial upper atmosphere system. One of the major scientific needs of the times is therefore to capture and comprehend the longitudinal dependence in all its detail so as to advance our understanding of the equatorial system which reflects, among other things, the myriad couplings within the near- Earth space environment. This calls for the deployment and operation close to the magnetic equator of cost-effective sensors optimally distributed in longitude taking advantage of the landmass in India and its neighborhood, South-East Asia and Brazil. It is worthwhile to note in this context that the thrust of experimental activity thus far had been towards establishment of latitudinal chain(s) of upper atmosphere diagnostics. The sensors that can be deployed as equatorial networks are low cost ionosondes, TEC and VHF/UHF/L-band scintillation monitors, day airglow/night airglow photometers and all-sky imagers, to name a few. This will help derive important information on the longitudinal structures of various scale sizes in the plasma and neutral atmosphere parameters. The recent work of Tsunoda (GRL, Vol 32, L08103, 2005), in fact, revealed the possible role and relevance of the large-scale wave structure (LSWS) in the plasma density of bottom side F-layer to the enigmatic day-to-day variability of equatorial spread-F, and highlighted the need for a cluster of longitudinally distributed ground-based sensors to monitor the upper atmosphere parameters. The Indian scientific community actively seeks and/or contributes to international collaborative and cooperative efforts aimed at the establishment and operation of equatorial ground based networks of radio and optical diagnostics under IHY program in the forthcoming years.

  3. South Atlantic magnetic anomaly ionization: A review and a new focus on electrodynamic effects in the equatorial ionosphere

    NASA Astrophysics Data System (ADS)

    Abdu, M. A.; Batista, I. S.; Carrasco, A. J.; Brum, C. G. M.

    2005-12-01

    Satellite observations of enhanced energetic particle fluxes in the South Atlantic Magnetic Anomaly (SAMA) region have been supported by ground-based observations of enhanced ionization induced by particle precipitation in the ionosphere over this region. Past observations using a variety of instruments such as vertical sounding ionosondes, riometers and VLF receivers have provided evidences of the enhanced ionization due to energetic particle precipitation in the ionosphere over Brazil. The extra ionization at E-layer heights could produce enhanced ionospheric conductivity within and around the SAMA region. The energetic particle ionization source that is operative even under “quiet” conditions can undergo significant enhancements during magnetospheric storm disturbances, when the geographic region of enhanced ionospheric conductivity can extend to magnetic latitudes closer to the equator where the magnetic field line coupling of the E and F regions plays a key role in the electrodynamics of the equatorial ionosphere. Of particular interest are the sunset electrodynamic processes responsible for equatorial spread F/plasma bubble irregularity generation and related dynamics (zonal and vertical drifts, etc.). The SAMA represents a source of significant longitudinal variability in the global description of the equatorial spread F irregularity phenomenon. Recent results from digital ionosondes operated at Fortaleza and Cachoeira Paulista have provided evidence that enhanced ionization due to particle precipitation associated with magnetic disturbances, in the SAMA region, can indeed significantly influence the equatorial electrodynamic processes leading to plasma irregularity generation and dynamics. Disturbance magnetospheric electric fields that penetrate the equatorial latitudes during storm events seem to be intensified in the SAMA region based on ground-based and satellite-borne measurements. This paper will review our current understanding of the influence of SAMA on the equatorial electrodynamic processes from the perspective outlined above.

  4. Effect of small-scale plasma turbulence on altitude profiles of electron drift velocity in the equatorial electrojet: An experimental study

    SciTech Connect

    Murthy, B.V.K.; Ravindran, S.

    1994-10-01

    The authors report recent observations of the effect of turbulence on the altitude behavior of the equatorial electrojet. Their results show that with an increase in observed turbulence that the altitude of maximum in the electron drift velocity shifts to higher altitudes. This is consistent with recent theoretical work which shows that small scale turbulence can produce large-scale changes in the dynamics of the equatorial electrojet.

  5. Equatorial MU Radar project

    NASA Astrophysics Data System (ADS)

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

    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.

  6. Doughnut-shaped soap bubbles

    E-print Network

    Deison Preve; Alberto Saa

    2015-09-26

    Soap bubbles are thin liquid films enclosing a fixed volume of air. Since the surface tension is typically assumed to be the only responsible for conforming the soap bubble shape, the realized bubble surfaces are always minimal area ones. Here, we consider the problem of finding the axisymmetric minimal area surface enclosing a fixed volume $V$ and with a fixed equatorial perimeter $L$. It is well known that the sphere is the solution for $V=L^3/6\\pi^2$, and this is indeed the case of a free soap bubble, for instance. Surprisingly, we show that for $Vformed by the juxtaposition of two spherical caps, but rather a toroidal surface. Practically, a doughnut-shaped bubble is known to be ultimately unstable and, hence, it will eventually lose its axisymmetry by breaking apart in smaller bubbles. Indisputably, however, the topological transition from spherical to toroidal surfaces is mandatory here for obtaining the global solution for this axisymmetric isoperimetric problem. Our result suggests that deformed bubbles with $Vfoams, for instance.

  7. Doughnut-shaped soap bubbles

    NASA Astrophysics Data System (ADS)

    Préve, Deison; Saa, Alberto

    2015-10-01

    Soap bubbles are thin liquid films enclosing a fixed volume of air. Since the surface tension is typically assumed to be the only factor responsible for conforming the soap bubble shape, the realized bubble surfaces are always minimal area ones. Here, we consider the problem of finding the axisymmetric minimal area surface enclosing a fixed volume V and with a fixed equatorial perimeter L . It is well known that the sphere is the solution for V =L3/6 ?2 , and this is indeed the case of a free soap bubble, for instance. Surprisingly, we show that for V bubble is known to be ultimately unstable and, hence, it will eventually lose its axisymmetry by breaking apart in smaller bubbles. Indisputably, however, the topological transition from spherical to toroidal surfaces is mandatory here for obtaining the global solution for this axisymmetric isoperimetric problem. Our result suggests that deformed bubbles with V

  8. Doughnut-shaped soap bubbles.

    PubMed

    Préve, Deison; Saa, Alberto

    2015-10-01

    Soap bubbles are thin liquid films enclosing a fixed volume of air. Since the surface tension is typically assumed to be the only factor responsible for conforming the soap bubble shape, the realized bubble surfaces are always minimal area ones. Here, we consider the problem of finding the axisymmetric minimal area surface enclosing a fixed volume V and with a fixed equatorial perimeter L. It is well known that the sphere is the solution for V=L^{3}/6?^{2}, and this is indeed the case of a free soap bubble, for instance. Surprisingly, we show that for Vbubble is known to be ultimately unstable and, hence, it will eventually lose its axisymmetry by breaking apart in smaller bubbles. Indisputably, however, the topological transition from spherical to toroidal surfaces is mandatory here for obtaining the global solution for this axisymmetric isoperimetric problem. Our result suggests that deformed bubbles with V

  9. Synchronised electrical monitoring and high speed video of bubble growth associated with individual discharges during plasma electrolytic oxidation

    NASA Astrophysics Data System (ADS)

    Troughton, S. C.; Nominé, A.; Nominé, A. V.; Henrion, G.; Clyne, T. W.

    2015-12-01

    Synchronised electrical current and high speed video information are presented from individual discharges on Al substrates during PEO processing. Exposure time was 8 ?s and linear spatial resolution 9 ?m. Image sequences were captured for periods of 2 s, during which the sample surface was illuminated with short duration flashes (revealing bubbles formed where the discharge reached the surface of the coating). Correlations were thus established between discharge current, light emission from the discharge channel and (externally-illuminated) dimensions of the bubble as it expanded and contracted. Bubbles reached radii of 500 ?m, within periods of 100 ?s, with peak growth velocity about 10 m/s. It is deduced that bubble growth occurs as a consequence of the progressive volatilisation of water (electrolyte), without substantial increases in either pressure or temperature within the bubble. Current continues to flow through the discharge as the bubble expands, and this growth (and the related increase in electrical resistance) is thought to be responsible for the current being cut off (soon after the point of maximum radius). A semi-quantitative audit is presented of the transformations between different forms of energy that take place during the lifetime of a discharge.

  10. Wave structure and polarization electric field development in the bottomside F layer leading to postsunset equatorial spread F

    NASA Astrophysics Data System (ADS)

    Abdu, M. A.; Souza, J. R.; Kherani, E. A.; Batista, I. S.; MacDougall, J. W.; Sobral, J. H. A.

    2015-08-01

    In this paper we present the results of a study on the characteristics of large-scale wave structure in the equatorial ionospheric F region that serve as precursor to postsunset development of the spread F/plasma bubble irregularities. The study is based on analysis of Digisonde data from three equatorial sites in Brazil (Fortaleza, Sao Luis, and Cachimbo) for a period of about 2 months at a medium solar activity phase. Small-amplitude oscillations in the F layer heights, extracted at a number of plasma frequencies, present characteristics as them being generated from upward propagating gravity waves. They represent wave structures in polarization electric field having zonal scale of a few hundred kilometers. Their amplitudes in the afternoon hours undergo amplification toward evening, leading to postsunset development of equatorial spread F/plasma bubble irregularities, on a statistical basis. On the days of their larger amplitudes they appear to occur in phase coherence on all days, and correspondingly, the evening prereversal vertical drift velocities are larger than on days of the smaller amplitudes of the wave structure that appear at random phase on the different days. The sustenance of these precursor wave structures is supported by the relatively large ratio (approaching unity) of the F region-to-total field line-integrated Pedersen conductivities as calculated using the Sheffield University Plasmasphere-Ionosphere Model simulation of the low-latitude ionosphere. The significant amplification in the wave structure toward sunset and the "phase coherent" nature of their occurrences on different days are explained tentatively on the basis of the spatial resonance mechanism.

  11. Recalcitrant bubbles.

    PubMed

    Shanahan, Martin E R; Sefiane, Khellil

    2014-01-01

    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

  12. Recalcitrant bubbles

    PubMed Central

    Shanahan, Martin E. R.; Sefiane, Khellil

    2014-01-01

    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

  13. Fringe field dynamics over equatorial and low-latitude ionosphere: A three-dimensional perspective

    NASA Astrophysics Data System (ADS)

    Kherani, E. A.; Patra, A. K.

    2015-08-01

    This paper presents a three-dimensional simulation of the collisional interchange instability generating equatorial plasma bubble (EPB) in the evening ionospheric F region and associated fringe field (FF) in the valley-upper-E (VE) region. This simulation is primarily intended to address hitherto unexplained radar observations of ascending irregularity structures only in the vicinity of the magnetic equator in association with the EPB phenomenon. Novel results of the present simulation are the following: (1) EPB-associated FF penetrating into the E region is found to be confined to a latitude belt of ±5?, (2) ascending irregularity structures from the E region is formed only when perturbation in plasma parameters similar to those responsible for forming EPB are present in the VE region, and (3) perturbation in the VE region provide conditions for the formation of ascending irregularity structures on the eastern wall of the plasma bubble. These results are in excellent agreement with radar observations and also account for the presence of metallic ions in the EPB at and above the F region peak.

  14. Prediction of the level of ionospheric scintillation at equatorial latitudes in Brazil using a neural network

    NASA Astrophysics Data System (ADS)

    Lima, G. R. T.; Stephany, S.; Paula, E. R.; Batista, I. S.; Abdu, M. A.

    2015-08-01

    Electron density irregularity structures, often associated with ionospheric plasma bubbles, drive amplitude and phase fluctuations in radio signals that, in turn, create a phenomenon known as ionospheric scintillation. The phenomenon occurs frequently around the magnetic equator where plasma instability mechanisms generate postsunset plasma bubbles and density depletions. A previous correlation study suggested that scintillation at the magnetic equator may provide a forecast of subsequent scintillation at the equatorial ionization anomaly southern peak. In this work, it is proposed to predict the level of scintillation over São Luís (2.52°S, 44.3°W; dip latitude: ~2.5°S) near the magnetic equator with lead time of hours but without specifying the moment at which the scintillation starts or ends. A collection of extended databases relating scintillation to ionospheric variables for São Luís is employed to perform the training of an artificial neural network with a new architecture. Two classes are considered, not strong (null/weak/moderate) and strong scintillation. An innovative scheme preprocesses the data taking into account similarities of the values of the variables for the same class. A formerly proposed resampling heuristic is employed to provide a balanced number of tuples of each class in the training set. Tests were performed showing that the proposed neural network is able to predict the level of scintillation over the station on the evening ahead of the data sample considered between 17:30 and 19:00 LT.

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

    PubMed

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

    2013-11-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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.

  17. Characteristics of an underwater direct current discharge in bubbles and the temperature distribution in the bubbles

    NASA Astrophysics Data System (ADS)

    Xiong, Ranhua; Nikiforov, Anton Yu.; Vanraes, Patrick; Leys, Christophe

    2012-02-01

    An underwater direct current (DC) discharge in artificially produced air bubbles is investigated. Electrical and optical emission properties of the plasma and temperature distribution in bubbles evaluated by using computational fluid dynamics (CFD) are presented. The behavior of plasma inside a bubble significantly depends on the bubble size. The discharge with water as a cathode is characterized by streamer nature, whereas the plasma with water as an anode appears diffuse and homogenous. The gas temperature is estimated from emission of the plasma, and it is much higher when water is a cathode. Bubble dynamics is investigated by CFD simulation, and results are in good agreement with experimental data. It shows the temperature distribution in bubbles strongly depends on the bubble dynamics, and gas-water interface has a sharp temperature gradient and acts as an efficient heat sink.

  18. Doughnut-shaped soap bubbles

    E-print Network

    Preve, Deison

    2015-01-01

    Soap bubbles are thin liquid films enclosing a fixed volume of air. Since the surface tension is typically assumed to be the only responsible for conforming the soap bubble shape, the realized bubble surfaces are always minimal area ones. Here, we consider the problem of finding the axisymmetric minimal area surface enclosing a fixed volume $V$ and with a fixed equatorial perimeter $L$. It is well known that the sphere is the solution for $V=L^3/6\\pi^2$, and this is indeed the case of a free soap bubble, for instance. Surprisingly, we show that for $V<\\alpha L^3/6\\pi^2$, with $\\alpha\\approx 0.21$, such a surface cannot be the usual lens-shaped surface formed by the juxtaposition of two spherical caps, but rather a toroidal surface. Practically, a doughnut-shaped bubble is known to be ultimately unstable and, hence, it will eventually lose its axisymmetry by breaking apart in smaller bubbles. Indisputably, however, the topological transition from spherical to toroidal surfaces is mandatory here for obtainin...

  19. Bubble Combustion

    NASA Technical Reports Server (NTRS)

    Corrigan, Jackie

    2004-01-01

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

  20. SWARM observations of equatorial electron densities and topside GPS track losses

    NASA Astrophysics Data System (ADS)

    Buchert, Stephan; Zangerl, Franz; Sust, Manfred; André, Mats; Eriksson, Anders; Wahlund, Jan-Erik; Opgenoorth, Hermann

    2015-04-01

    The SWARM satellites have both upward looking GPS receivers and Langmuir probes. The receivers repeatedly lost track of the L1 band signal in January-February 2014 at postsunset hours, when SWARM was at nearly 500 km altitude. This indicates that the signal was disturbed by ionospheric irregularities at this height and above. The track losses occurred right at density gradients associated with equatorial plasma bubbles and predominantly where the measured background density was highest. The signal showed strong phase scintillations rather than in amplitude, indicating that SWARM might be in the near field of an ionospheric phase screen. Density biteouts, depletions between steep gradients, were up to almost 3 orders of magnitude deep in the background of a more shallow trough centered at the magnetic equator. Comparison between satellites shows that the biteout structure strongly varied in longitude over ˜100 km and has in north-south steep walls.

  1. Forcasting Equatorial Spread-F on a Night to Night Basis in 5 Longitude Sectors

    NASA Astrophysics Data System (ADS)

    Anderson, D. N.; Redmon, R. J.; Bullett, T. W.

    2014-12-01

    When transionospheric radio waves propagate through an irregular ionosphere with plasma depletions or "bubbles", they are subject to sporadic enhancement and fading which is referred to as scintillation. Communication and navigation systems may be subject to these detrimental effects if the scintillation is strong enough. It is critical to have knowledge of the current ionospheric conditions so that system operators can distinguish between the natural radio environment and system-induced failures. In this paper, we present and describe a proven technique for forecasting UHF scintillation activity in the equatorial region after sunset and compare these forecasts with observed Equatorial Spread-F (ESF) on a night-to-night basis. The UHF scintillation forecasting technique described in Redmon et al. (Space Weather, Vol 8, 2010) utilizes the observed characteristic h'F from a ground-based, ionospheric sounder near the magnetic equator. This paper demonstrated that there exists an excellent correlation (R2 ~ 0.91) between h'F (1930LT) and the pre-reversal enhancement in vertical ExB drift velocity after sunset which is the prime driver for creating plasma depletions and bubbles. In addition, there exists a "threshold" in the h'F value at 1930 LT, h'Fthr, which can be used to predict post-sunset scintillation activity. A digital sounder near the magnetic equator provides the h'F values and the observations of ESF. The digital sounders are located at Jicamarca, Peru; Sao Luis, Brazil; Ilorin, Nigeria; Guam and the Kwajalein Atoll. The years that are covered are in 2010, 2011 and 2013. A previous study carried out at Jicamarca for 2013 which correlated the forecast of scintillation activity and the occurrence or non-occurrence of ESF achieved an overall forecasting success of 90%. The important aspect of this study is to determine if this high success rate can be achieved in different longitude sectors.

  2. Equatorial ionosphere bottom-type spread F observed by OI 630.0 nm airglow imaging

    NASA Astrophysics Data System (ADS)

    Takahashi, H.; Abdu, M. A.; Taylor, M. J.; Pautet, P.-D.; de Paula, E.; Kherani, E. A.; Medeiros, A. F.; Wrasse, C. M.; Batista, I. S.; Sobral, J. H. A.; Gobbi, D.; Arruda, D.; Paulino, I.; Vadas, S.; Fritts, D.

    2010-02-01

    Bottom-type spread F events were observed in the south American equatorial region by a VHF coherent radar and an ionosonde at São Luís (2.5°S, 44.3°W), an ionosonde at Fortaleza (3.9°S, 38.4° W) and an airglow OI 630.0 nm imager at Cariri (7.4°S, 36.5°W) and Brasilia (14.8°S, 47.6°W). In the evening of September 30, 2005, a long duration (˜70 minutes) bottom side scattering layer, confined in a narrow height region, was observed. At the same time all-sky imager observed sinusoidal intensity depletions in the zonal plane extending more than 1500 km and elongated along the magnetic meridian. No strong spread F structures developed during the period. Subsequently well developed plasma bubbles were observed. This suggests that the observed bottom-type spread F is an initial phase of the plasma bubbles. We report, for the first time, longitudinal and latitudinal extension of the bottom-type spread F as diagnosed by optical imagers.

  3. Bubble, Bubble, Toil and Trouble.

    ERIC Educational Resources Information Center

    Journal of Chemical Education, 2001

    2001-01-01

    Bubbles are a fun way to introduce the concepts of surface tension, intermolecular forces, and the use of surfactants. Presents two activities in which students add chemicals to liquid dishwashing detergent with water in order to create longer lasting bubbles. (ASK)

  4. Equatorial ionospheric response to the August 18,2003 geomagnetic storm

    NASA Astrophysics Data System (ADS)

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

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

  5. Effect of fine bubbles on electric discharge in water

    NASA Astrophysics Data System (ADS)

    Hayashi, Yui; Takada, Noriharu; Kanda, Hideki; Goto, Motonobu

    2015-10-01

    Ar or O2 fine bubbles of diameter??<80 ?m were introduced in water and a pulsed discharge plasma was generated between cylinder electrodes in water. Fine bubbles in water affected discharge ignition and caused low inception voltage and suppression of rising temperature. The contamination from electrodes was suppressed in the case of fine bubbles addition because fine bubbles assisted plasma generation. In addition, discharge with fine bubbles enhanced plasma emission with high electron density compared to the no-bubbling case. Discharge with fine bubbles at low-pH conditions generated intense plasma emission compared to neutral and high-pH conditions owing to the electric charge of the fine bubbles.

  6. Bubble diagnostics

    DOEpatents

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

    2003-01-01

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

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

    E-print Network

    2012-01-01

    PHYSICAL REVIEW E 86, 056407 (2012) Characterization of single and colliding laser-produced plasma combined with proton radiography data for comprehensive characterization of individual laser, 52.70.Kz I. INTRODUCTION Characterization of laser-produced plasmas is important in a variety

  8. The equatorial electrojet during geomagnetic storms and substorms

    NASA Astrophysics Data System (ADS)

    Yamazaki, Yosuke; Kosch, Michael J.

    2015-03-01

    The climatology of the equatorial electrojet during periods of enhanced geomagnetic activity is examined using long-term records of ground-based magnetometers in the Indian and Peruvian regions. Equatorial electrojet perturbations due to geomagnetic storms and substorms are evaluated using the disturbance storm time (Dst) index and auroral electrojet (AE) index, respectively. The response of the equatorial electrojet to rapid changes in the AE index indicates effects of both prompt penetration electric field and disturbance dynamo electric field, consistent with previous studies based on F region equatorial vertical plasma drift measurements at Jicamarca. The average response of the equatorial electrojet to geomagnetic storms (Dst<-50 nT) reveals persistent disturbances during the recovery phase, which can last for approximately 24 h after the Dst index reaches its minimum value. This "after-storm" effect is found to depend on the magnitude of the storm, solar EUV activity, season, and longitude.

  9. Signatures of 3-6 day planetary waves in the equatorial mesosphere and ionosphere

    NASA Astrophysics Data System (ADS)

    Takahashi, H.; Wrasse, C. M.; Pancheva, D.; Abdu, M. A.; Batista, I. S.; Lima, L. M.; Batista, P. P.; Clemesha, B. R.; Shiokawa, K.

    2006-12-01

    Common periodic oscillations have been observed in meteor radar measurements of the MLT winds at Cariri (7.4° S, 36.5° W) and Ascension Island (7.9° S, 14.4° W) and in the minimum ionospheric virtual height, h'F, measured at Fortaleza (3.9° S, 38.4° W) in 2004, all located in the near equatorial region. Wavelet analysis of these time series reveals that there are 3-4-day, 6-8-day and 12-16-day oscillations in the zonal winds and h'F. The 3-4 day oscillation appeared as a form of a wave packet from 7-17 August 2004. From the wave characteristics analyzed this might be a 3.5-day Ultra Fast Kelvin wave. The 6-day oscillation in the mesosphere was prominent during the period of August to November. In the ionosphere, however, it was apparent only in November. Spectral analysis suggests that this might be a 6.5-day wave previously identified. The 3.5-day and 6.5-day waves in the ionosphere could have important roles in the initiation of equatorial spread F (plasma bubble). These waves might modulate the post-sunset E×B uplifting of the base of the F-layer via the induced lower thermosphere zonal wind and/or the E-region conductivity.

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  11. Pump-probe imaging of nanosecond laser-induced bubbles in distilled water solutions: Observations of laser-produced-plasma

    SciTech Connect

    Evans, R.; Camacho-Lopez, S.

    2010-11-15

    This article presents the analysis of the laser-produced-plasma (LPP) formed by the focusing of a 9 ns laser pulse, {lambda}=532 nm, with a NA=0.6 aspherical lens using energies between 100-1500 {mu}J, into distilled water with varying solutions of table salt. Observations of the filamentation plasma were made, which are explained by self-focusing of the laser pulse by the LPP through ponderomotive cavitation of the electron plasma in the center of the beam. The filamentation of the beam through a low density plasma wave guide explains why the transmission of the pump laser through the interaction region was notably higher on previous experiments that we performed [R. Evans et al., Opt. Express 16, 7481 (2008)], than a very similar set of experiments performed by Noack and Vogel [IEEE J. Quantum Electron. 35, 1156 (1999)].

  12. COLD BUBBLE FORMATION DURING TOKAMAK DENSITY LIMIT DISRUPTIONS

    E-print Network

    Howard, John

    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. Another possible trigger mechanism for the disruption is the penetration to the plasma centre of a cold

  13. Tiny Bubbles.

    ERIC Educational Resources Information Center

    Kim, Hy

    1985-01-01

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

  14. Equatorial westward electrojet impacting equatorial ionization anomaly development during the 6 April 2000 superstorm

    NASA Astrophysics Data System (ADS)

    Horvath, Ildiko; Lovell, Brian C.

    2013-11-01

    investigate the forward plasma fountain and the equatorial ionosphere in the topside region during the 6 April 2000 superstorm in the Australian sector at ~0900 LT. Space- and ground-based multi-instrument measurements, Coupled Thermosphere-Ionosphere-Plasmasphere Electrodynamics (CTIPe) simulations, and field-aligned observations comprise our results. These reveal an unusual storm development during which the eastward prompt penetration electric (E) field (PPEF) developed and operated under the continuous effects of the westward disturbance dynamo E-field (DDEF) while large-scale traveling ionospheric disturbances (TIDs) traveled equatorward and generated strong equatorward wind surges. We have identified the eastward PPEF by the superfountain effect causing the equatorial ionization anomaly (EIA)'s development with crests situated at ~±28°N (geomagnetic) in the topside ionosphere at ~840 km altitude. The westward DDEF's occurrence is confirmed by mapping the "anti-Sq" current system wherein the equatorial westward current created a weak long-lasting westward electrojet event. Line plots of vertical drift data tracked large-scale TIDs. Four scenarios, covering ~3.5 h in universal time, demonstrate that the westward DDEF became superimposed on the eastward PPEF. As these E-fields of different origins became mapped into the F region, they could interact. Consequently, the eastward PPEF-related equatorial upward E × B drift became locally reduced by up to 75 m/s near the dip equator by the westward DDEF-related equatorial downward E × B drift. Meanwhile, the EIA displayed a better development as equatorial wind surges, reproduced by CTIPe, increased from 501 to 629 m/s, demonstrating the crucial role of mechanical wind effects keeping plasma density high.

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    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.

  17. Equatorial Electrojet Observations in the African Continent

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

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

  18. The role of the equatorial electrojet in the evening ionosphere

    SciTech Connect

    Haerendel, G.; Eccles, J.V. )

    1992-02-01

    This paper focuses on the role of the equatorial E region in the electrodynamics of the evening ionosphere. The influence and reaction of the electrojet current on the equatorial ionosphere at sunset is investigated using a field line integrated, one-dimensional, electrodynamic model. The one-dimensional, time-varying model predicts the divergence of the horizontal current of the equatorial electrojet for a given time variation of the horizontal electric field. The negative divergence of the horizontal current during the evening hours provides a net upward current out of the equatorial E region into the integrated ionosphere of higher equatorial altitudes. This upward current affects the vertical electric field magnitudes and subsequent horizontal plasma drifts of the overlying ionosphere. The model allows for chemical recombination and dynamic redistribution of ionization within the electrojet region under the assumption that the profile of the ionization density along a field lie is proportional to the chemical equilibrium profile. The eastward horizontal electric field and the net upward current during the 2 hours after sunset combine to lift the ionization out of the E region resulting in ionization densities less than the equilibrium values. As the ionization densities (conductivities) are reduced, the electrodynamics of the equatorial ionosphere is altered. This model of the equatorial electrojet current divergence can be used as a lower boundary to global, two-dimensional models of the equatorial electric fields. Finally, it is proposed that the equatorial electrojet current near sunset has a significant role in the determination of the postsunset enhancement of the horizontal electric field.

  19. Equatorial spread F statistics and empirical representation for IRI: A regional model for the Brazilian longitude sector

    NASA Astrophysics Data System (ADS)

    Abdu, M. A.; Souza, J. R.; Batista, I. S.; Sobral, J. H. A.

    The empirical representation of the equatorial spread F (ESF) statistics in the IRI scheme requires well established distribution statistics of ESF occurrence and intensity as a function of local time, season/month, latitude and solar and magnetic activity levels. We present here a regional model for the quiet-time spread F distribution in the Brazilian longitude sector. In view of the well known dependence of spread F occurrence on magnetic declination angle, and the fact that the declination angle varies rapidly from the west coast (Peruvian sector) to the east coast (Brazilian sector) of south America the present model can be said to be valid for the latter sector. 13 years of spread F data simultaneously collected (during 1978-1990) over the equatorial site Fortaleza and low latitude site Cachoeira Paulista are used in this model. Only spread F data that is believed to be related to plasma bubble developments is used in the model. The data were first grouped into solar flux range bins representing low, medium, and high solar activity levels, represented, respectively, by F10.7 ? 100; 100 < F10.7 < 180; and F10.7 ? 180. Spread F percentage occurrence as a function of (nocturnal) local time for each of the 12 months in each solar flux range was calculated, and form the database for the model. Cubic-B spline fits of the data in local time, latitude, season/month and solar flux nodes constitute the structure of the present model. The model confirms many characteristic features of the spread F statistics already known as well as brings out some new outstanding features for the Brazilian sector. Among the results to be highlighted are: The spread F onset and peak occurrence get delayed in local time with increasing distance from the equator, indicating the plasma bubble origin for the low latitude ionogram spread F traces; The plasma bubble occurrence as well as the vertical rise velocity increase with the increase in solar flux; They attain larger values in summer months (centered around December) than in equinoctial months (March and September). The latitudinal variation in spread F, though based only on two-station data sets in this study, looks compatible with the latitude variation of ion density fluctuations observed by the AE-E satellite. The model will be made available to interested users.

  20. Jupiter Equatorial Region

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This photographic mosaic of images from NASA's Galileo spacecraft covers an area of 34,000 kilometers by 22,000 kilometers (about 21,100 by 13,600 miles) in Jupiter's equatorial region. The dark region near the center of the mosaic is an equatorial 'hotspot' similar to the site where the Galileo Probe parachuted into Jupiter's atmosphere in December 1995. These features are holes in the bright, reflective, equatorial cloud layer where heat 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 oval in the upper right of the mosaic as well as the other smaller bright features are examples of upwelling of moist air and condensation. 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 camera system aboard Galileo.

    North is at the top. The mosaic covers latitudes 1 to 19 degrees and is centered at longitude 336 degrees west. The smallest resolved features are tens of kilometers in size.

    The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC.

    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at: http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at: http:/ /www.jpl.nasa.gov/galileo/sepo.

  1. Response of the Equatorial Ionosphere in the South Atlantic Region to the Great Magnetic Storm of July 15, 2000

    NASA Astrophysics Data System (ADS)

    Basu, S.; Groves, K. M.; Yeh, H.; Su, S.; Rich, F. J.; Sultan, P. J.

    2001-05-01

    The effects of the great magnetic storm of July 15, 2000 on the equatorial ionosphere have been studied by ground-based GPS and geostationary satellite measurements of ionospheric total electron content (TEC) and scintillations and in-situ measurements of ion density and ion drift by sun-synchronous polar orbiting DMSP satellites and the recently launched ROCSAT-1 satellite in a low inclination orbit. It is shown that the magnetic storm was associated with a large westward plasma drift in the evening equatorial ionosphere presumably due to the effects of the ionospheric disturbance dynamo. In the presence of the sustained effects of the disturbance dynamo, the Dst index decreased abruptly at the rate of 130 nT/hour for two hours, and became associated with the onset of 250 MHz and L-band scintillations at Ascension Island (150 W) and precipitous TEC decrease at Fortaleza, Brazil (380 W), bounding the narrow longitude region in the South Atlantic. It probably indicates that the abrupt change of the Dst index caused a prompt penetration of the eastward electric field over this limited longitude interval. The DMSP F-14 and F-15 in-situ measurements showed the presence of a severe ion density bite-out extending over  100 latitude around the magnetic equator in the South Atlantic Magnetic Anomaly region. The ROCSAT-1 satellite measured upward and large southward ion drifts in the same sector indicating the ionospheric plasma transport away from this region. At Ascension Island to the east of this region, the ground-based and satellite in-situ measurements showed the presence of plasma bubbles, TEC fluctuations, and amplitude scintillations at 250 MHz and at L-band.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  3. Nonlinear bounce resonances between magnetosonic waves and equatorially mirroring electrons

    NASA Astrophysics Data System (ADS)

    Chen, Lunjin; Maldonado, Armando; Bortnik, Jacob; Thorne, Richard M.; Li, Jinxing; Dai, Lei; Zhan, Xiaoya

    2015-08-01

    Equatorially mirroring energetic electrons pose an interesting scientific problem, since they generally cannot resonate with any known plasma waves and hence cannot be scattered down to lower pitch angles. Observationally it is well known that the flux of these equatorial particles does not simply continue to build up indefinitely, and so a mechanism must necessarily exist that transports these particles from an equatorial pitch angle of 90° down to lower values. However, this mechanism has not been uniquely identified yet. Here we investigate the mechanism of bounce resonance with equatorial noise (or fast magnetosonic waves). A test particle simulation is used to examine the effects of monochromatic magnetosonic waves on the equatorially mirroring energetic electrons, with a special interest in characterizing the effectiveness of bounce resonances. Our analysis shows that bounce resonances can occur at the first three harmonics of the bounce frequency (n?b, n = 1, 2, and 3) and can effectively reduce the equatorial pitch angle to values where resonant scattering by whistler mode waves becomes possible. We demonstrate that the nature of bounce resonance is nonlinear, and we propose a nonlinear oscillation model for characterizing bounce resonances using two key parameters, effective wave amplitude à and normalized wave number k~z. The threshold for higher harmonic resonance is more strict, favoring higher à and k~z, and the change in equatorial pitch angle is strongly controlled by k~z. We also investigate the dependence of bounce resonance effects on various physical parameters, including wave amplitude, frequency, wave normal angle and initial phase, plasma density, and electron energy. It is found that the effect of bounce resonance is sensitive to the wave normal angle. We suggest that the bounce resonant interaction might lead to an observed pitch angle distribution with a minimum at 90°.

  4. Diagnosing temperature change inside sonoluminescing bubbles by calculating line spectra

    NASA Astrophysics Data System (ADS)

    An, Yu; Li, Chaohui

    2009-10-01

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

  5. Unique Capabilities of the Situational Awareness Sensor Suite for the ISS (SASSI) Mission Concept to Study the Equatorial Ionosphere

    NASA Astrophysics Data System (ADS)

    Habash Krause, L.; Gilchrist, B. E.; Minow, J. I.; Gallagher, D. L.; Hoegy, W. R.; Coffey, V. N.; Willis, E. M.

    2014-12-01

    We present an overview of a mission concept named Situational Awareness Sensor Suite for the ISS (SASSI) with a special focus here on low-latitude ionospheric plasma turbulence measurements relevant to equatorial spread-F. SASSI is a suite of sensors that improves Space Situational Awareness for the ISS local space environment, as well as unique ionospheric measurements and support active plasma experiments on the ISS. As such, the mission concept has both operational and basic research objectives. We will describe two compelling measurement techniques enabled by SASSI's unique mission architecture. That is, SASSI provides new abilities to 1) measure space plasma potentials in low Earth orbit over ~100 m relative to a common potential, and 2) to investigate multi-scale ionospheric plasma turbulence morphology simultaneously of both ~ 1 cm and ~ 10 m scale lengths. The first measurement technique will aid in the distinction of vertical drifts within equatorial plasma bubbles from the vertical motions of the bulk of the layer due to zonal electric fields. The second will aid in understanding ionospheric plasma turbulence cascading in scale sizes that affect over the horizon radar. During many years of ISS operation, we have conducted effective (but not perfect) human and robotic extravehicular activities within the space plasma environment surrounding the ISS structure. However, because of the complexity of the interaction between the ISS and the space environment, there remain important sources of unpredictable environmental situations that affect operations. Examples of affected systems include EVA safety, solar panel efficiency, and scientific instrument integrity. Models and heuristically-derived best practices are well-suited for routine operations, but when it comes to unusual or anomalous events or situations, there is no substitute for real-time monitoring. SASSI is being designed to deploy and operate a suite of low-cost, medium/high-TRL plasma sensors on the ISS Express Logistics Carrier for long-term observations and the Space Station Remote Manipulator System for short-term focused campaigns. The presentation will include a description of the instrument complement and an overview of the operations concept.

  6. C/NOFS observations of plasma density and electric field irregularities at post-midnight local times

    NASA Astrophysics Data System (ADS)

    Burke, W. J.; de La Beaujardière, O.; Gentile, L. C.; Hunton, D. E.; Pfaff, R. F.; Roddy, P. A.; Su, Y.-J.; Wilson, G. R.

    2009-09-01

    We report on plasma densities and electric fields measured by the C/NOFS satellite between 10 and 20 June 2008. Midway through the interval, geomagnetic conditions changed from quiescent to disturbed as a high speed stream (HSS) in the solar wind passed Earth. During the HSS passage C/NOFS encountered post-midnight irregularities that ranged from strong equatorial plasma bubbles to longitudinally broad depletions. At the leading edge of the HSS the interplanetary magnetic field rapidly intensified and rotated causing auroral electrojet currents to rise and fall within a few hours. As the electrojet relaxed, C/NOFS witnessed a rapid transition from a weakly to a strongly disturbed equatorial ionosphere that lasted ˜10 hours. Eastward polarization electric fields intensified within locally depleted flux tubes. We discuss relative contributions of gravity-driven currents, overshielding electric fields and disturbance dynamos as drivers of post-midnight depletions.

  7. Bubbles and Superbubbles

    E-print Network

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

    2003-10-10

    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?

  8. Optical emissions in a sonoluminescing bubble

    NASA Astrophysics Data System (ADS)

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

    2000-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

  10. Longitudinal variation of sudden commencement of geomagnetic storm at equatorial stations

    SciTech Connect

    Rastogi, R.G.

    1993-09-01

    The author reports the observation of a correlation between the strength of storm sudden commencements in the equatorial electrojet region with the equatorial electrojet current itself, as a function of daytime, latitude, and longitude. The author argues that electric fields generated at the magnetopause by interaction with solar wind plasma transmits to the polar region along field lines, and there converts to magnetic waves which rapidly propogate to equatorial regions in the conducting plasma between the ionosphere and the earth. The strength of the arrival fields is dependent upon the ionospheric conductivity at the particular location in question.

  11. Low-voltage pulsed plasma discharges inside water using a bubble self-generating parallel plate electrode with a porous ceramic

    NASA Astrophysics Data System (ADS)

    Muradia, Sonia; Nagatsu, Masaaki

    2013-04-01

    Characteristics of pulsed bubbles discharges in water were investigated using parallel punched plate electrodes with a porous thin ceramic plate inserted between two metal plates. The micro-bubbles were generated just beneath the porous ceramic plate by flowing gas through it. The transition from spiky dielectric barrier discharges to pulsed glow discharges enables efficient bubble discharges at a relatively low voltage of 1.8 ˜ 4.0 kV of the 5 kHz square-waves with a pulse-width of about 750 ns. With 80% Ar and 20% O2 mixture gas at 4.0 kV, the 50 mg/l Indigo Carmine aqueous solution was efficiently decolorized within about 3 min.

  12. Non-invasive characterization of transverse beam emittance of electrons from a laser-plasma wakefield accelerator in the bubble regime using betatron x-ray radiation

    E-print Network

    Kneip, S; 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

    2011-01-01

    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 $v_{\\perp}/v_{\\parallel}$, the measured longitudinal spectrum $\\gamma_\\parallel$ and the transverse electron bunch size in the bubble $r_{\\perp}$. 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 \\textit{normalised} RMS beam transverse emittance $electron beam with 230 MeV energy in agreement with numerical modeling and analytic theory in the bubble regime.

  13. 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)

    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

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2004-01-01

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

  15. Measuring bubbles in a bubbly wake flow

    NASA Astrophysics Data System (ADS)

    Lee, Seung-Jae; Kawakami, Ellison; Arndt, Roger E. A.

    2012-11-01

    This paper presents measurements of the velocity and size distribution of bubbles in a bubbly wake. This was carried out by utilizing particle shadow velocimetry (PSV). This technique is a non-scattering approach that relies on direct in-line volume illumination by a pulsed source such as a light-emitting diode (LED). A narrow depth-of-field (DoF) is required for imaging a 2-dimensional plane within a flow volume. Shadows of the bubbles were collected by a high-speed camera. Once a reference image, taken when no bubbles were present in the flow, was subtracted from the images, the image was segmented using an edge detection technique. The Canny algorithm was determined to be best suited for this application. A curvature profile method was employed to distinguish individual bubbles within a cluster of highly overlapping bubbles. The utilized algorithm was made to detect partly overlapping bubbles and reconstruct the missing parts. The movement of recognized individual bubbles was tracked on a two dimensional plane within a flow volume. In order to obtain quantitative results, the wake of a ventilated hydrofoil was investigated by applying the shadowgraphy technique and the described bubble detection algorithm. These experiments were carried out in the high speed cavitation tunnel at Saint Anthony Falls Laboratory (SAFL) of the University of Minnesota. This research is jointly sponsored by the Office of Naval Re- search, Dr. Ron Joslin, program manager, and the Department of Energy, Golden Field Office.

  16. Studies on equatorial shock formation during plasmaspheric refilling

    NASA Technical Reports Server (NTRS)

    Singh, N.

    1994-01-01

    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.

  17. Modeling the equatorial electrojet

    SciTech Connect

    Stening, R.J.

    1985-02-01

    The equivalent circuit method has been modified to give greater accuracy and greater detail near the equator in order to model the equatorial electrojet. Electron collision frequencies used in the conductivity model are consistent with laboratory measurements. Variations with longitude are allowed, and the electrojet in the model is driven by suitable emf's generated by a global thermotidal wind system. The height of maximum current density in the Indian electrojet provided by the model at 104 km is consistent with some observations. The model gives the same height in Peru when an electron density profile typical of that region is used. The form of the electron density profile is shown to have a considerable affect on the current profile. The calculated variation with latitude of high-integrated current density gives good agreement. The two-layer equivalent circuit model is more successful than the single-layer model in modeling the latitude profile of the jet, but the observed depression in ..delta..H near 4/sup 0/ dip latitude requires much larger changes in currents with latitude than either model can provide. The theory that currents are limited by the two-stream instability does not agree with measured altitude profiles of the jet. Before latitude variations of ..delta..H and ..delta..Z on the ground can satisfactorily be explained, greater understanding of the contribution of conductivity anomalies to internal components will be required, but with suitable assumptions, a good fit with observed results is obtained. The effects produced by a simple local F region wind system are also investigated. A discrepancy with the observed relationship between integrated current densities and ..delta..H still awaits explanation.

  18. The interaction of positive streamers with bubbles floating on a liquid surface

    NASA Astrophysics Data System (ADS)

    Akishev, Yu; Arefi-Khonsari, F.; Demir, A.; Grushin, M.; Karalnik, V.; Petryakov, A.; Trushkin, N.

    2015-12-01

    This paper reports the results of a preliminary investigation on the interaction of a streamer discharge in air with bubbles filled with air and floating on a liquid surface. The bubbles are formed of tap water and transformer oil. It was shown that the strike of the streamer in a bubble is followed by the full bubble destroying. However, scenarios of the streamer discharge interaction with a conductive water bubble and dielectric oil bubble are different in their concrete details. A positive streamer smoothly and slowly slides on an external surface of a water bubble, but the streamer striking in an oil bubble quickly perforates it and penetrates into the bubble. The mechanisms for water and oil bubble destroying are discussed. The applicability of the results obtained to plasma-liquid systems based on the use of foam is discussed as well.

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

    NASA Astrophysics Data System (ADS)

    Lynn, Alan; Zhang, Yue; Hsu, Scott

    2010-11-01

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

  20. Equatorial Electrojet Instabilities - New Fluid Model Approach

    NASA Astrophysics Data System (ADS)

    Hassan, Ehab; Horton, Wendell; Smolyakov, Andrei; Hatch, David

    2014-10-01

    A fluid model combines both Farley-Buneman (Type-I) and Gradient-Drift (Type-II) plasma instabilities in the equatorial electrojet. The ion viscosity and electron inertia are considered in the ion and electron equations of motion, respectively. These two terms play an important role in stabilizing the growing modes in the linear regime and in driving Farley-Buneman instability into the saturation state. The simulation is stable in the saturated state and the results show good agreements with a number of rocket measurements and radar observations, where we find (1) a saturation of the plasma density around 7% relative to the ionosphere background, (2) the horizontal secondary electric field stabilizes at 8.7 (mV/m), (3) the phase velocity of the perturbed density wave has a value close to the ion-acoustic speed inside the electrojet, (5) an up-down asymmetry in the vertical particle fluxes of plasma density, (5) an east-west asymmetry in the plasma drifts in the zonal direction, and (6) a generation of the small-scale; of the order of 3 meter scale length and less, irregularities embedded in the large-scale structures in the vertical direction. The break-up of the large-scale structures into small-scale structures explains the disappearance of Type-II echoes in the presence of Ty.

  1. Fast and Ultra-fast Kelvin wave modulations of the equatorial evening F region vertical drift and spread F development.

    NASA Astrophysics Data System (ADS)

    Garnett Marques Brum, C.; Abdu, M. A.; Batista, P. P.; Gurubaran, S.; Pancheva, D.; Bageston, J. V.; Batista, I. S.; Takahashi, H.

    2014-12-01

    In this paper we investigate the role of eastward and upward propagating Fast (FK) and Ultrafast Kelvin (UFK) waves in the day-to-day variability of equatorial evening prereversal vertical drift and post sunset generation of spread F/plasma bubbles irregularities. Meteor wind data from Cariri and Cachoeira Paulista (Brazil) and medium Frequency (MF) radar wind data from Tirunelveli (India) are analyzed together with TIMED/SABER temperature in the 40 km - 100 km region to characterize the zonal and vertical propagations of these waves. Also analyzed are the F region evening vertical drift and spread F (ESF) development features as diagnosed by Digisondes operated at Fortaleza and Sao Luis in Brazil. The SABER temperature data permitted determination of the upward propagation characteristics of the FK (E1) waves with propagation speed in the range of 4 km/day. The radar Mesosphere and Lower Thermosphere (MLT) winds in the widely separated longitude sectors have yielded the eastward phase velocity of the both the FK and UFK waves. The vertical propagation of these waves cause strong oscillation in the F region evening prereversal vertical drift, observed for the first time at both FK and UFK periodicities. A delay of a few (~10) days is observed in the F region vertical drift perturbation with respect to the corresponding FK/UFK zonal wind oscillations, or temperature oscillations in the MLT region, which has permitted a direct identification of the sunset electro dynamic coupling process as responsible for the generation of the FK/UFK induced vertical drift oscillation. The vertical drift oscillations are found to cause significant modulation in the spread F/ plasma bubble irregularity development. The overall results highlight the role of FK/UFK waves in the day-to-day variability of the ESF in its occurrence season.

  2. Fast and ultrafast Kelvin wave modulations of the equatorial evening F region vertical drift and spread F development

    NASA Astrophysics Data System (ADS)

    Abdu, Mangalathayil A.; Brum, Christiano GM; Batista, Paulo P.; Gurubaran, Subramanian; Pancheva, Dora; Bageston, Jose V.; Batista, Inez S.; Takahashi, Hisao

    2015-12-01

    In this paper, we investigate the role of eastward and upward propagating fast (FK) and ultrafast Kelvin (UFK) waves in the day-to-day variability of equatorial evening prereversal vertical drift and post sunset generation of spread F/plasma bubble irregularities. Meteor wind data from Cariri and Cachoeira Paulista (Brazil) and medium frequency (MF) radar wind data from Tirunelveli (India) are analyzed together with Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) temperature in the 40- to 100-km region to characterize the zonal and vertical propagations of these waves. Also analyzed are the F region evening vertical drift and spread F (ESF) development features as diagnosed by Digisonde (Lowell Digisonde International, LLC, Lowell, MA, USA) operated at Fortaleza and Sao Luis in Brazil. The SABER temperature data permitted determination of the upward propagation characteristics of the FK (E1) waves with propagation speed in the range of 4 km/day. The radar mesosphere and lower thermosphere (MLT) winds in the widely separated longitude sectors have yielded the eastward phase velocity of both the FK and UFK waves. The vertical propagation of these waves cause strong oscillation in the F region evening prereversal vertical drift, observed for the first time at both FK and UFK periodicities. A delay of a few (approximately 10) days is observed in the F region vertical drift perturbation with respect to the corresponding FK/UFK zonal wind oscillations, or temperature oscillations in the MLT region, which has permitted a direct identification of the sunset electrodynamic coupling process as being responsible for the generation of the FK/UFK-induced vertical drift oscillation. The vertical drift oscillations are found to cause significant modulation in the spread F/plasma bubble irregularity development. The overall results highlight the role of FK/UFK waves in the day-to-day variability of the ESF in its occurrence season.

  3. Density Enhancements Associated with Equatorial Spread F

    NASA Astrophysics Data System (ADS)

    Krall, J.; Huba, J.; Joyce, G. R.

    2009-12-01

    Forces governing the three-dimensional structure of equatorial spread-F (ESF) plumes are examined using the NRL SAMI3/ESF three-dimensional simulation code [1]. As is the case with the equatorial ionization anomaly (IA), density crests within the plume occur where gravitational and diffusive forces are in balance. Large E×B drifts within the ESF plume place these crests on field lines with apex heights higher than those of the background IA crests. Large poleward field-aligned ion velocities within the plume result in large ion-neutral diffusive forces that support these ionization crests at altitudes higher background IA crest altitudes. We show examples in which density enhancements associated with ESF, also called “plasma blobs,” can occur within an ESF plume on density-crest field lines, at or above the density crests. Simulated ESF density enhancements reproduce all key features of those observed using satellites. [1] Huba, J.D., G. Joyce, and J. Krall, GRL, 35, L10102, doi:10.1029/2008GL033509, 2008

  4. Radio Bubbles in Clusters of Galaxies

    SciTech Connect

    Dunn, Robert J.H.; Fabian, A.C.; Taylor, G.B.; /NRAO, Socorro /KIPAC, Menlo Park

    2005-12-14

    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.

  5. Long wavelength irregularities in the equatorial electrojet

    SciTech Connect

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

    1982-06-01

    We have used the radar interferometer technique at Jicamarca to study in detail irregularities with wavelengths of a few kilometers generated in the unstable equatorial electrojet plasma during strong type 1 conditions. In-situ rocket observations of the same instability process are discussed in a companion paper. These large scale primary waves travel essentially horizontally and have large amplitudes. The vertical electron drift velocities driven by the horizontal wave electric fields reach or exceed the ion-acoustic velocity even though the horizontal phase velocity of the wave is considerably smaller. A straightforward extension to the long wavelength regime of the usual linear theory of the electrojet instability explains this and several other observed features of these dominant primary waves.

  6. Long wavelength irregularities in the equatorial electrojet

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

    The radar interferometer technique is used at Jicamarca to study in detail irregularities with wavelengths of a few kilometers generated in the unstable equatorial electrojet plasma during strong type 1 conditions. In-situ rocket observations of the same instability process are discussed in a companion paper. These large scale primary waves travel essentially horizontally and have large amplitudes. The vertical electron drift velocities driven by the horizontal wave electric fields reach or exceed the ion-acoustic velocity even though the horizontal phase velocity of the wave is considerably smaller. A straightforward extension to the long wavelength regime of the usual linear theory of the electrojet instability explains this and several other observed features of these dominant primary waves.

  7. The streaming-trapped ion interface in the equatorial inner magnetosphere

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    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.

  8. Electrical breakdown of a bubble in a water-filled capillary

    SciTech Connect

    Bruggeman, P.J.; Leys, C.A.; Vierendeels, J. A.

    2006-06-01

    In this Communication, the electrical breakdown of a static bubble in a water-filled capillary generated in a dc electrical field is studied. We present experimental results which indicate that the liquid layer between capillary and bubble wall can have an important influence on the breakdown mechanism of the bubble. The breakdown electrical field (atmospheric pressure) without a liquid layer in a (vapor) bubble is 18 kV/cm. When a liquid layer is present, the electrical breakdown of an air bubble is observed at electrical fields typically two times smaller. Local plasma formation is observed in this case possibly due to bubble deformation.

  9. 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)

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

    2011-01-01

    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.

  10. Photon Bubbles and the Vertical Structure of Accretion Disks

    NASA Astrophysics Data System (ADS)

    Begelman, Mitchell C.

    2006-06-01

    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.

  11. BUBBLE ENTRAINMENT AND LIQUID-BUBBLE INTERACTION UNDER UNSTEADY BREAKING

    E-print Network

    Kirby, James T.

    BUBBLE ENTRAINMENT AND LIQUID-BUBBLE INTERACTION UNDER UNSTEADY BREAKING WAVES BY MORTEZA DERAKHTI And Enstrophy . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 4.6 Reynolds Stress- and bubble-induced dissipation . . . . . . . . . . . . . 58 4.7.2 Time dependent breaking parameter, b

  12. Gas bubble detector

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  13. Sonochemistry and bubble dynamics.

    PubMed

    Mettin, Robert; Cairós, Carlos; Troia, Adriano

    2015-07-01

    The details of bubble behaviour in chemically active cavitation are still not sufficiently well understood. Here we report on experimental high-speed observations of acoustically driven single-bubble and few-bubble systems with the aim of clarification of the connection of their dynamics with chemical activity. Our experiment realises the sonochemical isomerization reaction of maleic acid to fumaric acid, mediated by bromine radicals, in a bubble trap set-up. The main result is that the reaction product can only be observed in a parameter regime where a small bubble cluster occurs, while a single trapped bubble stays passive. Evaluations of individual bubble dynamics for both cases are given in form of radius-time data and numerical fits to a bubble model. A conclusion is that a sufficiently strong collapse has to be accompanied by non-spherical bubble dynamics for the reaction to occur, and that the reason appears to be an efficient mixing of liquid and gas phase. This finding corroborates previous observations and literature reports on high liquid phase sonochemical activity under distinct parameter conditions than strong sonoluminescence emissions. PMID:25194210

  14. Prospects for bubble fusion

    SciTech Connect

    Nigmatulin, R.I.; Lahey, R.T. Jr.

    1995-09-01

    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.

  15. Drivers of Quiet-Time Equatorial Evening Electrodynamics

    NASA Astrophysics Data System (ADS)

    Richmond, A. D.; Fang, T.

    2013-12-01

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

  16. Gases in Tektite Bubbles.

    PubMed

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

    1962-07-20

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

  17. Let Them Blow Bubbles.

    ERIC Educational Resources Information Center

    Korenic, Eileen

    1988-01-01

    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.…

  18. The Vacuum Bubble Nucleation

    SciTech Connect

    Lee, Bum-Hoon; Lee, Wonwoo

    2009-07-10

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

  19. Evaporation, Boiling and Bubbles

    ERIC Educational Resources Information Center

    Goodwin, Alan

    2012-01-01

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

  20. Photon Bubbles and the Vertical Structure of Accretion Disks

    E-print Network

    Mitchell C. Begelman

    2006-02-01

    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.

  1. Interplay Between the Equatorial Geophysical Processes

    NASA Astrophysics Data System (ADS)

    Sridharan, R.

    2006-11-01

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

  2. Tribonucleation of bubbles

    PubMed Central

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

    2014-01-01

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

  3. Radio wave scintillations at equatorial regions

    NASA Technical Reports Server (NTRS)

    Poularikas, A. D.

    1972-01-01

    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.

  4. Equatorial refuge amid tropical warming

    NASA Astrophysics Data System (ADS)

    Karnauskas, Kristopher B.; Cohen, Anne L.

    2012-07-01

    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.

  5. Aerosol Transport Over Equatorial Africa

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

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

  6. Aerator Combined With Bubble Remover

    NASA Technical Reports Server (NTRS)

    Dreschel, Thomas W.

    1993-01-01

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

  7. Ventilation of the equatorial Atlantic by the equatorial deep jets Peter Brandt,1

    E-print Network

    Ventilation of the equatorial Atlantic by the equatorial deep jets Peter Brandt,1 Richard J 22 October 2012; published 12 December 2012. [1] Equatorial deep jets (EDJs) are a prominent flow than quadrature, implying a net eastward oxygen flux. The comparison of available observations

  8. Central Equatorial Pacific Experiment (CEPEX)

    SciTech Connect

    Not Available

    1993-01-01

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

  9. Chemistry in Soap Bubbles.

    ERIC Educational Resources Information Center

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

    2002-01-01

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

  10. What's in a Bubble?

    ERIC Educational Resources Information Center

    Saunderson, Megan

    2000-01-01

    Describes a unit on detergents and bubbles that establishes an interest in the properties of materials and focuses on active learning involving both hands- and minds-on learning rather than passive learning. (ASK)

  11. 2012 Problem 8: Bubbles

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  12. Bubble coalescence in magmas

    NASA Technical Reports Server (NTRS)

    Herd, Richard A.; Pinkerton, Harry

    1993-01-01

    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.

  13. The equatorial ionosphere measured by C/NOFS and COSMIC

    NASA Astrophysics Data System (ADS)

    Stoneback, R.; Heelis, R. A.

    2013-12-01

    The Ion Velocity Meter (IVM) onboard the Communications/Navigation Outage Forecasting System (C/NOFS) performs in-situ measurements of thermal plasma properties and ion drifts in three dimensions. The FormoSat-3 satellites (COSMIC) perform GPS Radio Occultation measurements which may be used to infer altitude profiles of electron density. Results from these independent measurement techniques should be correlated in the equatorial ionosphere due to the influence of the vertical ion drift at the geomagnetic equator upon the distribution of density. We present a data based model that combines measurements from both platforms based upon this physical connection using Data Interpolating Empirical Orthogonal Functions (DINEOFs).

  14. Fast bubble dynamics and sizing

    NASA Astrophysics Data System (ADS)

    Czarnecki, Krzysztof; Fouan, Damien; Achaoui, Younes; Mensah, Serge

    2015-11-01

    Single bubble sizing is usually performed by measuring the resonant bubble response using the Dual Frequency Ultrasound Method. However, in practice, the use of millisecond-duration chirp-like waves yields nonlinear distortions of the bubble oscillations. In comparison with the resonant curve obtained under harmonic excitation, it was observed that the bubble dynamic response shifted by up to 20 percent of the resonant frequency with bubble radii of less than 100 ?m. In the case of low pressure waves (P < 5 kPa), an approximate formula for the apparent frequency shift is derived. Simulated and experimental bubble responses are analyzed in the time-frequency domain using an enhanced concentrated (reassigned) spectrogram. The difference in the resonant frequency resulted from the persistence of the resonant mode in the bubble response. Numerical simulations in which these findings are extended to pairs of coupled bubbles and to bubble clouds are also presented.

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

    NASA Astrophysics Data System (ADS)

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

    2009-02-01

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

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

    SciTech Connect

    Cho, Myung-Hoon; Kim, Young-Kuk; Hur, Min Sup

    2013-09-15

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

  17. Colliding with a crunching bubble

    SciTech Connect

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

    2007-03-26

    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.

  18. Equatorial F-region evening vertical drift, and peak height, during southern winter months: a comparison of observational data with the IRI descriptions.

    NASA Astrophysics Data System (ADS)

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

    The equatorial F-region evening vertical drift, due to prereversal electric field enhancement, is an important condition for the spread F/plasma bubble irregularity generation, that is more frequent during summer-equinoctial months over South America. A comparative study of these vertical drifts with their IRI representations was presented at the Grahamstown IRI workshop. During southern winter months the post sunset ESF development is relatively infrequent due to the generally weaker intensity of the prereversal electric field, but its generation under magnetospheric forcing is determined by the background vertical drift. Therefore a detailed understanding of the characteristics of the evening F layer vertical drift and hmF2 during southern winter months is important for developing/improving their representations in the IRI scheme. In this paper we have undertaken a study of these parameters over the Brazilian equatorial sites, Sao Luis (2.33 S, 44.2W, dip angle: -.5, declination angle: 21° W) and Fortaleza (3.9 S, 38.45 W, dip angle: -9), and the low latitude site, Cachoeira Paulista (22.6 S, 315 E; dip angle: - 28) in comparison with their existing representations in the IRI. The study will be made as a function of the solar flux varying from the solar activity minimum to maximum conditions, and as function of magnetic activity. Some of the results in the Brazilian longitude sector will be compared with results from Jicamarca (12S, 76.9W; dip latitude: 1N, declination angle: ˜ 3°E) in Peru, separated by a large difference in magnetic declination angle. Systematic patterns of difference between their observed characteristics and IRI representations will be identified in an attempt to quantify them for proposing possible corrections to their existing representations in the IRI model.

  19. The Dueling Bubble Experiment

    NASA Astrophysics Data System (ADS)

    Roy, Anshuman; Borrell, Marcos; Felts, John; Leal, Gary; Hirsa, Amir

    2007-11-01

    When two drops or bubbles are brought into close proximity to each other, the thin film of the fluid between them drains as they are squeezed together. If the film becomes thin enough that intermolecular forces of attraction overwhelm capillary forces, the drops/bubbles coalesce and the time it takes for this to happen, starting from the point of apparent contact is referred to as the drainage time. One practical version of this scenario occurs during the formation of foams, when the thin film forms between gas bubbles that are growing in volume with time. We performed an experimental study that is intended to mimic this process in which the two drops (or bubbles) in the size range of 50-100 microns diameter are created by oozing a liquid/gas out of two capillaries of diameter less than 100 microns directly facing each other and immersed in a second fluid. We present measurements of drainage times for the cases of very low viscosity ratios PDMS drops in Castor oil (less than 0.05) and bubbles of air in PDMS, and highlight the differences that arise in part due to the different boundary conditions for thin film drainage for liquid-liquid versus gas-liquid systems, and in part due to the different Hamaker constants for the two systems.

  20. Fermi Bubbles with HAWC

    E-print Network

    Solares, H A Ayala; Hüntemeyer, P

    2015-01-01

    The Fermi Bubbles, which comprise two large and homogeneous regions of spectrally hard gamma-ray emission extending up to $55^{o}$ above and below the Galactic Center, were first noticed in GeV gamma-ray data from the Fermi Telescope in 2010. The mechanism or mechanisms which produce the observed hard spectrum are not understood. Although both hadronic and lep- tonic models can describe the spectrum of the bubbles, the leptonic model can also explain similar structures observed in microwave data from the WMAP and Planck satellites. Recent publications show that the spectrum of the Fermi Bubbles is well described by a power law with an exponential cutoff in the energy range of 100MeV to 500GeV. Observing the Fermi Bubbles at higher gamma-ray energies will help constrain the origin of the bubbles. A steeper cutoff will favor a leptonic model. The High Altitude Water Cherenkov (HAWC) Observatory, located 4100m above sea level in Mexico, is designed to measure high-energy gamma rays between 100GeV to 100TeV. With...

  1. A Bubble Bursts

    NASA Technical Reports Server (NTRS)

    2005-01-01

    RCW 79 is seen in the southern Milky Way, 17,200 light-years from Earth in the constellation Centaurus. The bubble is 70-light years in diameter, and probably took about one million years to form from the radiation and winds of hot young stars.

    The balloon of gas and dust is an example of stimulated star formation. Such stars are born when the hot bubble expands into the interstellar gas and dust around it. RCW 79 has spawned at least two groups of new stars along the edge of the large bubble. Some are visible inside the small bubble in the lower left corner. Another group of baby stars appears near the opening at the top.

    NASA's Spitzer Space Telescope easily detects infrared light from the dust particles in RCW 79. The young stars within RCW 79 radiate ultraviolet light that excites molecules of dust within the bubble. This causes the dust grains to emit infrared light that is detected by Spitzer and seen here as the extended red features.

  2. Bubble bursting mediated aerosols

    NASA Astrophysics Data System (ADS)

    Lhuissier, Henri; Villermaux, Emmanuel

    2009-11-01

    Wave breaking over the ocean in the surf zone is responsible for a substantial amount of atmospheric aerosols production. The objects mediating their formation are bubbles entrained below breaking waves, and bursting at the sea surface. We describe the mechanisms by which the liquid shell constitutive of a bubble ultimately results into small drops, also called film drops. A bubble bursts when a hole nucleates through the liquid shell. The hole grows at the Culick velocity balancing inertia with surface tension and is bordered by a rim collecting the shell liquid. This initially smooth toroidal rim corrugates when the centripetal acceleration caused by the recession motion is strong enough to trigger a Rayleigh-Taylor destabilization. Ligaments then emerge from corrugations crests and resolve by a Plateau-Rayleigh mechanism into droplets. The final myst properties are thus solely determined by the shell geometry at the bursting onset. It depends on the ratio of the bubble radius to the capillary length, and on the slow gravity drainage of the liquid on which are superimposed rearrangements due to the marginal regeneration at the bubble foot. Our findings will be discussed in connexion with know facts in that context.

  3. EQUATORIAL SUPERROTATION ON TIDALLY LOCKED EXOPLANETS

    SciTech Connect

    Showman, Adam P.; Polvani, Lorenzo M.

    2011-09-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  5. Equatorial electrojet as a nonlinear ULF antenna for the short-wave heating facility

    NASA Astrophysics Data System (ADS)

    Bespalov, Peter A.; Savina, Olga N.

    2015-11-01

    In this paper, we discuss some questions related to the nature and manifestation of the equatorial electrojet. We study theoretically the equatorial electrojet as a nonlinear antenna for generating ultra-low-frequency electromagnetic signals during periodic heating of the ionosphere by the short-wave heater radiation. It is shown that for periodic heating at the frequency corresponding to the ULF band the generation of electromagnetic signals can be significantly intensified. This effect is especially important for the daytime magnetosphere where there are eigenfrequencies of the plasma magnetospheric maser in the electron radiation belts in the same frequency band. This can lead to a modification of VLF emissions in the subauroral magnetosphere.

  6. Ethnic diversity deflates price bubbles

    E-print Network

    Levine, Sheen S.

    Markets are central to modern society, so their failures can be devastating. Here, we examine a prominent failure: price bubbles. Bubbles emerge when traders err collectively in pricing, causing misfit between market prices ...

  7. Mechanics of collapsing cavitation bubbles.

    PubMed

    van Wijngaarden, Leen

    2016-03-01

    A brief survey is given of the dynamical phenomena accompanying the collapse of cavitation bubbles. The discussion includes shock waves, microjets and the various ways in which collapsing bubbles produce damage. PMID:25890856

  8. Determination of vertical plasma drift and meridional wind using the Sheffield University Plasmasphere Ionosphere Model and ionospheric data at equatorial and low latitudes in Brazil: Summer solar minimum and maximum conditions

    NASA Astrophysics Data System (ADS)

    Souza, J. R.; Abdu, M. A.; Batista, I. S.; Bailey, G. J.

    2000-06-01

    The F region critical frequency f0F2 and peak height hmF2, measured simultaneously at the equatorial location Fortaleza (4°S, 38°W, magneticlatitude=3.5°S) and at the low-latitude location Cachoeira Paulista (22°S, 45°W, magnetic latitude=15°S), are compared with their values calculated by the Sheffield University Plasmasphere-Ionosphere Model (SUPIM) to determine the vertical (E×B) drift velocity at the equator and the magnetic meridional wind velocity over the two locations. The calculated and observed values of f0F2 are then matched at both Fortaleza and Cachoeira Paulista to obtain the magnetic meridional winds over their respective conjugate locations. To account for the observed f0F2 diurnal variation pattern over Cachoeira Paulista, it was found necessary to include a small source of ionization, attributable to energetic particle precipitation in the South Atlantic anomaly region. The vertical drift velocity and magnetic meridional wind velocity derived for summer months during both solar minimum and solar maximum are compared with their values given by other published models. While the diurnal variation of the modeled vertical drift velocity shows general agreement with the values based on Jicamarca radar measurements (the exception being during the sunset-midnight period at solar maximum and between 2000-2300 LT at solar minimum), the magnetic meridional wind shows significant differences with respect to the Horizontal Wind Model 1990 (HWM90) [Hedin et al., 1991] during both solar minimum and solar maximum at Fortaleza and at locations conjugate to Fortaleza and Cachoeira Paulista.

  9. Fluid Dynamics of Bubbly Liquids

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  10. Planetary waves in the equatorial mesosphere and ionosphere measurements

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

  11. Observations of discrete harmonics emerging from equatorial noise.

    PubMed

    Balikhin, Michael A; Shprits, Yuri Y; Walker, Simon N; Chen, Lunjin; Cornilleau-Wehrlin, Nicole; Dandouras, Iannis; Santolik, Ondrej; Carr, Christopher; Yearby, Keith H; Weiss, Benjamin

    2015-01-01

    A number of modes of oscillations of particles and fields can exist in space plasmas. Since the early 1970s, space missions have observed noise-like plasma waves near the geomagnetic equator known as 'equatorial noise'. Several theories were suggested, but clear observational evidence supported by realistic modelling has not been provided. Here we report on observations by the Cluster mission that clearly show the highly structured and periodic pattern of these waves. Very narrow-banded emissions at frequencies corresponding to exact multiples of the proton gyrofrequency (frequency of gyration around the field line) from the 17th up to the 30th harmonic are observed, indicating that these waves are generated by the proton distributions. Simultaneously with these coherent periodic structures in waves, the Cluster spacecraft observes 'ring' distributions of protons in velocity space that provide the free energy for the waves. Calculated wave growth based on ion distributions shows a very similar pattern to the observations. PMID:26169360

  12. Observations of discrete harmonics emerging from equatorial noise

    PubMed Central

    Balikhin, Michael A.; Shprits, Yuri Y.; Walker, Simon N.; Chen, Lunjin; Cornilleau-Wehrlin, Nicole; Dandouras, Iannis; Santolik, Ondrej; Carr, Christopher; Yearby, Keith H.; Weiss, Benjamin

    2015-01-01

    A number of modes of oscillations of particles and fields can exist in space plasmas. Since the early 1970s, space missions have observed noise-like plasma waves near the geomagnetic equator known as ‘equatorial noise'. Several theories were suggested, but clear observational evidence supported by realistic modelling has not been provided. Here we report on observations by the Cluster mission that clearly show the highly structured and periodic pattern of these waves. Very narrow-banded emissions at frequencies corresponding to exact multiples of the proton gyrofrequency (frequency of gyration around the field line) from the 17th up to the 30th harmonic are observed, indicating that these waves are generated by the proton distributions. Simultaneously with these coherent periodic structures in waves, the Cluster spacecraft observes ‘ring' distributions of protons in velocity space that provide the free energy for the waves. Calculated wave growth based on ion distributions shows a very similar pattern to the observations. PMID:26169360

  13. Inertial confinement fusion based on the ion-bubble trigger

    SciTech Connect

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

    2014-10-15

    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.

  14. DNS studies of bubbly flows

    NASA Astrophysics Data System (ADS)

    Tryggvason, Gretar; Esmaeeli, Asghar; Biswas, Souvik

    2004-11-01

    Recent stuies of bubbly flows, using direct numerical simulations, are discussed. The goal of this study is to examine the collective behavior of many bubbles as the rise Reynolds number is increased and and a single bubble rises unsteadily, as well as to examine the motion of bubbles in channels. A front-tracking/finite volume method is used to fully resolve all flow scales, including the bubbles and the flow around them. Two cases are simulated, for one the bubbles remain nearly spherical and for the other case the bubbles are deformable and wobble. The wobbly bubbles remains relatively uniformly distributed and are not susceptible to the streaming instability found by Bunner and Tryggvason (2003) for deformable bubbles at lower rise Reynolds numbers. The more spherical bubbles, on the other hand, form transients ``rafts'' somewhat similar to those seen in potential flow simulation of many bubbles. For channel flow we compare results from direct numerical simulations of bubbly flow with prediction of the steady-state two-fluid model of Antal, Lahey, and Flaherty (1991). The simulations are done assuming a two-dimensional system and the model coefficients are adjusted slightly to match the data for upflow. The results generally agree reasonably well, even though the simulated void fraction is considerably higher than the one assumed in the derivation of the model. Research supported by DOE.

  15. Forming equatorial rings around dying stars

    NASA Astrophysics Data System (ADS)

    Akashi, Muhammad; Sabach, Efrat; Yogev, Ohad; Soker, Noam

    2015-10-01

    We suggest that clumpy dense outflowing equatorial rings around evolved giant stars, such as in supernova 1987A and the Necklace planetary nebula, are formed by bipolar jets that compress gas towards the equatorial plane. The jets are launched from an accretion disc around a stellar companion. Using the FLASH hydrodynamics numerical code we perform 3D numerical simulations, and show that bipolar jets expanding into a dense spherical shell can compress gas towards the equatorial plane and lead to the formation of an expanding equatorial ring. Rayleigh-Taylor instabilities in the interaction region break the ring to clumps. Under the assumption that the same ring formation mechanism operates in massive stars and in planetary nebulae, we find this mechanism to be more promising for ring formation than mass-loss through the second Lagrangian point. The jets account also for the presence of a bipolar nebula accompanying many of the rings.

  16. Forming equatorial rings around dying stars

    E-print Network

    Akashi, Muhammad; Yogev, Ohad; Soker, Noam

    2015-01-01

    We suggest that clumpy-dense outflowing equatorial rings around evolved giant stars, such as in supernova 1987A and the Necklace planetary nebula, are formed by bipolar jets that compress gas toward the equatorial plane. The jets are launched from an accretion disk around a stellar companion. Using the FLASH hydrodynamics numerical code we perform 3D numerical simulations, and show that bipolar jets expanding into a dense spherical shell can compress gas toward the equatorial plane and lead to the formation of an expanding equatorial ring. Rayleigh-Taylor instabilities in the interaction region break the ring to clumps. Under the assumption that the same ring-formation mechanism operates in massive stars and in planetary nebulae, we find this mechanism to be more promising for ring formation than mass loss through the second Lagrangian point. The jets account also for the presence of a bipolar nebula accompanying many of the rings.

  17. Equatorial Opportunities for Humans on Mars

    NASA Astrophysics Data System (ADS)

    Mitchell, J. L.; Christensen, P. R.

    2015-10-01

    The equatorial exploration zone presented in this abstract includes both geologic and resource-based sites of interest. Proximity to recurring slope lineae, chloride deposits, and representation of major geologic processes are included in this EZ.

  18. Decadal changes in the equatorial Pacific circulation 

    E-print Network

    Urizar, S. Cristina

    2002-01-01

    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...

  19. EQUATORIAL ZONAL JETS AND JUPITER's GRAVITY

    SciTech Connect

    Kong, D.; Liao, X.; Zhang, K.; Schubert, G.

    2014-08-20

    The depth of penetration of Jupiter's zonal winds into the planet's interior is unknown. A possible way to determine the depth is to measure the effects of the winds on the planet's high-order zonal gravitational coefficients, a task to be undertaken by the Juno spacecraft. It is shown here that the equatorial winds alone largely determine these coefficients which are nearly independent of the depth of the non-equatorial winds.

  20. The storm-time equatorial electrojet

    NASA Technical Reports Server (NTRS)

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

    1976-01-01

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

  1. The storm-time equatorial electrojet

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

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

  2. Double Bubble? No Trouble!

    ERIC Educational Resources Information Center

    Shaw, Mike I.; Smith, Greg F.

    1995-01-01

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

  3. The Liberal Arts Bubble

    ERIC Educational Resources Information Center

    Agresto, John

    2011-01-01

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

  4. First incoherent-scatter measurements of the equatorial E layer obtained with the ALTAIR radar

    SciTech Connect

    Tsunoda, R.T.

    1995-04-01

    The author describes the first coherent-scatter (IS) radar measurements made of the daytime E layer at equatorial latitudes. Using ALTAIR, a steerable IS radar located in the Kwajalein Atoll, the author is not only able to show that the E-layer profiles are consistent with those obtained in situ by rockets, but presents the first direct evidence of a latitudinal gradient in plasma density in the bottomside E layer that extended from 3{degrees}N dip latitude to beyond 6{degrees}N. The author suggests that the gradient involves the electrodynamic transport of metallic ions, e.g., the gradient could be produced by the equatorial metallic-ion fountain or possibly by the dumping of metallic ions at the base of the E layer by the wind-shear mechanism for sporadic E. This article is closed with a brief discussion of the implications of such a gradient on the equatorial electrojet. 16 refs., 4 figs.

  5. Bubbly Little Star

    NASA Technical Reports Server (NTRS)

    2007-01-01

    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.

  6. DNA denaturation bubbles at criticality

    E-print Network

    Theodorakopoulos, Nikos

    2008-01-01

    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.

  7. Layers in the equatorial mesosphere, motions and aerosol: rocket and radar measurements during EQUIS II

    NASA Astrophysics Data System (ADS)

    Lehmacher, G. A.; Croskey, C. L.; Mitchell, J. D.; Friedrich, M.; Torkar, K.; Lübken, F.-J.; Rapp, M.; Kudeki, E.

    2005-08-01

    The NASA EQUIS II (Equatorial Ionosphere Studies) campaign was conducted in August/September 2004 at U.S. Army Kwajalein Atoll/Reagan Test Site on Roi-Namur, Marshall Islands (9°N, 168°E). The LEMMA (Layers in the Equatorial Mesosphere, Motions and Aerosol) program was devoted to neutral and plasma density fluctuations in the equatorial mesosphere and lower thermosphere. One objective was to detect layers of small scale structures that might be related to mesospheric VHF radar echoes observed regularly at equatorial and low latitudes. The payload carried multiple instruments from U.S. and European investigators, including an ionization gauge for the first in situ measurements of neutral turbulence fluctuations in the equatorial mesosphere. One sounding rocket and three falling spheres were launched successfully on September 20, 2004, supported by a large, steerable 422 MHz UHF radar receiving incoherent backscatter from ~85-700 km. We give an overview of the investigation and present some results including the comparison of in situ and ground based electron density measurements, neutral temperature and wind structure, and observations of neutral and electron density fluctuations.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  9. Latitudinal comparisons of equatorial Pacific zooplankton

    NASA Astrophysics Data System (ADS)

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

    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.

  10. Ring Bubbles of Dolphins

    NASA Technical Reports Server (NTRS)

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

    1996-01-01

    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.

  11. Expansion of bubbles under a pulsatile flow regime in decompressed ovine blood vessels.

    PubMed

    Arieli, Ran; Marmur, Abraham

    2016-02-01

    After decompression of ovine large blood vessels, bubbles nucleate and expand at active hydrophobic spots on their luminal aspect. These bubbles will be in the path of the blood flow within the vessel, which might replenish the supply of gas-supersaturated plasma in their vicinity and thus, in contrast with our previous estimations, enhance their growth. We used the data from our previous study on the effect of pulsatile flow in ovine blood vessels stretched on microscope slides and photographed after decompression from hyperbaric exposure. We measured the diameter of 46 bubbles in 4 samples taken from 3 blood vessels (pulmonary artery, pulmonary vein, and aorta) in which both a "multi-bubble active spot" (MBAS)-which produces several bubbles at a time, and at least one "single-bubble active spot" (SBAS)-which produces a single bubble at a time, were seen together. The linear expansion rate for diameter in SBAS ranged from 0.077 to 0.498mm/min and in MBAS from 0.001 to 0.332mm/min. There was a trend toward a reduced expansion rate for bubbles in MBAS compared with SBAS. The expansion rate for bubbles in an MBAS when it was surrounded by others was very low. Bubble growth is related to gas tension, and under a flow regime, bubbles expand from a diameter of 0.1 to 1mm in 2-24min at a gas supersaturation of 620kPa and lower. There are two phases of bubble development. The slow and disperse initiation of active spots (from nanobubbles to gas micronuclei) continues for more than 1h, whereas the fast increase in size (2-24min) is governed by diffusion. Bubble-based decompression models should not artificially reduce diffusion constants, but rather take both phases of bubble development into consideration. PMID:26592146

  12. Solar Wind Effects on Post-Midnight Plasma Depletions Observed by C/NOFS

    NASA Astrophysics Data System (ADS)

    Roddy, P. A.; Burke, W. J.; Gentile, L. C.; Sterner, N. L.; Crown, M.; de La Beaujardiere, O.; Hunton, D. E.; Pfaff, R. F.

    2009-12-01

    Correlating coronal hole observations from SoHO and STEREO with solar wind data from ACE and plasma density and electric field measurements from C/NOFS has allowed us to develop a new technique for scintillation activity alerts during solar minimum. As a high speed stream (HSS) in the solar wind passed Earth in June 2008, instruments on the C/NOFS satellite recorded post-midnight equatorial plasma bubbles (EPBs) and longitudinally broad depletions. Eastward polarization electric fields were consistently detected within locally depleted flux tubes. At the leading edge of the HSS the interplanetary magnetic field rapidly intensified and rotated causing auroral electrojet currents to rise and fall within a few hours. As the electrojet relaxed, C/NOFS recorded a rapid transition from a weakly to a strongly disturbed equatorial ionosphere that lasted ~10 hours. Similar effects were observed during passage of a HSS on 13-15 March 2009. Recurrence of midlatitude coronal holes, primary source regions for HSSs, with solar rotation facilitated advanced warnings of conditions conducive for scintillation activity during 7-9 April 2009.

  13. Space plasma physics research

    NASA Technical Reports Server (NTRS)

    Comfort, Richard H.; Horwitz, James L.

    1993-01-01

    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.

  14. Interchange Instability and "Bubbles" Gravitational Rayleigh-Taylor

    E-print Network

    Mauel, Michael E.

    al., JGR (1994) Jovian day is 11 hours! #12;Interchange Bubble seen in Jovian Magnetosphere? B. H nonlinear coupling! #12;Simulating Resonant Interchanges Solved on a 64 x 64 grid: 8 hours on one 2.0 GHz, ... Gravitational Rayleigh-Taylor #12;Rayleigh-Taylor Instability in Magnetized Plasma ßAnisotropic! (constant along

  15. Multiscale equatorial electrojet turbulence:Baseline 2-D model

    NASA Astrophysics Data System (ADS)

    Hassan, Ehab; Horton, W.; Smolyakov, A. I.; Hatch, D. R.; Litt, S. K.

    2015-02-01

    The spatial and spectral characteristics of the turbulent plasma density, electric fields, and ion drift in ionospheric E region are studied using a new set of nonlinear plasma fluid equations. The fluid model combines both Farley-Buneman (Type-I) and Gradient-Drift (Type-II) plasma instabilities in the equatorial electrojet. In our unified model of the plasma instabilities, we include the ion viscosity in the ion momentum equation and electron inertia in the electron momentum equation. These two terms play an important role in stabilizing the growing modes in the linear regime and in driving the Farley-Buneman instability into the saturation state. The simulation results show good agreements with a number of features of rocket and radar observations, such as (1) saturation of plasma density perturbations depends on the solar condition and reaches 7-15% relative to the background, (2) fluctuation of the horizontal secondary electric field reaches 8-15 mV/m, (3) stabilization of the phase velocity of the perturbed density wave around the value of the ion-acoustic speed inside the electrojet, (4) "up-down" asymmetry in the vertical fluxes of the plasma density, (5) "east-west" asymmetry of the plasma zonal drifts, and (6) generation of small scale of the order of meter scale lengths irregularities embedded in large-scale structures. Spectral analysis of the density fluctuations reveals the energy cascade due to the nonlinear coupling between structures of different scales. The break-up of the large-scale structures into small-scale structures explains the disappearance of Type-II echoes in the presence of Type-I instabilities.

  16. The Compressibility Bubble

    NASA Technical Reports Server (NTRS)

    Stack, John

    1935-01-01

    Simultaneous air-flow photographs and pressure-distribution measurements have been made of the NACA 4412 airfoil at high speeds in order to determine the physical nature of the compressibility bubble. The flow photographs were obtained by the Schlieren method and the pressures were simultaneously measured for 54 stations on the 5-inch-chord wing by means of a multiple-tube photographic manometer. Pressure-measurement results and typical Schlieren photographs are presented. The general nature of the phenomenon called the "compressibility bubble" is shown by these experiments. The source of the increased drag is the compression shock that occurs, the excess drag being due to the conversion of a considerable amount of the air-stream kinetic energy into heat at the compression shock.

  17. Mechanisms of gas bubble retention

    SciTech Connect

    Gauglitz, P.A.; Mahoney, L.A.; Mendoza, D.P.; Miller, M.C.

    1994-09-01

    Retention and episodic release of flammable gases are critical safety concerns regarding double-shell tanks (DSTs) containing waste slurries. Previous investigations have concluded that gas bubbles are retained by the slurry that has settled at the bottom of the DST. However, the mechanisms responsible for the retention of these bubbles are not well understood. In addition, the presence of retained gas bubbles is expected to affect the physical properties of the sludge, but essentially no literature data are available to assess the effect of these bubbles. The rheological behavior of the waste, particularly of the settled sludge, is critical to characterizing the tendency of the waste to retain gas bubbles. The objectives of this study are to elucidate the mechanisms contributing to gas bubble retention and release from sludge such as is in Tank 241-SY-101, understand how the bubbles affect the physical properties of the sludge, develop correlations of these physical properties to include in computer models, and collect experimental data on the physical properties of simulated sludges with bubbles. This report presents a theory and experimental observations of bubble retention in simulated sludge and gives correlations and new data on the effect of gas bubbles on sludge yield strength.

  18. Sonoluminescence, sonochemistry and bubble dynamics of single bubble cavitation

    NASA Astrophysics Data System (ADS)

    Hatanaka, Shin-ichi

    2012-09-01

    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.

  19. Bubble dynamics in drinks

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-05-01

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

  1. Equatorial noise emissions with quasiperiodic modulation of wave intensity

    NASA Astrophysics Data System (ADS)

    N?mec, F.; Santolík, O.; Hrbá?ková, Z.; Pickett, J. S.; Cornilleau-Wehrlin, N.

    2015-04-01

    Equatorial noise (EN) emissions are electromagnetic wave events at frequencies between the proton cyclotron frequency and the lower hybrid frequency observed in the equatorial region of the inner magnetosphere. They propagate nearly perpendicular to the ambient magnetic field, and they exhibit a harmonic line structure characteristic of the proton cyclotron frequency in the source region. However, they were generally believed to be continuous in time. We investigate more than 2000 EN events observed by the Spatio-Temporal Analysis of Field Fluctuations and Wide-Band Data Plasma Wave investigation instruments on board the Cluster spacecraft, and we show that this is not always the case. A clear quasiperiodic (QP) time modulation of the wave intensity is present in more than 5% of events. We perform a systematic analysis of these EN events with QP modulation of the wave intensity. Such events occur usually in the noon-to-dawn magnetic local time sector. Their occurrence seems to be related to the increased geomagnetic activity, and it is associated with the time intervals of enhanced solar wind flow speeds. The modulation period of these events is on the order of minutes. Compressional ULF magnetic field pulsations with periods about double the modulation periods of EN wave intensity and magnitudes on the order of a few tenths of nanotesla were identified in about 46% of events. We suggest that these compressional magnetic field pulsations might be responsible for the observed QP modulation of EN wave intensity, in analogy to formerly reported VLF whistler mode QP events.

  2. Stable Multibubble Sonoluminescence Bubble Patterns

    SciTech Connect

    Posakony, Gerald J.; Greenwood, Lawrence R.; Ahmed, Salahuddin

    2006-06-30

    Multibubble standing wave patterns can be generated from a flat piezoceramic transducer element propagating into water. By adding a second transducer positioned at 90 degrees from the transducer generating the standing wave, a 3-dimensional volume of stable single bubbles can be established. Further, the addition of the second transducer stabilizes the bubble pattern so that individual bubbles may be studied. The size of the bubbles and the separation of the standing waves depend on the frequency of operation. Two transducers, operating at frequencies above 500 kHz, provided the most graphic results for the configuration used in this study. At these frequencies stable bubbles exhibit a bright sonoluminescence pattern. Whereas stable SBSL is well-known, stable MBSL has not been previously reported. This paper includes discussions of the acoustic responses, standing wave patterns, and pictorial results of the separation of individual bubble of sonoluminescence in a multibubble sonoluminescence environment.

  3. Equatorial waves in the stratosphere of Uranus

    NASA Technical Reports Server (NTRS)

    Hinson, David P.; Magalhaes, Julio A.

    1991-01-01

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

  4. Lunar influence on equatorial atmospheric angular momentum

    NASA Astrophysics Data System (ADS)

    Bizouard, C.; Zotov, L.; Sidorenkov, N.

    2015-08-01

    This study investigates the relationship between the equatorial atmospheric angular momentum oscillation in the non-rotating frame and lunar tidal potential. Between 2 and 30 days, the corresponding equatorial component is mostly constituted of prograde circular motions, especially of a harmonic at 13.6 days, and of a weekly broad band variation. A simple equilibrium tide model explains the 13.6-day pressure term as result of the O1 lunar tide; the tidal lunar origin of the whole band from 2 to 30 days is attested by specific features, not occurring for seasonal band dominated by the solar thermal effect.

  5. Neutron detection via bubble chambers.

    PubMed

    Jordan, D V; Ely, J H; Peurrung, A J; Bond, L J; Collar, J I; Flake, M; Knopf, M A; Pitts, W K; Shaver, M; Sonnenschein, A; Smart, J E; Todd, L C

    2005-01-01

    Research investigating the application of pressure-cycled bubble chambers to fast neutron detection is described. Experiments with a Halon-filled chamber showed clear sensitivity to an AmBe neutron source and insensitivity to a (137)Cs gamma source. Bubble formation was documented using high-speed photography, and a ceramic piezo-electric transducer element registered the acoustic signature of bubble formation. In a second set of experiments, the bubble nucleation response of a Freon-134a chamber to an AmBe neutron source was documented with high-speed photography. PMID:16005238

  6. Bubble measuring instrument and method

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  7. Mid-Infrared Galactic Bubbles

    NASA Astrophysics Data System (ADS)

    Corn, Tyler; Watson, C.

    2008-03-01

    Using 2MASS, GLIMPSE, MIPSGAL, and MAGPIES surveys, we analyzed three bubbles centered at G8.1238-0.47712, G9.83464-0.71713, and G353.35010-0.14083. Each bubble has a circular PAH emission surrounding hot dust. Two bubbles observed also have PAH emission surrounding ionized gas. Physical properties (stellar mass, accretion rate, disk mass, inclination, etc.) are given for each YSO using a model fitter based on radiative transfer numerical simulations and a chi-squared minimization technique. YSOs are suggestive of triggered star formation in two bubbles. Ionizing stars can also be determined.

  8. When sound slows down bubbles

    E-print Network

    Remi Dangla; Cedric Poulain

    2010-04-06

    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.

  9. Droplets, Bubbles and Ultrasound Interactions.

    PubMed

    Shpak, Oleksandr; Verweij, Martin; de Jong, Nico; Versluis, Michel

    2016-01-01

    The interaction of droplets and bubbles with ultrasound has been studied extensively in the last 25 years. Microbubbles are broadly used in diagnostic and therapeutic medical applications, for instance, as ultrasound contrast agents. They have a similar size as red blood cells, and thus are able to circulate within blood vessels. Perfluorocarbon liquid droplets can be a potential new generation of microbubble agents as ultrasound can trigger their conversion into gas bubbles. Prior to activation, they are at least five times smaller in diameter than the resulting bubbles. Together with the violent nature of the phase-transition, the droplets can be used for local drug delivery, embolotherapy, HIFU enhancement and tumor imaging. Here we explain the basics of bubble dynamics, described by the Rayleigh-Plesset equation, bubble resonance frequency, damping and quality factor. We show the elegant calculation of the above characteristics for the case of small amplitude oscillations by linearizing the equations. The effect and importance of a bubble coating and effective surface tension are also discussed. We give the main characteristics of the power spectrum of bubble oscillations. Preceding bubble dynamics, ultrasound propagation is introduced. We explain the speed of sound, nonlinearity and attenuation terms. We examine bubble ultrasound scattering and how it depends on the wave-shape of the incident wave. Finally, we introduce droplet interaction with ultrasound. We elucidate the ultrasound-focusing concept within a droplets sphere, droplet shaking due to media compressibility and droplet phase-conversion dynamics. PMID:26486337

  10. Bubble Measuring Instrument and Method

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  11. Helium bubble bursting in tungsten

    SciTech Connect

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

    2013-12-28

    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.

  12. C/NOFS Observations of AC Electric Field Fields Associated with Equatorial Spread-F

    NASA Technical Reports Server (NTRS)

    Pfaff, R.; Liebrecht, C.

    2009-01-01

    The Vector Electric Field Investigation (VEFI) on the C/NOFS equatorial satellite provides a unique data set in which to acquire detailed knowledge of irregularities associated with the equatorial ionosphere and in particular with spread-F depletions. We present vector AC electric field observations, primarily gathered within the ELF band (1 Hz to 250 Hz) on C/NOFS that address a variety of key questions regarding how plasma irregularities, from meter to kilometer scales, are created and evolve. The data will be used to explore the anisotropy/isotropy of the waves, their wavelength and phase velocity, as well as their spectral distributions. When analyzed in conjunction with the driving DC electric fields and detailed plasma number density measurements, the combined data reveal important information concerning the instability mechanisms themselves. We also present high resolution, vector measurements of intense lower hybrid waves that have been detected on numerous occasions by the VEFI burst memory VLF electric field channels.

  13. Three-Dimensional Numerical Simulations of Equatorial Spread F: Results and Observations in the Pacific Sector

    NASA Technical Reports Server (NTRS)

    Aveiro, H. C.; Hysell, D. L.; Caton, R. G.; Groves, K. M.; Klenzing, J.; Pfaff, R. F.; Stoneback, R.; Heelis, R. A.

    2012-01-01

    A three-dimensional numerical simulation of plasma density irregularities in the postsunset equatorial F region ionosphere leading to equatorial spread F (ESF) is described. The simulation evolves under realistic background conditions including bottomside plasma shear flow and vertical current. It also incorporates C/NOFS satellite data which partially specify the forcing. A combination of generalized Rayleigh-Taylor instability (GRT) and collisional shear instability (CSI) produces growing waveforms with key features that agree with C/NOFS satellite and ALTAIR radar observations in the Pacific sector, including features such as gross morphology and rates of development. The transient response of CSI is consistent with the observation of bottomside waves with wavelengths close to 30 km, whereas the steady state behavior of the combined instability can account for the 100+ km wavelength waves that predominate in the F region.

  14. Implications of the small aspect angles of equatorial spread F

    SciTech Connect

    Hysell, D.L.; Farley, D.T.

    1996-03-01

    Small-scale equatorial spread F irregularities are almost perfectly aligned with the geomagnetic field. The authors develop here an analytic plasma kinetic theory of small-scale, quasi-field-aligned irregularities that include ion viscosity and finite Larmor radius effects. They conclude, for one thing, that the measured aspect angles are too small to be consistent with a dissipative drift wave source of 3-m irregularities. Nonlinearly driven flute modes appear to be the only available mechanism. The authors compare the relative influence of parallel and perpendicular dissipation and conclude that the aspect width depends only weakly on any single geophysical parameters, such as collision frequency, gradient length, temperature, etc. This finding is consistent with their observation that the measured aspect angles vary little with altitude and only weakly with instability level. 29 refs., 5 figs.

  15. Statistical description of low-latitude plasma blobs as observed by DMSP F15 and KOMPSAT-1

    NASA Astrophysics Data System (ADS)

    Park, J.; Min, K. W.; Kim, V. P.; Kil, H.; Kim, H. J.; Lee, J. J.; Lee, E.; Kim, S. J.; Lee, D. Y.; Hairston, M.

    We investigated the global distribution of low-latitude plasma blobs using in-situ plasma density measurements from Korea Multi-Purpose Satellite-1 KOMPSAT-1 and Defense Meteorological Satellite Program DMSP F15 The seasonal-longitudinal S L distribution of blobs is generally consistent with that of equatorial plasma bubbles EPBs but between them exist two notable differences First during equinoxes the blob activity is inhibited around the Atlantic region Second during the June solstice the African peak is rather suppressed in the distribution KOMPSAT-1 at the lower altitude encountered blobs more frequently than DMSP F15 The occurrence probability of plasma blobs is less subjected to the yearly variation of solar activity And the latitudinal distribution of the blobs shows strong asymmetry during solstices Most of them are concentrated on the winter hemisphere where the background density is low and the inter-hemispheric plasma transport is poleward along the geomagnetic field line And the asymmetry becomes weak as the solar activity decreases suggesting that the blob generation bears connection with the fountain effect inside EPBs and the poleward plasma transport

  16. Abnormal evening vertical plasma drift and effects on ESF and EIA over Brazil-South Atlantic sector during the 30 October 2003 superstorm

    NASA Astrophysics Data System (ADS)

    Abdu, M. A.; de Paula, E. R.; Batista, I. S.; Reinisch, B. W.; Matsuoka, M. T.; Camargo, P. O.; Veliz, O.; Denardini, C. M.; Sobral, J. H. A.; Kherani, E. A.; de Siqueira, P. M.

    2008-07-01

    Equatorial F region vertical plasma drifts, spread F and anomaly responses, in the south American longitude sector during the superstorm of 30 October 2003, are analyzed using data from an array of instruments consisting of Digisondes, a VHF radar, GPS TEC and scintillation receivers in Brazil, and a Digisonde and a magnetometer in Jicamarca, Peru. Prompt penetrating eastward electric field of abnormally large intensity drove the F layer plasma up at a velocity ˜1200 ms-1 during post dusk hours in the eastern sector over Brazil. The equatorial anomaly was intensified and expanded poleward while the development of spread F/plasma bubble irregularities and GPS signal scintillations were weaker than their quiet time intensity. Significantly weaker F region response over Jicamarca presented a striking difference in the intensity of prompt penetration electric field between Peru and eastern longitudes of Brazil. The enhanced post dusk sector vertical drift over Brazil is attributed to electro-dynamics effects arising energetic particle precipitation in the South Atlantic Magnetic Anomaly (SAMA). These extraordinary results and their longitudinal differences are presented and discussed in this paper.

  17. Bubble levitation and translation under single-bubble sonoluminescence conditions

    NASA Astrophysics Data System (ADS)

    Matula, Thomas J.

    2003-08-01

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

  18. Bubble levitation and translation under single-bubble sonoluminescence conditions.

    PubMed

    Matula, Thomas J

    2003-08-01

    Bubble levitation in an acoustic standing wave is re-examined for conditions relevant to single-bubble sonoluminescence. Unlike a previous examination [Matula et al., J. Acoust. Soc. Am. 102, 1522-1527 (1997)], the stable parameter space [Pa,R0] is accounted for in this realization. Forces such as the added mass force and drag are included, and the results are compared with a simple force balance that equates the Bjerknes force to the buoyancy force. Under normal sonoluminescence conditions, the comparison is quite favorable. A more complete accounting of the forces shows that a stably levitated bubble does undergo periodic translational motion. The asymmetries associated with translational motion are hypothesized to generate instabilities in the spherical shape of the bubble. A reduction in gravity results in reduced translational motion. It is hypothesized that such conditions may lead to increased light output from sonoluminescing bubbles. PMID:12942960

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

    PubMed

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

    2015-01-01

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

  20. Equatorial currents in the Western Indian ocean.

    PubMed

    Luyten, J R; Fieux, M; Gonella, J

    1980-08-01

    Measurements were made in the equatorial Indian Ocean during spring and summer 1979 from the Somali coast to 62 degrees E in the interior of the western basin. The detailed vertical profiles of horizontal current show that the energetic dominance throughout the region of variability was on vertical scales of several hundreds of meters, confined to within a few degrees of the equator, as observed in 1976. The near-surface equatorial circulation responded directly to variations in the wind field, and satellite-tracked drifter buoys showed the equatorial surface jet extending across the width of the ocean. This eastward flow is generated by the eastward winds that appear in the interval between the northeast and southwest monsoons. The zonal velocity fluctuations extended in a consistent pattern over the observation region. The time and meridional scales of the variability were similar to those observed in 1976, suggesting that the velocity field is dominated by long-term, equatorially trapped motions with long zonal scales. PMID:17756843

  1. Influence of the equatorial deep jets on the north equatorial countercurrent

    NASA Astrophysics Data System (ADS)

    Matthießen, Jan-Dirk; Greatbatch, Richard J.; Brandt, Peter; Claus, Martin; Didwischus, Sven-Helge

    2015-08-01

    An ocean circulation model is run using two different idealized equatorial basin configurations under steady wind forcing. Both model versions produce bands of vertically alternating zonal flow at depth, similar to observed Equatorial Deep Jets (EDJs) and with a time scale corresponding to that of the gravest equatorial basin mode for the dominant baroclinic vertical normal mode. Both model runs show evidence for enhanced variability in the surface signature of the North Equatorial Counter Current (NECC) with the same time scale. We also find the same link between the observed NECC and the EDJs in the Atlantic by comparing the signature of the EDJ in moored zonal velocity data at 23° W on the equator with the signature of the NECC in geostrophic velocities from altimeter data. We argue that the presence of a peak in variability in the NECC associated with the EDJ basin mode period is evidence that the influenceatthis time scale is upward, from the EDJ to the NECC.

  2. Subsurface ocean argon disequilibrium reveals the equatorial Pacific shadow zone

    E-print Network

    Subsurface ocean argon disequilibrium reveals the equatorial Pacific shadow zone Eric Gehrie,1), Subsurface ocean argon disequilibrium reveals the equatorial Pacific shadow zone, Geophys. Res. Lett., 33, L, 1972]. We present new data from the equatorial Pacific Ocean. 2. Methods 2.1. Measurement [6] Samp

  3. Scholarly Paper Coupled Instability in the Equatorial Pacific Ocean

    E-print Network

    Maryland at College Park, University of

    Scholarly Paper Coupled Instability in the Equatorial Pacific Ocean Hua Chen Advisor: Raghu's a cycle or an event depends on the mean state of equatorial Pacific Ocean, which is influenced by mean problem in the equatorial Pacific ocean. The control run with a coupling coefficient 0.4 and relatively

  4. Optical behavior of surface bubbles

    NASA Astrophysics Data System (ADS)

    Straulino, Samuele; Gambi, Cecilia M. C.; Molesini, Giuseppe

    2015-11-01

    The observation of diamond-like light spots produced by surface bubbles obliquely illuminated is reported. The phenomenon is discussed in terms of geometrical optics, and an explanation is provided attributing the effect to the astigmatism introduced by the deformation of the liquid surface surrounding the bubble. An essential ray tracing program is outlined and used to reconstruct the observed phenomenon numerically.

  5. Wave Forcing of Saturn's Equatorial Oscillation

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  6. Bubble formation in microgravity

    NASA Technical Reports Server (NTRS)

    Antar, Basil N.

    1994-01-01

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

  7. Bubble formation in microgravity

    NASA Technical Reports Server (NTRS)

    Antar, Basil N.

    1996-01-01

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

  8. Mechanisms of single bubble cleaning.

    PubMed

    Reuter, Fabian; Mettin, Robert

    2016-03-01

    The dynamics of collapsing bubbles close to a flat solid is investigated with respect to its potential for removal of surface attached particles. Individual bubbles are created by nanosecond Nd:YAG laser pulses focused into water close to glass plates contaminated with melamine resin micro-particles. The bubble dynamics is analysed by means of synchronous high-speed recordings. Due to the close solid boundary, the bubble collapses with the well-known liquid jet phenomenon. Subsequent microscopic inspection of the substrates reveals circular areas clean of particles after a single bubble generation and collapse event. The detailed bubble dynamics, as well as the cleaned area size, is characterised by the non-dimensional bubble stand-off ?=d/Rmax, with d: laser focus distance to the solid boundary, and Rmax: maximum bubble radius before collapse. We observe a maximum of clean area at ??0.7, a roughly linear decay of the cleaned circle radius for increasing ?, and no cleaning for ?>3.5. As the main mechanism for particle removal, rapid flows at the boundary are identified. Three different cleaning regimes are discussed in relation to ?: (I) For large stand-off, 1.8bubble collapse induced vortex flows touch down onto the substrate and remove particles without significant contact of the gas phase. (II) For small distances, ?<1.1, the bubble is in direct contact with the solid. Fast liquid flows at the substrate are driven by the jet impact with its subsequent radial spreading, and by the liquid following the motion of the collapsing and rebounding bubble wall. Both flows remove particles. Their relative timing, which depends sensitively on the exact ?, appears to determine the extension of the area with forces large enough to cause particle detachment. (III) At intermediate stand-off, 1.1bubble collapse touches the substrate, but acts with cleaning mechanisms similar to an effective small ? collapse: particles are removed by the jet flow and the flow induced by the bubble wall oscillation. Furthermore, the observations reveal that the extent of direct bubble gas phase contact to the solid is partially smaller than the cleaned area, and it is concluded that three-phase contact line motion is not a major cause of particle removal. Finally, we find a relation of cleaning area vs. stand-off ? that deviates from literature data on surface erosion. This indicates that different effects are responsible for particle removal and for substrate damage. It is suggested that a trade-off of cleaning potential and damage risk for sensible surfaces might be achieved by optimising ?. PMID:26187759

  9. Signature of anisotropic bubble collisions

    NASA Astrophysics Data System (ADS)

    Salem, Michael P.

    2010-09-01

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

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

    SciTech Connect

    Guo Fulai; Mathews, William G.; Oh, S. Peng

    2012-09-10

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

  11. Roles of Equatorial Waves and Western Boundary Reflection in the Seasonal Circulation of the Equatorial Indian Ocean

    E-print Network

    Han, Weiqing

    of the Equatorial Indian Ocean DONGLIANG YUAN Institute of Oceanology, Chinese Academy of Sciences, and First boundary reflection in the seasonal circulation of the equatorial Indian Ocean. The western boundary semiannual oscillations of surface zonal currents in the central equatorial Indian Ocean are investigated

  12. Micro Bubble Trapping By Acoustic Energy

    NASA Astrophysics Data System (ADS)

    Yoshiki, Yamakoshi

    2005-03-01

    Micro bubble trapping by acoustic energy is a promising technology for a future drug or gene delivery system, because the method can control the bubble dynamics using an applied ultrasonic wave. In this paper, acoustic radiation forces which are applied to the micro bubbles are reviewed as well as their applications for micro bubble manipulation. One of the problems in micro bubble trapping by acoustic energy is that the force applied to the micro bubbles is insufficient for some bubbles. This is severe problem when the bubble has a relatively hard shell. In order to increase the trapping force on the micro bubbles, a novel method is proposed. This method uses seed bubbles in order to manipulate target bubbles.

  13. Lithospheric Flexural Modeling of Iapetus' Equatorial Ridge

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    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.

  14. Strings on Bubbling Geometries

    E-print Network

    Hai Lin; Alexander Morisse; Jonathan P. Shock

    2011-07-27

    We study gauge theory operators which take the form of a product of a trace with a Schur polynomial, and their string theory duals. These states represent strings excited on bubbling AdS geometries which are dual to the Schur polynomials. These geometries generically take the form of multiple annuli in the phase space plane. We study the coherent state wavefunction of the lattice, which labels the trace part of the operator, for a general Young tableau and their dual description on the droplet plane with a general concentric ring pattern. In addition we identify a density matrix over the coherent states on all the geometries within a fixed constraint. This density matrix may be used to calculate the entropy of a given ensemble of operators. We finally recover the BMN string spectrum along the geodesic near any circle from the ansatz of the coherent state wavefunction.

  15. Strings on bubbling geometries

    NASA Astrophysics Data System (ADS)

    Lin, Hai; Morisse, Alexander; Shock, Jonathan P.

    2010-06-01

    We study gauge theory operators which take the form of a product of a trace with a Schur polynomial, and their string theory duals. These states represent strings excited on bubbling AdS geometries which are dual to the Schur polynomials. These geometries generically take the form of multiple annuli in the phase space plane. We study the coherent state wavefunction of the lattice, which labels the trace part of the operator, for a general Young tableau and their dual description on the droplet plane with a general concentric ring pattern. In addition we identify a density matrix over the coherent states on all the geometries within a fixed constraint. This density matrix may be used to calculate the entropy of a given ensemble of operators. We finally recover the BMN string spectrum along the geodesic near any circle from the ansatz of the coherent state wave-function.

  16. Strings on Bubbling Geometries

    E-print Network

    Lin, Hai; Shock, Jonathan P

    2010-01-01

    We study gauge theory operators which take the form of a product of a trace with a Schur polynomial, and their string theory duals. These states represent strings excited on bubbling AdS geometries which are dual to the Schur polynomials. These geometries generically take the form of multiple annuli in the phase space plane. We study the coherent state wavefunction of the lattice, which labels the trace part of the operator, for a general Young tableau and their dual description on the droplet plane with a general concentric ring pattern. In addition we identify a density matrix over the coherent states on all the geometries within a fixed constraint. This density matrix may be used to calculate the entropy of a given ensemble of operators. We finally recover the BMN string spectrum along the geodesic near any circle from the ansatz of the coherent state wavefunction.

  17. Anatomy of bubbling solutions

    E-print Network

    Kostas Skenderis; Marika Taylor

    2008-05-23

    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.

  18. Variability of an additional layer in the equatorial ionosphere over Fortaleza

    NASA Astrophysics Data System (ADS)

    Balan, N.; Batista, I. S.; Abdu, M. A.; Bailey, G. J.; Watanabe, S.; MacDougall, J.; Sobral, J. H. A.

    2000-05-01

    The day-to-day variations (or the weather) of an additional layer, called the F3 layer, that has been predicted to exist at altitudes above the F2 peak in the equatorial ionosphere are studied through ionosonde observations and theoretical modeling. The ionograms recorded in 1995 at the equatorial station Fortaleza (4°S, 38°W dip angle 9°S) in Brazil show the occurrence of the F3 layer during daytime from 0800 to 1630 LT, with the duration of occurrence ranging from 15 min to 6 hours. Although the layer occurs most frequently (75% of the days) in local summer as previously predicted, there are consecutive and individual magnetically quiet and disturbed days when the layer does not occur. There are also days when the layer reoccurs. The model results, obtained using the Sheffield University plasmasphere-ionosphere model, show that the day-to-day variations of the F3 layer arise from the corresponding variations of the vertical plasma velocity. The layer occurs when the time-cumulative vertical velocity displaces the daytime F2 peak to high altitudes, to form the F3 layer, while the normal F2 layer develops at low altitudes. Sudden displacements result in more distinct F3 layers than gradual displacements. Model results also show that the plasma temperature within the F3 layer decreases as the plasma density increases, and, like the plasma density, the plasma temperature also undergoes large day-to-day variations.

  19. Hot Gas in the Circumstellar Bubble S308

    E-print Network

    Y. -H. Chu; M. A. Guerrero; R. A. Gruendl; G. Garcia-Segura; H. J. Wendker

    2003-09-05

    S308 is a circumstellar bubble blown by the WN4 star HD50896. It is one of the only two single-star bubbles that show detectable diffuse X-ray emission. We have obtained XMM-Newton EPIC observations of the northwest quadrant of S308. The diffuse X-ray emission shows a limb-brightened morphology, with a clear gap extending from the outer edge of the diffuse X-ray emission to the outer rim of the nebular shell. The X-ray spectrum of the diffuse emission is very soft, and is well fitted by an optically thin plasma model for a N-enriched plasma at temperatures of ~1.1x10^6 K. A hotter gas component may exist but its temperature is not well constrained as it contributes less than 6% of the observed X-ray flux. The total X-ray luminosity of S308, extrapolated from the bright northwest quadrant, is <=(1.2+-0.5)x10^{34} ergs/s. We have used the observed bubble dynamics and the physical parameters of the hot interior gas of S308 in conjunction with the circumstellar bubble model of Garcia-Segura & Mac Low (1995) to demonstrate that the X-ray-emitting gas must be dominated by mixed-in nebular material.

  20. Fuel system bubble dissipation device

    SciTech Connect

    Iseman, W.J.

    1987-11-03

    This patent describes a bubble dissipation device for a fuel system wherein fuel is delivered through a fuel line from a fuel tank to a fuel control with the pressure of the fuel being progressively increased by components including at least one pump stage and an ejector in advance of the pump state. The ejector an ejector casing with a wall defining an elongate tubular flow passage which forms a portion of the fuel line to have all of the fuel flow through the tubular flow passage in flowing from the fuel tank to the fuel control, a nozzle positioned entirely within the tubular flow passage and spaced from the wall to permit fuel flow. The nozzle has an inlet and an outlet with the inlet connected to the pump stage to receive fuel under pressure continuously from the pump stage, a bubble accumulation chamber adjoining and at a level above the ejector casing and operatively connected to the fuel line in advance of the ejector casing. The bubble accumulation chamber is of a size to function as a fuel reservoir and hold an air bubble containing vapor above the level of fuel therein and having an outlet adjacent the bottom thereof operatively connected to the tubular flow passage in the ejector casing at an inlet end, a bubble accumulation chamber inlet above the level of the bubble accumulation chamber outlet whereby fuel can flow through the bubble accumulation chamber from the inlet to the outlet thereof with a bubble in the fuel rising above the fuel level in the bubble accumulation chamber.

  1. Bubble Growth in Lunar Basalts

    NASA Astrophysics Data System (ADS)

    Zhang, Y.

    2009-05-01

    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.

  2. Metallic ions in the equatorial ionosphere

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

    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.

  3. Swarm equatorial electric field chain: First results

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    The eastward equatorial electric field (EEF) in the E region ionosphere drives many important phenomena at low latitudes. We developed a method of estimating the EEF from magnetometer measurements of near-polar orbiting satellites as they cross the magnetic equator, by recovering a clean signal of the equatorial electrojet current and modeling the observed current to determine the electric field present during the satellite pass. This algorithm is now implemented as an official Level-2 Swarm product. Here we present first results of EEF estimates from nearly a year of Swarm data. We find excellent agreement with independent measurements from the ground-based coherent scatter radar at Jicamarca, Peru, as well as horizontal field measurements from the West African Magnetometer Network magnetic observatory chain. We also calculate longitudinal gradients of EEF measurements made by the A and C lower satellite pair and find gradients up to about 0.05 mV/m/deg with significant longitudinal variability.

  4. AMISR-14: Observations of equatorial spread F

    NASA Astrophysics Data System (ADS)

    Rodrigues, F. S.; Nicolls, M. J.; Milla, M. A.; Smith, J. M.; Varney, R. H.; Strømme, A.; Martinis, C.; Arratia, J. F.

    2015-07-01

    A new, 14-panel Advanced Modular Incoherent Scatter Radar (AMISR-14) system was recently deployed at the Jicamarca Radio Observatory. We present results of the first coherent backscatter radar observations of equatorial spread F(ESF) irregularities made with the system. Colocation with the 50 MHz Jicamarca Unattended Long-term studies of the Ionosphere and Atmosphere (JULIA) radar allowed unique simultaneous observations of meter and submeter irregularities. Observations from both systems produced similar Range-Time-Intensity maps during bottom-type and bottomside ESF events. We were also able to use the electronic beam steering capability of AMISR-14 to "image" scattering structures in the magnetic equatorial plane and track their appearance, evolution, and decay with a much larger field of view than previously possible at Jicamarca. The results suggest zonal variations in the instability conditions leading to irregularities and demonstrate the dynamic behavior of F region scattering structures as they evolve and drift across the radar beams.

  5. Global Structure of Isothermal Diffuse X-Ray Emission along the Fermi Bubbles

    NASA Astrophysics Data System (ADS)

    Kataoka, J.; Tahara, M.; Totani, T.; Sofue, Y.; Inoue, Y.; Nakashima, S.; Cheung, C. C.

    2015-07-01

    In our previous works, we found absorbed thermal X-ray plasma with kT ? 0.3 keV observed ubiquitously near the edges of the Fermi bubbles and interpreted this emission as weakly shock-heated Galactic halo gas. Here we present a systematic and uniform analysis of archival Suzaku (29 pointings; 6 newly presented) and Swift (68 pointings; 49 newly presented) data within Galactic longitudes | l| < 20° and latitude 5°? | b| < 60°, covering the whole extent of the Fermi bubbles. We show that the plasma temperature is constant at kT ? 0.30 ± 0.07 keV, while the emission measure (EM) varies by an order of magnitude, increasing toward the Galactic center (i.e., low | b| ) with enhancements at the North Polar Spur (NPS), SE-claw, and NW-clump features. Moreover, the EM distribution of kT ? 0.30 keV plasma is highly asymmetric in the northern and southern bubbles. Although the association of the X-ray emission with the bubbles is not conclusive, we compare the observed EM properties with simple models assuming (i) a filled halo without bubbles, whose gas density follows a hydrostatic isothermal model (King profile), and (ii) a bubble-in-halo in which two identical bubbles expand into the halo, forming thick shells of swept halo gas. We argue that the EM profile in the north (b > 0°) favors (ii), whereas that of the south (b < 0°) is rather close to (i), but a weak excess signature is clearly detected also in the south like NPS (South Polar Spur). Such an asymmetry, if due to the bubbles, cannot be fully understood only by the inclination of bubbles’ axis against the Galactic disk normal, thus suggesting asymmetric outflow due to different environmental/initial conditions.

  6. Global Specification of the Post-Sunset Equatorial Ionization Anomaly

    NASA Astrophysics Data System (ADS)

    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

    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).

  7. Equatorial deep jets in the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Ponte, Rui M.; Luyten, James; Richardson, Philip L.

    1990-04-01

    We report here a vertical profile of velocity measured in the equatorial Atlantic (0°00'N, 30°22'W) which reveals short vertical scale zonal jets with amplitudes of 10-20 cm s -1 over the upper 2500 m, alternating in the east-west direction with depth. Particularly prominent was an eastward jet centered at a depth of 1000 m with an amplitude of 28 cm s -1.

  8. The Physics of Ion Decoupling in Magnetized Plasma Explosions

    SciTech Connect

    Hewett, D; Larson, D; Brecht, S

    2011-02-08

    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.

  9. Aspherical bubble dynamics and oscillation times

    SciTech Connect

    Vogel, A.; Noack, J.; Chapyak, E.J.; Godwin, R.P.

    1999-06-01

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

  10. A Campaign to Study Equatorial Ionospheric Phenomena over Guam

    NASA Astrophysics Data System (ADS)

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

    2007-05-01

    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.

  11. An equatorial oscillation in Saturn's middle atmosphere.

    PubMed

    Fouchet, T; Guerlet, S; Strobel, D F; Simon-Miller, A A; Bézard, B; Flasar, F M

    2008-05-01

    The middle atmospheres of planets are driven by a combination of radiative heating and cooling, mean meridional motions, and vertically propagating waves (which originate in the deep troposphere). It is very difficult to model these effects and, therefore, observations are essential to advancing our understanding of atmospheres. The equatorial stratospheres of Earth and Jupiter oscillate quasi-periodically on timescales of about two and four years, respectively, driven by wave-induced momentum transport. On Venus and Titan, waves originating from surface-atmosphere interaction and inertial instability are thought to drive the atmosphere to rotate more rapidly than the surface (superrotation). However, the relevant wave modes have not yet been precisely identified. Here we report infrared observations showing that Saturn has an equatorial oscillation like those found on Earth and Jupiter, as well as a mid-latitude subsidence that may be associated with the equatorial motion. The latitudinal extent of Saturn's oscillation shows that it obeys the same basic physics as do those on Earth and Jupiter. Future highly resolved observations of the temperature profile together with modelling of these three different atmospheres will allow us determine the wave mode, the wavelength and the wave amplitude that lead to middle atmosphere oscillation. PMID:18464737

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

    SciTech Connect

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

    2014-06-15

    The design of the ITER Electron Cyclotron Heating and Current Drive (EC H and 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.

  13. How does a bubble chamber work?

    SciTech Connect

    Konstantinov, D.; Homsi, W.; Luzuriaga, J.; Su, C.K.; Weilert, M.A.; Maris, H.J.

    1998-11-01

    A charged particle passing through a bubble chamber produces a track of bubbles. The way in which these bubbles are produced has been a matter of some controversy. The authors consider the possibility that in helium and hydrogen bubble chambers the production of bubbles is primarily a mechanical process, rather than a thermal process as has often been assumed. The model the authors propose gives results which are in excellent agreement with experiment.

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

    E-print Network

    S. Heinz; E. Churazov

    2005-09-26

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

  15. A Comparison of Solar Cycle Variations in the Equatorial Rotation Rates of the Sun's Subsurface, Surface, Corona, and Sunspot Groups

    NASA Astrophysics Data System (ADS)

    Javaraiah, J.

    2013-10-01

    Using the Solar Optical Observing Network (SOON) sunspot-group data for the period 1985 - 2010, the variations in the annual mean equatorial-rotation rates of the sunspot groups are determined and compared with the known variations in the solar equatorial-rotation rates determined from the following data: i) the plasma rotation rates at 0.94R?,0.95R?,…,1.0R? measured by the Global Oscillation Network Group (GONG) during the period 1995 - 2010, ii) the data on the soft-X-ray corona determined from Yohkoh/SXT full-disk images for the years 1992 - 2001, iii) the data on small bright coronal structures (SBCS) that were traced in Solar and Heliospheric Observatory (SOHO)/EIT images during the period 1998 - 2006, and iv) the Mount Wilson Doppler-velocity measurements during the period 1986 - 2007. A large portion (up to ? 30? latitude) of the mean differential-rotation profile of the sunspot groups lies between those of the internal differential-rotation rates at 0.94R? and 0.98R?. The variation in the yearly mean equatorial-rotation rate of the sunspot groups seems to be lagging behind that of the equatorial-rotation rate determined from the GONG measurements by one to two years. The amplitude of the GONG measurements is very small. The solar-cycle variation in the equatorial-rotation rate of the solar corona closely matches that determined from the sunspot-group data. The variation in the equatorial-rotation rate determined from the Mount Wilson Doppler-velocity data closely resembles the corresponding variation in the equatorial-rotation rate determined from the sunspot-group data that included the values of the abnormal angular motions (> |3?| day-1) of the sunspot groups. Implications of these results are pointed out.

  16. Transient bubbles, bublets and breakup

    NASA Astrophysics Data System (ADS)

    Keen, Giles; Blake, John

    1999-11-01

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

  17. Magnetism. Blowing magnetic skyrmion bubbles.

    PubMed

    Jiang, Wanjun; Upadhyaya, Pramey; Zhang, Wei; Yu, Guoqiang; Jungfleisch, M Benjamin; Fradin, Frank Y; Pearson, John E; Tserkovnyak, Yaroslav; Wang, Kang L; Heinonen, Olle; te Velthuis, Suzanne G E; Hoffmann, Axel

    2015-07-17

    The formation of soap bubbles from thin films is accompanied by topological transitions. Here we show how a magnetic topological structure, a skyrmion bubble, can be generated in a solid-state system in a similar manner. Using an inhomogeneous in-plane current in a system with broken inversion symmetry, we experimentally "blow" magnetic skyrmion bubbles from a geometrical constriction. The presence of a spatially divergent spin-orbit torque gives rise to instabilities of the magnetic domain structures that are reminiscent of Rayleigh-Plateau instabilities in fluid flows. We determine a phase diagram for skyrmion formation and reveal the efficient manipulation of these dynamically created skyrmions, including depinning and motion. The demonstrated current-driven transformation from stripe domains to magnetic skyrmion bubbles could lead to progress in skyrmion-based spintronics. PMID:26067256

  18. Driving bubbles out of glass

    NASA Technical Reports Server (NTRS)

    Mattox, D. M.

    1981-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    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?

  20. On the Necessity and Feasibility of an Equatorial Magnetospheric Constellation

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

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

  1. Ionospheric Storms in Equatorial Region: Digisonde Observations

    NASA Astrophysics Data System (ADS)

    Paznukhov, V.; Altadill, D.; Blanch, E.

    2011-12-01

    We present a study of the ionospheric storms observed in the low-latitude and equatorial ionosphere at several digisonde stations: Jicamarca (Geomagnetic Coordinates: 2.0 S, 355.3 E), Kwajalein Island (3.8 N, 238.2 E), Ascension Island (2.5 S, 56.8 E), Fortaleza (4.8 N, 33.7 W), and Ramey (28.6 N, 5.2 E). The strongest geomagnetic storms from years 1995-2009 have been analyzed. The main ionospheric characteristics, hmF2 and foF2 were used in the study, making it possible to investigate the changes in the ionosphere peak density and height during the storms. All digisonde data were manually processed to assure the accuracy of the measurements. Solar wind data, geomagnetic field variations, and auroral activity indices have been used to characterize the geomagnetic environment during the events. It was found in our analysis that the major drivers for the ionospheric storms, electric field and neutral wind have approximately equal importance at the low-latitude and equatorial latitudes. This is noticeably different from the behavior of the ionsphere in the middle latitudes, where the neutral wind is usually a dominant factor. It was found that the auroral index, AE is the best precursor of the ionospheric effects observed during the storms in this region. We analyze the difference between time delays of the storm effects observed at the stations located in different local time sectors. The overall statistics of the time delays of the storms as a function of the local time at the stations is also presented. Several very interesting cases of sudden very strong ionospheric uplifting and their possible relation to the equatorial super fountain effect are investigated in greater details.

  2. Lunar influence on equatorial atmospheric angular momentum

    NASA Astrophysics Data System (ADS)

    Bizouard, Christian; Zotov, Leonid; Sidorenkov, Nikolay

    2014-11-01

    This study investigates the relationship between the equatorial atmospheric angular momentum oscillation in the nonrotating frame and the quasi-diurnal lunar tidal potential. Between 2 and 30 days, the corresponding equatorial component, called Celestial Atmospheric Angular Momentum (CEAM), is mostly constituted of prograde circular motions, especially of a harmonic at 13.66 days, a sidelobe at 13.63 days, and of a weekly broadband variation. A simple equilibrium tide model explains the 13.66 day pressure term as a result of the O1 lunar tide. The powerful episodic fluctuations between 5 and 8 days possibly reflect an atmospheric normal mode excited by the tidal waves Q1 (6.86 days) and ?1 (7.095 days). The lunar tidal influence on the spectral band from 2 to 30 days is confirmed by two specific features, not occurring for seasonal band dominated by the solar thermal effect. First, Northern and Southern Hemispheres contribute equally and synchronously to the CEAM wind term. Second, the pressure and wind terms are proportional, which follows from angular momentum budget considerations where the topographic and friction torques on the solid Earth are much smaller than the one resulting from the equatorial bulge. Such a configuration is expected for the case of tidally induced circulation, where the surface pressure variation is tesseral and cannot contribute to the topographic torque, and tidal winds blow only at high altitudes. The likely effects of the lunar-driven atmospheric circulation on Earth's nutation are estimated and discussed in light of the present-day capabilities of space geodetic techniques.

  3. The equatorial electrojet satellite and surface comparison

    NASA Technical Reports Server (NTRS)

    Cain, J. C. (editor); Sweeney, R. E. (editor)

    1972-01-01

    The OGO 4 and 6 (POGO) magnetic field results for the equatorial electrojet indicate that while the present models are approximately correct, the possibility of a westward component must be incorporated. The scatter diagrams of POGO amplitudes and surface data show a correlation. The ratios between the amplitudes estimated from surface data and those at 400 km altitude are as follows: India 5 to 8, East Africa (Addis Ababa) 4, Central Africa 3, West Africa (Nigeria) 3, South America (Huancayo) 5, and Philippines 5. The variation in the ratio is due to the conductivity structure of the earth in various zones.

  4. Large scale turbulence in the equatorial electrojet

    SciTech Connect

    Ronchi, C.

    1990-01-01

    The turbulent dynamics of kilometer-scale irregularities of the daytime equatorial electrojet are studied analytically and numerically, within the framework of a two-fluid nonlocal theory of the gradient drift instability. The emphasis is on the effects of including the altitude variations of the relevant physical parameters, such as mobilities and diffusion coefficients, on the nonlinear evolution of the instability. In the linear regime, researchers investigated how the nonlocal modes differ from the local ones by applying eikonal analysis to the motion of wave packets propagating in a inhomogeneous medium. The mechanism by which velocity shear can stabilize part of the linearly unstable spectrum is discussed and described in detail.

  5. Equatorial Oscillations in Jupiter's and Saturn's Atmospheres

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  6. An equatorial coronal hole at solar minimum

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

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

  7. Typhoon Vamei: An equatorial tropical cyclone formation

    NASA Astrophysics Data System (ADS)

    Chang, C.-P.; Liu, Ching-Hwang; Kuo, Hung-Chi

    2003-02-01

    Due to the diminishing Coriolis effect, the belt 300 km either side of the equator has been considered tropical cyclone-free. Typhoon Vamei, which developed near Singapore on 27 December 2001, was the first recorded tropical cyclone formation within 1.5 degrees of the equator. The development was the result of two interacting systems, a weak Borneo vortex that drifted into the southern tip of the South China Sea and remained there for four days, and a strong and persistent cold surge that created the large background cyclonic vorticity at the equator. The probability of a similar equatorial development is estimated to be once every 100-400 years.

  8. Climatology of the equatorial and low latitude ionosphere over Brazil during solar minimum of solar cycle 23/24

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    We present a study of the Brazilian equatorial and low latitude ionosphere during the solar minimum of the solar cycle 23 and the initial phase of solar cycle 24. We analyzed data from ground-based sounding with digisondes at two equatorial sites, São Luís (44.2° W, 2.33° S, dip angle: -6.9°) and Fortaleza (38.45°W, 3.9° S, dip angle: -16°) and at a low latitude site Cachoeira Paulista (22.4° S, 45° W, dip angle: -37°). The plasma densities and the F-layer heights presented values lower than the previous solar minimum of solar cycle 22/23. The spread-F occurrence was investigated and revealed some distinct features such as the occurrence of abnormal spread-F signatures in ionograms associated with post-midnight irregularities. In the equatorial region, it was observed significant decreases in the plasma densities during nighttime hours lasting for several hours with no-echoes in ionograms. We present a statistic study of the plasma irregularities occurrence as well as some examples of unusual signatures of spread-F/plasma irregularities observed in ionograms.

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

    NASA Astrophysics Data System (ADS)

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

    2008-11-01

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

  10. Pulsed electrical discharge in gas bubbles in water

    NASA Astrophysics Data System (ADS)

    Gershman, Sophia

    A phenomenological picture of pulsed electrical discharge in gas bubbles in water is produced by combining electrical, spectroscopic, and imaging methods. The discharge is generated by applying one microsecond long 5 to 20 kilovolt pulses between the needle and disk electrodes submerged in water. A gas bubble is generated at the tip of the needle electrode. The study includes detailed experimental investigation of the discharge in argon bubbles and a brief look at the discharge in oxygen bubbles. Imaging, electrical characteristics, and time-resolved optical emission data point to a fast streamer propagation mechanism and formation of a plasma channel in the bubble. Spectroscopic methods based on line intensity ratios and Boltzmann plots of line intensities of argon, atomic hydrogen, and argon ions and the examination of molecular emission bands from molecular nitrogen and hydroxyl radicals provide evidence of both fast beam-like electrons and slow thermalized ones with temperatures of 0.6 -- 0.8 electron-volts. The collisional nature of plasma at atmospheric pressure affects the decay rates of optical emission. Spectroscopic study of rotational-vibrational bands of hydroxyl radical and molecular nitrogen gives vibrational and rotational excitation temperatures of the discharge of about 0.9 and 0.1 electron-volt, respectively. Imaging and electrical evidence show that discharge charge is deposited on the bubble wall and water serves as a dielectric barrier for the field strength and time scales of this experiment. Comparing the electrical and imaging information for consecutive pulses applied at a frequency of 1 Hz indicates that each discharge proceeds as an entirely new process with no memory of the previous discharge aside from long-lived chemical species, such as ozone and oxygen. Intermediate values for the discharge gap and pulse duration, low repetition rate, and unidirectional character of the applied voltage pulses make the discharge process here unique compared to the traditional corona or dielectric barrier discharges. These conditions make the experimental evidence presented in this work valuable for the advancement of modeling and the theoretical understanding of the discharge in bubbles in water.

  11. Bubble rearrangements dynamics in foams

    NASA Astrophysics Data System (ADS)

    Le Merrer, Marie; Costa, Severine; Cohen-Addad, Sylvie; Hoehler, Reinhard

    2011-11-01

    Liquid foams are jammed dispersions of gas bubbles in a surfactant solution. Their structure evolves with time because surface tension drives a diffusive gas exchange between neighboring bubbles. This coarsening leads to a build-up of stresses which are relaxed upon local intermittent bubble rearrangements. These events govern the slow viscoelastic foam response, and similar bubble rearrangements are the elementary processes of plastic flow. Thus, the rearrangement duration is a key parameter describing how the microstructure dynamics control the macroscopic rheological response. We probe the duration of coarsening-induced rearrangements in 3D foams using a multiple light scattering technique (time resolved Diffusing-Wave Spectroscopy) as a function of the surfactant chemistry and the liquid fraction. As the foam becomes wetter, the confinement pressure of the packing goes to zero and the contacts between bubbles vanish. For mobile interfaces, we find that the rearrangements slow down as the jamming point is approached. These findings are compared to scaling laws which reveal an analogy between rearrangements dynamics in foams and granular suspensions.

  12. Ethnic diversity deflates price bubbles

    PubMed Central

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

    2014-01-01

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

  13. Dynamics in reactive bubbly flow

    NASA Astrophysics Data System (ADS)

    Sundararajan, Pavithra; Koch, Donald; Stroock, Abraham

    2010-11-01

    Multiphase flow in microfluidic channels encompasses a rich collection of phenomena of widespread interest in both fundamental and technological context. While studies on non reactive multiphase flow focus on the dynamics of bubble breakup, coalescence and stability, a reactive multiphase flow opens up a broader spectrum of dynamics, like nucleation, growth and detachment of bubbles as well as the secondary mixing in the slugs during these processes. Our interest lies in the flow in an electrochemical microfluidic fuel cell with liquid reactants reacting at catalyst walls producing gaseous products which choke the fuel cell efficiency due to uncontrolled bubbly flow. This challenge is an opportunity in itself provided the multiphase flow dynamics can be characterized to achieve a stable Taylor regime. Taylor regime allows for promisingly high efficiencies due to improved mass transfer of reactants to the concentration boundary layer of the electrodes achieved by the secondary flow in the liquid phase present between bubbles. Here, I will experimentally explore the different regimes of reactive bubbly flow in a microchannel. The phase diagram of the reactive multiphase flows would be used to identify the stable regime for efficient fuel cell operation. Further, I will study the mass transfer in the presence of multiphase flow to regimes of enhanced mass transfer, and compare it with numerical models.

  14. Ethnic diversity deflates price bubbles.

    PubMed

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

    2014-12-30

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

  15. Aspherical bubble dynamics and oscillation times

    SciTech Connect

    Godwin, R.P.; Chapyak, E.J.; Noack, J.; Vogel, A.

    1999-03-01

    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.

  16. Central Equatorial Pacific Experiment (CEPEX). Design document

    SciTech Connect

    Not Available

    1993-04-01

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

  17. Fading of Jupiter's South Equatorial Belt

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

    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.

  18. Nighttime ionospheric D region: Equatorial and nonequatorial

    NASA Astrophysics Data System (ADS)

    Thomson, Neil R.; McRae, Wayne M.

    2009-08-01

    Nighttime ionospheric D region parameters are found to be generally well modeled by the traditional H? and ? as used by Wait and by the U.S. Navy in their Earth-ionosphere VLF radio waveguide programs. New comparisons with nonequatorial, mainly all-sea VLF path observations reported over several decades are shown to be consistent with the previously determined height H? ˜ 85.0 km and sharpness ? ˜ 0.63 km-1. These paths include NPM (Hawaii) to Washington, D. C., Omega Hawaii and NLK (Seattle) to Japan, NWC (N.W. Australia) to Madagascar, and NBA (Panama) to Colorado. In marked contrast, transequatorial path observations (even when nearly all-sea) are found to be often not well modeled: for example, for Omega Japan and JJI (Japan) to Dunedin, New Zealand, the observed amplitudes are markedly lower than those which would be expected from H? ˜ 85.0 km and ? ˜ 0.63 km-1, or any other realistic values of H? and ?. Other transequatorial observations compared with modeling include NWC to Japan, Omega Hawaii to Dunedin, and NPM (Hawaii) to Dunedin. It is suggested that the effects of irregularities in the equatorial electrojet may extend down into the nighttime D region and so account for the observed equatorial VLF perturbations through scattering or mode conversion.

  19. Nighttime Ionospheric D-region: Equatorial and Non-equatorial Neil R. Thomson,1 and Wayne M. McRae2

    E-print Network

    Otago, University of

    in the equatorial electrojet may extend down into the nighttime D-region and so account for the observed equatorial1 Nighttime Ionospheric D-region: Equatorial and Non-equatorial Neil R. Thomson,1 and Wayne M. Mc, Perth, WA6009, Australia #12;2 Abstract Nighttime ionospheric D-region parameters are found

  20. Bubbles Responding to Ultrasound Pressure

    NASA Technical Reports Server (NTRS)

    2003-01-01

    The Bubble and Drop Nonlinear Dynamics (BDND) experiment was designed to improve understanding of how the shape and behavior of bubbles respond to ultrasound pressure. By understanding this behavior, it may be possible to counteract complications bubbles cause during materials processing on the ground. This 12-second sequence came from video downlinked from STS-94, July 5 1997, MET:3/19:15 (approximate). The BDND guest investigator was Gary Leal of the University of California, Santa Barbara. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). Advanced fluid dynamics experiments will be a part of investigations plarned for the International Space Station. (435KB, 13-second MPEG, screen 160 x 120 pixels; downlinked video, higher quality not available) A still JPG composite of this movie is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300162.html.

  1. Magnetosonic equatorial noise at Earth: Polar and RBSP observations

    NASA Astrophysics Data System (ADS)

    Hospodarsky, G. B.; Sigsbee, K. M.; Santolik, O.; Kurth, W. S.; Kletzing, C.; Gurnett, D. A.; Wygant, J. R.; Bonnell, J. W.

    2012-12-01

    Low-frequency electromagnetic emissions between about twice the proton gyrofrequency and half the lower hybrid frequency are often detected by spacecraft near the Earth's geomagnetic equator and are commonly known as equatorial noise. These fast magnetosonic waves can accelerate electrons and are believed to play an important role in transferring energy from the ring current particles to the Van Allen radiation belts. These emissions show a wide range of frequency structure, from macroscopic structures in the form of funnel-shaped time-frequency spectrogram features, to finer scale structures in the form of narrow frequency bands with spacings near the gyrofrequencies of various inner magnetosphere ion species (a few Hertz to tens of Hertz). A survey of the properties of these emissions detected by the Polar Plasma Wave Instrument (PWI) will be presented. These results will be compared to the initial observations of the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) Waves instrument on the Radiation Belt Storm Probes (RBSP) spacecraft.

  2. Bursting Bubbles and Bilayers

    PubMed Central

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

    2012-01-01

    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

  3. Observations of the generation of eastward equatorial electric fields near dawn

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    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.

  4. Observations of the Generation of Eastward Equatorial Electric Fields near Dawn

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

    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 per meter, 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.

  5. From rational bubbles to crashes

    NASA Astrophysics Data System (ADS)

    Sornette, D.; Malevergne, Y.

    2001-10-01

    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.

  6. Removal of hydrogen bubbles from nuclear reactors

    NASA Technical Reports Server (NTRS)

    Jenkins, R. V.

    1980-01-01

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

  7. A study of bubble wetting on surfaces

    E-print Network

    Day, Julia Katherine

    2010-01-01

    In microfluidics, the formation of bubbles within devices obstructs flow and can damage the microfluidic chip or the samples contained therein. This thesis works toward a better understand of bubble wetting on surfaces, ...

  8. Bubble memory module for spacecraft application

    NASA Technical Reports Server (NTRS)

    Hayes, P. J.; Looney, K. T.; Nichols, C. D.

    1985-01-01

    Bubble domain technology offers an all-solid-state alternative for data storage in onboard data systems. A versatile modular bubble memory concept was developed. The key module is the bubble memory module which contains all of the storage devices and circuitry for accessing these devices. This report documents the bubble memory module design and preliminary hardware designs aimed at memory module functional demonstration with available commercial bubble devices. The system architecture provides simultaneous operation of bubble devices to attain high data rates. Banks of bubble devices are accessed by a given bubble controller to minimize controller parts. A power strobing technique is discussed which could minimize the average system power dissipation. A fast initialization method using EEPROM (electrically erasable, programmable read-only memory) devices promotes fast access. Noise and crosstalk problems and implementations to minimize these are discussed. Flight memory systems which incorporate the concepts and techniques of this work could now be developed for applications.

  9. 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...

  10. Behavior of Rapidly Sheared Bubble Suspensions

    NASA Technical Reports Server (NTRS)

    Sangani, A. S.; Kushch, V. I.; Hoffmann, M.; Nahra, H.; Koch, D. L.; Tsang, Y.

    2002-01-01

    An experiment to be carried out aboard the International Space Station is described. A suspension consisting of millimeter-sized bubbles in water containing some dissolved salt, which prevents bubbles from coalescing, will be sheared in a Couette cylindrical cell. Rotation of the outer cylinder will produce centrifugal force which will tend to accumulate the bubbles near the inner wall. The shearing will enhance collisions among bubbles creating thereby bubble phase pressure that will resist the tendency of the bubbles to accumulate near the inner wall. The bubble volume fraction and velocity profiles will be measured and compared with the theoretical predictions. Ground-based research on measurement of bubble phase properties and flow in vertical channel are described.

  11. Effects of the ultra-fast Kelvin waves on the Brazilian equatorial ionosphere

    NASA Astrophysics Data System (ADS)

    Onohara, Amelia; Takahashi, Hisao; Batista, Inez S.; Prado Batista, Paulo; Clemesha, Barclay; Lima, Lourivaldo

    In this work we investigated the effects of an ultra-fast Kelvin wave (an equatorial planetary wave with period of almost 3 days) on the ionospheric parameters over the Brazilian equatorial region. For this purpose, the meteor wind data from São João do Cariri (7.4° S, 36.5° W) a a and ionospheric data from digissonde installed at Fortaleza (3.9° S, 38.4° W) for the year 2005 were used. Zonal and meridional winds, h'F and foF2 were submitted to a wavelet analysis in order to find the oscillation appeared in the temporal series. The study was conducted for the time intervals in which the ultra-fast Kelvin wave signature was present in both mesospheric and ionospheric parameters. For each of these intervals, the amplitude and phase of the prop-agating wave were calculated from the wind data. The effect of the ultra-fast Kelvin waves on the ionospheric parameters was tested using an ionospheric model that solves the coupled electrodynamics of the equatorial ionosphere and calculates the electrostatic potential for the E region and the F region vertical and horizontal plasma drifts. Some relevant results obtained from the comparison between observation and model results will be discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    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.

  13. The good, the bad and the bubbly. Micro bubble behavior under ultrasound.

    E-print Network

    Greenaway, Alan

    The good, the bad and the bubbly. Micro bubble behavior under ultrasound. Michael Conneely Division of Physics The good, the bad and the bubbly. Micro bubble behavior under ultrasound. PaLS Open Day 2013 #12 and diagnostic clinical modalities; namely targeted drug delivery and molecular imaging. The good, the bad

  14. 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...

  15. Observation of neutral winds during an equatorial electrojet

    NASA Technical Reports Server (NTRS)

    Bedinger, J. F.

    1977-01-01

    The vertical profile of the horizontal wind in a strong equatorial electrojet is distinctly different from profiles observed previously at other times and locations. The zonal wind speed is small and varies slowly with altitude, whereas the meridional component manifests a cross-equatorial oscillation with altitude which may result from a unique interaction of the ionized and neutral motions.

  16. The middle-atmosphere Hadley circulation and equatorial inertial adjustment

    E-print Network

    Wirosoetisno, Djoko

    The middle-atmosphere Hadley circulation and equatorial inertial adjustment Article Published Version Semeniuk, K. and Shepherd, T. G. (2001) The middle- atmosphere Hadley circulation and equatorial inertial adjustment. Journal of the Atmospheric Sciences, 58 (21). pp. 3077-3096. ISSN 1520-0469 doi: 10

  17. Equatorial waves in High Resolution Dynamics Limb Sounder (HIRDLS) data

    E-print Network

    Alexander, M. Joan

    Equatorial waves in High Resolution Dynamics Limb Sounder (HIRDLS) data M. J. Alexander1 and D. A December 2010. [1] We examine equatorial wave structure in temperature measurements from the High Resolution Dynamics Limb Sounder (HIRDLS) on the Aura satellite. Waves with periods longer than 1 day

  18. Magma mixing enhanced by bubble segregation

    NASA Astrophysics Data System (ADS)

    Wiesmaier, S.; Daniele, M.; Renggli, C.; Perugini, D.; De Campos, C.; Hess, K. U.; Ertel-Ingrisch, W.; Lavallée, Y.; Dingwell, D. B.

    2014-12-01

    Rising bubbles may significantly affect magma mixing paths as has been demonstrated by analogue experiments in the past. Here, bubble-advection experiments are performed for the first time employing natural materials at magmatic temperatures. Cylinders of basaltic glass were placed below cylinders of rhyolite glass. Upon melting, interstitial air formed bubbles that rose into the rhyolite melt, thereby entraining tails of basaltic liquid. The formation of plume-like filaments of advected basalt within the rhyolite was characterized by microCT and subsequent high-resolution EMP analyses. Melt entrainment by bubble ascent appears as efficient mechanism to mingle contrasting melt compositions. MicroCT imaging shows bubbles trailing each other and trails of multiple bubbles having converged. Rheological modelling of the filaments yields viscosities of up to 2 orders of magnitude lower than for the surrounding rhyolitic liquid. Such a viscosity contrast implies that subsequent bubbles rising are likely to follow the same pathways that previously ascending bubbles have generated. Filaments formed by multiple bubbles would thus experience episodic replenishment with mafic material. Fundamental implications for the concept of bubble advection in magma mixing are thus a) an acceleration of mixing because of decreased viscous resistance for bubbles inside filaments and b) non-conventional diffusion systematics because of intermittent supply of mafic material (instead of a single pulse) inside a filament. Inside these filaments, the mafic material was variably hybridised to andesitic through rhyolitic composition. Compositional profiles alone are ambiguous, however, to determine whether single or multiple bubbles were involved during formation of a filament. Statistical analysis, employing concentration variance as measure of homogenisation, demonstrates that also filaments appearing as single-bubble filaments are likely to have experienced multiple bubbles passing through. Whenever bubbles were essential for magma mixing, standard diffusion calculus may thus be inapplicable for constraining timescales. However, data analysis employing concentration variance allows distinguishing conventional single-pulse filaments from multiple bubble ascent advection in natural samples.

  19. Single-bubble sonoluminescence in microgravity

    PubMed

    Matula

    2000-03-01

    Single-bubble sonoluminescence refers to the emission of light from an acoustically trapped bubble undergoing highly nonlinear, presumably radial oscillations. The intensity of the emitted light depends strongly on the forcing pressure, and is limited by the development of instabilities that ultimately results in the extinction of the bubble. In this article, we discuss a possible contributing factor for the generation of instabilities; specifically, we examine the effect of the gravitational force on a sonoluminescence bubble. PMID:10829726

  20. Heat emission of gas bubbles in a rotating bubbling layer

    SciTech Connect

    Borisov, I.I.; Khalatov, A.A.; Ikonnikova, E.E.

    1995-08-01

    Based on an experimental study of contact heat transfer between a liquid and a gas in an eddy-generating bubbler and on results processed using the equation of nonstationary heat conduction, we obtained a dimensionless relation for calculating the coefficient that characterizes heat transfer in a gas bubble within the framework of a model based on effective coefficients of heat conduction.

  1. Dependence on zenith angle of the strength of 3-meter equatorial electrojet irregularities

    SciTech Connect

    Ierkic, H.M.; Fejer, B.G.; Farley, D.T.

    1980-07-01

    Radar measurements in Peru were used to deduce the zenith angle dependence of the scattering cross section of plasma irregularities generated by instabilities in the equatorial electrojet. The irregularities probed by the 50 MHz Jicamarca radar had a wavelength of 3m. The cross section for the type 2 irregularities was isotopic in the plane perpendicular to the magnetic field, while the cross section for the stronger type 1 irregularities varied with zenith angle at a rate of approximately 0.3 dB/degree; the horizontally traveling waves were more than 100 times stronger than those traveling vertically.

  2. The dependence of zenith angle of the strength of 3-meter equatorial electrojet irregularities

    NASA Technical Reports Server (NTRS)

    Ierkic, H. M.; Fejer, B. G.; Farley, D. T.

    1980-01-01

    Radar measurements in Peru were used to deduce the zenith angle dependence of the scattering cross section of plasma irregularities generated by instabilities in the equatorial electrojet. The irregularities probed by the 50 MHz Jicamarca radar had a wavelength of 3m. The cross section for the type 2 irregularities was isotropic in the plane perpendicular to the magnetic field, while the cross section for the stronger type 1 irregularities varied with zenith angle at a rate of approximately 0.3 dB/degree; the horizontally traveling waves were more than 100 times stronger than those traveling vertically.

  3. Equatorial transport of Saturn's ionosphere as driven by a dust-ring current system

    SciTech Connect

    Ip, W.; Mendis, D.A.

    1983-03-01

    The diurnal modulation of the dust ring current of Saturn's D-ring causes field-aligned Birkeland currents ot flow near the dawn and dusk terminators and close across the mid-latitude ionosphere. One consequence of this current system is the establishment of a global convection pattern in the equatorial outer ionosphere. Outward motion of the dayside ionosheric plasma as well as the corresponding absorption effect of the inner ring system might be one physical cause of the depletion of the ionospheric content of Saturn.

  4. Equatorial radius of the earth: A dynamical determination

    NASA Technical Reports Server (NTRS)

    Khan, M. A.

    1972-01-01

    An interesting variation on the familiar method of determining the earth's equatorial radius a sub e, from a knowledge of the earth's equatorial gravity is suggested. The value of equatorial radius thus found is 6378,142 + or - 5 meters. The associated parameters are GM = 3,986008 + or - 4 X 1014 cu cm/sec/sec which includes the relative mass of atmosphere approximately 0.000001 x GM, the equatorial gravity gamma sub e = 978,030.9 milligals (constrained in this solution by the Potsdam Correction of 13.67 milligals as the Potsdam Correction is more directly, or less indirectly, measurable than the equatorial gravity) and an ellipsoidal flattening of f = 1/298.255.

  5. Microfluidic Actuation Using Electrochemically Generated Bubbles

    E-print Network

    Sachs, Frederick

    , a technology commonly referred to as "lab-on-a-chip".1-5 Applications range from combi- natorial and analytical with advances in microfabrication, for example, "soft" lithography.11-14 Bubble-based actuators are of interest-19 While electrochemical bubbles require low power in the microwatt range, and the bubble inflation rates

  6. Frictional drag reduction by bubble injection

    NASA Astrophysics Data System (ADS)

    Murai, Yuichi

    2014-07-01

    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.

  7. Upscaling energy concentration in multifrequency single-bubble sonoluminescence with strongly degassed sulfuric acid

    NASA Astrophysics Data System (ADS)

    Dellavale, Damián; Rechiman, Ludmila; Rosselló, Juan Manuel; Bonetto, Fabián

    2012-07-01

    Single-bubble sonoluminescence (SBSL) was explored under a variety of multifrequency excitations. In particular, biharmonic excitation was used to produce SBSL for unprecedented low dissolved noble gas concentrations in a sulfuric acid solution. Reducing the amount of dissolved noble gas makes it possible to reach higher acoustic pressures on the SL bubble, which otherwise are not attainable because of the Bjerknes instability. By using biharmonic excitation, we were able to experimentally trap and to spatially stabilize SL bubbles for xenon pressure overhead as low as 1mbar. As a result, we have access to regions in phase space where the plasma temperatures are higher than the ones reached before for bubbles driven at ?30kHz.

  8. Data collapse of the spectra of water-based stable single-bubble sonoluminescence

    NASA Astrophysics Data System (ADS)

    Levinsen, Mogens T.

    2010-09-01

    In the early days of stable single-bubble sonoluminescence, it was strongly debated whether the emission was blackbody radiation or whether the bubble was transparent to its own radiation (volume emission). Presently, the volume emission picture is nearly universally accepted. We present new measurements of spectra with apparent color temperatures ranging from 6000 to 21 000 K. We show through data collapse that within experimental uncertainty, apart from a constant, the spectra of strongly driven stable single-bubble sonoluminescence in water can be written as the product between a universal function of wavelength and a functional form that only depends on wavelength and apparent temperature but has no reference to any other parameter specific to the experimental situation. This remarkable result does question our theoretical understanding of the state of the plasma in the interior of strongly driven stable sonoluminescent bubbles.

  9. Physical mechanism and statistics of occurrence of an additional layer in the equatorial ionosphere

    NASA Astrophysics Data System (ADS)

    Balan, N.; Batista, I. S.; Abdu, M. A.; MacDougall, J.; Bailey, G. J.

    1998-12-01

    A physical mechanism and the location and latitudinal extent of an additional layer, called the F3 layer, that exists in the equatorial ionosphere are presented. A statistical analysis of the occurrence of the layer recorded at the equatorial station Fortaleza (4°S, 38°W dip 9°S) in Brazil is also presented. The F3 layer forms during the morning-noon period in that equatorial region where the combined effect of the upward E×B drift and neutral wind provides a vertically upward plasma drift velocity at altitudes near and above the F2 peak. This velocity causes the F2 peak to drift upward and form the F3 layer while the normal F2 layer develops at lower altitudes through the usual photochemical and dynamical effects of the equatorial region. The peak electron density of the F3 layer can exceed that of the F2 layer. The F3 layer is predicted to be distinct on the summer side of the geomagnetic equator during periods of low solar activity and to become less distinct as the solar activity increases. Ionograms recorded at Fortaleza in 1995 show the existence of an F3 layer on 49% of the days, with the occurrence being most frequent (75%) and distinct in summer, as expected. During summer the layer occurs earlier and lasts longer compared to the other seasons; on the average, the layer occurs at around 0930 LT and lasts for about 3 hours. The altitude of the layer is also high in summer, with the mean peak virtual height being about 570 km. However, the critical frequency of the layer (foF3) exceeds that of the F2 layer (foF2) by the largest amounts in winter and equinox; foF3 exceeds foF2 by a yearly average of about 1.3 MHz.

  10. Observed equatorial Rossby waves and ENSO-related warm water volume changes in the equatorial Pacific Ocean

    E-print Network

    and geostrophic transports of warm water, the latter being estimated from SLA and validated against in situObserved equatorial Rossby waves and ENSO-related warm water volume changes in the equatorial; accepted 26 February 2008; published 4 June 2008. [1] Modifications of the volume of warm water above

  11. Investigation of TEC variations over the magnetic equatorial and equatorial anomaly regions of the African sector

    NASA Astrophysics Data System (ADS)

    Oryema, B.; Jurua, E.; D'ujanga, F. M.; Ssebiyonga, N.

    2015-11-01

    This paper presents the annual, seasonal and diurnal variations in ionospheric TEC along the African equatorial region. The study also investigated the effects of a geomagnetic storm on ionospheric TEC values. Dual-frequency GPS derived TEC data obtained from four stations within the African equatorial region for the high solar activity year 2012 were used in this study. Annual variations showed TEC having two peaks in the equinoctial months, while minima values were observed in the summer and winter solstices. The diurnal pattern showed a pre-dawn minimum, a steady increase from about sunrise to an afternoon maximum and then a gradual fall after sunset to attain a minimum just before sunrise. Nighttime enhancements of TEC were observed mostly in the equinoctial months. There was comparably higher percentage TEC variability during nighttime than daytime and highest during equinoxes, moderate in winter and least during summer solstice. TEC was observed to exhibit a good correlation with geomagnetic storm indices.

  12. Solitonic bubbles and phase transitions

    SciTech Connect

    Masperi, L. , 8400 San Carlos de Bariloche, Rio Negro, )

    1990-05-15

    It is shown that the nontopological bubble-shaped classical solutions which are possible in a scalar field theory with quartic and sextic self-interactions in 1+1 dimensions are responsible for the discontinuous transition in the quantum problem between a phase with a degenerate excited level and a disordered one.

  13. Electrolysis Bubbles Make Waterflow Visible

    NASA Technical Reports Server (NTRS)

    Schultz, Donald F.

    1990-01-01

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

  14. Impurity bubbles in a BEC

    NASA Astrophysics Data System (ADS)

    Timmermans, Eddy; Blinova, Alina; Boshier, Malcolm

    2013-05-01

    Polarons (particles that interact with the self-consistent deformation of the host medium that contains them) self-localize when strongly coupled. Dilute Bose-Einstein condensates (BECs) doped with neutral distinguishable atoms (impurities) and armed with a Feshbach-tuned impurity-boson interaction provide a unique laboratory to study self-localized polarons. In nature, self-localized polarons come in two flavors that exhibit qualitatively different behavior: In lattice systems, the deformation is slight and the particle is accompanied by a cloud of collective excitations as in the case of the Landau-Pekar polarons of electrons in a dielectric lattice. In natural fluids and gases, the strongly coupled particle radically alters the medium, e.g. by expelling the host medium as in the case of the electron bubbles in superfluid helium. We show that BEC-impurities can self-localize in a bubble, as well as in a Landau-Pekar polaron state. The BEC-impurity system is fully characterized by only two dimensionless coupling constants. In the corresponding phase diagram the bubble and Landau-Pekar polaron limits correspond to large islands separated by a cross-over region. The same BEC-impurity species can be adiabatically Feshbach steered from the Landau-Pekar to the bubble regime. This work was funded by the Los Alamos LDRD program.

  15. Pulling bubbles from a bath

    E-print Network

    Kao, Justin C. T.

    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 ...

  16. The Coming Law School Bubble

    ERIC Educational Resources Information Center

    Krauss, Michael I.

    2011-01-01

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

  17. Neutron Detection via Bubble Chambers

    SciTech Connect

    Jordan, David V.; Ely, James H.; Peurrung, Anthony J.; Bond, Leonard J.; Collar, J. I.; Flake, Matthew; Knopf, Michael A.; Pitts, W. K.; Shaver, Mark W.; Sonnenschein, Andrew; Smart, John E.; Todd, Lindsay C.

    2005-10-06

    The results of a Pacific Northwest National Laboratory (PNNL) exploratory research project investigating the feasibility of fast neutron detection using a suitably prepared and operated, pressure-cycled bubble chamber are described. The research was conducted along two parallel paths. Experiments with a slow pressure-release Halon chamber at the Enrico Fermi Institute at the University of Chicago showed clear bubble nucleation sensitivity to an AmBe neutron source and insensitivity to the 662 keV gammas from a 137Cs source. Bubble formation was documented via high-speed (1000 frames/sec) photography, and the acoustic signature of bubble formation was detected using a piezo-electric transducer element mounted on the base of the chamber. The chamber’s neutron sensitivity as a function of working fluid temperature was mapped out. The second research path consisted of the design, fabrication, and testing of a fast pressure-release Freon-134a chamber at PNNL. The project concluded with successful demonstrations of the PNNL chamber’s AmBe neutron source sensitivity and 137Cs gamma insensitivity. The source response tests of the PNNL chamber were documented with high-speed photography.

  18. Galactic and extragalactic hot bubbles: Feedback from massive stars

    NASA Astrophysics Data System (ADS)

    Montmerle, T.

    2011-11-01

    We briefly review the feedback effects of massive stars, via their stellar winds and supernova explosions, on the star-forming regions in which they were born. We give a few examples, spanning a wide range of spatial scales, from ˜100 pc out to ˜10 kpc: the so-called "Local Bubble" (in reality an open bipolar structure extending on both sides of the galactic disk); the Extended Orion Nebula and its open cavity filled with a hot, MK outflowing plasma; the Great Carina Nebula and its extended diffuse X-ray emission; the 30 Dor region in the LMC and its various bubbles; and the extended, bipolar outflow of the prototype starburst galaxy M 82, influenced by a nearby group of galaxies. We conclude by stressing the similarity of these phenomena across all spatial scales, galactic and extragalactic.

  19. Equatorial trench at the magnetopause under saturation

    E-print Network

    Dmitriev, A; 10.1029/2012JA017834

    2013-01-01

    Magnetic data from GOES geosynchronous satellites were applied for statistical study of the low-latitude dayside magnetopause under a strong interplanetary magnetic field of southward orientation when the reconnection at the magnetopause was saturated. From minimum variance analysis, we determined the magnetopause orientation and compared it with predictions of a reference model. The magnetopause shape was found to be substantially distorted by a duskward shifting such that the nose region appeared in the postnoon sector. At equatorial latitudes, the shape of magnetopause was characterized by a prominent bluntness and by a trench formed in the postnoon sector. The origin of distortions was regarded in the context of the storm-time magnetospheric currents and the large-scale quasi-state reconnection at the dayside magnetopause.

  20. Three dimensional Visualization of Jupiter's Equatorial Region

    NASA Technical Reports Server (NTRS)

    1997-01-01

    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.

  1. The morphological catalogue of galaxies equatorial survey

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  2. Theory of supercompression of vapor bubbles and nanoscale thermonuclear fusion

    SciTech Connect

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

    2005-10-01

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

  3. Ozone variability in the equatorial middle atmosphere

    SciTech Connect

    Sun, Chirong; Leovy, C. )

    1990-08-20

    Ozone variability in the equatorial middle atmosphere is investigated and related to temperature and zonal wind variations using data from the Nimbus 7 and Solar Mesosphere Explorer (SME) satellite. The dominant component of the seasonal variability at most levels from the middle stratosphere to the lower thermosphere is the semiannual oscillation (SAO) which has maxima near 10, 3, 0.07, 0.01 mbar, and near or above 0.0024 mbar. There is evidence that the 10-mbar peak is due to vertical advection of odd nitrogen (NO{sub y}) by the semiannually varying residual mean circulation, while temperature dependence of chemical reactions coupled with the thermal SAO near the stratopause and in the upper mesosphere is responsible for the peaks near 3 and 0.07 mbar. The seasonal dependence suggests a contribution from gravity wave modulated vertical mixing of water vapor near the 0.01 mbar level, and the authors speculate that semiannually modulated mixing of atomic oxygen by the (1,1) mode of the thermal tide contributes to the SAO ozone peak above 0.0024 mbar. The negative correlation between temperature and ozone is so strong in the 7- to 0.5-mbar layer that ozone is a useful proxy for temperature variability on time scales from a few days to many months. A preliminary look at annual and interannual variations shows that differing patterns of winter high latitude Rossby wave variability in the two hemispheres are reflected in the signatures of equatorial ozone and temperature in the same layer.

  4. Charging El Niño with off-equatorial westerly wind events

    NASA Astrophysics Data System (ADS)

    McGregor, Shayne; Timmermann, Axel; Jin, Fei-Fei; Kessler, William S.

    2015-11-01

    The buildup of the warm water in the equatorial Pacific prior to an El Niño event is considered a necessary precondition for event development, while the event initiation is thought to be triggered by bursts of westerly wind. However, in contrast to the view that warm water slowly builds up years before an El Niño event, the volume of warm water in the equatorial Pacific doubled in the first few months of 2014 reaching values that were consistent with the warm water buildup prior to the extreme 1997/1998 El Niño. It is notable that this dramatic warm water buildup coincided with a series of westerly wind bursts in the western tropical Pacific. This study uses linear wave theory to determine the effect of equatorial and off-equatorial westerly wind events on the Warm Water Volume (WWV) of the Pacific. It is found that westerly wind events have a significant impact on equatorial WWV with all events initially acting to increase WWV, which highlights why WWEs are so effective at exciting ENSO. In fact, our results suggest that the single westerly wind burst, which peaked in the first few days of March in 2014, was largely responsible for the coincident dramatic observed increase in WWV. How long the equatorial region remains charged, however, depends on the latitude of the westerly wind event. For instance, a single equatorially symmetric westerly wind event ultimately acts to discharge WWV via the reflection of upwelling Rossby waves, which makes it difficult to more gradually build WWV given multiple WWEs. In contrast, when the wind events occur off the equator, the subsequent discharge is significantly damped and in some cases the equatorial region can hold the heat charge for the duration of the simulations (~6 months). As such, off-equatorial WWEs can not only charge equatorial region WWV in the short term, but are also a mechanism to more gradually build equatorial region WWV in the longer term. Given that these off-equatorial WWEs have a relatively small projection onto the equatorial Kelvin wave, we argue these events can be considered as a mechanism to modulate the background state in which ENSO operates.

  5. Observations of Interannual Equatorial Fresh Water Jets in the Western Equatorial Pacific

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Clarke, A. J.

    2014-12-01

    Using upper ocean monthly salinity and temperature data from the moored TAO/TRITON array in the western equatorial Pacific since the late 1990s, we found, consistent with previous work, that the region experiences large interannual fluctuations in salinity. On the equator at 147 degrees E, 156 degrees E and 165 degrees E the interannual sea surface salinity (SSS) has peak to peak amplitudes that often exceed 1 psu. The salinity variability, which matches well the comparatively short record of overlapping SSS estimated by the Aquarius satellite, changes little over the top 50 m of the water column. Beneath this mixed layer depth the amplitude of the salinity variability steadily decreases over the remaining part of the order 100 m thick isothermal layer. Corresponding hydrostatic estimates of dynamic height over the isothermal layer lead to interannual sea level variability of only a few cm amplitude. However, the sea level due to the fresher water is associated geostrophically with a strong fresh water zonal equatorial interannual jet that at 156 degrees E has an amplitude of about 27 cm/s. Along-track altimeter data give a geostrophic equatorial zonal interannual flow that agrees well with this, suggesting that the near-surface interannual flow in the region is due to the shallow fresh jet. A zonal momentum balance indicates that this jet is mostly due to zonal wind stress forcing. The fresh water jet is maximally correlated with the Nino3.4 El Nino index when the jet leads by 3 months.

  6. Tiny Bubbles in my BEC

    SciTech Connect

    Blinova, Alina A.

    2012-08-01

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

  7. Bubble Universe Dynamics After Free Passage

    E-print Network

    Pontus Ahlqvist; Kate Eckerle; Brian Greene

    2014-12-26

    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.

  8. Acoustic wave equation in a bubbly liquid

    NASA Astrophysics Data System (ADS)

    Miao, Boya; An, Yu

    2015-10-01

    In certain cases, a bubbly liquid may be treated as a two-phase fluid mixture, in which acoustic waves can be described by a linear wave equation using the speed of sound in the two-phase fluid mixture. However, when there is appreciable acoustically driven bubble oscillation, treatment of the two-phase fluid mixture becomes inaccurate. A more accurate description of acoustic waves in bubbly liquids should combine the nonlinear wave equation with an equation describing the dynamics of bubble oscillation. As an example, we investigate the case of an ultrasonic wave in water passing through a bubbly liquid layer. For intense ultrasonic waves or bubbly liquids with high number density of bubble, significant differences are found between the results obtained with the different methods.

  9. Generation of Bubbly Suspensions in Low Gravity

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

  10. Sensitivity study of Bubble diameter for prediction of flow pattern in homogeneous bubble column regime

    NASA Astrophysics Data System (ADS)

    Pourtousi, M.; Ganesan, P.; Sahu, J. N.; Redzwan, Ghufran

    2015-09-01

    Determining the bubble diameter size in a bubble column rector plays an important role to accurately predict flow pattern in a bubble column reactor. This paper employs the Eulerian-Eulerian method to numerically investigate the sensitivity study of bubble diameter size in a cylindrical bubble column reactor. Existing experimental results in the literature are used to validate the implementation of the proposed numerical method. In our simulation various bubble diameter size (i.e., 35.5mm) are used to find an appropriate bubble size inside the bubble column when the regime is homogeneous (superficial gas velocity = 0.005m/s). The result shows that bubble diameter 4mm is a reasonable size for flow pattern prediction inside the column.

  11. Topside Equatorial Zonal Ion Velocities Measured by C/NOFS During a Rising Solar Cycle

    NASA Astrophysics Data System (ADS)

    Coley, W. R.; Stoneback, R.; Hairston, M. R.

    2012-12-01

    The Ion Velocity Meter (IVM), a part of the CINDI instrument package on the C/NOFS spacecraft, has made over four years of in-situ measurements of plasma temperatures, composition, densities, and velocities in the 400-850 km altitude range of the equatorial ionosphere. These measured ion velocities are then transformed into a coordinate system with components parallel and perpendicular to the geomagnetic field allowing us to examine the zonal (horizontal and perpendicular to Bg) component of plasma motion. The general pattern of local time variation of the equatorial zonal ion velocity is well known as westward during the day and eastward during the night, with the larger nighttime velocities leading to a net ionospheric superrotation. Since the C/NOFS launch in April 2008, F10.7 cm radio fluxes have gradually increased from around 70 sfu to levels in the 130-150 sfu range. The comprehensive coverage of C/NOFS over the low-latitude ionosphere allows us to examine variations of the topside zonal ion velocity over a wide level of solar activity as well as the dependence of the zonal velocity on apex altitude (magnetic latitude), longitude, and solar local time.

  12. Three dimensional Visualization of Jupiter's Equatorial Region

    NASA Technical Reports Server (NTRS)

    1997-01-01

    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.

  13. Three dimensional Visualization of Jupiter's Equatorial Region

    NASA Technical Reports Server (NTRS)

    1997-01-01

    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.

  14. Three dimensional Visualization of Jupiter's Equatorial Region

    NASA Technical Reports Server (NTRS)

    1997-01-01

    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.

  15. Three dimensional Visualization of Jupiter's Equatorial Region

    NASA Technical Reports Server (NTRS)

    1997-01-01

    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.

  16. Three dimensional Visualization of Jupiter's Equatorial Region

    NASA Technical Reports Server (NTRS)

    1997-01-01

    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.

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

    SciTech Connect

    Albert, J.M. ); Similon, P.L. ); Sudan, R.N. )

    1991-09-01

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

  18. Sonoporation from Jetting Cavitation Bubbles

    PubMed Central

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

    2006-01-01

    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 ?-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

  19. Etiology of gas bubble disease

    SciTech Connect

    Bouck, G.R.

    1980-11-01

    Gas bubble disease is a noninfectious, physically induced process caused by uncompensated hyperbaric pressure of total dissolved gases. When pressure compensation is inadequate, dissolved gases may form emboli (in blood) and emphysema (in tissues). The resulting abnormal physical presence of gases can block blood vessels (hemostasis) or tear tissues, and may result in death. Population mortality is generally skewed, in that the median time to death occurs well before the average time to death. Judged from mortality curves, three stages occur in gas bubble disease: (1) a period of gas pressure equilibrium, nonlethal cavitation, and increasing morbidity; (2) a period of rapid and heavy mortality; and (3) a period of protracted survival, despite lesions, and dysfunction that eventually terminates in total mortality. Safe limits for gas supersaturation depend on species tolerance and on factors that differ among hatcheries and rivers, between continuous and intermittent exposures, and across ranges of temperature and salinity.

  20. Bubble-induced cave collapse.

    PubMed

    Girihagama, Lakshika; Nof, Doron; Hancock, Cathrine

    2015-01-01

    Conventional wisdom among cave divers is that submerged caves in aquifers, such as in Florida or the Yucatan, are unstable due to their ever-growing size from limestone dissolution in water. Cave divers occasionally noted partial cave collapses occurring while they were in the cave, attributing this to their unintentional (and frowned upon) physical contact with the cave walls or the aforementioned "natural" instability of the cave. Here, we suggest that these cave collapses do not necessarily result from cave instability or contacts with walls, but rather from divers bubbles rising to the ceiling and reducing the buoyancy acting on isolated ceiling rocks. Using familiar theories for the strength of flat and arched (un-cracked) beams, we first show that the flat ceiling of a submerged limestone cave can have a horizontal expanse of 63 meters. This is much broader than that of most submerged Florida caves (~ 10 m). Similarly, we show that an arched cave roof can have a still larger expanse of 240 meters, again implying that Florida caves are structurally stable. Using familiar bubble dynamics, fluid dynamics of bubble-induced flows, and accustomed diving practices, we show that a group of 1-3 divers submerged below a loosely connected ceiling rock will quickly trigger it to fall causing a "collapse". We then present a set of qualitative laboratory experiments illustrating such a collapse in a circular laboratory cave (i.e., a cave with a circular cross section), with concave and convex ceilings. In these experiments, a metal ball represented the rock (attached to the cave ceiling with a magnet), and the bubbles were produced using a syringe located at the cave floor. PMID:25849088

  1. Bubble-Induced Cave Collapse

    PubMed Central

    Girihagama, Lakshika; Nof, Doron; Hancock, Cathrine

    2015-01-01

    Conventional wisdom among cave divers is that submerged caves in aquifers, such as in Florida or the Yucatan, are unstable due to their ever-growing size from limestone dissolution in water. Cave divers occasionally noted partial cave collapses occurring while they were in the cave, attributing this to their unintentional (and frowned upon) physical contact with the cave walls or the aforementioned “natural” instability of the cave. Here, we suggest that these cave collapses do not necessarily result from cave instability or contacts with walls, but rather from divers bubbles rising to the ceiling and reducing the buoyancy acting on isolated ceiling rocks. Using familiar theories for the strength of flat and arched (un-cracked) beams, we first show that the flat ceiling of a submerged limestone cave can have a horizontal expanse of 63 meters. This is much broader than that of most submerged Florida caves (~ 10 m). Similarly, we show that an arched cave roof can have a still larger expanse of 240 meters, again implying that Florida caves are structurally stable. Using familiar bubble dynamics, fluid dynamics of bubble-induced flows, and accustomed diving practices, we show that a group of 1-3 divers submerged below a loosely connected ceiling rock will quickly trigger it to fall causing a “collapse”. We then present a set of qualitative laboratory experiments illustrating such a collapse in a circular laboratory cave (i.e., a cave with a circular cross section), with concave and convex ceilings. In these experiments, a metal ball represented the rock (attached to the cave ceiling with a magnet), and the bubbles were produced using a syringe located at the cave floor. PMID:25849088

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

    NASA Astrophysics Data System (ADS)

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

    2001-05-01

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

  3. Unsteady thermocapillary migration of bubbles

    NASA Technical Reports Server (NTRS)

    Dill, Loren H.; Balasubramaniam, R.

    1988-01-01

    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.

  4. Recent computational studies of the equatorial electrojet. Memorandum report

    SciTech Connect

    Keskinen, M.J.

    1980-03-24

    A brief review of recent computational studies of the E-region equatorial electrojet is presented. Agreement and discrepancies between numerical simulation studies and both theory and experiment are given. Some outstanding problems are identified and new experiments suggested.

  5. Equatorial Electric Fields Derived from Swarm Magnetometer Data

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The Swarm Level-2 operational equatorial electric field (EEF) productis producing estimates of the EEF for each dayside orbit of all threesatellites. The EEF plays a crucial role in E and F region daytimeequatorial ionospheric dynamics. It is responsible for driving theequatorial electrojet (EEJ) current system, equatorial vertical ion drifts,and the equatorial ionization anomaly (EIA). The EEF is recovered byanalyzing the EEJ signature seen in the Swarm absolute scalar magnetometer(ASM) data. We will present first results of Swarm-derived EEJ currentsand their corresponding EEF estimates, compare the results betweensatellites, and finally validate them against independent groundmeasurements. We will further compare the magnetometer-derived EEF inthe E-region with measurements from the Electric Field Instrument (EFI) toexplore vertical gradients in the equatorial electric field.

  6. Erosion and Sedimentation on the Carnegie Ridge, Eastern Equatorial Pacific 

    E-print Network

    Brooks, Caroline Kelly

    2014-11-17

    AND SEDIMENTATION ON THE CARNEGIE RIDGE, EASTERN EQUATORIAL PACIFIC A Thesis by CAROLINE KELLY BROOKS Submitted to the Office of Graduate and Professional Studies of Texas A&M University in partial fulfillment of the requirements for the degree...

  7. The Deep Currents in the Eastern Equatorial Atlantic Ocean

    E-print Network

    /IRD/CNES/UPS), 31401 Toulouse, France. 5 Université de Cocody, Abidjan, Ivory-Coast. Abstract The deep equatorial to the north toward the coast of Ivory Coast along 7°W (Fig. 1). In this paper we mainly discuss top

  8. Dynamics of the equatorial undercurrent and its determination

    E-print Network

    Wacongne, Sophie

    1988-01-01

    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 ...

  9. Experimental and Numerical Studies of Magnetic Bubble Expansion as a Model for Extra-Galactic Radio Lobes

    NASA Astrophysics Data System (ADS)

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

    2007-11-01

    Recent work in plasma astrophysics has suggested that magnetic energy features prominently in the large-scale evolution of active galaxies. The Plasma Bubble Expansion Experiment (PBEX) will conduct laboratory experiments and coordinated numerical modeling to address outstanding nonlinear plasma physics issues related to how magnetic energy and helicity carried by extra-galactic jets interacts with the intergalactic medium to form extra-galactic radio lobe structures. Experiments will be conducted in the 4 meter long, 50 cm diameter HELCAT linear plasma device at UNM. A new pulsed coaxial gun will form and inject magnetized plasma bubbles into a lower pressure background plasma formed by the helicon and/or hot cathode source in HELCAT. Experimental parameters will be adjusted so that important dimensionless parameters are relevant to the astrophysical context. Preliminary magnetic probe measurements and MHD modeling will be presented.

  10. Electron injection by a nanowire in the bubble regime.

    SciTech Connect

    Shen, B.; Li, Y.; Nemeth, K.; Shang, H.; Soliday, R.; Crowell, R.; Frank, E.; Gropp, W.; Cary, J.; Shanghai Inst.of optics and Fine Mechanics; Univ. of Colorado; Tech-X Corp.

    2007-01-01

    The triggering of wave-breaking in a three-dimensional laser plasma wake (bubble) is investigated. The Coulomb potential from a nanowire is used to disturb the wake field to initialize the wave-breaking. The electron acceleration becomes more stable and the laser power needed for self-trapping is lowered. Three-dimensional particle-in-cell simulations were performed. Electrons with a charge of about 100 pC can be accelerated stably to energy about 170 MeV with a laser energy of 460 mJ. The first step towards tailoring the electron beam properties such as the energy, energy spread, and charge is discussed.

  11. FERMI BUBBLE ?-RAYS AS A RESULT OF DIFFUSIVE INJECTION OF GALACTIC COSMIC RAYS

    SciTech Connect

    Thoudam, Satyendra

    2013-11-20

    Recently, the Fermi Space Telescope discovered two large ?-ray emission regions, the so-called Fermi bubbles, that extend up to ?50° above and below the Galactic center (GC). The ?-ray emission from the bubbles is found to follow a hard spectrum with no significant spatial variation in intensity and spectral shape. The origin of the emission is still not clearly understood. Suggested explanations include the injection of cosmic-ray (CR) nuclei from the GC by high-speed Galactic winds, electron acceleration by multiple shocks, and stochastic electron acceleration inside the bubbles. In this Letter, it is proposed that the ?-rays may be the result of diffusive injection of Galactic CR protons during their propagation through the Galaxy. Considering that the bubbles are slowly expanding, and CRs undergo much slower diffusion inside the bubbles than in the average Galaxy and at the same time suffer losses due to adiabatic expansion and inelastic collisions with the bubble plasma, this model can explain the observed intensity profile, the emission spectrum and the measured luminosity without invoking any additional particle production processes, unlike other existing models.

  12. Nanoplankton mixotrophy in the eastern equatorial Pacific

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

    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.

  13. Equatorial Kelvin waves: A UARS MLS view

    SciTech Connect

    Canziani, P.O.; Holton, J.R.; Fishbein, E.; Froidevaux, L.; Waters, J.W.

    1994-10-01

    Data from the Microwave Limb Sounder (MLS) instrument on the Upper Atmosphere Research Satellite (UARS) are used to compare two periods of Kelvin wave activity during different stages of the equatorial quasi-biennial oscillation. The analysis is carried out using an asynoptic mapping technique. A wide bandpass filter is used to isolate the frequency bands where Kelvin waves have been identified in previous studies. Time-height and time-latitude plots of the bandpassed data are used to identify Kelvin wave activity in the temperature and ozone fields. Frequency spectra of temperature and ozone amplitudes are constructed to further analyze the latitudinal and meridional distribution of Kelvin wave activity in zonal wavenumbers 1 and 2. The characteristics identified in these plots agree well with theoretical predictions and previous observations of middle atmosphere Kelvin waves. The time-height and time-latitude plots support the existence of Kelvin waves in discrete frequency bands; the slow, fast, and ultrafast Kelvin modes are all identified in the data. The characteristics of these modes do not vary much despite different mean flow conditions in the two periods examined. For the Kelvin wave-induced perturbations in ozone, the change from a transport-dominated regime below 10 hPa to a photochemically controlled regime above 10 hPa is clearly apparent in the height dependence of the phase difference between temperature and ozone.

  14. POGO observations of the equatorial electrojet

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

    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.

  15. Condor equatorial electrojet campaign: Radar results

    SciTech Connect

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

    1987-12-01

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

  16. Gradient drift eigenmodes in the equatorial electrojet

    SciTech Connect

    Wang, X.H.; Bhattacharjee, A.

    1994-07-01

    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 density 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 shooter 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. 27 refs., 9 figs.

  17. Gradient drift eigenmodes in the equatorial electrojet

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    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.

  18. Light deflection in Kerr field for off-equatorial source

    E-print Network

    Sarani Chakraborty; A. K. Sen

    2015-04-13

    Deflection angle for a light ray travelling in the equatorial plane of a rotating Kerr mass has been already calculated by various investigators. Considering the light ray to be travelling only slightly above the equatorial plane, calculations have been made for such a ray for its deflection angle. In this paper, we calculate deflection angles for the light ray at various heights, which are small compared to the impact parameter and derive corresponding analytical expressions for deflection angle.

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

    NASA Astrophysics Data System (ADS)

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

    2007-10-01

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

  20. Manipulating bubbles with secondary Bjerknes forces

    E-print Network

    Lanoy, Maxime; Tourin, Arnaud; Leroy, Valentin

    2015-01-01

    Gas bubbles in a sound field are submitted to a radiative force, known as the secondary Bjerknes force. We propose an original experimental setup that allows us to investigate in details this force between two bubbles, as a function of the sonication frequency, as well as the bubbles radii and distance. We report the observation of both attractive and, more interestingly, repulsive Bjerknes force, when the two bubbles are driven in antiphase. Our experiments show the importance of taking multiple scattering into account, which leads to a strong acoustic coupling of the bubbles when their radii are similar. Our setup demonstrates the accuracy of secondary Bjerknes forces for attracting or repealing a bubble, and could lead to new acoustic tools for non contact manipulation in microfluidic devices.

  1. Manipulating bubbles with secondary Bjerknes forces

    E-print Network

    Maxime Lanoy; Caroline Derec; Arnaud Tourin; Valentin Leroy

    2015-10-23

    Gas bubbles in a sound field are submitted to a radiative force, known as the secondary Bjerknes force. We propose an original experimental setup that allows us to investigate in details this force between two bubbles, as a function of the sonication frequency, as well as the bubbles radii and distance. We report the observation of both attractive and, more interestingly, repulsive Bjerknes force, when the two bubbles are driven in antiphase. Our experiments show the importance of taking multiple scattering into account, which leads to a strong acoustic coupling of the bubbles when their radii are similar. Our setup demonstrates the accuracy of secondary Bjerknes forces for attracting or repealing a bubble, and could lead to new acoustic tools for non contact manipulation in microfluidic devices.

  2. Mechanism of bubble detachment from vibrating walls

    SciTech Connect

    Kim, Dongjun; Park, Jun Kwon Kang, Kwan Hyoung; Kang, In Seok

    2013-11-15

    We discovered a previously unobserved mechanism by which air bubbles detach from vibrating walls in glasses containing water. Chaotic oscillation and subsequent water jets appeared when a wall vibrated at greater than a critical level. Wave forms were developed at water-air interface of the bubble by the wall vibration, and water jets were formed when sufficiently grown wave-curvatures were collapsing. Droplets were pinched off from the tip of jets and fell to the surface of the glass. When the solid-air interface at the bubble-wall attachment point was completely covered with water, the bubble detached from the wall. The water jets were mainly generated by subharmonic waves and were generated most vigorously when the wall vibrated at the volume resonant frequency of the bubble. Bubbles of specific size can be removed by adjusting the frequency of the wall's vibration.

  3. BUBBLE DYNAMICS AT GAS-EVOLVING ELECTRODES

    SciTech Connect

    Sides, Paul J.

    1980-12-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

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

  5. Constraining bubbling of methane from thermokarst lakes

    NASA Astrophysics Data System (ADS)

    Balcerak, Ernie

    2013-08-01

    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.

  6. Collapse of vacuum bubbles in a vacuum

    SciTech Connect

    Ng, Kin-Wang; Wang, Shang-Yung

    2011-02-15

    We revisit the dynamics of a false vacuum bubble in a background de Sitter spacetime. We find that there exists a large parameter space that allows the bubble to collapse into a black hole or to form a wormhole. This may have interesting implications for the creation of a baby universe in the laboratory, the string landscape where the bubble nucleation takes place among a plenitude of metastable vacua, and the inflationary physics.

  7. Cusped Bubbles Rising through Polyelectrolyte Solutions

    NASA Astrophysics Data System (ADS)

    Belmonte, Andrew; Sostarecz, Michael

    2000-11-01

    It is well known that a bubble rising in a polymer fluid can have a cusp-like tail. We report on an experimental study of bubbles rising through solutions of glycerol/water with the addition of the polymer xanthan gum, a polyelectrolyte which becomes more rigid as the free ion concentration is increased. The addition of salt also decreases the elasticity of the xanthan gum solutions, and we observe its effects on the velocity and shape of the cusped bubble.

  8. DNA Bubble Life Time in Denaturation

    E-print Network

    Zh. S. Gevorkian; Chin-Kun Hu

    2010-10-11

    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.

  9. An experimental study of bubble mediated gas exchange for a single bubble

    NASA Astrophysics Data System (ADS)

    Mori, Nobuhito; Imamura, Masahiro; Yamamoto, Ryosuke

    An experimental study of bubble mediated gas exchange for a single bubble was performed. Medium sized air bubbles were generated into a water column by a computer-controlled electromagnetic valve. Temporal variations of gas concentration were analyzed by a gas chromatography with a head space method. The total amount of gas exchange for a single bubble with several radii are compared with the experimental results and theory.

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

    NASA Technical Reports Server (NTRS)

    Tkachev, L. G.

    1988-01-01

    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.

  11. Multiple Spark-Generated Bubble Interactions

    NASA Astrophysics Data System (ADS)

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

    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.

  12. Bubble departure radii at solidification interfaces

    NASA Technical Reports Server (NTRS)

    Cole, R.; Papazian, J. M.; Wilcox, W. R.

    1980-01-01

    A model has been developed for the prediction of bubble departure radii from flat solidification interfaces, including the effect of thermocapillary forces. Under normal gravity conditions, the necessary gas bubble radius required for departure from a CBr4 solidification interface is predicted to be approximately 1/2 mm in agreement with measured values. Under microgravity conditions, however, where surface forces predominate, the model predicts a seemingly prohibitive value of 40 mm. This result is at least in agreement with the microgravity tests conducted on the NASA SPAR I and SPAR III sounding rockets (1978) where the bubbles were not larger than 2 mm in radius and no bubble detachment was observed.

  13. Cosmic ray confinement in fossil cluster bubbles

    NASA Astrophysics Data System (ADS)

    Ruszkowski, M.; Enßlin, T. A.; Brüggen, M.; Begelman, M. C.; Churazov, E.

    2008-02-01

    Most cool core clusters of galaxies possess active galactic nuclei (AGN) in their centres. These AGN inflate buoyant bubbles containing non-thermal radio-emitting particles. If such bubbles efficiently confine cosmic rays (CRs) then this could explain `radio relics' seen far from cluster centres. We simulate the diffusion of CRs from buoyant bubbles inflated by AGN. Our simulations include the effects of the anisotropic particle diffusion introduced by magnetic fields. Our models are consistent with the X-ray morphology of AGN bubbles, with disruption being suppressed by the magnetic draping effect. We conclude that for such magnetic field topologies, a substantial fraction of CRs can be confined inside the bubbles on buoyant rise time-scales even when the parallel diffusivity coefficient is very large. For isotropic diffusion at a comparable level, CRs would leak out of the bubbles too rapidly to be consistent with radio observations. Thus, the long confinement times associated with the magnetic suppression of CRs diffusion can explain the presence of radio relics. We show that the partial escape of CRs is mostly confined to the wake of the rising bubbles and speculate that this effect could: (i) account for the excitation of the H? filaments trailing behind the bubbles in the Perseus cluster, (ii) inject entropy into the metal-enriched material being lifted by the bubbles and, thus, help to displace it permanently from the cluster centre and (iii) produce observable ?-rays via the interaction of the diffusing CRs with the thermal intracluster medium.

  14. Modeling bubble clusters in compressible liquids

    NASA Astrophysics Data System (ADS)

    Fuster, Daniel; Colonius, Tim

    2010-11-01

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

  15. Bubbles in graphene - a computational study

    NASA Astrophysics Data System (ADS)

    Settnes, Mikkel; Power, Stephen R.; Lin, Jun; Petersen, Dirch H.; Jauho, Antti-Pekka

    2015-10-01

    Strain-induced deformations in graphene are predicted to give rise to large pseudomagnetic fields. We examine theoretically the case of gas-inflated bubbles to determine whether signatures of such fields are present in the local density of states. Sharp-edged bubbles are found to induce Friedel-type oscillations which can envelope pseudo-Landau level features in certain regions of the bubble. However, bubbles which minimise interference effects are also unsuitable for pseudo-Landau level formation due to more spatially varying field profiles.

  16. Climatology of equatorial stratosphere over Lagos, Nigeria

    NASA Astrophysics Data System (ADS)

    Oyekola, Oyedemi Samuel

    We have used 12 complete calendar years (January 1993-December 2004) of monthly averages of measurements made by the Dobson spectrophotometer instrument over an urban site, Lagos (6.6oN, 3.3oE), southwest Nigeria, to study equatorial stratospheric column ozone variations and trends. Our results indicate that the time-averaged total column ozone has a seasonal cy-cle, which maximizes in June and July with a value of 259 Dobson units (DU) and minimizes in February with a magnitude of 250 DU. Statistical analysis of the climatological mean monthly total Dobson O3 record for 1993-2004 show that the local trend is approximately +0.041±0.0011 DU/year (+0.49±0.013% per decade). Spectral analysis was applied to the monthly averages series. The significant periodicity at 95% confidence level demonstrate prominent spectra peaks near 1.9 and 3.6 years, representative of quasi-biennial oscillation (QBO) and quasi-triennial oscillation (QTO), respectively. Signal due to semiannual variation is also identified at Lagos sounding site. Comparison with the ozone observations from Total Ozone Mapping Spectrom-eter (TOMS) on board the Earth-Probe (EP) satellite for the period from 1997 to 2002 reveal that EP/TOMS instrument consistently larger than the ground-based measurement from Dob-son station. Percentage mean relative disparity ranges from -11% to 15%. The root mean square error (RMSE) between satellite and ground-based observations over Lagos ranges be-tween ˜35-83 DU with largest and lowest variability occurring during the ascending phase of solar activity (1999, 10.7 cm radio flux, F10.7 equals 154 flux units) and during the peak phase of solar activity (2001, F10.7 equals 181), respectively.

  17. Neotectonics in the northern equatorial Brazilian margin

    NASA Astrophysics Data System (ADS)

    Rossetti, Dilce F.; Souza, Lena S. B.; Prado, Renato; Elis, Vagner R.

    2012-08-01

    An increasing volume of publications has addressed the role of tectonics in inland areas of northern Brazil during the Neogene and Quaternary, despite its location in a passive margin. Hence, northern South America plate in this time interval might have not been as passive as usually regarded. This proposal needs further support, particularly including field data. In this work, we applied an integrated approach to reveal tectonic structures in Miocene and late Quaternary strata in a coastal area of the Amazonas lowland. The investigation, undertaken in Marajó Island, mouth of the Amazonas River, consisted of shallow sub-surface geophysical data including vertical electric sounding and ground penetrating radar. These methods were combined with morphostructural analysis and sedimentological/stratigraphic data from shallow cores and a few outcrops. The results revealed two stratigraphic units, a lower one with Miocene age, and an upper one of Late Pleistocene-Holocene age. An abundance of faults and folds were recorded in the Miocene deposits and, to a minor extent, in overlying Late Pleistocene-Holocene strata. In addition to characterize these structures, we discuss their origin, considering three potential mechanisms: Andean tectonics, gravity tectonics related to sediment loading in the Amazon Fan, and rifting at the continental margin. Amongst these hypotheses, the most likely is that the faults and folds recorded in Marajó Island reflect tectonics associated with the history of continental rifting that gave rise to the South Atlantic Ocean. This study supports sediment deposition influenced by transpression and transtension associated with strike-slip divergence along the northern Equatorial Brazilian margin in the Miocene and Late Pleistocene-Holocene. This work records tectonic evidence only for the uppermost few ten of meters of this sedimentary succession. However, available geological data indicate a thickness of up to 6 km, which is remarkably thick for an area regarded as a passive margin.

  18. A Drying Trend in Central Equatorial Africa

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  19. Fluid mechanics of bubble capture by the diving bell spider

    E-print Network

    Brooks, Alice (Alice P.)

    2010-01-01

    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 ...

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

    SciTech Connect

    Benedetti, C.; Schroeder, C. B.; Esarey, E.; Leemans, W. P.; Rossi, F.

    2013-10-15

    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.

  1. Magma mixing enhanced by bubble segregation

    NASA Astrophysics Data System (ADS)

    Wiesmaier, S.; Morgavi, D.; Renggli, C.; Perugini, D.; De Campos, C. P.; Hess, K.-U.; Ertel-Ingrisch, W.; Lavallée, Y.; Dingwell, D. B.

    2015-04-01

    That rising bubbles may significantly affect magma mixing paths has already been demon strated by analogue experiments. Here, for the first time, bubble-advection experiments are performed employing volcanic melts at magmatic temperatures. Cylinders of basaltic glass were placed below cylinders of rhyolite glass. Upon melting, interstitial air formed bubbles that rose into the rhyolite melt, thereby entraining tails of basaltic liquid. The formation of plume-like filaments of advected basalt within the rhyolite was characterized by microCT and subsequent high-resolution EMP analyses. Melt entrainment by bubble ascent appears to be an efficient mechanism for mingling volcanic melts of highly contrasting compositions and properties. MicroCT imaging reveals bubbles trailing each other and multiple filaments coalescing into bigger ones. Rheological modelling of the filaments yields viscosities of up to 2 orders of magnitude lower than for the surrounding rhyolitic liquid. Such a viscosity contrast implies that bubbles rising successively are likely to follow this pathway of low resistance that previously ascending bubbles have generated. Filaments formed by multiple bubbles would thus experience episodic replenishment with mafic material. Inevitable implications for the concept of bubble advection in magma mixing include thereby both an acceleration of mixing because of decreased viscous resistance for bubbles inside filaments and non-conventional diffusion systematics because of intermittent supply of mafic material (instead of a single pulse) inside a material. Inside the filaments, the mafic material was variably hybridised to andesitic through rhyolitic composition. Compositional profiles alone are ambiguous, however, to determine whether single or multiple bubbles were involved during formation of a filament. Statistical analysis, employing concentration variance as measure of homogenisation, demonstrates that also filaments appearing as single-bubble filaments are likely to have experienced multiple bubbles passages. In cases where bubbles have been essential for magma mixing, standard diffusion analysis may thus be inadequate for constraining timescales. However, data analysis employing concentration variance relaxation permits the distinction of conventional single-pulse filaments from multiple bubble ascent advection in natural samples, demonstrating yet another powerful application of this novel petrological tool.

  2. Neural basis of economic bubble behavior.

    PubMed

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

    2014-04-18

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

  3. Bubbling in unbounded coflowing liquids.

    PubMed

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

    2006-03-31

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

  4. Multi-point observations of the inner boundary of the plasma sheet during geomagnetic disturbances

    E-print Network

    California at Berkeley, University of

    of the equatorial dusk-side plasma in the string-of-pearls configuration, allowing the dynamics of particle- sphere in a string-of-pearls configuration, successively crossing geostationary orbit, allowing

  5. Seasonal influence of ENSO on the Atlantic ITCZ and equatorial South America

    NASA Astrophysics Data System (ADS)

    Münnich, M.; Neelin, J. D.

    2005-11-01

    In late boreal spring, especially May, a strong relationship exists in observations among precipitation anomalies over equatorial South America and the Atlantic intertropical convergence zone (ITCZ), and eastern equatorial Pacific and central equatorial Atlantic sea surface temperature anomalies (SSTA). A chain of correlations of equatorial Pacific SSTA, western equatorial Atlantic wind stress (WEA), equatorial Atlantic SSTA, sea surface height, and precipitation supports a causal chain in which El Niño/Southern Oscillation (ENSO) induces WEA stress anomalies, which in turn affect Atlantic equatorial ocean dynamics. These correlations show strong seasonality, apparently arising within the atmospheric links of the chain. This pathway and the influence of equatorial Atlantic SSTA on South American rainfall in May appear independent of that of the northern tropical Atlantic. Brazil's Nordeste is affected by the northern tropical Atlantic. The equatorial influence lies further to the north over the eastern Amazon and the Guiana Highlands.

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    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.

  7. Bubbles, Gating, and Anesthetics in Ion Channels

    PubMed Central

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

    2008-01-01

    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

  8. Videotaping the Lifespan of a Soap Bubble.

    ERIC Educational Resources Information Center

    Ramme, Goran

    1995-01-01

    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)

  9. The Minnaert Bubble: An Acoustic Approach

    ERIC Educational Resources Information Center

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

    2008-01-01

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

  10. The Physics of Foams, Droplets and Bubbles

    ERIC Educational Resources Information Center

    Sarker, Dipak K.

    2013-01-01

    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…

  11. Measuring the surface tension of soap bubbles

    NASA Technical Reports Server (NTRS)

    Sorensen, Carl D.

    1992-01-01

    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.

  12. Simple improvements to classical bubble nucleation models

    NASA Astrophysics Data System (ADS)

    Tanaka, Kyoko K.; Tanaka, Hidekazu; Angélil, Raymond; Diemand, Jürg

    2015-08-01

    We revisit classical nucleation theory (CNT) for the homogeneous bubble nucleation rate and improve the classical formula using a correct prefactor in the nucleation rate. Most of the previous theoretical studies have used the constant prefactor determined by the bubble growth due to the evaporation process from the bubble surface. However, the growth of bubbles is also regulated by the thermal conduction, the viscosity, and the inertia of liquid motion. These effects can decrease the prefactor significantly, especially when the liquid pressure is much smaller than the equilibrium one. The deviation in the nucleation rate between the improved formula and the CNT can be as large as several orders of magnitude. Our improved, accurate prefactor and recent advances in molecular dynamics simulations and laboratory experiments for argon bubble nucleation enable us to precisely constrain the free energy barrier for bubble nucleation. Assuming the correction to the CNT free energy is of the functional form suggested by Tolman, the precise evaluations of the free energy barriers suggest the Tolman length is ?0.3 ? independently of the temperature for argon bubble nucleation, where ? is the unit length of the Lennard-Jones potential. With this Tolman correction and our prefactor one gets accurate bubble nucleation rate predictions in the parameter range probed by current experiments and molecular dynamics simulations.

  13. Bubble Boy Disease History of SCID

    E-print Network

    Brutlag, Doug

    Bubble Boy Disease Oz Hasbún #12;History of SCID v It was between the years of 1968 and 1973 Disease became widely known during the 1970s and 1980s, and was dubbed the "Bubble Boy Disease" because of the widely-publicized case of David Veter, a boy with X-linked SCID, who lived for 12 years in a plastc, germ

  14. Structure of nanoscale gas bubbles in metals

    SciTech Connect

    Caro, A. Schwen, D.; Martinez, E.

    2013-11-18

    A usual way to estimate the amount of gas in a bubble inside a metal is to assume thermodynamic equilibrium, i.e., the gas pressure P equals the capillarity force 2?/R, with ? the surface energy of the host material and R the bubble radius; under this condition there is no driving force for vacancies to be emitted or absorbed by the bubble. In contrast to the common assumption that pressure inside a gas or fluid bubble is constant, we show that at the nanoscale this picture is no longer valid. P and density can no longer be defined as global quantities determined by an equation of state (EOS), but they become functions of position because the bubble develops a core-shell structure. We focus on He in Fe and solve the problem using both continuum mechanics and empirical potentials to find a quantitative measure of this effect. We point to the need of redefining an EOS for nanoscale gas bubbles in metals, which can be obtained via an average pressure inside the bubble. The resulting EOS, which is now size dependent, gives pressures that differ by a factor of two or more from the original EOS for bubble diameters of 1?nm and below.

  15. Controlled transport of captive bubbles on plastrons.

    PubMed

    Huynh, So Hung; Lau, Chun Yat; Cheong, Brandon Huey-Ping; Muradoglu, Murat; Liew, Oi Wah; Ng, Tuck Wah

    2015-10-14

    Captive bubbles that reside on superhydrophobic surfaces with plastrons move uncontrollably when tilted. A system based on creating moveable local apexes on flexible superhydrophobic foils is shown to allow controlled transport. Simulations done reveal that specific bubble transport speeds are needed to form concentration gradients suited for aerotaxis study and sensing. PMID:26305149

  16. Particle Motion Induced by Bubble Cavitation

    NASA Astrophysics Data System (ADS)

    Poulain, Stéphane; Guenoun, Gabriel; Gart, Sean; Crowe, William; Jung, Sunghwan

    2015-05-01

    Cavitation bubbles induce impulsive forces on surrounding substrates, particles, or surfaces. Even though cavitation is a traditional topic in fluid mechanics, current understanding and studies do not capture the effect of cavitation on suspended objects in fluids. In the present work, the dynamics of a spherical particle due to a cavitation bubble is experimentally characterized and compared with an analytical model. Three phases are observed: the growth of the bubble where the particle is pushed away, its collapse where the particle approaches the bubble, and a longer time scale postcollapse where the particle continues to move toward the collapsed bubble. The particle motion in the longer time scale presumably results from the asymmetric cavitation evolution at an earlier time. Our theory considering the asymmetric bubble dynamics shows that the particle velocity strongly depends on the distance from the bubble as an inverse-fourth-power law, which is in good agreement with our experimentation. This study sheds light on how small free particles respond to cavitation bubbles in fluids.

  17. Equatorial Density Irregularity Structures at Intermediate Scales and Their Temporal Evolution

    NASA Technical Reports Server (NTRS)

    Kil, Hyosub; Heelis, R. A.

    1998-01-01

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

  18. The annual cycle in equatorial convection and sea surface temperature

    SciTech Connect

    Mitchell, T.P.; Wallace, J.M. NASA, Goddard Space Flight Center, Greenbelt, MD )

    1992-10-01

    The coupled atmosphere-ocean system in the equatorial eastern Pacific and Atlantic exhibits a distinct annual cycle that is reflected in contrasting conditions at the times of the two equinoxes. The contrasts are so strong that they dominate the annual march of zonally averaged outgoing long wave radiation for the equatorial belt. The March equinox corresponds to the warm season when the equatorial cold tongues in the eastern Pacific and Atlantic area absent. With the onset of summer monsoon convection over Colombia, Central America, and West Africa in May-June, northward surface winds strengthen over the eastern Pacific and Atlantic, the equatorial cold tongues reappear, and the marine convection shifts from the equatorial belt to the intertropical convergence zones (ITCZs) along 8 deg N. On the basis of observational evidence concerning the timing and year-to-year regularity of the surface wind changes during the development of the cold tongues, it is argued that (1) the increase in the northward surface winds in response to the onset of the northern summer monsoon may be instrumental in reestablishing the cold tongues, and (2) positive feedbacks involving both the zonal and meridional wind components contribute to the remarkable robustness of the cold tongue-ITCZs complexes in both oceans. 36 refs.

  19. Longitudinal and seasonal structure of the ionospheric equatorial electric field

    NASA Astrophysics Data System (ADS)

    Alken, P.; Chulliat, A.; Maus, S.

    2013-03-01

    The daytime eastward equatorial electric field (EEF) in the ionospheric E-region plays an important role in equatorial ionospheric dynamics. It is responsible for driving the equatorial electrojet (EEJ) current system, equatorial vertical ion drifts, and the equatorial ionization anomaly. Due to its importance, there is much interest in accurately measuring and modeling the EEF. In this work we propose a method of estimating the EEF using CHAMP satellite-derived latitudinal current profiles of the daytime EEJ along with ? H measurements from ground magnetometer stations. Magnetometer station pairs in both Africa and South America were used for this study to produce time series of electrojet current profiles. These current profiles were then inverted for estimates of the EEF by solving the governing electrostatic equations. We compare our results with the Ion Velocity Meter (IVM) instrument on board the Communication/Navigation Outage Forecasting System satellite. We find high correlations of about 80% with the IVM data; however, we also find a constant offset of about 0.3 mV/m between the two data sets in Africa. Further investigation is needed to determine its cause. We compare the EEF structure in Africa and South America and find differences which can be attributed to the effect of atmospheric nonmigrating tides. This technique can be extended to any pair of ground magnetometer stations which can capture the day-to-day strength of the EEJ.

  20. Equatorial Winds on Saturn and the Stratospheric Oscillation

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  1. Sources of variability in equatorial topside ionospheric and plasmaspheric temperatures

    NASA Astrophysics Data System (ADS)

    Varney, Roger H.; Hysell, David L.; Huba, J. D.

    2013-10-01

    Jicamarca measurements of electron temperatures at high altitudes (500-1500km) from the last solar minimum routinely show variations of hundreds of Kelvin from day-to-day. Possible sources of these variations are explored using the SAMI2-PE is another model of the ionosphere including photoelectron transport (SAMI2-PE) model, which includes a multistream photoelectron transport model. Changes to the electric fields, meridional winds, and thermospheric densities can all change the electron densities and temperatures at high altitudes. The high altitude electron temperatures are primarily determined by a balance between heating from photoelectrons which travel up the field lines and thermal diffusion which carries heat back down the field lines. The winds and electric fields will change the altitude and densities of the off-equatorial F-region peaks, especially on the field lines connected to the equatorial arcs. The densities and temperatures in the plasmasphere will self consistently adjust themselves to achieve diffusive equilibrium with the off-equatorial F-regions. Furthermore, decreases in the density and/or altitude of the F-region makes it easier for photoelectrons to escape to high altitudes. These connections between the equatorial plasmasphere, the off-equatorial F-regions, and the neutral thermosphere suggest that high altitude measurements at Jicamarca could be used to study thermospheric variability.

  2. Intense spreading of radar echoes from ionospheric plasmas

    E-print Network

    Dorfman, Seth E

    2005-01-01

    On December 25, 2004, a large-scale ionospheric plasma bubble was observed over Arecibo Observatory in Puerto Rico, inducing significant range spreading on ionograms. This phenomena may be explained by means of the E x B ...

  3. Magma mixing enhanced by bubble segregation

    NASA Astrophysics Data System (ADS)

    Wiesmaier, S.; Morgavi, D.; Renggli, C. J.; Perugini, D.; De Campos, C. P.; Hess, K.-U.; Ertel-Ingrisch, W.; Lavallée, Y.; Dingwell, D. B.

    2015-08-01

    In order to explore the materials' complexity induced by bubbles rising through mixing magmas, bubble-advection experiments have been performed, employing natural silicate melts at magmatic temperatures. A cylinder of basaltic glass was placed below a cylinder of rhyolitic glass. Upon melting, bubbles formed from interstitial air. During the course of the experimental runs, those bubbles rose via buoyancy forces into the rhyolitic melt, thereby entraining tails of basaltic liquid. In the experimental run products, these plume-like filaments of advected basalt within rhyolite were clearly visible and were characterised by microCT and high-resolution EMP analyses. The entrained filaments of mafic material have been hybridised. Their post-experimental compositions range from the originally basaltic composition through andesitic to rhyolitic composition. Rheological modelling of the compositions of these hybridised filaments yield viscosities up to 2 orders of magnitude lower than that of the host rhyolitic liquid. Importantly, such lowered viscosities inside the filaments implies that rising bubbles can ascend more efficiently through pre-existing filaments that have been generated by earlier ascending bubbles. MicroCT imaging of the run products provides textural confirmation of the phenomenon of bubbles trailing one another through filaments. This phenomenon enhances the relevance of bubble advection in magma mixing scenarios, implying as it does so, an acceleration of bubble ascent due to the decreased viscous resistance facing bubbles inside filaments and yielding enhanced mass flux of mafic melt into felsic melt via entrainment. In magma mixing events involving melts of high volatile content, bubbles may be an essential catalyst for magma mixing. Moreover, the reduced viscosity contrast within filaments implies repeated replenishment of filaments with fresh end-member melt. As a result, complex compositional gradients and therefore diffusion systematics can be expected at the filament-host melt interface, due to the repetitive nature of the process. However, previously magmatic filaments were tacitly assumed to be of single-pulse origin. Consequently, the potential for multi-pulse filaments has to be considered in outcrop analyses. As compositional profiles alone may remain ambiguous for constraining the origin of filaments, and as 3-D visual evidence demonstrates that filaments may have experienced multiple bubbles passages even when featuring standard diffusion gradients, therefore, the calculation of diffusive timescales may be inadequate for constraining timescales in cases where bubbles have played an essential role in magma mixing. Data analysis employing concentration variance relaxation in natural samples can distinguish conventional single-pulse filaments from advection via multiple bubble ascent advection in natural samples, raising the prospect of yet another powerful application of this novel petrological tool.

  4. Kinetics of Bubble Generation in Mafic Enclaves

    NASA Astrophysics Data System (ADS)

    Jackson, B. A.; Gardner, J. E.

    2014-12-01

    Volcanically erupted mafic enclaves are typically vesicular, with the bubbles forming when the mafic magma cools after it is injected and disaggregated into a cooler silicic magma. This study uses hydrothermal experiments to investigate the kinetics of pre-eruptive bubble nucleation and growth within mafic magmas, focused on the efficiency of nucleation on different minerals, and to quantify the growth rate of bubbles with varying cooling rates. Starting materials are natural mafic enclaves from Southwest Trident, Alaska. Experiments were initially equilibrated with H2O at 85 MPa and 1065 °C for 2 hours, producing a melt with blocky crystals of plagioclase and pyroxene, and spherical bubbles with a mean 30 ?m diameter and number density (Nv) of 7.2x104 cm-3. Upon cooling to 1015 °C at 2 °C/h, the mineralogy and Nv did not change (although total crystallinity increased), while the mean bubble diameter increased to 90 ?m. Cooling further to 985 °C at 2 °C/h, resulted in the crystallization of Fe-Ti oxides, along with an abrupt Nv increase (3.0x105 cm-3) of bubbles with a mean diameter of 60 ?m. This abrupt bubble nucleation event, coinciding with the formation of Fe-Ti oxides, suggests that plagioclase and pyroxene are poor bubble nucleation sites in mafic melts, and that Fe-Ti oxides are good bubble nucleation sites, similar to previous results using rhyolite melts. Additionally, the occurrence of this nucleation event suggests that cooling related diffusive growth of bubbles in mafic enclaves, under magma chamber conditions, is too slow to keep up with increasing volatile saturation in the melt, and that the melt may become supersaturated until nucleation sites for new bubbles become available. Rapid cooling (1065-985 °C at 110 °C/h) produced abundant acicular plagioclase and pyroxene crystals (no Fe-Ti oxides), and bubbles with a nearly identical mean diameter and Nv to experiments equilibrated at 1065 °C. It is therefore likely that bubbles will not nucleate or grow significantly during rapid cooling and crystallization of mafic enclaves until Fe-Ti oxide nucleation sites are available. Overall, these experimental results indicate that cooling and crystallization induced pre-eruptive bubble generation in mafic enclaves is strongly controlled by the availability of Fe-Ti oxide nucleation sites.

  5. A signature of anisotropic bubble collisions

    E-print Network

    Michael P. Salem

    2010-06-04

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

  6. Bubble growth and rise in soft sediments

    NASA Astrophysics Data System (ADS)

    Boudreau, Bernard P.; Algar, Chris; Johnson, Bruce D.; Croudace, Ian; Reed, Allen; Furukawa, Yoko; Dorgan, Kelley M.; Jumars, Peter A.; Grader, Abraham S.; Gardiner, Bruce S.

    2005-06-01

    The mechanics of uncemented soft sediments during bubble growth are not widely understood and no rheological model has found wide acceptance. We offer definitive evidence on the mode of bubble formation in the form of X-ray computed tomographic images and comparison with theory. Natural and injected bubbles in muddy cohesive sediments are shown to be highly eccentric oblate spheroids (disks) that grow either by fracturing the sediment or by reopening preexisting fractures. In contrast, bubbles in soft sandy sediment tend to be spherical, suggesting that sand acts fluidly or plastically in response to growth stresses. We also present bubble-rise results from gelatin, a mechanically similar but transparent medium, that suggest that initial rise is also accomplished by fracture. Given that muddy sediments are elastic and yield by fracture, it becomes much easier to explain physically related phenomena such as seafloor pockmark formation, animal burrowing, and gas buildup during methane hydrate melting.

  7. Bubble chamber as a trace chemical detector

    SciTech Connect

    Luo, X.; McCreary, E.I.; Atencio, J.H.; McCown, A.W.; Sander, R.K.

    1998-08-01

    A novel concept for trace chemical analysis in liquid has been demonstrated. The technique utilizes light absorption in a superheated liquid. Although a superheated liquid is thermodynamically unstable, a high degree of superheating can be dynamically achieved for a short period of time. During this time the superheated liquid is extremely sensitive to boiling at nucleation sites produced by energy deposition. Observation of bubbles in the superheated liquid in some sense provides amplification of the initial energy deposition. Bubble chambers containing superheated liquids have been used to detect energetic particles; now a bubble chamber is used to detect a trace chemical in superheated liquid propane by observing bubble formation initiated by optical absorption. Crystal violet is used as a test case and can be detected at the subpart-per-10{sup 12} level by using a Nd:YAG laser. The mechanism for bubble formation and ideas for further improvement are discussed. {copyright} 1998 Optical Society of America

  8. Bubble mobility in mud and magmatic volcanoes

    NASA Astrophysics Data System (ADS)

    Tran, Aaron; Rudolph, Maxwell L.; Manga, Michael

    2015-03-01

    The rheology of particle-laden fluids with a yield stress, such as mud or crystal-rich magmas, controls the mobility of bubbles, both the size needed to overcome the yield stress and their rise speed. We experimentally measured the velocities of bubbles and rigid spheres in mud sampled from the Davis-Schrimpf mud volcanoes adjacent to the Salton Sea, Southern California. Combined with previous measurements in the polymer gel Carbopol, we obtained an empirical model for the drag coefficient and bounded the conditions under which bubbles overcome the yield stress. Yield stresses typical of mud and basaltic magmas with sub-mm particles can immobilize millimeter to centimeter sized bubbles. At Stromboli volcano, Italy, a vertical yield stress gradient in the shallow conduit may immobilize bubbles with diameter ? 1 cm and hinder slug coalescence.

  9. Mechanism of gas bubble shoot-off and motion during spark discharge in liquid

    NASA Astrophysics Data System (ADS)

    Yavtushenko, I. O.; Orlov, A. M.; Zharkov, S. V.

    2012-07-01

    The conditions of the excitation of a pulsed plasma discharge on the surface of a processed metal (copper) sample immersed in a conducting aqueous solution have been studied. Cathode polarization of the metal was provided by a high-voltage capacitor bank (4?F) charged to U = 200-1100 V after each discharge. It is established that electric breakdown with a duration not exceeding 0.1 ?s is always preceded by the formation of small hydrogen bubbles (with radii r ? 37-40 ?m) on the polarized metal surface, which takes about 139-159 ?s. A mechanism of passivation of the processed metal surface by these hydrogen bubbles, which are synchronously shot off from the electrode surface under the action of the spark discharge, is proposed. Consistent matching of the experimental data and model calculations is used to estimate the main parameters determining the kinetics of bubble detachment from the electrode surface at various voltages U on the capacitor bank.

  10. Global structure of isothermal X-ray emission along the Fermi bubbles

    E-print Network

    Kataoka, J; Totani, T; Sofue, Y; Inoue, Y; Nakashima, S; Cheung, C C

    2015-01-01

    In our previous works (Kataoka et al. 2013, Tahara et al. 2015), we found absorbed thermal X-ray plasma with kT ~ 0.3 keV observed ubiquitously near the edges of the Fermi bubbles and interpreted this emission as weakly shock-heated Galactic halo (GH) gas. Here we present a systematic and uniform analysis of archival Suzaku (29 pointings; 6 newly presented) and Swift (68 pointings; 49 newly presented) data within Galactic longitudes |l| 0 deg) favors (ii), whereas that of the south (b NPS (South Polar Spur; SPS). Such an asymmetry, if due to the bubbles, cannot be fully understood only by the inclination of bubbles' axis against the Galactic disk normal, thus suggesting asymmetric outflow due to different environmental/initial condition.

  11. Time dependent response of equatorial ionospheric electric fields to magnetospheric disturbances

    SciTech Connect

    Fejer, B.G.; Scherliess, L.

    1995-04-01

    The authors use extensive radar measurements of F region vertical plasma drifts and auroral electrojet indices to determine the storm time dependence of equatorial zonal electric fields. These disturbance drifts result from the prompt penetration of high latitude electric fields and from the dynamo action of storm time winds which produce the largest perturbations a few hours after the onset of magnetic activity. The signatures of the equatorial disturbance electric fields change significantly depending on the relative contributions of these two components. The prompt electric field responses, with lifetimes of about one hour, are in excellent agreement with results from global convection models. The electric fields generated by storm time winds have longer lifetimes, amplitudes proportional to the energy input into the high latitude ionosphere, and a daily variation which follows closely the disturbance dynamo pattern of Blanc and Richmond. The storm wind driven electric fields are responsible for the larger amplitudes and longer lifetimes of the drift perturbations following sudden decreases in convection compared to those associated with sudden convection enhancements. 14 refs., 6 figs., 1 tab.

  12. Radar and satellite investigations of equatorial evening vertical drifts and spread F

    NASA Astrophysics Data System (ADS)

    Smith, J. M.; Rodrigues, F. S.; de Paula, E. R.

    2015-11-01

    We analyzed pre-midnight equatorial F region observations made by the 30 MHz coherent backscatter radar of São Luis, Brazil between August 2010 and February 2012. These measurements were processed, and used to create monthly maps of the echo occurrence as a function of local time and height. The maps show the inter-annual variability associated with equatorial spread F (ESF) occurrence in the Brazilian longitude sector. We also constructed monthly curves of the evening vertical drifts, for the Brazilian sector, using measurements by the ion velocity meter (IVM) onboard the C/NOFS satellite. The IVM evening drifts show a good overall agreement with the Scherliess and Fejer (1999) empirical model. Measured and model drifts show the development of the pre-reversal enhancement (PRE) of the vertical plasma drifts during ESF season. Using joint radar and satellite measurements, we found that evening (18:00-18:30 LT) mean non-negative drifts provide a necessary but not sufficient condition for the occurrence of topside ESF echoes. Evening downward (negative) drifts preceded the absence of topside ESF irregularities.

  13. Equatorial F region neutral winds and shears near sunset measured with chemical release techniques

    NASA Astrophysics Data System (ADS)

    Kiene, A.; Larsen, M. F.; Kudeki, E.

    2015-10-01

    The period near sunset is a dynamic and critical time for the daily development of the equatorial nighttime ionosphere and the instabilities that occur there. It is during these hours that the preconditions necessary for the later development of Equatorial Spread F (ESF) plasma instabilities occur. The neutral dynamics of the sunset ionosphere are also of critical importance to the generation of currents and electric fields; however, the behavior of the neutrals is experimentally understood primarily through very limited single-altitude measurements or measurements that provide weighted altitude means of the winds as a function of time. To date, there have been very few vertically resolved neutral wind measurements in the F region at sunset. We present two sets of sounding rocket chemical release measurements, one from a launch in the Marshall Islands on Kwajalein atoll and one from Alcantara, Brazil. Analysis of the release motions has yielded vertically resolved neutral wind profiles that show both the mean horizontal winds and the vertical shears in the winds. In both experiments, we observe significant vertical gradients in the zonal wind that are unexpected by classical assumptions about the behavior of the neutral wind at these altitudes at sunset near the geomagnetic equator.

  14. Air bubble migration rates as a proxy for bubble pressure distribution in ice cores

    NASA Astrophysics Data System (ADS)

    Dadic, Ruzica; Schneebeli, Martin; Bertler, Nancy

    2015-04-01

    Air bubble migration can be used as a proxy to measure the pressure of individual bubbles and can help constrain the gradual close-off of gas bubbles and the resulting age distribution of gases in ice cores. The close-off depth of single bubbles can vary by tens of meters, which leads to a distribution of pressures for bubbles at a given depth. The age distribution of gases (along with gas-age-ice-age differences) decreases the resolution of the gas level reconstructions from ice cores and limits our ability to determine the phase relationship between gas and ice, and thus, the impact of rapid changes of greenhouse gases on surface temperatures. For times of rapid climate change, including the last 150 years, and abrupt climate changes further back in the past, knowledge of the age distribution of the gases trapped in air bubbles will enable us to refine estimates of atmospheric changes. When a temperature gradient is applied to gas bubbles in an ice sample, the bubbles migrate toward warmer ice. This motion is caused by sublimation from the warm wall and subsequent frost deposition on the cold wall. The migration rate depends on ice temperature and bubble pressure and is proportional to the temperature gradient. The spread in migration rates for bubbles in the same samples at given temperatures should therefore reflect the variations in bubble pressures within a sample. Air bubbles with higher pressures would have been closed off higher in the firn column and thus have had time to equilibrate with the surrounding ice pressure, while air bubbles that have been closed off recently would have pressures that are similar to todays atmospheric pressure above the firn column. For ice under pressures up to ~13-16 bar, the pressure distribution of bubbles from a single depth provides a record of the trapping function of air bubbles in the firn column for a certain time in the past. We will present laboratory experiments on air bubble migration, using Antarctic ice core samples from a range of depths, to show that air bubble migration is a valid proxy for bubble pressure and can thus be used to determine the trapping function of air bubbles and gas age distribution for past conditions.

  15. The effect of islands on low frequency equatorial motions

    NASA Technical Reports Server (NTRS)

    Cane, M. A.; Du Penhoat, Y.

    1982-01-01

    A complete analytic solution is presented for the influence of equatorial islands on steady low-frequency waves. If the island is small (the meridional extent is much less than the equatorial radius of deformation, R), the waves pass it almost undisturbed, with the mass flux incident on the upstream side flowing around it nearly equally to the north and to the south and continuing on downstream in the lee of the island. For large islands (comparable in extent with R or larger), the principal response is organized as it would be if the island barrier were meridionally infinite. An incident Kelvin wave is largely reflected as long Rossby waves; symmetric long Rossby waves are reflected as equatorial Kelvin waves, while antisymmetric ones stop at the island barrier. In all cases, a boundary current composed of short Rossby waves forms at the eastern side of the island and accomplishes the required meridional redistribution of the zonal mass flux.

  16. Propagation of VLF waves through the equatorial anomaly

    NASA Astrophysics Data System (ADS)

    Tanaka, Y.; Cairo, L.

    1980-12-01

    The propagation characteristics of artificial VLF waves (NBA, 24.0 kHz) through the equatorial ionosphere have been studied by means of data obtained onboard the FR-1 satellite at 750 km altitude over Latin America. Large latitudinal variations of the vertical component of the wave normal generally appear in the evening at geomagnetic latitudes of 10 to 15 deg, and they also appear on most of the passes examined at night at latitudes of 5 to 10 deg. Ray and wave normal directions of the VLF waves are computed in various models of field-aligned equatorial anomaly. The latitudinal variations in the evening are due to large negative latitudinal gradients of electron density associated with the equatorial anomaly, and the latitudinal variations at night are due to relatively small density gradients.

  17. Metal quotas of plankton in the equatorial Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Twining, Benjamin S.; Baines, Stephen B.; Bozard, James B.; Vogt, Stefan; Walker, Elyse A.; Nelson, David M.

    2011-03-01

    The micronutrient metals Mn, Fe, Co, Ni and Zn are required for phytoplankton growth, and their availability influences ocean productivity and biogeochemistry. Here we report the first direct measurements of these metals in phytoplankton and protozoa from the equatorial Pacific Ocean. Cells representing 4 functional groups (diatoms, autotrophic flagellates, heterotrophic flagellates and autotrophic picoplankton) were collected from the surface mixed layer using trace-metal clean techniques during transects across the equator at 110°W and along the equator between 110°W and 140°W. Metal quotas were determined for individual cells with synchrotron x-ray fluorescence microscopy, and cellular stoichiometries were calculated relative to measured P and S, as well as to C calculated from biovolume. Bulk particulate (>3 ?m) metal concentrations were also determined at 3 stations using inductively coupled plasma mass spectrometry for comparison to single-cell stoichiometries. Phosphorus-normalized Mn, Fe, Ni and Zn ratios were significantly higher in diatoms than other cell types, while Co stoichiometries were highest in autotrophic flagellates. The magnitude of these effects ranged from approximately 2-fold for Mn in diatoms and autotrophic flagellates to nearly an order of magnitude for Fe in diatoms and picoplankton. Variations in S-normalized metal stoichiometries were also significant but of lower magnitude (1.4 to 6-fold). Cobalt and Mn quotas were 1.6 and 3-fold higher in autotrophic than heterotrophic flagellates. Autotrophic picoplankton were relatively enriched in Ni but depleted in Zn, matching expectations based on known uses of these metals in prokaryotes and eukaryotes. Significant spatial variability in metal stoichiometries was also observed. At two stations deviations in Fe stoichiometries reflected features in the dissolved Fe distribution. At these same stations, high Ni stoichiometries in autotrophic flagellates were correlated with elevated ammonium and depressed nitrate concentrations. The spatial effects may have resulted from the passage of tropical instability waves along the equator. Comparison of bulk and single-cell results show similar Mn:P ratios at 2 of 3 stations, but Fe:P and Ni:P were systematically higher in bulk material and Co:P was lower. These results suggest an overrepresentation of diatoms or diatom-based detritus in the bulk fraction. Taken together, the analyses present a generalized stoichiometry of Fe?Zn>Mn?Ni>Co in the plankton. Diatom Fe quotas exceeded minimum subsistence levels, characteristic of cells growing actively on oxidized N sources. This study demonstrates the subst antial biogeochemical insight that can be gained from studies of metal quotas in individual functional groups.

  18. The Annual Cycle in Equatorial Convection and Sea Surface Temperature.

    NASA Astrophysics Data System (ADS)

    Mitchell, Todd P.; Wallace, John M.

    1992-10-01

    The coupled atmosphere-ocean system in the equatorial eastern Pacific and Atlantic exhibits a distinct annual cycle that is reflected in contrasting conditions at the times of the two equinoxes. The contrasts are so strong that they dominate the annual march of zonally averaged outgoing longwave radiation for the equatorial belt. The March equinox corresponds to the warm season when the equatorial cold tongues in the eastern Pacific and Atlantic are absent. With the onset of summer monsoon convection over Colombia, Central America, and West Africa in May-June, northward surface winds strengthen over the eastern Pacific and Atlantic, the equatorial cold tongues reappear, and the marine convection shifts from the equatorial belt to the intertropical convergence zones (ITCZs) along 8°N. As the northern summer program the ITCZs remain strong and shift northward to new 10°N, while sea surface temperature (SST) continues to drop over the cold tongues and the southern tropics, perhaps in response to the expanding stratocumulus cloud decks in the latter region. The cold tongui-ITCZ complex persists through the September equinox, which is characterized by suppressed conviction, not only over the cold tongues but also over much of equatorial South America.On the basis of observational evidence concerning the timing and year-to-year regularity of the surface wind changes during the development of the cold tongues, it is argued that 1) the increase in the northward surface winds in response to the onset of the northern summer monsoon may be instrumental in reestablishing the cold tongues and 2) positive feedbacks involving both the zonal and meridional wind components contribute to the remarkable robustness of the cold tongue-ITCZ complexes in both oceans.

  19. Magma mixing enhanced by bubble ascent

    NASA Astrophysics Data System (ADS)

    Wiesmaier, S.; Morgavi, D.; Perugini, D.; De Campos, C. P.; Hess, K.; Lavallee, Y.; Dingwell, D. B.

    2012-12-01

    Understanding the processes that affect the rate of liquid state homogenization provides fundamental clues on the otherwise inaccessible subsurface dynamics of magmatic plumbing systems. Compositional heterogeneities detected in the matrix of magmatic rocks represent the arrested state of a chemical equilibration. Magmatic homogenization has been divided into a) the mechanical interaction of magma batches (mingling) and b) the diffusive equilibration of compositional gradients, where diffusive equilibration is exponentially enhanced by progressive mechanical interaction [1]. The mechanical interaction between two distinct batches of magma has commonly been attributed to shear and folding movements between two liquids of distinct viscosities. A mode of mechanical interaction scarcely invoked is the advection of mafic material into a felsic one through bubble motion. Yet, experiments with analogue materials demonstrated that bubble ascent has the potential to enhance the fluid mechanical component of magma mixing [2]. Here, we present preliminary results from bubble-advection experiments. For the first time, experiments of this kind were performed using natural materials at magmatic temperatures. Cylinders of Snake River Plain (SRP) basalt were drilled with a cavity of defined volume and placed underneath cylinders of SRP rhyolite. Upon melting, the gas pocket, or bubble trapped within the cavity, rose into the rhyolite, so entraining a layer of basalt. Successive iterations of the same experiment at progressive intervals ensured a time series of magmatic interaction caused by bubble segregation. Variations in initial bubble size allowed the tracking of bubble volume to advected material ratio at defined viscosity contrast. The resulting plume-like structures that the advected basalt formed within the rhyolite were characterized by microCT and subsequent high-resolution EMP analyses. The mass of advected material per bubble correlated positively with bubble size. The progressive loss of advected basalt during bubble motion was quantified by microCT for defined viscosity couples. The diffusional gradient around the plume tail showed a progressive evolution of equilibration from bottom to top of the plume tail. A future aim is to compute the impact of bubble motion on the efficiency of magma mixing in dependence of volatile solubilities and pressure and viscosity variations. This has implications for the capacity of magma to produce bubbles in e.g. stratified magma chambers. [1] De Campos, C., D. Perugini, W. Ertel-Ingrisch, D. Dingwell, and G. Poli (2011), Enhancement of magma mixing efficiency by chaotic dynamics: an experimental study, Contrib. Mineral. Petrol., 161(6), 863-881. [2] Thomas, N., S. Tait, and T. Koyaguchi (1993), Mixing of stratified liquids by the motion of gas bubbles: application to magma mixing, Earth Planet. Sci. Lett., 115(1-4), 161-175.

  20. Agglutinated abyssal foraminifers of the equatorial pacific

    NASA Astrophysics Data System (ADS)

    Burmistrova, I. I.; Khusid, T. A.; Belyaeva, N. V.; Chekhovskaya, M. P.

    2007-12-01

    The quantitative study of the distribution and taxonomic composition of recent living and dead (without plasma) benthic foraminifers revealed three foraminiferal assemblages in the bottom sediments of the Pacific Ocean at depths of 3350 to 4981 m. The assemblage dominated by the epibenthic Lagenammina difflugiformis, Reophax dentaliniformis, and Saccorhiza ramosa occupies the slopes of underwater hills. The assemblage with a high share of the infaunal Cribrostomoides subglobosum, C. nitidum, and Ammobaculites agglutinans is registered on the abyssal plateau. The assemblage with a significant proportion of the large Astrorhiza and Reophax species, which are characterized by an active way of life, populates gentle slopes and narrow depressions with potentially strong bottom currents.

  1. Effect of surfactants on single bubble sonoluminescence behavior and bubble surface stability

    NASA Astrophysics Data System (ADS)

    Leong, Thomas; Yasui, Kyuichi; Kato, Kazumi; Harvie, Dalton; Ashokkumar, Muthupandian; Kentish, Sandra

    2014-04-01

    The effect of surfactants on the radial dynamics of a single sonoluminescing bubble has been investigated. Experimentally, it is observed that an increase in the surfactant concentration leads to a decline in the oscillation amplitude and hence light emission intensity. Numerical simulations support this result, showing that under the driving pressures required to achieve single bubble sonoluminescence (SBSL), the surface properties, namely, the surface elasticity and dilatational viscosity, contribute to the damping of the radial amplitude in the bubble oscillation. In most cases this stabilizes the bubble surface, and contributes to a decreased light intensity. A stronger driving pressure is necessary to achieve equivalent light emission to a surfactant-free bubble. However, as the driving pressure is increased, the surface stability also decreases, making it practically very difficult for a bubble to achieve high SBSL intensities in concentrated surfactant solutions. Although more stable owing to more mild pulsations, the instability mechanism for a surfactant-coated bubble at higher ambient radii is more likely to be of the Rayleigh-Taylor type than that of a clean bubble at the same given acoustic parameters, which can lead to bubble disintegration before correcting mechanisms can bring the bubble back into the stable sonoluminescence regime.

  2. Optimal joint remote state preparation of equatorial states

    NASA Astrophysics Data System (ADS)

    Li, Xihan; Ghose, Shohini

    2015-10-01

    We present a scheme for optimal joint remote state preparation of two-qubit equatorial states. Our protocol improves on a previous scheme (Choudhury and Dhara in Quantum Inf Process 14:373-379, 2015) that had a success probability of 25 %, which increased to 50 % when extra classical information is sent to the receiver. We show that using our modified scheme, the desired state can be prepared deterministically with the same quantum channel. Moreover, we generalize the scheme to prepare N-qubit equatorial states in which the receiver can reconstruct the original state with 100 % success probability.

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

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

  4. Optimal joint remote state preparation of equatorial states

    E-print Network

    Xihan Li; Shohini Ghose

    2015-08-11

    We present a scheme for optimal joint remote state preparation of two-qubit equatorial states. Our protocol improves on a previous scheme (B. S. Choudhury and A. Dhara 2015 Quantum Inf. Process. 14 373) that had a success probability of 25%, which increased to 50% when extra classical information is sent to the receiver. We show that using our modified scheme, the desired state can be prepared deterministically with the same quantum channel. Moreover, we generalize the scheme to prepare N-qubit equatorial states in which the receiver can reconstruct the original state with 100% success probability.

  5. Effect of bubble's arrangement on the viscous torque in bubbly Taylor-Couette flow

    NASA Astrophysics Data System (ADS)

    Fokoua, G. Ndongo; Gabillet, C.; Aubert, A.; Colin, C.

    2015-03-01

    An experimental investigation of the interactions between bubbles, coherent motion, and viscous drag in a Taylor-Couette flow with the outer cylinder at rest is presented. The cylinder radii ratio ? is 0.91. Bubbles are injected inside the gap through a needle at the bottom of the apparatus. Different bubbles sizes are investigated (ratio between the bubble diameter and the gap width ranges from 0.05 to 0.125) for very small void fraction (? ? 0.23%). Different flow regimes are studied corresponding to Reynolds number Re based on the gap width and velocity of the inner cylinder, ranging from 6 × 102 to 2 × 104. Regarding these Re values, Taylor vortices are persistent leading to an axial periodicity of the flow. A detailed characterization of the vortices is performed for the single-phase flow. The experiment also develops bubbles tracking in a meridian plane and viscous torque of the inner cylinder measurements. The findings of this study show evidence of the link between bubbles localisation, Taylor vortices, and viscous torque modifications. We also highlight two regimes of viscous torque modification and various types of bubbles arrangements, depending on their size and on the Reynolds number. Bubbles can have a sliding and wavering motion near the inner cylinder and be either captured by the Taylor vortices or by the outflow areas near the inner cylinder. For small buoyancy effect, bubbles are trapped, leading to an increase of the viscous torque. When buoyancy induced bubbles motion is increased by comparison to the coherent motion of the liquid, a decrease in the viscous torque is rather observed. The type of bubble arrangement is parameterized by the two dimensionless parameters C and H introduced by Climent et al. ["Preferential accumulation of bubbles in Couette-Taylor flow patterns," Phys. Fluids 19, 083301 (2007)]. Phase diagrams summarizing the various types of bubbles arrangements, viscous torque modifications, and axial wavelength evolution are built.

  6. Numerical Simulations and Forecasts of Equatorial Spread F in the American Sector Based on ISR and HF Measurements

    NASA Astrophysics Data System (ADS)

    Hysell, D. L.; Milla, M. A.

    2014-12-01

    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 have been measured at the Jicamarca Radio Observatory in campaigns in 2013 and 2014. Coherent radar backscatter from plasma irregularities has been recorded simultaneously, and images of the irregularities have been generated using aperture synthesis methods. A fully 3D numerical simulation of ionospheric irregularities, initialized and forced using parametrizations derived from measurements and empirical models, has been used in attempts to reproduce the ESF activity observed. Emphasis is placed on representing currents in the bottomside F region completely with the simulation. The simulations have been able to recover many of the features of the irregularities, although some important exceptions have been noted. ESF events in which the first appearance of radar plumes occurs either very early or very late cannot be reproduced in simulation and may be indicative of nonlocal influences. A new multistatic network of HF beacons is being deployed to estimate and track nonlocal influences on ionospheric stability. The network eploys PRN coding, Doppler discrimination, and interferometry and provides data suitable for inverse modeling. Preliminary results from the network will be presented.

  7. Distinctive effects of interplanetary electric field and substorm on nighttime equatorial F layer: A case study

    NASA Astrophysics Data System (ADS)

    Chakrabarty, D.; Sekar, R.; Sastri, J. H.; Ravindran, Sudha

    2008-10-01

    A geomagnetic storm event is identified wherein the base of the equatorial F layer (h'F) over dip equator moved unusually upward till premidnight hours and descended thereafter. The h'F variation is linearly correlated with the variation in the smoothed auroral electrojet index (AE) which varies slowly. The fast fluctuations (residuals) with periodicity ~42 min in the vertical plasma drift are found to be causally related with the fast fluctuations in the dawn-to-dusk component of interplanetary electric field (IEFy) and interestingly, not with the fast fluctuations in AE. However, during the interval when a substorm was triggered in association with sharp transitions in IEFy polarity, the drift fluctuations follow the AE fluctuations and are out of phase with IEFy fluctuations. The investigation demonstrates distinctive effects of IEFy and substorm-related current systems on the zonal electric field over dip equator in the premidnight hours during geomagnetic storms.

  8. Rocket observations in the equatorial electrojet - Current status and critical problems

    NASA Technical Reports Server (NTRS)

    Pfaff, R. F., Jr.

    1991-01-01

    The current status of in situ investigations in the equatorial electrojet is reviewed. Emphasis is placed on: (1) the relation of the vertical polarization field to the electrojet current and the electron number density; (2) the puzzling square shapes of the large amplitude kilometer-scale horizontal electric field structures; (3) the intense vertical, meter-scale waves observed on the topside of the electrojet associated with horizontal laminar-like primary two-stream waves; (4) measurements of upgoing and downgoing secondary two-stream and gradient drift wave packets driven by delta E x B drifts; (5) the nonlinear meter-scale 'turbulence' with small mean phase velocities observed by radars at altitudes outside the regions of high Cowling conductivity, and wave-particle heating by the plasma instabilities.

  9. Bubbles in live-stranded dolphins

    PubMed Central

    Dennison, S.; Moore, M. J.; Fahlman, A.; Moore, K.; Sharp, S.; Harry, C. T.; Hoppe, J.; Niemeyer, M.; Lentell, B.; Wells, R. S.

    2012-01-01

    Bubbles in supersaturated tissues and blood occur in beaked whales stranded near sonar exercises, and post-mortem in dolphins bycaught at depth and then hauled to the surface. To evaluate live dolphins for bubbles, liver, kidneys, eyes and blubber–muscle interface of live-stranded and capture-release dolphins were scanned with B-mode ultrasound. Gas was identified in kidneys of 21 of 22 live-stranded dolphins and in the hepatic portal vasculature of 2 of 22. Nine then died or were euthanized and bubble presence corroborated by computer tomography and necropsy, 13 were released of which all but two did not re-strand. Bubbles were not detected in 20 live wild dolphins examined during health assessments in shallow water. Off-gassing of supersaturated blood and tissues was the most probable origin for the gas bubbles. In contrast to marine mammals repeatedly diving in the wild, stranded animals are unable to recompress by diving, and thus may retain bubbles. Since the majority of beached dolphins released did not re-strand it also suggests that minor bubble formation is tolerated and will not lead to clinically significant decompression sickness. PMID:21993505

  10. Bubbly Suspension Generated in Low Gravity

    NASA Technical Reports Server (NTRS)

    Nahra, Henry K.

    2000-01-01

    Bubbly suspensions are crucial for mass and heat transport processes on Earth and in space. These processes are relevant to pharmaceutical, chemical, nuclear, and petroleum industries on Earth. They are also relevant to life support, in situ resource utilization, and propulsion processes for long-duration space missions such as the Human Exploration and Development of Space program. Understanding the behavior of the suspension in low gravity is crucial because of factors such as bubble segregation, which could result in coalescence and affect heat and mass transport. Professors A. Sangani and D. Koch, principal investigators in the Microgravity Fluid Physics Program managed by the NASA Glenn Research Center at Lewis Field, are studying the physics of bubbly suspension. They plan to shear a bubbly suspension in a couette cell in microgravity to study bubble segregation and compare the bubble distribution in the couette gap with the one predicted by the suspension-averaged equations of motion. Prior to the Requirement Definition Review of this flight experiment, a technology for generating a bubbly suspension in microgravity has to be established, tested, and verified.

  11. Release of multiple bubbles from cohesive sediments

    NASA Astrophysics Data System (ADS)

    Algar, Christopher K.; Boudreau, Bernard P.; Barry, Mark A.

    2011-04-01

    Methane is a strong greenhouse gas, and marine and wetland sediments constitute significant sources to the atmosphere. This flux is dominated by the release of bubbles, and quantitative prediction of this bubble flux has been elusive because of the lack of a mechanistic model. Our previous work has shown that sediments behave as elastic fracturing solids during bubble growth and rise. We now further argue that bubbles can open previously formed, partially annealed, rise tracts (fractures) and that this mechanism can account for the observed preferential release at low tides in marine settings. When this mechanical model is applied to data from Cape Lookout Bight, NC (USA), the results indicate that methanogenic bubbles released at this site do indeed follow previously formed rise tracts and that the calculated release rates are entirely consistent with the rise of multiple bubbles on tidal time scales. Our model forms a basis for making predictions of future bubble fluxes from warming sediments under the influence of climate change.

  12. Numerical modeling of bubble dynamics in magmas

    NASA Astrophysics Data System (ADS)

    Huber, Christian; Su, Yanqing; Parmigiani, Andrea

    2014-05-01

    Understanding the complex non-linear physics that governs volcanic eruptions is contingent on our ability to characterize the dynamics of bubbles and its effect on the ascending magma. The exsolution and migration of bubbles has also a great impact on the heat and mass transport in and out of magma bodies stored at shallow depths in the crust. Multiphase systems like magmas are by definition heterogeneous at small scales. Although mixture theory or homogenization methods are convenient to represent multiphase systems as a homogeneous equivalent media, these approaches do not inform us on possible feedbacks at the pore-scale and can be significantly misleading. In this presentation, we discuss the development and application of bubble-scale multiphase flow modeling to address the following questions : How do bubbles impact heat and mass transport in magma chambers ? How efficient are chemical exchanges between the melt and bubbles during magma decompression? What is the role of hydrodynamic interactions on the deformation of bubbles while the magma is sheared? Addressing these questions requires powerful numerical methods that accurately model the balance between viscous, capillary and pressure stresses. We discuss how these bubble-scale models can provide important constraints on the dynamics of magmas stored at shallow depth or ascending to the surface during an eruption.

  13. Variations of equatorial electrojet as possible seismo-ionospheric precursor at the occurrence of TEC anomalies before strong earthquake

    NASA Astrophysics Data System (ADS)

    Klimenko, M. V.; Klimenko, V. V.; Zakharenkova, I. E.; Pulinets, S. A.

    2012-02-01

    The measurements of GPS signal delays show that the local areas of increased/decreased Total Electron Content (TEC) of the ionosphere can be observed before strong earthquakes. The main possible cause of these TEC disturbances is the vertical plasma drift under the action of zonal electric field. The spatial pattern of electric potentials for such electric field was proposed. The model calculations were done to investigate the efficiency of the proposed mechanism. The calculation results revealed the agreement with TEC variations observed before strong earthquakes and showed that the equatorial electrojet variations can be considered as precursors of earthquakes.

  14. Dynamics of two-dimensional bubbles.

    PubMed

    Piedra, Saúl; Ramos, Eduardo; Herrera, J Ramón

    2015-06-01

    The dynamics of two-dimensional bubbles ascending under the influence of buoyant forces is numerically studied with a one-fluid model coupled with the front-tracking technique. The bubble dynamics are described by recording the position, shape, and orientation of the bubbles as functions of time. The qualitative properties of the bubbles and their terminal velocities are described in terms of the Eötvos (ratio of buoyancy to surface tension) and Archimedes numbers (ratio of buoyancy to viscous forces). The terminal Reynolds number result from the balance of buoyancy and drag forces and, consequently, is not an externally fixed parameter. In the cases that yield small Reynolds numbers, the bubbles follow straight paths and the wake is steady. A more interesting behavior is found at high Reynolds numbers where the bubbles follow an approximately periodic zigzag trajectory and an unstable wake with properties similar to the Von Karman vortex street is formed. The dynamical features of the motion of single bubbles are compared to experimental observations of air bubbles ascending in a water-filled Hele-Shaw cell. Although the comparison is not strictly valid in the sense that the effect of the lateral walls is not incorporated in the model, most of the dynamical properties observed are in good qualitative agreement with the numerical calculations. Hele-Shaw cells with different gaps have been used to determine the degree of approximation of the numerical calculation. It is found that for the relation between the terminal Reynolds number and the Archimedes number, the numerical calculations are closer to the observations of bubble dynamics in Hele-Shaw cells of larger gaps. PMID:26172798

  15. MAGNETIC TOPOLOGY OF BUBBLES IN QUIESCENT PROMINENCES

    SciTech Connect

    Dudik, J.; Aulanier, G.; Schmieder, B.; Zapior, M.; Heinzel, P.

    2012-12-10

    We study a polar-crown prominence with a bubble and its plume observed in several coronal filters by the SDO/AIA and in H{alpha} by the MSDP spectrograph in Bialkow (Poland) to address the following questions: what is the brightness of prominence bubbles in EUV with respect to the corona outside of the prominence and the prominence coronal cavity? What is the geometry and topology of the magnetic field in the bubble? What is the nature of the vertical threads seen within prominences? We find that the brightness of the bubble and plume is lower than the brightness of the corona outside of the prominence, and is similar to that of the coronal cavity. We constructed linear force-free models of prominences with bubbles, where the flux rope is perturbed by inclusion of parasitic bipoles. The arcade field lines of the bipole create the bubble, which is thus devoid of magnetic dips. Shearing the bipole or adding a second one can lead to cusp-shaped prominences with bubbles similar to the observed ones. The bubbles have complex magnetic topology, with a pair of coronal magnetic null points linked by a separator outlining the boundary between the bubble and the prominence body. We conjecture that plume formation involves magnetic reconnection at the separator. Depending on the viewing angle, the prominence can appear either anvil-shaped with predominantly horizontal structures, or cusp-shaped with predominantly vertical structuring. The latter is an artifact of the alignment of magnetic dips with respect to the prominence axis and the line of sight.

  16. The Minnaert bubble: an acoustic approach

    NASA Astrophysics Data System (ADS)

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

    2008-11-01

    We propose an ab initio introduction to the well-known Minnaert pulsating bubble at graduate level. After a brief recall of the standard stuff, we begin with a detailed discussion of the radial movements of an air bubble in water. This discussion is managed from an acoustic point of view, and using the Lagrangian rather than the Eulerian variables. In unbounded water, the air-water system has a continuum of eigenmodes, some of them correspond to regular Fabry-Pérot resonances. A singular resonance, the lowest one, is shown to coincide with that of Minnaert. In bounded water, the eigenmodes spectrum is discrete, with a finite fundamental frequency. A spectacular quasi-locking of the latter occurs if it happens to exceed the Minnaert frequency, which provides an unforeseen one-bubble alternative version of the famous 'hot chocolate effect'. In the (low) frequency domain in which sound propagation inside the bubble reduces to a simple 'breathing' (i.e. inflation/deflation), the light air bubble can be 'dressed' by the outer water pressure forces, and is turned into the heavy Minnaert bubble. Thanks to this unexpected renormalization process, we demonstrate that the Minnaert bubble definitely behaves like a true harmonic oscillator of the spring-bob type, but with a damping term and a forcing term in apparent disagreement with those commonly admitted in the literature. Finally, we underline the double role played by the water. In order to tell the water motion associated with water compressibility (i.e. the sound) from the simple incompressible accompaniment of the bubble breathing, we introduce a new picture analogous to the electromagnetic radiative picture in Coulomb gauge, which naturally leads us to split the water displacement in an instantaneous and a retarded part. The Minnaert renormalized mass of the dressed bubble is then automatically recovered.

  17. Dynamics of two-dimensional bubbles

    NASA Astrophysics Data System (ADS)

    Piedra, Saúl; Ramos, Eduardo; Herrera, J. Ramón

    2015-06-01

    The dynamics of two-dimensional bubbles ascending under the influence of buoyant forces is numerically studied with a one-fluid model coupled with the front-tracking technique. The bubble dynamics are described by recording the position, shape, and orientation of the bubbles as functions of time. The qualitative properties of the bubbles and their terminal velocities are described in terms of the Eötvos (ratio of buoyancy to surface tension) and Archimedes numbers (ratio of buoyancy to viscous forces). The terminal Reynolds number result from the balance of buoyancy and drag forces and, consequently, is not an externally fixed parameter. In the cases that yield small Reynolds numbers, the bubbles follow straight paths and the wake is steady. A more interesting behavior is found at high Reynolds numbers where the bubbles follow an approximately periodic zigzag trajectory and an unstable wake with properties similar to the Von Karman vortex street is formed. The dynamical features of the motion of single bubbles are compared to experimental observations of air bubbles ascending in a water-filled Hele-Shaw cell. Although the comparison is not strictly valid in the sense that the effect of the lateral walls is not incorporated in the model, most of the dynamical properties observed are in good qualitative agreement with the numerical calculations. Hele-Shaw cells with different gaps have been used to determine the degree of approximation of the numerical calculation. It is found that for the relation between the terminal Reynolds number and the Archimedes number, the numerical calculations are closer to the observations of bubble dynamics in Hele-Shaw cells of larger gaps.

  18. Topside equatorial zonal ion velocities measured by C/NOFS during rising solar activity

    NASA Astrophysics Data System (ADS)

    Coley, W. R.; Stoneback, R. A.; Heelis, R. A.; Hairston, M. R.

    2014-02-01

    The Ion Velocity Meter (IVM), a part of the Coupled Ion Neutral Dynamic Investigation (CINDI) instrument package on the Communication/Navigation Outage Forecast System (C/NOFS) spacecraft, has made over 5 yr of in situ measurements of plasma temperatures, composition, densities, and velocities in the 400-850 km altitude range of the equatorial ionosphere. These measured ion velocities are then transformed into a coordinate system with components parallel and perpendicular to the geomagnetic field allowing us to examine the zonal (horizontal and perpendicular to the geomagnetic field) component of plasma motion over the 2009-2012 interval. The general pattern of local time variation of the equatorial zonal ion velocity is well established as westward during the day and eastward during the night, with the larger nighttime velocities leading to a net ionospheric superrotation. Since the C/NOFS launch in April 2008, F10.7 cm radio fluxes have gradually increased from around 70 sfu to levels in the 130-150 sfu range. The comprehensive coverage of C/NOFS over the low-latitude ionosphere allows us to examine variations of the topside zonal ion velocity over a wide level of solar activity as well as the dependence of the zonal velocity on apex altitude (magnetic latitude), longitude, and solar local time. It was found that the zonal ion drifts show longitude dependence with the largest net eastward values in the American sector. The pre-midnight zonal drifts show definite solar activity (F10.7) dependence. The daytime drifts have a lower dependence on F10.7. The apex altitude (magnetic latitude) variations indicate a more westerly flow at higher altitudes. There is often a net topside subrotation at low F10.7 levels, perhaps indicative of a suppressed F region dynamo due to low field line-integrated conductivity and a low F region altitude at solar minimum.

  19. Single Bubble Sonoluminescence in Low Gravity and Optical Radiation Pressure Positioning of the Bubble

    NASA Technical Reports Server (NTRS)

    Thiessen, D. B.; Young, J. E.; Marr-Lyon, M. J.; Richardson, S. L.; Breckon, C. D.; Douthit, S. G.; Jian, P. S.; Torruellas, W. E.; Marston, P. L.

    1999-01-01

    Several groups of researchers have demonstrated that high frequency sound in water may be used to cause the regular repeated compression and luminescence of a small bubble of gas in a flask. The phenomenon is known as single bubble sonoluminescence (SBSL). It is potentially important because light emitted by the bubble appears to be associated with a significant concentration of energy within the volume of the bubble. Unfortunately, the detailed physical mechanisms causing the radiation of light by oscillating bubbles are poorly understood and there is some evidence that carrying out experiments in a weightless environment may provide helpful clues. In addition, the radiation pressure of laser beams on the bubble may provide a way of simulating weightless experiments in the laboratory. The standard model of SBSL attributes the light emission to heating within the bubble by a spherically imploding shock wave to achieve temperatures of 50,000 K or greater. In an alternative model, the emission is attributed to the impact of a jet of water which is required to span the bubble and the formation of the jet is linked to the buoyancy of the bubble. The coupling between buoyancy and jet formation is a consequence of the displacement of the bubble from a velocity node (pressure antinode) of the standing acoustic wave that drives the radial bubble oscillations. One objective of this grant is to understand SBSL emission in reduced buoyancy on KC-135 parabolic flights. To optimize the design of those experiments and for other reasons which will help resolve the role of buoyancy, laboratory experiments are planned in simulated low gravity in which the radiation pressure of laser light will be used to position the bubble at the acoustic velocity node of the ultrasonic standing wave. Laser light will also be used to push the bubble away from the velocity node, increasing the effective buoyancy. The original experiments on the optical levitation and radiation pressure on bubbles in water by Unger and Marston noted above were carried out using a continuous wave (CW) beam of an Argon laser. For lateral stability the beam had a intensity minimum along its axis. Calculations of the optical radiation force on an SBSL bubble indicate that ion laser technology is a poor choice for providing the magnitude of the average optical radiation force required. Consequently it is necessary to examine various diode-pumped solid state laser technologies. The approach for this part of the research will be to achieve optical levitation of a quiescent bubble based on contemporary laser technology and then to strobe the laser synchronously with the SBSL bubble oscillations.

  20. Observations and modelling of deep equatorial currents in the central Pacific

    E-print Network

    Ponte, Rui Vasques de Melo

    1988-01-01

    Analysis of vertical profiles of absolute horizontal velocity collected in January 1981, February 1982 and April 1982 in the central equatorial Pacific as part of the Pacific Equatorial Ocean Dynamics (PEQUOD) program, ...