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Sample records for delta frequency bursting

  1. LTP in Hippocampal Area CA1 Is Induced by Burst Stimulation over a Broad Frequency Range Centered around Delta

    ERIC Educational Resources Information Center

    Grover, Lawrence M.; Kim, Eunyoung; Cooke, Jennifer D.; Holmes, William R.

    2009-01-01

    Long-term potentiation (LTP) is typically studied using either continuous high-frequency stimulation or theta burst stimulation. Previous studies emphasized the physiological relevance of theta frequency; however, synchronized hippocampal activity occurs over a broader frequency range. We therefore tested burst stimulation at intervals from 100…

  2. Burst-by-burst laser frequency monitor

    NASA Technical Reports Server (NTRS)

    Esproles, Carlos (Inventor)

    1994-01-01

    The invention is a system for real-time frequency monitoring and display of an RF burst where the burst frequency is analyzed and displayed on a burst-by-burst basis in order to allow for frequency control. Although the invention was made for monitoring the laser frequency of a LIDAR system, it has other applications where realtime monitoring is required. The novelty of the invention resides in the use of a counter that is reset at the beginning of each unit time of monitoring and then gated for a unit of time. The invention also has an LED bar graph for displaying the measure of frequency at the end of each unit time in either a bar length mode or a moving dot mode. In the latter mode, the operator makes necessary adjustments to maintain the dot at the center of the bar graph.

  3. CMEs and frequency cutoff of solar bursts

    NASA Astrophysics Data System (ADS)

    Stanislavsky, Al.; Konovalenko, Al.; Koval, Ar.; Volvach, Y.; Zarka, P.

    2016-05-01

    Radio observations of solar bursts with high-frequency cutoff by the radio telescope UTR-2 (near Kharkiv, Ukraine) at 8-33 MHz on 17-19 August 2012 are presented. Such cutoff may be attributed to the emergence of the burst sources behind limb of the Sun with respect to an observer on the Earth. The events are strongly associated with solar eruptions occurred in a new active region. Ray tracing simulations show that the CMEs play a constructive role for the behind-limb bursts to be detected in ground-based observations. Likely, due to tunnel-like cavities with low density in CMEs, the radio emission of behind-limb solar bursts can be directed towards the Earth.

  4. Bursting frequency prediction in turbulent boundary layers

    SciTech Connect

    LIOU,WILLIAM W.; FANG,YICHUNG

    2000-02-01

    The frequencies of the bursting events associated with the streamwise coherent structures of spatially developing incompressible turbulent boundary layers were predicted using global numerical solution of the Orr-Sommerfeld and the vertical vorticity equations of hydrodynamic stability problems. The structures were modeled as wavelike disturbances associated with the turbulent mean flow. The global method developed here involves the use of second and fourth order accurate finite difference formula for the differential equations as well as the boundary conditions. An automated prediction tool, BURFIT, was developed. The predicted resonance frequencies were found to agree very well with previous results using a local shooting technique and measured data.

  5. Damped Oscillator with Delta-Kicked Frequency

    NASA Technical Reports Server (NTRS)

    Manko, O. V.

    1996-01-01

    Exact solutions of the Schrodinger equation for quantum damped oscillator subject to frequency delta-kick describing squeezed states are obtained. The cases of strong, intermediate, and weak damping are investigated.

  6. Numerical study of the vortex burst phenomenon for delta wings

    NASA Technical Reports Server (NTRS)

    Hartwich, PETER-M.; Hsu, C.-H.; Luckring, James M.; Liu, C. H.

    1988-01-01

    A flux-difference splitting scheme is employed to compute low-speed flows over a delta wing for angles of attack from 0 to 40 deg as steady-state solutions to the three-dimensional, Reynolds-averaged Navier-Stokes equations in their thin-layer approximation. The finite-difference scheme is made spatially second-order accurate by applying a total variation diminishing-like discretization to the inviscid fluxes and central differencing to the viscous shear fluxes. Using first-order accurate Euler backward-time differencing, an efficient implicit algorithm is constructed, which combines approximate factorization in cross planes with a symmetric planar Gauss-Seidel relaxation in the remaining third spatial direction. The geometry of the thin (maximum thickness is 0.021), slender (aspect ratio is unity), sharp-edged delta wing is taken from Hummel's (1967, 1978) wind tunnel model. Over the entire angle-of-attack range, the computed values of lift and pitching moment are in good agreement with the experimental data. Also details of the flow-fieldlike spanwise surface pressure distributions compare well with the experiment. Computed flow-field results with a bubble-type vortex burst are analyzed in detail.

  7. Transcriptional burst frequency and burst size are equally modulated across the human genome

    SciTech Connect

    Dar, Roy D.; Simpson, Michael L; Weinberger, Leor S.; Razooky, B; Cox, Chris D.; McCollum, James M.; Trimeloni, Tom; Singh, A

    2012-01-01

    Gene expression occurs either as an episodic process, characterized by pulsatile bursts or as a constitutive, Poisson-like accumulation of gene products. It is not clear which mode of gene expression (constitutive versus bursty) predominates across a genome or how transcriptional dynamics are influenced by genomic position and promoter sequence. Here, we use time-lapse fluorescence microscopy, building off of theoretical studies that exploit the time-resolved structure of stochastic fluctuations in gene expression, to develop a three-dimensional method for mapping underlying gene-regulatory mechanisms. Over 8,000 individual human genomic loci were analyzed, and at virtually all loci, episodic bursting as opposed to constitutive expression was found to be the predominant mode of expression. Quantitative analysis of the expression dynamics at these 8,000 loci indicates that both frequency and size of transcriptional bursts vary equally across the human genome independent of promoter sequence. Strikingly, weaker expression loci modulate burst frequency to increase activity, while stronger expression loci modulate burst size to increase activity. Transcriptional activators, such as TNF, generate similar patterns of change in burst frequency and burst size. In summary, transcriptional bursting dominates across the human genome, both burst frequency and burst size vary by chromosomal location, and transcriptional activators alter burst frequency and burst size, depending on the expression level of the locus.

  8. Solar S-bursts at Frequencies of 10 - 30 MHz

    NASA Astrophysics Data System (ADS)

    Melnik, V. N.; Konovalenko, A. A.; Rucker, H. O.; Dorovskyy, V. V.; Abranin, E. P.; Lecacheux, A.; Lonskaya, A. S.

    2010-06-01

    Solar S-bursts observed by the radio telescope UTR-2 in the period 2001 - 2002 are studied. The bursts chosen for a detailed analysis occurred in the periods 23 - 26 May 2001, 13 - 16 and 27 - 39 July 2002 during three solar radio storms. More than 800 S-bursts were registered in these days. Properties of S-bursts are studied in the frequency band 10 - 30 MHz. All bursts were always observed against a background of other solar radio activity such as type III and IIIb bursts, type III-like bursts, drift pairs and spikes. Moreover, S-bursts were observed during days when the active region was situated near the central meridian. Characteristic durations of S-bursts were about 0.35 and 0.4 - 0.6 s for the May and July storms, respectively. For the first time, we found that the instantaneous frequency width of S-bursts increased with frequency linearly. The dependence of drift rates on frequency followed the McConnell dependence derived for higher frequencies. We propose a model of S-bursts based on the assumption that these bursts are generated due to the confluence of Langmuir waves with fast magnetosonic waves, whose phase and group velocities are equal.

  9. Transcriptional burst frequency and burst size are equally modulated across the human genome

    PubMed Central

    Dar, Roy D.; Razooky, Brandon S.; Singh, Abhyudai; Trimeloni, Thomas V.; McCollum, James M.; Cox, Chris D.; Simpson, Michael L.; Weinberger, Leor S.

    2012-01-01

    Gene expression occurs either as an episodic process, characterized by pulsatile bursts, or as a constitutive process, characterized by a Poisson-like accumulation of gene products. It is not clear which mode of gene expression (constitutive versus bursty) predominates across a genome or how transcriptional dynamics are influenced by genomic position and promoter sequence. Here, we use time-lapse fluorescence microscopy to analyze 8,000 individual human genomic loci and find that at virtually all loci, episodic bursting—as opposed to constitutive expression—is the predominant mode of expression. Quantitative analysis of the expression dynamics at these 8,000 loci indicates that both the frequency and size of the transcriptional bursts varies equally across the human genome, independent of promoter sequence. Strikingly, weaker expression loci modulate burst frequency to increase activity, whereas stronger expression loci modulate burst size to increase activity. Transcriptional activators such as trichostatin A (TSA) and tumor necrosis factor α (TNF) only modulate burst size and frequency along a constrained trend line governed by the promoter. In summary, transcriptional bursting dominates across the human genome, both burst frequency and burst size vary by chromosomal location, and transcriptional activators alter burst frequency and burst size, depending on the expression level of the locus. PMID:23064634

  10. Comparative Study of Solar Bursts at Sub-THz Frequencies

    NASA Astrophysics Data System (ADS)

    Fernandes, L. O. T.; Kaufmann, P.; Correia, E.; Marun, A.; Pereyra, P.; Raulin, J.-P.; Valio, A. B. M.

    2016-04-01

    We analyze a large set of 17 solar radio bursts observed at sub-THz (0.2 and 0.4 THz) in 2012-2014 together with the new solar patrol radio telescopes (45 and 90 GHz), operated at El Leoncito, in the Argentinean Andes, allowing the derivation of complete burst spectra in this unexplored range of frequencies. We discuss the uncertainties in sub-THz flux estimates caused by calibration techniques and the corrections for atmospheric transmission. The burst spectra were completed with microwave bursts data obtained by the Radio Solar Telescope Network - RSTN. The events selection was based on GOES soft X-rays burst reported for classes stronger then C. Nearly 50 percent of the bursts exhibited a frequency increasing sub-THz spectral component. The results suggest that the THz component might be always present, with the minimum turn-over frequencies shifting to higher frequencies for larger energies of the electrons producing the emissions.

  11. Frequency-modulated nuclear localization bursts coordinate gene regulation

    PubMed Central

    Cai, Long; Dalal, Chiraj K.; Elowitz, Michael B.

    2008-01-01

    In yeast, the transcription factor Crz1 is dephosphorylated and translocates into the nucleus in response to extracellular calcium. Using time-lapse microscopy, we found that Crz1 exhibited short bursts of nuclear localization (∼2 minutes) that occurred stochastically in individual cells and propagated to the expression of downstream genes. Strikingly, calcium concentration controlled the frequency, but not duration, of localization bursts. Using an analytic model, we found that this frequency modulation (FM) of bursts ensures proportional expression of multiple target genes across a wide dynamic range of expression levels, independent of promoter characteristics. We experimentally confirmed this theory with natural and synthetic Crz1 target promoters. Another stress response transcription factor, Msn2, exhibits similar, but largely uncorrelated, localization bursts under calcium stress. These results suggest that FM regulation of localization bursts may be a general control strategy utilized by the cell to coordinate multi-gene responses to external signals. PMID:18818649

  12. Simultaneous multi-frequency imaging observations of solar microwave bursts

    NASA Technical Reports Server (NTRS)

    Kundu, M. R.; White, S. M.; Schmahl, E. J.

    1989-01-01

    The results of simultaneous two-frequency imaging observations of solar microwave bursts with the Very Large Array are reviewed. Simultaneous 2 and 6 cm observations have been made of bursts which are optically thin at both frequencies, or optically thick at the lower frequency. In the latter case, the source structure may differ at the two frequencies, but the two sources usually seem to be related. However, this is not always true of simultaneous 6 and 20 cm observations. The results have implications for the analysis of nonimaging radio data of solar and stellar flares.

  13. High-Frequency Cutoff in Type III Bursts

    NASA Astrophysics Data System (ADS)

    Stanislavsky, A. A.; Konovalenko, A. A.; Volvach, Ya. S.; Koval, A. A.

    In this article we report about a group of solar bursts with high-frequency cutoff, observed on 19 August of 2012 near 8:23 UT, simultaneously by three different radio telescopes: the Ukrainian decameter radio telescope (8-33 MHz), the French Nancay Decametric Array (10-70 MHz) and the Italian San Vito Solar Observatory of RSTN (25-180 MHz). Morphologically the bursts are very similar to the type III bursts. The solar activity is connected with the emergency of a new group of solar spots on the far side of the Sun with respect to observers on Earth. The solar bursts accompany many moderate flares over eastern limb. The refraction of the behind-limb radio bursts towards the Earth is favorable, if CMEs generate low-density cavities in solar corona.

  14. Radio frequency interference affecting type III solar burst observations

    NASA Astrophysics Data System (ADS)

    Anim, N. M.; Hamidi, Z. S.; Abidin, Z. Z.; Monstein, C.; Rohizat, N. S.

    2013-05-01

    The solar burst extinguish from the Sun's corona atmosphere and it dynamical structure of the magnetic field in radio wavelength are studied. Observation of solar radio burst with Compact Astronomical Low cost Low frequency Instrument for Spectroscopy and Transportable Observatory (CALLISTO) from ETH, Zurich in frequency range of 45 until 870 MHz. Observation done at Pusat Angkasa Negara, Banting, Selangor and successfully detected the solar burst type III on 9th March 2012 from 4:22:00 UT until 4:28:00 UT. The solar burst emission is associated with M6.3 solar flare which occurred at sunspot AR1429 at 03:58UT were observed by NOAA. Frequency ranges chosen as the best ranges for solar monitoring in Malaysia is 150 MHz until 400 MHz. The highest signal amplitude within this frequency ranges is 1.7619 dB at 153.188 MHz (Government Use) have potential to influence the detection of solar radio burst type III within 20 until 400 MHz.

  15. Observations and modeling of dynamically triggered high frequency burst events

    NASA Astrophysics Data System (ADS)

    Fischer, Adam David

    2008-10-01

    A series of high-frequency (>20Hz) bursts of energy are observed on strong motion records during the 1999 Chi-Chi, Taiwan Earthquake Mw7.6. We hypothesized that these bursts originated near the individual stations as small, shallow events that were dynamically triggered by the P- and S-waves generated by the Chi-Chi mainshock. These bursts were originally interpreted as a mainshock source signal by Chen et al., [2006] but our observations of events on strong motion records recorded at stations up to 170 km from the mainshock epicenter is consistent with the local triggering hypothesis. If the bursts originated on the Chi-Chi fault plane, as hypothesized by Chen et al. [2006] based on their analysis of recordings within 20Km from the Chelungpu fault, then they should not be observable at this distance assuming any reasonable value of crustal attenuation. The bursts on all strong motion stations in the Taiwan Central Weather Bureau network (TWCB) were identified using a numerical algorithm approach. This data set was analyzed in the context of local dynamic triggering which resulted in a stress threshold for triggering in the range 0.03 to 0.05 MPa for S-wave triggering and 0.0013 to 0.0033 MPa for P-wave triggering, consistent with prior observations of surface wave triggering. In an attempt to better characterize the nature of high frequency bursts, similar analysis of strong motion records was performed on the records of the 2004 Parkfield, CA earthquake (Mw6) at the USGS UPSAR array. The average array spacing was relatively small compared to the instruments in Taiwan so that further constraint of the location of bursts was possible. Bursts were found to be incoherent even for stations spaced 40m apart, suggesting that they occur in a region approximately 20m from the stations. The triggering threshold was found to be ~0.02Mpa, consistent with the observations from Taiwan. To test the possibility of nucleating unstable slip events in the very shallow crust we

  16. Spectral Trends of Solar Bursts at Sub-THz Frequencies

    NASA Astrophysics Data System (ADS)

    Fernandes, L. O. T.; Kaufmann, P.; Correia, E.; Giménez de Castro, C. G.; Kudaka, A. S.; Marun, A.; Pereyra, P.; Raulin, J.-P.; Valio, A. B. M.

    2017-01-01

    Previous sub-THz studies were derived from single-event observations. We here analyze for the first time spectral trends for a larger collection of sub-THz bursts. The collection consists of a set of 16 moderate to small impulsive solar radio bursts observed at 0.2 and 0.4 THz by the Solar Submillimeter-wave Telescope (SST) in 2012 - 2014 at El Leoncito, in the Argentinean Andes. The peak burst spectra included data from new solar patrol radio telescopes (45 and 90 GHz), and were completed with microwave data obtained by the Radio Solar Telescope Network, when available. We critically evaluate errors and uncertainties in sub-THz flux estimates caused by calibration techniques and the corrections for atmospheric transmission, and introduce a new method to obtain a uniform flux scale criterion for all events. The sub-THz bursts were searched during reported GOES soft X-ray events of class C or larger, for periods common to SST observations. Seven out of 16 events exhibit spectral maxima in the range 5 - 40 GHz with fluxes decaying at sub-THz frequencies (three of them associated to GOES class X, and four to class M). Nine out of 16 events exhibited the sub-THz spectral component. In five of these events, the sub-THz emission fluxes increased with a separate frequency from that of the microwave spectral component (two classified as X and three as M), and four events have only been detected at sub-THz frequencies (three classified as M and one as C). The results suggest that the THz component might be present throughout, with the minimum turnover frequency increasing as a function of the energy of the emitting electrons. The peculiar nature of many sub-THz burst events requires further investigations of bursts that are examined from SST observations alone to better understand these phenomena.

  17. Ionic and neuromodulatory regulation of burst discharge controls frequency tuning.

    PubMed

    Mehaffey, W Hamish; Ellis, Lee D; Krahe, Rüdiger; Dunn, Robert J; Chacron, Maurice J

    2008-01-01

    Sensory neurons encode natural stimuli by changes in firing rate or by generating specific firing patterns, such as bursts. Many neural computations rely on the fact that neurons can be tuned to specific stimulus frequencies. It is thus important to understand the mechanisms underlying frequency tuning. In the electrosensory system of the weakly electric fish, Apteronotus leptorhynchus, the primary processing of behaviourally relevant sensory signals occurs in pyramidal neurons of the electrosensory lateral line lobe (ELL). These cells encode low frequency prey stimuli with bursts of spikes and high frequency communication signals with single spikes. We describe here how bursting in pyramidal neurons can be regulated by intrinsic conductances in a cell subtype specific fashion across the sensory maps found within the ELL, thereby regulating their frequency tuning. Further, the neuromodulatory regulation of such conductances within individual cells and the consequences to frequency tuning are highlighted. Such alterations in the tuning of the pyramidal neurons may allow weakly electric fish to preferentially select for certain stimuli under various behaviourally relevant circumstances.

  18. Low-Frequency Radio Bursts and Space Weather

    NASA Technical Reports Server (NTRS)

    Gopalswamy, N.

    2016-01-01

    Low-frequency radio phenomena are due to the presence of nonthermal electrons in the interplanetary (IP) medium. Understanding these phenomena is important in characterizing the space environment near Earth and other destinations in the solar system. Substantial progress has been made in the past two decades, because of the continuous and uniform data sets available from space-based radio and white-light instrumentation. This paper highlights some recent results obtained on IP radio phenomena. In particular, the source of type IV radio bursts, the behavior of type III storms, shock propagation in the IP medium, and the solar-cycle variation of type II radio bursts are considered. All these phenomena are closely related to solar eruptions and active region evolution. The results presented were obtained by combining data from the Wind and SOHO missions.

  19. Observations of Fast Radio Bursts and perspectives at low frequencies

    NASA Astrophysics Data System (ADS)

    Zarka, P.; Mottez, F.

    2016-12-01

    We briefly summarize the characteristics of the elusive Fast Radio Bursts from existing observations. Then we emphasize the interest of low-frequency observations, e.g. with NenuFAR. In order to define the best observing parameters and detection scheme, we have built a simulation program of FRB at low-frequencies, that proceeds in 2 steps: (i) FRB generation and dilution in a dynamic spectrum with given characteristics, and (ii) definition of the FRB spectrum, and detection on the galactic radio background by means of parametric dedispersion. We carry on a preliminary simulation study, that allows us to draw first conclusions, among which the possibility to detect Lorimer-like FRB with NenuFAR.

  20. Fast and slow frequency-drifting millisecond bursts in Jovian decametric radio emissions

    NASA Astrophysics Data System (ADS)

    Ryabov, V. B.; Zarka, P.; Hess, S.; Konovalenko, A.; Litvinenko, G.; Zakharenko, V.; Shevchenko, V. A.; Cecconi, B.

    2014-08-01

    We present an analysis of several Jovian Io-related decametric radio storms recorded in 2004-2012 at the Ukrainian array UTR-2 using the new generation of baseband digital receivers. Continuous baseband sampling within sessions lasting for several hours enabled us to study the evolution of multiscale spectral patterns during the whole storm at varying time and frequency resolutions and trace the temporal transformation of burst structures in unprecedented detail. In addition to the well-known frequency drifting millisecond patterns known as S bursts we detected two other classes of events that often look like S bursts at low resolution but reveal a more complicated structure in high resolution dynamic spectra. The emissions of the first type (LS bursts, superposition of L and S type emissions) have a much lower frequency drift rate than the usual quasi linearly drifting S bursts (QS) and often occur within a frequency band where L emission is simultaneously present, suggesting that both LS and at least part of L emissions may come from the same source. The bursts of the second type (modulated S bursts called MS) are formed by a wideband frequency-modulated envelope that can mimic S bursts with very steep negative (or even positive) drift rates. Observed with insufficient time-frequency resolution, MS look like S bursts with complex shapes and varying drifts; MS patterns often occur in association with (i) narrowband emission; (ii) S burst trains; or (iii) sequences of fast drift shadow events. We propose a phenomenological description for various types of S emissions, that should include at least three components: high- and low-frequency limitation of the overall frequency band of the emission, fast frequency modulation of emission structures within this band, and emergence of elementary S burst substructures, that we call "forking" structures. All together, these three components can produce most of the observed spectral structures, including S bursts with

  1. Low-Frequency Type III Bursts and Solar Energetic Particle Events

    NASA Technical Reports Server (NTRS)

    Gopalswamy, Nat; Makela, Pertti

    2010-01-01

    We analyzed the coronal mass ejections (CMEs), flares, and type 11 radio bursts associated with a set of six low frequency (<14 MHz) extended type III bursts from active region 10588. The durations were measured at 1 and 14 MHz using high resolution data from Wind/WAVES and were within the range (>15 min) normally used to define these bursts. All but one of the type III bursts was not associated with a type 11 burst in the metric or longer wavelength domains. The burst without type 11 burst also lacked a solar energetic particle (SEP) event at energies >25 MeV. The 1-MHz duration of the type III burst (28 min) is near the median value of type III durations found for gradual SEP events and ground level enhancement (GLE) events. Yet, there was no sign of SEP events. On the other hand, two other type III bursts from the same active region had similar duration but accompanied by WAVES type 11 bursts; these bursts were also accompanied by SEP events detected by SOHO/ERNE. The CMEs were of similar speeds and the flares are also of similar size and duration. This study suggests that the type III burst duration may not be a good indicator of an SEP event.

  2. Differential regulation of sympathetic burst frequency and amplitude following acute hypoxia in humans.

    PubMed

    Steinback, Craig D; Kevin Shoemaker, J

    2012-09-15

    Current evidence suggests that the persistent sympathetic nerve activity (SNA), commonly observed after exposure to hypoxia (HX), is mediated by chemoreceptor sensitization and or baroreflex resetting. Evidence in humans and animals suggests that these reflexes may independently regulate the frequency (gating) and amplitude (neuronal recruitment) of SNA bursts. In humans (n = 7), we examined the regulation of SNA following acute isocapnic HX (5 min; end-tidal P(O2) = 45 Torr) and euoxic hypercapnia (HC; 5 min; end-tidal P(CO2) = +10 from baseline). HX increased SNA burst frequency (21 ± 7 to 28 ± 8 bursts/min, P < 0.05) and amplitude (99 ± 10 to 125 ± 19 au, P < 0.05) as did HC (14 ± 6 to 22 ± 10 bursts/min, P < 0.05 and 100 ± 12 to 133 ± 29 au, P < 0.05, respectively). Burst frequency (26 ± 7 bursts/min, P < 0.05), but not amplitude (97 ± 12 au), remained elevated 10 min post-HX. The change in burst amplitude (but not frequency) was significantly related to the measured change in ventilation (r(2) = 0.527, P < 0.001). Both frequency and amplitude decreased during recovery following HC. These data indicate the differential regulation of pattern and magnitude of sympathetic outflow in humans with sympathetic persistence following HX being specific to burst frequency and not amplitude.

  3. Investigation of Millimeter Wave Bursts at ECE Frequencies in DIII-D Plasmas

    NASA Astrophysics Data System (ADS)

    Wu, S. M.; Austin, M. E.

    2005-10-01

    Intense bursts of narrowband millimeter wave radiation have been observed in low density H-mode and QH-mode plasmas in the DIII-D tokamak. These bursts occur in the range of second harmonic electron cyclotron frequencies and have bandwidths of 1 to 4 GHz. The narrow frequency width suggests that the bursting is not classic runaway electron emission which typically has a bandwidth of 10 GHz or more. ECE bursting has been observed in three different conditions. The burst occurs simultaneously with edge-localized mode (ELM) precursors, edge harmonic oscillations, or plasma disruption precursors. In the precursor cases the bursts precede the collapse phase and are coincident with similar types of MHD events. The data will be compared to models of stimulated and scattered emission for electrons in the high energy tail of the distribution.

  4. Spatial-temporal variation of low-frequency earthquake bursts near Parkfield, California

    USGS Publications Warehouse

    Wu, Chunquan; Guyer, Robert; Shelly, David R.; Trugman, D.; Frank, William; Gomberg, Joan S.; Johnson, P.

    2015-01-01

    Tectonic tremor (TT) and low-frequency earthquakes (LFEs) have been found in the deeper crust of various tectonic environments globally in the last decade. The spatial-temporal behaviour of LFEs provides insight into deep fault zone processes. In this study, we examine recurrence times from a 12-yr catalogue of 88 LFE families with ∼730 000 LFEs in the vicinity of the Parkfield section of the San Andreas Fault (SAF) in central California. We apply an automatic burst detection algorithm to the LFE recurrence times to identify the clustering behaviour of LFEs (LFE bursts) in each family. We find that the burst behaviours in the northern and southern LFE groups differ. Generally, the northern group has longer burst duration but fewer LFEs per burst, while the southern group has shorter burst duration but more LFEs per burst. The southern group LFE bursts are generally more correlated than the northern group, suggesting more coherent deep fault slip and relatively simpler deep fault structure beneath the locked section of SAF. We also found that the 2004 Parkfield earthquake clearly increased the number of LFEs per burst and average burst duration for both the northern and the southern groups, with a relatively larger effect on the northern group. This could be due to the weakness of northern part of the fault, or the northwesterly rupture direction of the Parkfield earthquake.

  5. Decameter type III bursts with positive and negative frequency drift rates

    NASA Astrophysics Data System (ADS)

    Melnik, V. N.; Brazhenko, A. I.; Konovalenko, A. A.; Briand, C.; Dorovskyy, V. V.; Zarka, P.; Frantzusenko, A. V.; Rucker, H. O.; Rutkevych, B. P.; Panchenko, M.; Zaqarashvili, T.; Shergelashvili, B.

    2013-09-01

    We report about observations of decameter type III bursts whose frequency drift rates vary their signs from negative to positive. Moreover drift rates of some bursts vary the sign some times. Positive drift rates for some bursts are changed from 0.44 MHz/s to 12 MHz/s. At the same time the negative drift rates of these bursts are standard values for decameter type III bursts. A possible interpretation of such phenomenon on the base of plasma mechanism of type III burst generation is discussed. The sense of this interpretation is that group velocity of type III electromagnetic waves generated by fast electrons at some conditions can be smaller than velocity of these electrons.

  6. On the Directivity of Low-Frequency Type IV Radio Bursts

    NASA Technical Reports Server (NTRS)

    Gopalswamy, N.; Akiyama, S.; Makela, P.; Yashiro, S.; Cairns, I. H.

    2016-01-01

    An intense type IV radio burst was observed by the STEREO Behind (STB) spacecraft located about 144 deg. behind Earth. The burst was associated with a large solar eruption that occurred on the backside of the Sun (N05E151) close to the disk center in the STB view. The eruption was also observed by the STEREO Ahead (STA) spacecraft (located at 149 deg. ahead of Earth) as an eruption close to the west limb (N05W60) in that view. The type IV burst was complete in STB observations in that the envelope reached the lowest frequency and then receded to higher frequencies. The burst was partial viewed from STA, revealing only the edge coming down to the lowest frequency. The type IV burst was not observed at all near Earth because the source was 61 deg. behind the east limb. The eruption was associated with a low-frequency type II burst observed in all three views, although it was not very intense. Solar energetic particles were also observed at both STEREOs and at SOHO, suggesting that the shock was much extended, consistent with the very high speed of the CME (2048 km/s). These observations suggest that the type IV emission is directed along a narrow cone above the flare site. We confirm this result statistically using the type IV bursts of solar cycle 23.

  7. Phase-locking of bursting neuronal firing to dominant LFP frequency components

    PubMed Central

    Constantinou, Maria; Elijah, Daniel H.; Squirrell, Daniel; Gigg, John; Montemurro, Marcelo A.

    2015-01-01

    Neuronal firing in the hippocampal formation relative to the phase of local field potentials (LFP) has a key role in memory processing and spatial navigation. Firing can be in either tonic or burst mode. Although bursting neurons are common in the hippocampal formation, the characteristics of their locking to LFP phase are not completely understood. We investigated phase-locking properties of bursting neurons using simulations generated by a dual compartmental model of a pyramidal neuron adapted to match the bursting activity in the subiculum of a rat. The model was driven with stochastic input signals containing a power spectral profile consistent with physiologically relevant frequencies observed in LFP. The single spikes and spike bursts fired by the model were locked to a preferred phase of the predominant frequency band where there was a peak in the power of the driving signal. Moreover, the preferred phase of locking shifted with increasing burst size, providing evidence that LFP phase can be encoded by burst size. We also provide initial support for the model results by analysing example data of spontaneous LFP and spiking activity recorded from the subiculum of a single urethane-anaesthetised rat. Subicular neurons fired single spikes, two-spike bursts and larger bursts that locked to a preferred phase of either dominant slow oscillations or theta rhythms within the LFP, according to the model prediction. Both power-modulated phase-locking and gradual shift in the preferred phase of locking as a function of burst size suggest that neurons can use bursts to encode timing information contained in LFP phase into a spike-count code. PMID:26305338

  8. Interaction between pulsed discharge and radio frequency discharge burst at atmospheric pressure

    SciTech Connect

    Zhang, Jie; Guo, Ying; Shi, Yuncheng; Zhang, Jing; Shi, J. J.

    2015-08-15

    The atmospheric pressure glow discharges (APGD) with dual excitations in terms of pulsed voltage and pulse-modulation radio frequency (rf) power are studied experimentally between two parallel plates electrodes. Pulse-modulation applied in rf APGD temporally separates the discharge into repetitive discharge bursts, between which the high voltage pulses are introduced to ignite sub-microsecond pulsed discharge. The discharge characteristics and spatio-temporal evolution are investigated by means of current voltage characteristics and time resolved imaging, which suggests that the introduced pulsed discharge assists the ignition of rf discharge burst and reduces the maintain voltage of rf discharge burst. Furtherly, the time instant of pulsed discharge between rf discharge bursts is manipulated to study the ignition dynamics of rf discharge burst.

  9. Turnover Frequency in Solar Microwave Bursts with an Extremely Flat Optically Thin Spectrum

    NASA Astrophysics Data System (ADS)

    Song, Q. W.; Nakajima, H.; Huang, G. L.; Tan, B. L.; Huang, Y.; Wu, Z.

    2016-12-01

    Four microwave bursts have been selected from the Nobeyama Radio Polarimeter (NoRP) observations with an extremely flat spectrum in the optically thin part and a very hard spectral index between 0 and -1 in the maximum phase of all bursts. It is found that the time evolution of the turnover frequency is inversely proportional to the time profiles of the radio flux in all bursts. Based on the nonthermal gyrosynchrotron theory of Ramaty ( Astrophys. J. 158, 753, 1969), the local magnetic field strength and the electron spectral index are calculated uniquely from the observed radio spectral index and the turnover frequency. We found that the electron energy spectrum is very hard (spectral index 1 - 2), and the time variation of the magnetic field strength is also inversely proportional to the radio flux as a function of time in all bursts. Hence, the time evolution of the turnover frequency can be explained directly by its dependence on the local magnetic field strength. The high turnover frequency (several tens of GHz) is mainly caused by a strong magnetic field of up to several hundred gauss, and probably by the Razin effect under a high plasma density over 10^{10} cm^{-3} in the maximum phase of these bursts. Therefore, the extremely flat microwave spectrum can be well understood by the observed high turnover frequency and the calculated hard electron spectral index.

  10. On-off control of burst high frequency electrical stimulation to suppress 4-AP induced seizures

    NASA Astrophysics Data System (ADS)

    Chiang, Chia-Chu; Lin, Chou-Ching K.; Ju, Ming-Shaung

    2013-06-01

    Objective. The goal of this study was to investigate, using model simulations and animal experiments, the efficiency and the side effects of burst high frequency stimulation combined with on-off control in seizure suppression. Approach. A modified mathematical hippocampal seizure model was created to provide evidence of the eligibility of this approach. In the experimental setup, two recording electrodes were inserted into bilateral septal CA1 of the hippocampus, and a stimulation electrode was placed on the ventral hippocampal commissure of a rat. After seizures had been induced by 4-aminopyridine treatment, on-off control stimulation was used to suppress the seizures at 20 s intervals. The stimulation time, cumulative charge and post-stimulation suppression were used to assess the effects of burst duration. Main results. The results showed that burst stimulation could suppress the seizures during the control period and burst stimulation of a shorter duration could keep the seizure suppressed with less effort. By decreasing the burst duration, the cumulative stimulation time became shorter, the delivered cumulative charge became lower, and the cumulative time of post-stimulation suppression became longer. Significance. The on-off control stimulation not only prolonged the duration of suppression but also avoided the side effects of the conversion of seizure patterns. In particular, decreasing the specified burst duration increased the efficiency of the burst stimulation.

  11. Decameter Type III Bursts with Changing Frequency Drift-Rate Signs

    NASA Astrophysics Data System (ADS)

    Melnik, V. N.; Brazhenko, A. I.; Konovalenko, A. A.; Briand, C.; Dorovskyy, V. V.; Zarka, P.; Frantsuzenko, A. V.; Rucker, H. O.; Rutkevych, B. P.; Panchenko, M.; Denis, L.; Zaqarashvili, T.; Shergelashvili, B.

    2015-01-01

    We discuss properties of type III bursts that change the sign of their drift rate from negative to positive and vice versa. Moreover, these bursts may change the sign of their drift rates more than once. These particular type III bursts were observed simultaneously by the radio telescopes UTR-2 ( Ukrainian T-shaped Radio telescope, Kharkov, Ukraine), URAN-2 ( Ukrainian Radio telescope of the Academy of Sciences, Poltava, Ukraine), and by the NDA ( Nançay Decametric Array, Nancay, France) in the frequency range 8 - 41 MHz. The negative drift rates of these bursts are similar to those of previously reported decameter type III bursts and vary from -0.7 MHz s-1 to -1.7 MHz s-1, but their positive drift rates vary in a wider range from 0.44 MHz s-1 to 6 MHz s-1. Unlike inverted U-bursts, the tracks of these type III bursts have C- or inverted C-shapes.

  12. Decametric radio bursts associated with the 13 July 2004 CME event at frequencies 10-30 MHz

    NASA Astrophysics Data System (ADS)

    Boiko, A. I.; Melnik, V. N.; Konovalenko, A. A.; Abranin, E. P.; Dorovskyy, V. V.; Rucker, H. O.

    2012-03-01

    We report on the observations of solar type IV burst and its precursors on the 13 of July 2004 at frequencies 10-30 MHz. The radio telescope UTR-2 observational data compiled from SOHO, WIND, NDA, RHESSI, GOES data were used. The main properties (frequency drift rate, duration, flux) of type IV burst and its precursors, namely solar type III and type II bursts, are analysed. We consider the type IV burst connected with appearance of the coronal mass ejection, which occurrence coincides with the type IV burst beginning. Several physical characteristics of this CME were estimated.

  13. Novel Burst Suppression Segmentation in the Joint Time-Frequency Domain for EEG in Treatment of Status Epilepticus

    PubMed Central

    Lee, Jaeyun; Song, Woo-Jin; Lee, Hyang Woon

    2016-01-01

    We developed a method to distinguish bursts and suppressions for EEG burst suppression from the treatments of status epilepticus, employing the joint time-frequency domain. We obtained the feature used in the proposed method from the joint use of the time and frequency domains, and we estimated the decision as to whether the measured EEG was a burst segment or suppression segment by the maximum likelihood estimation. We evaluated the performance of the proposed method in terms of its accordance with the visual scores and estimation of the burst suppression ratio. The accuracy was higher than the sole use of the time or frequency domains, as well as conventional methods conducted in the time domain. In addition, probabilistic modeling provided a more simplified optimization than conventional methods. Burst suppression quantification necessitated precise burst suppression segmentation with an easy optimization; therefore, the excellent discrimination and the easy optimization of burst suppression by the proposed method appear to be beneficial. PMID:27872655

  14. DELTAE

    SciTech Connect

    Ward, W.C. ); Swift, G.W. )

    1993-11-01

    In thermoacoustic engines and refrigerators, and in many simple acoustic systems, a one dimensional wave equation determines the spatial dependence of the acoustic pressure and velocity. DELTAE numerically integrates such wave equations in the acoustic approximation, in gases or liquids, in user-defined geometries. Boundary conditions can include conventional acoustic boundary conditions of geometry and impedance, as well as temperature and thermal power in thermoacoustic systems. DELTAE can be used easily for apparatus ranging from simple duct networks and resonators to thermoacoustic engines refrigerators and combinations thereof. It can predict how a given apparatus will perform, or can allow the user to design an apparatus to achieve desired performance. DELTAE views systems as a series of segments; twenty segment types are supported. The purely acoustic segments include ducts and cones, and lumped impedances including compliances, series impedances, and endcaps. Electroacoustics tranducer segments can be defined using either frequency-independent coefficients or the conventional parameters of loudspeaker-style drivers: mass, spring constant, magnetic field strength, etc. Tranducers can be current driven, voltage driven, or connected to an electrical load impedance. Thermoacoustic segment geometries include parallel plates, circular and rectangular pores, and pin arrays. Side branches can be defined with fixed impedances, frequency-dependent radiation impedances, or as an auxiliary series of segments of any types. The user can select working fluids from among air, helium, neon, argon, hydrogen, deuterium, carbon dioxide, nitrogen, helium-argon mixtures, helium-xenon mixtures, liquid sodium, and eutectic sodium-potassium. Additional fluids and solids can be defined by the user.

  15. Potential Impacts of Tsangpo Lake-Burst Megafloods and Their Preservation in the Bengal Basin and Delta System

    NASA Astrophysics Data System (ADS)

    Diamond, M. S.; Goodbred, S. L., Jr.; Palamenghi, L.; Hossain, S.; Pickering, J.; Sincavage, R.; Spiess, V.; Williams, L. A.

    2014-12-01

    Large, glacially-dammed lakes formed via the impoundment of the Tsangpo River in Tibet led to lake-burst floods during the late Pleistocene and at least two intervals in the early and late Holocene. We present the first critical examination of the potential effects that the Holocene lake drainages had on the downstream Bengal delta and their preservation in the geologic record. Based on stratigraphic evidence from cores drilled across the delta, digital elevation models, seismic data, and hydraulic flow calculations, we propose that lake-burst floods could be responsible for (a) triggering short-lived avulsion events of the Brahmaputra River into the Sylhet basin, (b) the formation of two apparent overflow channels on the Madhupur Terrace, and (c) the deposition of a large, mass transport deposit in the submarine Swatch of No Ground canyon system. Comparing the early and late Holocene events, we expect the distribution of the floodwaters and their deposits in the two intervals to differ sharply owing to major differences in flood volume and the paleotopography of the delta. Despite much higher discharge, the early Holocene floods were largely accommodated within the vast lowstand valley of the Brahmaputra, with some spillover into the Sylhet basin. In contrast, the late Holocene floods likely spread over a larger area due to the relatively even, low-gradient topography. Offshore, a 40 m thick chaotic, semi-transparent seismic facies observed in the canyon corresponds temporally with the early Holocene floods and is tentatively interpreted as a subaqueous debris flow generated by the flood pulse directed to the canyon via the lowstand river valley. We examine the theoretical preservation potential of rare flood events in light of signal shredding mechanisms to help explain why evidence of the larger, early Holocene floods is preserved whereas we have found no clear signal from the younger floods.

  16. Auroral medium frequency burst radio emission associated with the 23 March 2007 THEMIS study substorm

    NASA Astrophysics Data System (ADS)

    Bunch, N. L.; Labelle, J.; Weatherwax, A. T.; Hughes, J. M.

    2008-01-01

    Auroral medium frequency (MF) burst is an impulsive auroral radio emission associated with substorm onset detected by ground-based instruments between 1.3 and 4.5 MHz. On 23 March 2007 an MF burst emission was detected by the Dartmouth radio interferometer located near Toolik Lake, Alaska. This emission temporally coincides with the onset of the 23 March 2007 Time History of Events and Macroscale Interactions during Substorms (THEMIS) study substorm. Directions of arrival computed using the Dartmouth radio interferometer for this event also coincide spatially with the location of the expanding auroral arcs to the south observed by the all-sky imager at Fort Yukon, Alaska. This observation represents the first example of a direction of arrival measurement for MF burst. It strongly supports the association of MF burst with intense auroral arcs accompanying substorm onset. The direction of arrival of the MF burst is consistent with the direction to the eastern edge of the substorm onset location determined by multiple data sets during this substorm and suggests that location of MF burst radio emissions may be an effective method of locating substorm onsets, much as radio atmospherics are used to locate lightning.

  17. Temporal Intraspeech Masking of Plosive Bursts: Effects of Hearing Loss and Frequency Shaping

    ERIC Educational Resources Information Center

    Mackersie, Carol L.

    2007-01-01

    Purpose: The purposes were (a) to compare masking of consonant bursts by adjacent vowels for listeners with and without hearing loss and (b) to determine the extent to which the temporal intraspeech masking can be reduced by a simulated hearing-aid frequency-response shaping. Method: Fourteen adults with sensorineural hearing loss and 10 with…

  18. Membrane resonance in bursting pacemaker neurons of an oscillatory network is correlated with network frequency.

    PubMed

    Tohidi, Vahid; Nadim, Farzan

    2009-05-20

    Network oscillations typically span a limited range of frequency. In pacemaker-driven networks, including many central pattern generators (CPGs), this frequency range is determined by the properties of bursting pacemaker neurons and their synaptic connections; thus, factors that affect the burst frequency of pacemaker neurons should play a role in determining the network frequency. We examine the role of membrane resonance of pacemaker neurons on the network frequency in the crab pyloric CPG. The pyloric oscillations (frequency of approximately 1 Hz) are generated by a group of pacemaker neurons: the anterior burster (AB) and the pyloric dilator (PD). We examine the impedance profiles of the AB and PD neurons in response to sinusoidal current injections with varying frequency and find that both neuron types exhibit membrane resonance, i.e., demonstrate maximal impedance at a given preferred frequency. The membrane resonance frequencies of the AB and PD neurons fall within the range of the pyloric network oscillation frequency. Experiments with pharmacological blockers and computational modeling show that both calcium currents I(Ca) and the hyperpolarization-activated inward current I(h) are important in producing the membrane resonance in these neurons. We then demonstrate that both the membrane resonance frequency of the PD neuron and its suprathreshold bursting frequency can be shifted in the same direction by either direct current injection or by using the dynamic-clamp technique to inject artificial conductances for I(h) or I(Ca). Together, these results suggest that membrane resonance of pacemaker neurons can be strongly correlated with the CPG oscillation frequency.

  19. FIRST VERY LOW FREQUENCY DETECTION OF SHORT REPEATED BURSTS FROM MAGNETAR SGR J1550-5418

    SciTech Connect

    Tanaka, Y. T.; Takahashi, T.; Raulin, Jean-Pierre; Bertoni, Fernando C. P.; Fagundes, P. R.; Chau, J.; Schuch, N. J.; Hayakawa, M.; Hobara, Y.; Terasawa, T.

    2010-09-20

    We report on the first detection of ionospheric disturbances caused by short repeated gamma-ray bursts from the magnetar SGR J1550-5418. Very low frequency (VLF) radio wave data obtained in South America clearly show sudden amplitude and phase changes at the corresponding times of eight soft gamma-ray repeater bursts. Maximum amplitude and phase changes of the VLF signals appear to be correlated with the gamma-ray fluence. On the other hand, VLF recovery timescales do not show any significant correlation with the fluence, possibly suggesting that the bursts' spectra are not similar to each other. In summary, Earth's ionosphere can be used as a very large gamma-ray detector and the VLF observations provide us with a new method to monitor high-energy astrophysical phenomena without interruption such as Earth occultation.

  20. Solar burst with millimetre-wave emission at high frequency only

    NASA Technical Reports Server (NTRS)

    Kaufmann, P.; Correia, E.; Costa, J. E. R.; Vaz, A. M. Z.; Dennis, B. R.

    1985-01-01

    The first high sensitivity and high time-resolution observations of a solar burst taken simultaneously at 90 GHz and at 30 GHz are presented. These identify a unique impulsive burst on May 21, 1984 with fast pulsed emission that was considerably more intense at 90 GHz than at lower frequencies. Hard X-ray time structures at energies above 25 keV were almost identical to the 90 GHz structures to better than 1 s. The structure of the onset of the major 90 GHz burst coincided with the hard X-ray structure to within 128 ms. All 90 GHz major time structures consisted of trains of multiple subsecond pulses with rise times as short as 0.03 s and amplitudes that were large compared with the mean flux. When detectable, the 30 GHz subsecond pulses had smaller relative amplitude and were in phase with the corresponding 90 GHz pulses.

  1. On the propagation and mode conversion of auroral medium frequency bursts

    NASA Astrophysics Data System (ADS)

    Broughton, M. C.; LaBelle, J.; Kim, E.-H.; Yoon, P. H.; Johnson, J. R.; Cairns, I. H.

    2016-02-01

    Auroral medium frequency (MF) bursts are broadband, impulsive radio emissions associated with local substorm onsets. MF bursts consist of a characteristic fine structure whereby the higher frequencies arrive 10-100 ms before the lower frequencies. LaBelle (2011a) proposed that MF bursts originate as Langmuir/Z mode waves on the topside of the ionosphere that mode-convert to LO mode waves and propagate to ground level, with the fine structure resulting by propagation delays due to the topside ionospheric density profile. We investigate three aspects of this mechanism. First, full-wave calculations are used to simulate the MF burst fine structure using a realistic ionospheric density profile. The delay between the highest and lowest frequencies is 21 ms. This value is smaller than the experimentally determined delays of ˜100 ms presented in Bunch and LaBelle (2009), but differences between the topside electron number density profile used in the simulations and the number density profile during disturbed conditions make comparisons only approximate. Second, the Landau damping of Langmuir/Z mode waves on the topside ionosphere is calculated, assuming the electron distribution function consists of a cold background population (ne0) and a warm secondary population (nse). The Landau damping is small when nse/ne0 = 0.04% (consistent with Maggs and Lotko (1981)) but is significant when nse/ne0 > 0.4%. Finally, full-wave calculations are used to determine the mode conversion efficiency from Langmuir/Z mode waves to LO mode waves. These imply that waves would suffer an attenuation of wave energy density of approximately 5-10% if they are generated with their wave vectors in a narrow cone centered around the local magnetic field. Taken together, these calculations suggest that for small values of nse/ne0 <0.4%, the mechanism proposed by LaBelle (2011a) is a plausible explanation for the origin of MF bursts.

  2. Frequency of delta F508 in a Mexican sample of cystic fibrosis patients.

    PubMed Central

    Orozco, L; Salcedo, M; Lezana, J L; Chávez, M; Valdez, H; Moreno, M; Carnevale, A

    1993-01-01

    This paper reports the frequency of the delta F508 mutation in a cohort of 50 Mexican patients with cystic fibrosis (CF). The mutation was detected by PCR mediated site directed mutagenesis. delta F508 was found in 39% of CF chromosomes, a frequency lower than that reported in Argentina and Spain. The high rate of CF cases who die undiagnosed, the ethnic origin of Mexican populations, and the limited number of cases studied could account for the low frequency of the delta F508 mutation found in this preliminary report. Images PMID:8326494

  3. The membrane potential waveform of bursting pacemaker neurons is a predictor of their preferred frequency and the network cycle frequency

    PubMed Central

    Tseng, Hua-an; Nadim, Farzan

    2010-01-01

    Many oscillatory networks involve neurons that exhibit intrinsic rhythmicity, but possess a large variety of voltage-gated currents which interact in a complex fashion making it difficult to determine which factors control frequency. Yet, these neurons often have preferred (resonance) frequencies that can be close to the network frequency. Because the preferred frequency results from the dynamics of ionic currents, it can be assumed to depend on parameters that determine the neuron’s oscillatory waveform shape. The pyloric network frequency in the crab Cancer borealis is correlated with the preferred frequency of its bursting pacemaker neurons AB and PD. We measure the preferred frequency of the PD neuron in voltage-clamp, which allows control of the oscillation voltage range and waveforms (sine waves and realistic oscillation waveforms), and showthat1) the preferred frequency depends on the voltage range of the oscillating voltage waveform; 2) the slope of the waveform near its peak has a strongly negative correlation with the preferred frequency; and 3) correlations between parameters of the PD neuron oscillation waveform and its preferred frequency can be used to predict shifts in the network frequency. As predicted by these results, dynamic clamp shifts of the upper or lower voltage limits of the PD neuron waveform during ongoing oscillations changed the network frequency, consistent with the predictions from the preferred frequency. These results show that the voltage waveform of oscillatory neurons can be predictive of their preferred frequency and thus the network oscillation frequency. PMID:20702710

  4. The membrane potential waveform of bursting pacemaker neurons is a predictor of their preferred frequency and the network cycle frequency.

    PubMed

    Tseng, Hua-an; Nadim, Farzan

    2010-08-11

    Many oscillatory networks involve neurons that exhibit intrinsic rhythmicity but possess a large variety of voltage-gated currents that interact in a complex fashion, making it difficult to determine which factors control frequency. Yet these neurons often have preferred (resonance) frequencies that can be close to the network frequency. Because the preferred frequency results from the dynamics of ionic currents, it can be assumed to depend on parameters that determine the neuron's oscillatory waveform shape. The pyloric network frequency in the crab Cancer borealis is correlated with the preferred frequency of its bursting pacemaker neurons anterior burster and pyloric dilator (PD). We measured the preferred frequency of the PD neuron in voltage clamp, which allows control of the oscillation voltage range and waveforms (sine waves and realistic oscillation waveforms), and showed that (1) the preferred frequency depends on the voltage range of the oscillating voltage waveform; (2) the slope of the waveform near its peak has a strongly negative correlation with the preferred frequency; and (3) correlations between parameters of the PD neuron oscillation waveform and its preferred frequency can be used to predict shifts in the network frequency. As predicted by these results, dynamic clamp shifts of the upper or lower voltage limits of the PD neuron waveform during ongoing oscillations changed the network frequency, consistent with the predictions from the preferred frequency. These results show that the voltage waveform of oscillatory neurons can be predictive of their preferred frequency and thus the network oscillation frequency.

  5. Frequency modulation of stochastic gene expression bursts by strongly interacting small RNAs.

    PubMed

    Kumar, Niraj; Jia, Tao; Zarringhalam, Kourosh; Kulkarni, Rahul V

    2016-10-01

    The sporadic nature of gene expression at the single-cell level-long periods of inactivity punctuated by bursts of mRNA or protein production-plays a critical role in diverse cellular processes. To elucidate the cellular role of bursting in gene expression, synthetic biology approaches have been used to design simple genetic circuits with bursty mRNA or protein production. Understanding how such genetic circuits can be designed with the ability to control burst-related parameters requires the development of quantitative stochastic models of gene expression. In this work, we analyze stochastic models for the regulation of gene expression bursts by strongly interacting small RNAs. For the parameter range considered, results based on mean-field approaches are significantly inaccurate and alternative analytical approaches are needed. Using simplifying approximations, we obtain analytical results for the corresponding steady-state distributions that are in agreement with results from stochastic simulations. These results indicate that regulation by small RNAs, in the strong interaction limit, can be used to effectively modulate the frequency of bursting. We explore the consequences of such regulation for simple genetic circuits involving feedback effects and switching between promoter states.

  6. Frequency modulation of stochastic gene expression bursts by strongly interacting small RNAs

    NASA Astrophysics Data System (ADS)

    Kumar, Niraj; Jia, Tao; Zarringhalam, Kourosh; Kulkarni, Rahul V.

    2016-10-01

    The sporadic nature of gene expression at the single-cell level—long periods of inactivity punctuated by bursts of mRNA or protein production—plays a critical role in diverse cellular processes. To elucidate the cellular role of bursting in gene expression, synthetic biology approaches have been used to design simple genetic circuits with bursty mRNA or protein production. Understanding how such genetic circuits can be designed with the ability to control burst-related parameters requires the development of quantitative stochastic models of gene expression. In this work, we analyze stochastic models for the regulation of gene expression bursts by strongly interacting small RNAs. For the parameter range considered, results based on mean-field approaches are significantly inaccurate and alternative analytical approaches are needed. Using simplifying approximations, we obtain analytical results for the corresponding steady-state distributions that are in agreement with results from stochastic simulations. These results indicate that regulation by small RNAs, in the strong interaction limit, can be used to effectively modulate the frequency of bursting. We explore the consequences of such regulation for simple genetic circuits involving feedback effects and switching between promoter states.

  7. [Frequency of the coreceptor CCR5 gene delta 32 mutation in different French regions].

    PubMed

    Lucotte, G; Mercier, G

    1998-05-01

    We studied the frequency of the coreceptor CCR5 gene delta 32 mutation on 1,836 DNA samples originating from ten French regions. This mutation confers, in the homozygous state, resistance to HIV-1 infection. For the whole territory, the mean percentage presence of the delta 32 mutation is 9.2%. The mutation is statistically more frequent in the north (11.2%) than in the south (6.3%) of the country; this differentiation corresponds probably to a gradient of decreasing frequencies of the delta 32 mutation in Europe.

  8. Frequency of the delta ccr5 deletion allele in the urban Brazilian population.

    PubMed

    Passos, G A; Picanço, V P

    1998-04-01

    Studies on screening genes conferring resistance to HIV-1 and AIDS onset have shown a direct relationship between a 32 base pair (bp) deletion in the CCR5 beta-chemokine receptor gene (delta ccr5 mutant allele) and long survival of HIV-1 infected individuals bearing this mutation. These findings led to an interest in studies of delta ccr5 allele distribution in human populations. In the present study, polymerase chain reactions (PCR) in genomic DNA samples, using specific CCR5 oligonucleotide primers surrounding the breakpoint deletion, detected a 193-bp product from the normal CCR5 allele and a 161-bp product from the 32-bp deletion allele. In an investigation of the urban Brazilian population we detected a 93% frequency of normal CCR5/CCR5 homozygous individuals and a 7% frequency of CCR5/delta ccr5 heterozygous individuals. The frequency of the delta ccr5 mutant allele in this population is 0.035; however, no homozygous delta ccr5 individual has been detected thus far. This is the first evidence for the contribution of the delta ccr5 allele to the genetic background of the urban Brazilian population, which is characterized by intense ethnic admixture. These findings open perspectives for further studies on the relationship between delta ccr5 allele frequency and AIDS onset in high-risk HIV-1 exposures individuals.

  9. Deka-keV X-ray observations of solar bursts with WATCH/GRANAT: frequency distributions of burst parameters

    NASA Astrophysics Data System (ADS)

    Crosby, N.; Vilmer, N.; Lund, N.; Sunyaev, R.

    1998-06-01

    Solar flare observations in the deka-keV range are performed by the WATCH experiment on board the GRANAT satellite. The WATCH experiment is presented, including the energy calibration as applied in the present work. The creation of the solar burst catalogue covering two years of observation is described and some examples of solar observations are given. The estimated energy releases in the flares presented here are found to extend below the range of hard X-ray flares which were previously studied by ISEE-3 and HXRBS/SMM detectors. The X-ray emitting component cannot be exclusively explained by contributions from a thermal plasma around a few keV. Either a hotter component or a non-thermal population of particles must also be present to produce the observed deka-keV emission. The WATCH data furthermore shows that the relative contributions of these components may change during an event or from event to event and that the injection of energy contained in suprathermal electrons may occur throughout an event and not only during the rise phase. For the most energetic WATCH flares simultaneous observations performed by other experiments at higher energies further indicate that non-thermal emission can be observed as low as 10 keV. A statistical study is performed on the total WATCH solar database and frequency distributions are built on measured X-ray flare parameters. It is also investigated how the properties of these frequency distributions behave when subgroups of events defined by different ranges of parameters are considered. No correlation is found between the elapsed time interval between successive flares arising from the same active region and the peak intensity of the flare.

  10. EMG burst presence probability: a joint time-frequency representation of muscle activity and its application to onset detection.

    PubMed

    Liu, Jie; Ying, Dongwen; Rymer, William Zev

    2015-04-13

    The purpose of this study was to quantify muscle activity in the time-frequency domain, therefore providing an alternative tool to measure muscle activity. This paper presents a novel method to measure muscle activity by utilizing EMG burst presence probability (EBPP) in the time-frequency domain. The EMG signal is grouped into several Mel-scale subbands, and the logarithmic power sequence is extracted from each subband. Each log-power sequence can be regarded as a dynamic process that transits between the states of EMG burst and non-burst. The hidden Markov model (HMM) was employed to elaborate this dynamic process since HMM is intrinsically advantageous in modeling the temporal correlation of EMG burst/non-burst presence. The EBPP was eventually yielded by HMM based on the criterion of maximum likelihood. Our approach achieved comparable performance with the Bonato method.

  11. Direction of Arrival Studies of Medium Frequency Burst Radio Emissions at Toolik Lake, AK

    NASA Astrophysics Data System (ADS)

    Bunch, N.; Labelle, J.; Weatherwax, A.; Lummerzheim, D.; Stenbaek-Nielsen, H.

    2008-05-01

    MF burst is an impulsive radio emission of auroral origin, which can be detected by ground-based instruments at frequencies between 1,300 and 4,500kHz. MF burst has been shown to be associated with substorm onset, but its exact generation mechanism remains unknown, although it is thought to arise from mode conversion radiation [see review by LaBelle and Treumann, 2002] . In search of the generation mechanism of this emission, Dartmouth College has deployed radio interferometers in Alaska, Northern Canada, Greenland, and Antarctica, including a three-element interferometer deployed to Toolik Field Station in Alaska during the summer of 2006. This instrument measured spectra, amplitudes and directions of arrival (DOA's) of over 47 MF burst events between November 30, 2006 and May 26, 2007. These data represent the first DOA measurements of impulsive MF burst, of which selected case studies were presented at the Fall 2007 AGU conference. Here we present a statistical survey of all 47 events as well as detailed analysis of three events occurring on: Mar 5, Mar 23, and Nov 20, 2007. For the statistical survey, we present distributions of DOA as a function of local time and frequency. In each case study we analyze the direction of arrival of the emissions as a function of both time and frequency within each event. The time variations will be compared with the time variations of optical auroral forms simultaneously measured with all-sky cameras. The dependence of the arrival direction on frequency enables a significant test of the generation mechanism whereby the waves are emitted at the local plasma or upper hybrid frequency in the topside ionosphere, predicting that higher frequencies should originate at lower altitudes. These three events have been selected because All-Sky camera data are available at these times from Toolik Lake and Fort Yukon, Alaska. These are critical both for identifying which optical features are associated with the radio emissions as well as for

  12. Possible reasons for the frequency splitting of the harmonics of type II solar radio bursts

    NASA Astrophysics Data System (ADS)

    Eselevich, V. G.; Eselevich, M. V.; Zimovets, I. V.

    2016-01-01

    AIA/SDO data in the 193 Å channel preceding a coronal mass ejection observed at the solar limb on June 13, 2010 are used to simultaneously identify and examine two different shock fronts. The angular size of each front relative to the CME center was about 20°, and their propagation directions differed by ≈25° (≈4° in position angle). The faster front, called the blast shock, advanced the other front, called the piston shock, by R ≈ (0.02-0.03) R⊙ ( R⊙ is the solar radius) and had a maximum initial speed of V B ≈ 850 km/s (with V P ≈ 700 km/s for the piston shock). The appearance and motion of these shocks were accompanied by a Type II radio burst observed at the fundamental frequency F and second harmonic H. Each frequency was split into two close frequencies f 1 and f 2 separated by Δ f = f 2 - f 1 ≪ F, H. It is concluded that the observed frequency splitting Δ f of the F and H components of the Type II burst could result from the simultaneous propagation of piston and blast shocks moving with different speeds in somewhat different directions displaying different coronal-plasma densities.

  13. Analysis and modeling of time-variant amplitude-frequency couplings of and between oscillations of EEG bursts.

    PubMed

    Witte, Herbert; Putsche, Peter; Hemmelmann, Claudia; Schelenz, Christoph; Leistritz, Lutz

    2008-08-01

    Low-frequency (0.5-2.5 Hz) and individually defined high-frequency (7-11 or 8-12 Hz; 11-15 or 14-18 Hz) oscillatory components of the electroencephalogram (EEG) burst activity derived from thiopental-induced burst-suppression patterns (BSP) were investigated in seven sedated patients (17-26 years old) with severe head injury. The predominant high-frequency burst oscillations (>7 Hz) were detected for each patient by means of time-variant amplitude spectrum analysis. Thereafter, the instantaneous envelope (IE) and the instantaneous frequency (IF) were computed for these low- and high-frequency bands to quantify amplitude-frequency dependencies (envelope-envelope, envelope-frequency, and frequency-frequency correlations). Time-variant phase-locking, phase synchronization, and quadratic phase couplings are associated with the observed amplitude-frequency characteristics. Additionally, these time-variant analyses were carried out for modeled burst patterns. Coupled Duffing oscillators were adapted to each EEG burst and by means of these models data-based burst simulations were generated. Results are: (1) strong envelope-envelope correlations (IE courses) can be demonstrated; (2) it can be shown that a rise of the IE is associated with an increase of the IF (only for the frequency bands 0.5-2.5 and 7-11 or 8-12 Hz); (3) the rise characteristics of all individually averaged envelope-frequency courses (IE-IF) are strongly correlated; (4) for the 7-11 or 8-12 Hz oscillation these associations are weaker and the variation between the time courses of the patients is higher; (5) for both frequency ranges a quantitative amplitude-frequency dependency can be shown because higher IE peak maxima are accompanied by stronger IF changes; (6) the time range of significant phase-locking within the 7-11 or 8-12 Hz frequency bands and of the strongest quadratic phase couplings (between 0.5-2.5 and 7-11 or 8-12 Hz) is between 0 and 1,000 ms; (7) all phase coupling characteristics of the

  14. A novel network of multipolar bursting interneurons generates theta frequency oscillations in neocortex.

    PubMed

    Blatow, Maria; Rozov, Andrei; Katona, Istvan; Hormuzdi, Sheriar G; Meyer, Axel H; Whittington, Miles A; Caputi, Antonio; Monyer, Hannah

    2003-06-05

    GABAergic interneurons can phase the output of principal cells, giving rise to oscillatory activity in different frequency bands. Here we describe a new subtype of GABAergic interneuron, the multipolar bursting (MB) cell in the mouse neocortex. MB cells are parvalbumin positive but differ from fast-spiking multipolar (FS) cells in their morphological, neurochemical, and physiological properties. MB cells are reciprocally connected with layer 2/3 pyramidal cells and are coupled with each other by chemical and electrical synapses. MB cells innervate FS cells but not vice versa. MB to MB cell as well as MB to pyramidal cell synapses exhibit paired-pulse facilitation. Carbachol selectively induced synchronized theta frequency oscillations in MB cells. Synchrony required both gap junction coupling and GABAergic chemical transmission, but not excitatory glutamatergic input. Hence, MB cells form a distinct inhibitory network, which upon cholinergic drive can generate rhythmic and synchronous theta frequency activity, providing temporal coordination of pyramidal cell output.

  15. Quadri-Pulse Theta Burst Stimulation using Ultra-High Frequency Bursts - A New Protocol to Induce Changes in Cortico-Spinal Excitability in Human Motor Cortex.

    PubMed

    Jung, Nikolai H; Gleich, Bernhard; Gattinger, Norbert; Hoess, Catrina; Haug, Carolin; Siebner, Hartwig R; Mall, Volker

    2016-01-01

    Patterned transcranial magnetic stimulation (TMS) such as theta burst stimulation (TBS) or quadri-pulse stimulation (QPS) can induce changes in cortico-spinal excitability, commonly referred to as long-term potentiation (LTP)-like and long-term depression (LTD)-like effects in human motor cortex (M1). Here, we aimed to test the plasticity-inducing capabilities of a novel protocol that merged TBS and QPS. 360 bursts of quadri-pulse TBS (qTBS) were continuously given to M1 at 90% of active motor threshold (1440 full-sine pulses). In a first experiment, stimulation frequency of each burst was set to 666 Hz to mimic the rhythmicity of the descending cortico-spinal volleys that are elicited by TMS (i.e., I-wave periodicity). In a second experiment, burst frequency was set to 200 Hz to maximize postsynaptic Ca2+ influx using a temporal pattern unrelated to I-wave periodicity. The second phase of sinusoidal TMS pulses elicited either a posterior-anterior (PA) or anterior-posterior (AP) directed current in M1. Motor evoked potentials (MEPs) were recorded before and after qTBS to probe changes in cortico-spinal excitability. PA-qTBS at 666 Hz caused a decrease in PA-MEP amplitudes, whereas AP-qTBS at 666 Hz induced an increase in mean AP-MEP amplitudes. At a burst frequency of 200 Hz, PA-qTBS and AP-qTBS produced an increase in cortico-spinal excitability outlasting for at least 60 minutes in PA- and AP-MEP amplitudes, respectively. Continuous qTBS at 666 Hz or 200 Hz can induce lasting changes in cortico-spinal excitability. Induced current direction in the brain appears to be relevant when qTBS targets I-wave periodicity, corroborating that high-fidelity spike timing mechanisms are critical for inducing bi-directional plasticity in human M1.

  16. Energetic electrons from solar flares and associated type 3 radio bursts from metric to hectometric wave frequencies

    NASA Technical Reports Server (NTRS)

    Sakurai, K.

    1972-01-01

    Distinct Kev electron events as observed by satellites near the earth are, in general, associated with solar flares which are accompained by the emission of both metric and hectometric type 3 radio bursts. The positions of these flares are mainly on the western hemisphere of the sun. These results show that Kev electrons propagate under the control of the magnetic field in the interplanetary space and that, while propagating through this space, these electrons excite type 3 radio bursts from metric to hectometric wave frequencies. Emission characteristics of hectometric type 3 bursts are briefly considered in relation to the positions of associated flares.

  17. Cosine Directional Tuning of Theta Cell Burst Frequencies: Evidence for Spatial Coding by Oscillatory Interference

    PubMed Central

    Welday, Adam C.; Shlifer, I. Gary; Bloom, Matthew L.; Zhang, Kechen

    2011-01-01

    The rodent septohippocampal system contains “theta cells,” which burst rhythmically at 4–12 Hz, but the functional significance of this rhythm remains poorly understood (Buzsáki, 2006). Theta rhythm commonly modulates the spike trains of spatially tuned neurons such as place (O'Keefe and Dostrovsky, 1971), head direction (Tsanov et al., 2011a), grid (Hafting et al., 2005), and border cells (Savelli et al., 2008; Solstad et al., 2008). An “oscillatory interference” theory has hypothesized that some of these spatially tuned neurons may derive their positional firing from phase interference among theta oscillations with frequencies that are modulated by the speed and direction of translational movements (Burgess et al., 2005, 2007). This theory is supported by studies reporting modulation of theta frequency by movement speed (Rivas et al., 1996; Geisler et al., 2007; Jeewajee et al., 2008a), but modulation of theta frequency by movement direction has never been observed. Here we recorded theta cells from hippocampus, medial septum, and anterior thalamus of freely behaving rats. Theta cell burst frequencies varied as the cosine of the rat's movement direction, and this directional tuning was influenced by landmark cues, in agreement with predictions of the oscillatory interference theory. Computer simulations and mathematical analysis demonstrated how a postsynaptic neuron can detect location-dependent synchrony among inputs from such theta cells, and thereby mimic the spatial tuning properties of place, grid, or border cells. These results suggest that theta cells may serve a high-level computational function by encoding a basis set of oscillatory signals that interfere with one another to synthesize spatial memory representations. PMID:22072668

  18. Ion Acoustic Wave Frequencies and Onset Times During Type 3 Solar Radio Bursts

    NASA Technical Reports Server (NTRS)

    Cairns, Iver H.; Robinson, P. A.

    1995-01-01

    Conflicting interpretations exist for the low-frequency ion acoustic (S) waves often observed by ISEE 3 in association with intense Langmuir (L) waves in the source regions of type III solar radio bursts near 1 AU. Two indirect lines of observational evidence, as well as plasma theory, suggest they are produced by the electrostatic (ES) decay L yields L(PRIME) + S. However, contrary to theoretical predictions, an existing analysis of the wave frequencies instead favors the electromagnetic (EM) decays L yields T + S, where T denotes an EM wave near the plasma frequency. This conflict is addressed here by comparing the observed wave frequencies and onset times with theoretical predictions for the ES and EM decays, calculated using the time-variable electron beam and magnetic field orientation data, rather than the nominal values used previously. Field orientation effects and beam speed variations are shown analytically to produce factor-of-three effects, greater than the difference in wave frequencies predicted for the ES and EM decays; effects of similar magnitude occur in the events analyzed here. The S-wave signals are extracted by hand from a sawtooth noise background, greatly improving the association between S waves and intense L waves. Very good agreement exists between the time-varying predictions for the ES decay and the frequencies of most (but not all) wave bursts. The waves occur only after the ES decay becomes kinematically allowed, which is consistent with the ES decay proceeding and producing most of the observed signals. Good agreement exists between the EM decay's predictions and a significant fraction of the S-wave observations while the EM decay is kinematically allowed. The wave data are not consistent, however, with the EM decay being the dominant nonlinear process. Often the observed waves are sufficiently broadband to overlap simultaneously the frequency ranges predicted for the ES and EM decays. Coupling the dominance of the ES decay with this

  19. FREQUENCY DEPENDENCE OF POLARIZATION OF ZEBRA PATTERN IN TYPE-IV SOLAR RADIO BURSTS

    SciTech Connect

    Kaneda, Kazutaka; Misawa, H.; Tsuchiya, F.; Obara, T.; Iwai, K.

    2015-08-01

    We investigated the polarization characteristics of a zebra pattern (ZP) in a type-IV solar radio burst observed with AMATERAS on 2011 June 21 for the purpose of evaluating the generation processes of ZPs. Analyzing highly resolved spectral and polarization data revealed the frequency dependence of the degree of circular polarization and the delay between two polarized components for the first time. The degree of circular polarization was 50%–70% right-handed and it varied little as a function of frequency. Cross-correlation analysis determined that the left-handed circularly polarized component was delayed by 50–70 ms relative to the right-handed component over the entire frequency range of the ZP and this delay increased with the frequency. We examined the obtained polarization characteristics by using pre-existing ZP models and concluded that the ZP was generated by the double-plasma-resonance process. Our results suggest that the ZP emission was originally generated in a completely polarized state in the O-mode and was partly converted into the X-mode near the source. Subsequently, the difference between the group velocities of the O-mode and X-mode caused the temporal delay.

  20. Frequency of the CCR5-delta 32 chemokine receptor gene mutation in the Lebanese population.

    PubMed

    Karam, W; Jurjus, R; Khoury, N; Khansa, H; Assad, C; Zalloua, P; Jurjus, A

    2004-01-01

    A direct correlation between HIV infection and mutation in the chemokine receptor (CCR5) gene has been established. However, such correlation has never been investigated in Lebanon. We report the frequency of the CCR5-delta 32 mutation in a random sample of 209 healthy, HIV-1 seronegative Lebanese aged 19-68. Overall, 4.8% were heterozygous for the mutation. Homozygosity was absent from our sample. The frequency for the CCR5-delta 32 allele was 2.5%. Distribution of the mutation was unaffected by sex, age, religion or educational level. The frequency in the Lebanese population is consistent with that in the origin of the mutation in northern Europe. This could be attributed to a gene flow into the Middle East from northern Europe.

  1. Solar Radio Burst Data Processing of CALLISTO and Frequency Drift Rate Determination of Solar Radio Burst Detected by CALLISTO Network in Indonesia

    NASA Astrophysics Data System (ADS)

    Batubara, M.; Manik, T.; Suryana, R.; Lathif, M.; Sitompul, P.; Zamzam, M.; Mumtahana, F.

    2017-03-01

    Space Science Center of Indonesian Institute of Aeronautics and Space called LAPAN has installed several solar radio receivers named CALLISTO in various parts of Indonesia. The equipment has made some solar radio observational data which is indicate solar radio burst since its operation. All of the observational data stored in the file format of Flexible Image Transport System (FITS) which is the raw data. Therefore, it is required a such kind of related data processing to produce a data that can be used for further research. In this paper will discuss how the observational data of CALLISTO could be generated included the information of data format, CALLISTO data processing techniques used in these activities as well as some of the data processing based on data indicating solar radio bursts. As the results, a map of solar radio spectrum as spectrograph profiles and some determinations of frequency drift base on the data will also be discussed in this paper.

  2. Mitigation of impedance changes due to electroporation therapy using bursts of high-frequency bipolar pulses

    PubMed Central

    2015-01-01

    Background For electroporation-based therapies, accurate modeling of the electric field distribution within the target tissue is important for predicting the treatment volume. In response to conventional, unipolar pulses, the electrical impedance of a tissue varies as a function of the local electric field, leading to a redistribution of the field. These dynamic impedance changes, which depend on the tissue type and the applied electric field, need to be quantified a priori, making mathematical modeling complicated. Here, it is shown that the impedance changes during high-frequency, bipolar electroporation therapy are reduced, and the electric field distribution can be approximated using the analytical solution to Laplace's equation that is valid for a homogeneous medium of constant conductivity. Methods Two methods were used to examine the agreement between the analytical solution to Laplace's equation and the electric fields generated by 100 µs unipolar pulses and bursts of 1 µs bipolar pulses. First, pulses were applied to potato tuber tissue while an infrared camera was used to monitor the temperature distribution in real-time as a corollary to the electric field distribution. The analytical solution was overlaid on the thermal images for a qualitative assessment of the electric fields. Second, potato ablations were performed and the lesion size was measured along the x- and y-axes. These values were compared to the analytical solution to quantify its ability to predict treatment outcomes. To analyze the dynamic impedance changes due to electroporation at different frequencies, electrical impedance measurements (1 Hz to 1 MHz) were made before and after the treatment of potato tissue. Results For high-frequency bipolar burst treatment, the thermal images closely mirrored the constant electric field contours. The potato tissue lesions differed from the analytical solution by 39.7 ± 1.3 % (x-axis) and 6.87 ± 6.26 % (y-axis) for conventional unipolar pulses

  3. Improved dichotomous search frequency offset estimator for burst-mode continuous phase modulation

    NASA Astrophysics Data System (ADS)

    Zhai, Wen-Chao; Li, Zan; Si, Jiang-Bo; Bai, Jun

    2015-11-01

    A data-aided technique for carrier frequency offset estimation with continuous phase modulation (CPM) in burst-mode transmission is presented. The proposed technique first exploits a special pilot sequence, or training sequence, to form a sinusoidal waveform. Then, an improved dichotomous search frequency offset estimator is introduced to determine the frequency offset using the sinusoid. Theoretical analysis and simulation results indicate that our estimator is noteworthy in the following aspects. First, the estimator can operate independently of timing recovery. Second, it has relatively low outlier, i.e., the minimum signal-to-noise ratio (SNR) required to guarantee estimation accuracy. Finally, the most important property is that our estimator is complexity-reduced compared to the existing dichotomous search methods: it eliminates the need for fast Fourier transform (FFT) and modulation removal, and exhibits faster convergence rate without accuracy degradation. Project supported by the National Natural Science Foundation of China (Grant No. 61301179), the Doctorial Programs Foundation of the Ministry of Education, China (Grant No. 20110203110011), and the Programme of Introducing Talents of Discipline to Universities, China (Grant No. B08038).

  4. Dispersion by pulsars, magnetars, fast radio bursts and massive electromagnetism at very low radio frequencies

    NASA Astrophysics Data System (ADS)

    Bentum, Mark J.; Bonetti, Luca; Spallicci, Alessandro D. A. M.

    2017-01-01

    Our understanding of the universe relies mostly on electromagnetism. As photons are the messengers, fundamental physics is concerned in testing their properties. Photon mass upper limits have been earlier set through pulsar observations, but new investigations are offered by the excess of dispersion measure (DM), sometimes observed with pulsar and magnetar data at low frequencies, or with the fast radio bursts (FRBs), of yet unknown origin. Arguments for the excess of DM do not reach a consensus, but are not mutually exclusive. Thus, we remind that for massive electromagnetism, dispersion goes as the inverse of the frequency squared. Thereby, new avenues are offered also by the recently operating ground observatories in 10-80 MHz domain and by the proposed Orbiting Low Frequency Antennas for Radio astronomy (OLFAR). The latter acts as a large aperture dish by employing a swarm of nano-satellites observing the sky for the first time in the 0.1-15 MHz spectrum. The swarm must be deployed sufficiently away from the ionosphere to avoid distorsions from terrestrial interference, especially during solar maxima, and offer stable conditions for calibration during observations.

  5. Quadri-Pulse Theta Burst Stimulation using Ultra-High Frequency Bursts – A New Protocol to Induce Changes in Cortico-Spinal Excitability in Human Motor Cortex

    PubMed Central

    Jung, Nikolai H.; Gleich, Bernhard; Gattinger, Norbert; Hoess, Catrina; Haug, Carolin; Siebner, Hartwig R.; Mall, Volker

    2016-01-01

    Patterned transcranial magnetic stimulation (TMS) such as theta burst stimulation (TBS) or quadri-pulse stimulation (QPS) can induce changes in cortico-spinal excitability, commonly referred to as long-term potentiation (LTP)-like and long-term depression (LTD)-like effects in human motor cortex (M1). Here, we aimed to test the plasticity-inducing capabilities of a novel protocol that merged TBS and QPS. 360 bursts of quadri-pulse TBS (qTBS) were continuously given to M1 at 90% of active motor threshold (1440 full-sine pulses). In a first experiment, stimulation frequency of each burst was set to 666 Hz to mimic the rhythmicity of the descending cortico-spinal volleys that are elicited by TMS (i.e., I-wave periodicity). In a second experiment, burst frequency was set to 200 Hz to maximize postsynaptic Ca2+ influx using a temporal pattern unrelated to I-wave periodicity. The second phase of sinusoidal TMS pulses elicited either a posterior-anterior (PA) or anterior-posterior (AP) directed current in M1. Motor evoked potentials (MEPs) were recorded before and after qTBS to probe changes in cortico-spinal excitability. PA-qTBS at 666 Hz caused a decrease in PA-MEP amplitudes, whereas AP-qTBS at 666 Hz induced an increase in mean AP-MEP amplitudes. At a burst frequency of 200 Hz, PA-qTBS and AP-qTBS produced an increase in cortico-spinal excitability outlasting for at least 60 minutes in PA- and AP-MEP amplitudes, respectively. Continuous qTBS at 666 Hz or 200 Hz can induce lasting changes in cortico-spinal excitability. Induced current direction in the brain appears to be relevant when qTBS targets I-wave periodicity, corroborating that high-fidelity spike timing mechanisms are critical for inducing bi-directional plasticity in human M1. PMID:27977758

  6. DNA in nanopores: negative capacitance and delta-relaxation at high frequency.

    PubMed

    Mandal, S K

    2006-05-01

    We measured the high frequency dielectric relaxation behavior of DNA molecules confined in nanopores of polycarbonate membrane. The data revealed the existence of a critical frequency omega(c) approximately GHz at which the ac conductivity showed delta-relaxation. Interestingly, the DNA molecules also exhibited a crossover from positive to negative capacitance corresponding to omega(c). The negative capacitance at the critical frequency suggested a strong inductive behavior of DNA molecules in the high frequency regime. The results are interpreted in terms of the confined geometry of the DNA molecules in the nanopores. The interfacial water H-bonded to DNA played a crucial role in determining the high frequency relaxation of DNA molecules. The results indicated that the DNA in nanopores could be designed for application in high frequency bandpass/notch filters.

  7. Astrophysically motivated time frequency clustering for burst gravitational wave search: application to TAMA300 data

    NASA Astrophysics Data System (ADS)

    Honda, Ryota; Yamagishi, Shougo; Kanda, Nobuyuki; TAMA Collaboration

    2008-09-01

    We have developed a method of 'time frequency (TF) clustering' to find burst gravitational waves for TAMA data analysis. The TF clustering method on the sonogram (spectrogram) shows some characteristics of short-duration signals. Burst gravitational waveforms from stellar-core collapse of supernovae that are predicted by Dimmelmeier et al [1, 2] (DFM waveforms) have short durations on the order of 10 ms and have a large spike and ringing tail in time series. On the other hand, typical detector instrumental noise transients of the same timescale have different waveforms as like as simpler spikes. Since the numerically predicted waveforms may not be reliable given conditions and model dependency, using one search algorithm is not robust to differentiate gravitational waves from instrumental noises. Our proposal for performing the separation is to compare many parameters of the cluster that represent the signal waveform. This approach will be useful for cases when the difference between gravitational waves and noise is not clear for one parameter. We employ TF clustering to represent the waveform characteristics. We calculated the parameters of each respective cluster, such as the magnitude and the Nth momentum around the center of a power distribution of the cluster. Using these parameters, we can efficiently identify some predicted gravitational waveforms and can exclude the TAMA detector's typical unstable spike-like noises due to the instruments. Our selection criteria for TF cluster shape parameters achieved an average efficiency of roughly 50% for injected DFM waveforms of h_rss\\sim 2 \\times 10^{-20}\\; {Hz^{-1/2}} (source distance of 350 pc) with false alarm rate of ~1 Hz. In addition, the false alarm rate for larger noises, such as SNR > 100, is improved 10-fold by applying the selection criteria for TF cluster parameters.

  8. Effect of Variation in the Burst Mode and Carrier Frequency of High Intensity Electrical Stimulation on Muscle Fatigue and Pain Perception of Healthy Subjects

    DTIC Science & Technology

    1988-10-22

    MVC; ( c ) Subjects pain tolerance is contingent upon the stimulating frequency and the amplitude of stimulation. Variations in either burst mode or...Body Weight and Force Data ..... ............. .132 C . Suoject Pain Ratings for all Combinations of Bursts and Carrier Frequencies...work supports the "size principle’ espoused by Henneman (1965) and confirmed by electromyographic studies using fine wire electrodes (Hannez, 1974

  9. Single-Bit All Digital Frequency Synthesis Using Homodyne Sigma-Delta Modulation.

    PubMed

    Sotiriadis, Paul

    2016-10-05

    All-digital frequency synthesis using band-pass sigma-delta modulation to achieve spectrally clean single-bit output is presented and mathematically analyzed resulting in a complete model to predict stability and output spectrum. The quadrature homodyne filter architecture is introduced resulting in efficient implementations of carrier-frequency centred bandpass filters for the modulator. A multiplier-less version of the quadrature homodyne filter architecture is also introduced to reduce complexity maintaining clean in-band spectrum. MATLAB and SIMULINK simulation results present the potential capabilities of the synthesizer architectures and validate the accuracy of the developed theoretical framework.

  10. High energy, single frequency, tunable laser source operating in burst mode for space based LIDAR applications

    NASA Astrophysics Data System (ADS)

    Cosentino, Alberto; Mondello, Alessia; Sapia, Adalberto; D'Ottavi, Alessandro; Brotini, Mauro; Nava, Enzo; Stucchi, Emanuele; Trespidi, Franco; Mariottini, Cristina; Wazen, Paul; Falletto, Nicolas; Fruit, Michel

    2004-06-01

    This paper describes the laser transmitter assembly used in the ALADIN instrument currently in C/D development phase for the ESA ADM-AEOLUS mission (EADS Astrium as prime contractor for the satellite and the instrument). The Laser Transmitter Assembly (TXA), based on a diode pumped tripled Nd:YAG laser, is used to generate tunable laser pulses of 150 mJ at a nominal wavelength of 355 nm. This laser is operated in burst mode, with a pulse repetition cycle of 100 Hz. The TXA is composed of the following units: a diode-pumped CW Nd:YAG Laser named Reference Laser Head (RLH), used to inject a diode-pumped, Q-switched, amplified and frequency tripled Nd:YAG Laser working in the third harmonic referred as Power Laser Head (PLH) and a Transmitter Laser Electronics (TLE) containing all the control and power electronics needed for PLH and RLH operation. The TXA is made by an European consortium under the leadership of Galileo Avionica (It), and including CESI (It), Quantel (Fr), TESAT (Ge) and Thales (Fr).

  11. Two-frequency /Delta k/ microwave scatterometer measurements of ocean wave spectra from an aircraft

    NASA Technical Reports Server (NTRS)

    Johnson, J. W.; Jones, W. L.; Weissman, D. E.

    1981-01-01

    A technique for remotely sensing the large-scale gravity wave spectrum on the ocean surface using a two frequency (Delta k) microwave scatterometer has been demonstrated from stationary platforms and proposed from moving platforms. This measurement takes advantage of Bragg type resonance matching between the electromagnetic wavelength at the difference frequency and the length of the large-scale surface waves. A prominent resonance appears in the cross product power spectral density (PSD) of the two backscattered signals. Ku-Band aircraft scatterometer measurements were conducted by NASA in the North Sea during the 1979 Maritime Remote Sensing (MARSEN) experiment. Typical examples of cross product PSD's computed from the MARSEN data are presented. They demonstrate strong resonances whose frequency and bandwidth agree with the surface characteristics and the theory. Directional modulation spectra of the surface reflectivity are compared to the gravity wave spectrum derived from surface truth measurements.

  12. A HIGH-FREQUENCY TYPE II SOLAR RADIO BURST ASSOCIATED WITH THE 2011 FEBRUARY 13 CORONAL MASS EJECTION

    SciTech Connect

    Cho, K.-S.; Kim, R.-S.; Gopalswamy, N.; Kwon, R.-Y.; Yashiro, S.

    2013-03-10

    We examine the relationship between the high-frequency (425 MHz) type II radio burst and the associated white-light coronal mass ejection (CME) that occurred on 2011 February 13. The radio burst had a drift rate of 2.5 MHz s{sup -1}, indicating a relatively high shock speed. From SDO/AIA observations we find that a loop-like erupting front sweeps across high-density coronal loops near the start time of the burst (17:34:17 UT). The deduced distance of shock formation (0.06 Rs) from the flare center and speed of the shock (1100 km s{sup -1}) using the measured density from SDO/AIA observations are comparable to the height (0.05 Rs, from the solar surface) and speed (700 km s{sup -1}) of the CME leading edge observed by STEREO/EUVI. We conclude that the type II burst originates even in the low corona (<59 Mm or 0.08 Rs, above the solar surface) due to the fast CME shock passing through high-density loops.

  13. Magnetothermoacoustics from magnetic nanoparticles by short bursting or frequency chirped alternating magnetic field: A theoretical feasibility analysis

    PubMed Central

    Piao, Daqing; Towner, Rheal A.; Smith, Nataliya; Chen, Wei R.

    2013-01-01

    Purpose: To propose an alternative method of thermoacoustic wave generation based on heating of magnetic nanoparticles (MNPs) using alternating magnetic field (AMF). Methods: The feasibility of thermoacoustic wave generation from MNPs by applying a short-burst of AMF or a frequency-modulated AMF is theoretically analyzed. As the relaxation of MNPs is strongly dependent upon the amplitude and frequency of AMF, either an amplitude modulated, fixed frequency AMF (termed time-domain AMF) or a frequency modulated, constant amplitude AMF (termed frequency-domain AMF) will result in time-varying heat dissipation from MNPs, which has the potential to generate thermoacoustic waves. Following Rosensweig's model of specific power loss of MNPs in a steady-state AMF, the time-resolved heat dissipations of MNPs of superparamagnetic size when exposed to a short bursting of AMF and/or to a linearly frequency chirped AMF are derived, and the resulted acoustic propagation is presented. Based on experimentally measured temperature-rise characteristics of a superparamagnetic iron-oxide nanoparticle (SPION) matrix in a steady-state AMF of various frequencies, the heat dissipations of the SPION under time-domain and frequency-domain AMF configurations that could have practical utility for thermoacoustic wave generation are estimated. Results: The initial rates of the temperature-rise of the SPION matrix were measured at an iron-weight concentration of 0.8 mg/ml and an AMF frequency of 88.8 kHz to 1.105 MHz. The measured initial rates of temperature-rise were modeled by Rosensweig's theory, and projected to 10 MHz AMF frequency, at which a 1 μs bursting corresponding to a 1.55 mm axial resolution of acoustic detection could contain 10 complete cycles of AMF oscillation and the power dissipation is approximately 84 times of that at 1 MHz. Exposing the SPION matrix to a 1 μs bursting of AMF at 10 MHz frequency and 100 Oe field intensity would produce a volumetric heat dissipation of 7

  14. Frequency Drift Rate Investigation of Solar Radio Burst Type II Due to Coronal Mass Ejections Occurrence on 4th November 2015 Captured by CALLISTO at Sumedang-Indonesia

    NASA Astrophysics Data System (ADS)

    Batubara, M.; Manik, T.; Suryana, R.; Lathif, M.; Sitompul, P.; Zamzam, M.; Mumtahana, F.

    2017-03-01

    The formations type of solar radio bursts can be known base on the frequency range that is detected. The CALLISTO system works with a wide band of the frequency making it possible to detect several types of solar burst. Indonesia exactly at Sumedang, CALLISTO system detected the formation of solar radio bursts forms of type II for the first time on 5 November 2014. On the other side, CALLISTO spectrometer detects and traces the phenomenon of CME (Coronal Mass Ejections) which causes the solar radio burst type II occurrence. In this paper will be calculated frequency drift rate during the occurrence of solar radio bursts of type II phenomenon on 4th November 2015 at 03:30 UT. The results of these calculations will be discussed as a related study of drift rate during the phenomenon of burst type II radio bursts associated with CME. The obtained drift rate during the solar radio bursts events above 2.8 MHz / s with low drift rate so that the speed of the CME that occurred only about 790 km / s as shown from LASCO.

  15. Detailed Analysis of the Pulsations During and After Bursts from the Bursting Pulsar (GROJ1744-28)

    NASA Technical Reports Server (NTRS)

    Woods, Peter M.; Kouveliotou, Chryssa; vanParadijs, Jan; Koshut, Thomas M.; Finger, Mark H.; Briggs, Michael S.; Fishman, G. J.; Lewin, W. H. G.

    2000-01-01

    The hard X-ray bursts observed during both major outbursts of the Bursting Pulsar (GRO J1744-28) show pulsations near the neutron star spin frequency with an enhanced amplitude relative to that of the persistent emission. Consistent with previous work, we find that the pulsations within bursts lag behind their expected arrival times based upon the persistent pulsar ephemeris. For an ensemble of 1293 bursts recorded with the Burst and Transient Source Experiment, the average burst pulse time delay (DELTA t (sub FWHM)) is 61.0 plus or minus 0.8 ms in the 25 - 50 keV energy range and 72 plus or minus 5 ms in the 50 - 100 keV band. The residual time delay (DELTA t (sub resid)) from 10 to 240 s following the start of the burst is 18.1 plus or minus 0.7 ms (25 - 50 keV). A significant correlation of the average burst time delay with burst peak flux is found. Our results are consistent with the model of the pulse time lags presented by Miller (1996).

  16. EEG synchronization characteristics of functional connectivity and complex network properties of memory maintenance in the delta and theta frequency bands.

    PubMed

    Tóth, Brigitta; Boha, Roland; Pósfai, Márton; Gaál, Zsófia Anna; Kónya, Anikó; Stam, Cornelis Jan; Molnár, Márk

    2012-03-01

    Task-dependent changes of nonlinear-linear synchronization features and graph theoretical properties of the delta and theta frequencies were analyzed in the present EEG study that were related to episodic memory maintenance processes. Synchronization was found to increase with respect to both the delta and theta bands within the frontal and parietal areas and also between these regions. Results of graph theoretical analysis indicated a task-related shift towards small-world network topology in the theta band.

  17. Search for high frequency gravitational-wave bursts in the first calendar year of LIGO's fifth science run

    SciTech Connect

    Abbott, B. P.; Abbott, R.; Adhikari, R.; Anderson, S. B.; Araya, M.; Armandula, H.; Aso, Y.; Ballmer, S.; Barton, M. A.; Betzwieser, J.; Billingsley, G.; Black, E.; Blackburn, J. K.; Bork, R.; Boschi, V.; Brooks, A. F.; Cannon, K. C.; Cardenas, L.; Cepeda, C.; Chalermsongsak, T.

    2009-11-15

    We present an all-sky search for gravitational waves in the frequency range 1 to 6 kHz during the first calendar year of LIGO's fifth science run. This is the first untriggered LIGO burst analysis to be conducted above 3 kHz. We discuss the unique properties of interferometric data in this regime. 161.3 days of triple-coincident data were analyzed. No gravitational events above threshold were observed and a frequentist upper limit of 5.4 year{sup -1} on the rate of strong gravitational-wave bursts was placed at a 90% confidence level. Implications for specific theoretical models of gravitational-wave emission are also discussed.

  18. Light Echos in Kerr Geometry: A Source of High Frequency QPOs from Random X-ray Bursts

    NASA Technical Reports Server (NTRS)

    Fukumura, K.; Kazanas, D.

    2008-01-01

    We propose that high frequency quasi-periodic oscillations (HFQPOs) can be produced from randomly-formed X-ray bursts (flashes) by plasma interior to the ergosphere of a rapidly-rotating black hole. We show by direct computation of their orbits that the photons comprising the observed X-ray light curves, if due to a multitude of such flashes, are affected significantly by the black hole's dragging of inertial frames; the photons of each such burst arrive to an observer at infinity in multiple (double or triple), distinct 'bunches' separated by a roughly constant time lag of t/M approximately equal to 14, regardless of the bursts' azimuthal position. We argue that every other such 'bunch' represents photons that follow trajectories with an additional orbit around the black hole at the photon circular orbit radius (a photon 'echo'). The presence of this constant lag in the response function of the system leads to a QPO feature in its power density spectra, even though the corresponding light curve consists of a totally stochastic signal. This effect is by and large due to the black hole spin and is shown to gradually diminish as the spin parameter a decreases or the radial position of the burst moves outside the static limit surface (ergosphere). Our calculations indicate that for a black hole with Kerr parameter of a/M=0.99 and mass of M=10*Msun the QPO is expected at a frequency of approximately 1.3-1.4 kHz. We discuss the plausibility and observational implications of our model/results as well as its limitations.

  19. Delta-sarcoglycan gene polymorphism frequency in Amerindian and Mestizo populations of Mexico.

    PubMed

    Ordoñez-Razo, Rosa María; Canizales-Quinteros, Samuel; Rodríguez-Cruz, Maricela; Peñaloza, Rosenda; Minauro-Sanmiguel, Fernando; Canto-Cetina, Thelma; Canto, Patricia; Coral-Vázquez, Ramón; Salamanca-Gómez, Fabio

    2010-04-01

    Mutations on the delta-sarcoglycan gene have been associated with the development of both hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy. Recently, the polymorphism c.-94C>G was associated with HCM in Japanese patients. The aim of our study was to evaluate the frequency of c.-94C>G polymorphism in Mexican-Amerindian and Mexican-Mestizo populations. We analyzed the frequency of this polymorphism in 165 Mexican-Amerindian individuals (23 Triquis, 25 Zapotecos, 24 Mayas, 41 Nahuas, and 52 Mixtecos) and 100 unrelated Mexican-Mestizos. Allele frequencies were similar in all Amerindian groups (0.33 Triquis, 0.54 Zapotecos, 0.54 Mayas, 0.46 Nahuas, and 0.49 Mixtecos). When compared with Mexican-Mestizos, only Triquis were different (p = 0.00742). However, when comparing the total sample of the Amerindian population with the Mestizos, the difference was not significant (p = 0.12225). Allele frequencies of Mexican populations were higher than in Asians and less than African and European populations (p < 0.05). These data show that the distribution of the C allele is higher in Mexican populations studied and consequently it is necessary to define if this may be associated with genetic susceptibility for HCM in the Mexican patients.

  20. Evidence for Harmonic Content and Frequency Evolution of Oscillations During the Rising Phase of X-ray Bursts From 4U 1636-536

    NASA Technical Reports Server (NTRS)

    Bgattacharyya, Sudip; Strohmayer, E.

    2005-01-01

    We report on a study of the evolution of burst oscillation properties during the rising phase of X-ray bursts from 4U 1636-536 observed with the proportional counter array (PCA) on board the Rossi X-Ray Timing Explorer (RXTE) . We present evidence for significant harmonic structure of burst oscillation pulses during the early rising phases of bursts. This is the first such detection in burst rise oscillations, and is very important for constraining neutron star structure parameters and the equation of state models of matter at the core of a neutron star. The detection of harmonic content only during the initial portions of the burst rise is consistent with the theoretical expectation that with time the thermonuclear burning region becomes larger, and hence the fundamental and harmonic amplitudes both diminish. We also find, for the first time from this source, strong evidence of oscillation frequency increase during the burst rise. The timing behavior of harmonic content, amplitude, and frequency of burst rise oscillations may be important in understanding the spreading of thermonuclear flames under the extreme physical conditions on neutron star surfaces.

  1. Direction of Arrival Measurements of Auroral Medium Frequency Burst Radio Emissions at Toolik Lake, AK

    NASA Astrophysics Data System (ADS)

    Bunch, N. L.; Labelle, J. W.; Hughes, J. M.; Weatherwax, A. T.; Ye, S.; Lummerzheim, D.

    2007-12-01

    MF burst is an impulsive radio emission of auroral origin detected by ground-based instruments approximately between 1,300 and 3,700 kHz, and associated with substorm onsets. Its exact generation mechanism is unknown, though it has been speculated that it arises from mode conversion radiation. To discover the generation mechanism and the relation of MF burst to auroral processes, Dartmouth has deployed radio interferometers in Alaska, Northern Canada, Greenland, and Antarctica, including a three-element interferometer deployed at Toolik Lake Field Station in Alaska in 2006. This instrument measured spectra, amplitudes, and directions of arrival (DOA's) of over 47 MF burst events occurring between November 30, 2006 and May 26, 2007. These represent the first DOA measurements ever reported for the impulsive MF burst phenomenon. Preliminary analysis shows that the events originated from a wide range of directions in the sky, with all azimuths represented in the distribution of DOA's. The DOA of each individual event is well-defined, however. Many events show apparent motion, with southward motions more common than northward among the subset of events analyzed so far. Some of the events were detected simultaneously on an interferometer deployed at Kaktovik, Alaska, 400 km away. The all-sky imager at Toolik Lake was also operational for some events. Further analysis of these data promises to reveal first information about the locations and motions of MF burst sources, a first step towards discovering the generation mechanism of this mysterious radio emission and its relation to auroral processes.

  2. Frequency of the CCR5-delta32 allele in Brazilian populations: A systematic literature review and meta-analysis.

    PubMed

    Silva-Carvalho, Wlisses Henrique Veloso; de Moura, Ronald Rodrigues; Coelho, Antonio Victor Campos; Crovella, Sergio; Guimarães, Rafael Lima

    2016-09-01

    The CCR5 is a chemokine receptor widely expressed by several immune cells that are engaged in inflammatory responses. Some populations have individuals exhibiting a 32bp deletion in the CCR5 gene (CCR5-delta32) that produces a truncated non-functional protein not expressed on the cell surface. This polymorphism, known to be associated with susceptibility to infectious and inflammatory diseases, such as osteomyelitis, pre-eclampsia, systemic lupus erythematous, juvenile idiopathic arthritis, rheumatoid arthritis and HIV/AIDS, is more commonly found in European populations with average frequency of 10%. However, it is also possible to observe a significant frequency in other world populations, such as the Brazilian one. We performed a systematic review and meta-analysis of CCR5-delta32 genetic association studies in Brazilian populations throughout the country to estimate the frequency of this polymorphism. We also compared CCR5-delta32 frequencies across Brazilian regions. The systematic literature reviewed studies involving delta32 allele in Brazilian populations published from 1995 to 2015. Among the reviewed literature, 25 studies including 30 Brazilian populations distributed between the North, Northeast, South and Southeast regions were included in our meta-analysis. We observed an overall allelic frequency of 4% (95%-CI, 0.03-0.05), that was considered moderate and, notably, higher than some European populations, such as Cyprus (2.8%), Italy (3%) and Greece (2.4%). Regarding the regional frequency comparisons between North-Northeast (N-NE) and South-Southeast (S-SE) regions, we observed an allelic frequency of 3% (95%-CI, 0.02-0.04) and 4% (95%-CI, 0.03-0.05), respectively. The populations from S-SE regions had a slightly higher CCR5-delta32 frequency than N-NE regions (OR=1.41, p=0.002). Although there are several studies about the CCR5-delta32 polymorphism and its effect on the immune response of some infectious diseases, this report is the first meta

  3. Quantification of cell membrane permeability induced by monopolar and high-frequency bipolar bursts of electrical pulses.

    PubMed

    Sweeney, Daniel C; Reberšek, Matej; Dermol, Janja; Rems, Lea; Miklavčič, Damijan; Davalos, Rafael V

    2016-11-01

    High-frequency bipolar electric pulses have been shown to mitigate undesirable muscle contraction during irreversible electroporation (IRE) therapy. Here, we evaluate the potential applicability of such pulses for introducing exogenous molecules into cells, such as in electrochemotherapy (ECT). For this purpose we develop a method for calculating the time course of the effective permeability of an electroporated cell membrane based on real-time imaging of propidium transport into single cells that allows a quantitative comparison between different pulsing schemes. We calculate the effective permeability for several pulsed electric field treatments including trains of 100μs monopolar pulses, conventionally used in IRE and ECT, and pulse trains containing bursts or evenly-spaced 1μs bipolar pulses. We show that shorter bipolar pulses induce lower effective membrane permeability than longer monopolar pulses with equivalent treatment times. This lower efficiency can be attributed to incomplete membrane charging. Nevertheless, bipolar pulses could be used for increasing the uptake of small molecules into cells more symmetrically, but at the expense of higher applied voltages. These data indicate that high-frequency bipolar bursts of electrical pulses may be designed to electroporate cells as effectively as and more homogeneously than conventional monopolar pulses.

  4. A new class of solar burst with MM-wave emission but only at the highest frequency (90 GHz)

    NASA Technical Reports Server (NTRS)

    Kaufmann, P.; Correia, E.; Costa, J. E. R.; Vaz, A. M. Z.; Dennis, B. R.

    1984-01-01

    High sensitivity and high time resolution solar observations at 90 GHz (lambda = 3.3 mm) have identified a unique impulsive burst on May 21, 1984 with emission that was more intense at this frequency than at lower frequencies. The first major time structure of the burst was over 10 times more intense at 90 GHz than at 30 GHz, 7 GHz, or 2.8 GHz.Only 6 seconds later, the 30 GHz impulsive structures started to be observed but still with lower intensity than at 90 GHz. Hard X-ray time structures at energies above 25 keV were almost identical to the 90 GHZ structures (to better than one second). All 90 GHz major time structures consisted of trains of multiple subsecond pulses with rise times as short as 0.03 sec and amplitudes large compared to the mean flux. When detectable, the 30 GHz subsecond pulses had smaller relative amplitude and were in phase with the corresponding 90 GHz pulses.

  5. Putative EEG measures of social anxiety: Comparing frontal alpha asymmetry and delta-beta cross-frequency correlation.

    PubMed

    Harrewijn, A; Van der Molen, M J W; Westenberg, P M

    2016-12-01

    The goal of the present study was to examine whether frontal alpha asymmetry and delta-beta cross-frequency correlation during resting state, anticipation, and recovery are electroencephalographic (EEG) measures of social anxiety. For the first time, we jointly examined frontal alpha asymmetry and delta-beta correlation during resting state and during a social performance task in high (HSA) versus low (LSA) socially anxious females. Participants performed a social performance task in which they first watched and evaluated a video of a peer, and then prepared their own speech. They believed that their speech would be videotaped and evaluated by a peer. We found that HSA participants showed significant negative delta-beta correlation as compared to LSA participants during both anticipation of and recovery from the stressful social situation. This negative delta-beta correlation might reflect increased activity in subcortical brain regions and decreased activity in cortical brain regions. As we hypothesized, no group differences in delta-beta correlation were found during the resting state. This could indicate that a certain level of stress is needed to find EEG measures of social anxiety. As for frontal alpha asymmetry, we did not find any group differences. The present frontal alpha asymmetry results are discussed in relation to the evident inconsistencies in the frontal alpha asymmetry literature. Together, our results suggest that delta-beta correlation is a putative EEG measure of social anxiety.

  6. Structure of proton centers and associated nonthermal bursts at microwave frequencies

    NASA Technical Reports Server (NTRS)

    Enome, S.; Tanaka, H.

    1973-01-01

    A very broad band of electromagnetic radiation is emitted during solar flares, especially at the explosive phase. The existence of a large variety of plasmas with various densities and a wide range of temperatures or energies is proposed as the initiating agent. The manner in which the plasmas are heated and accelerated to subrelativistic and relativistic energies is discussed. Observational evidence on the characteristics of active regions which produced proton flares and on the structure of the associated nonthermal microwave bursts of the sun is presented. The behavior of subrelativistic electrons on the sun is described.

  7. Gamma-ray burst constraints on the galactic frequency of extrasolar Oort Clouds

    NASA Technical Reports Server (NTRS)

    Shull, J. Michael; Stern, S. Alan

    1995-01-01

    With the strong Compton Gamma-Ray Observatory/Burst and Transient Source Experiment (CGRO/BATSE) evidence that most gamma-ray bursts do not come from galactic neutron stars, models involving the accretion of a comet onto a neutron star (NS) no longer appear to be strong contenders for explaining the majority of bursts. If this is the case, then it is worth asking whether the lack of an observed galactic gamma-ray burst population provides a useful constraint on the number of comets and comet clouds in the galaxy. Owing to the previously unrecognized structural weakness of cometary nuclei, we find the capture cross sections for comet-NS events to be much higher than previously published estimates, with tidal breakup at distances R(sub b) approx. equals 4 x 10(exp 10) cm from the NS. As a result, impacts of comets onto field NSs penetrating the Oort Clouds of other stars are found to dominate all other galactic NS-comet capture rates by a factor of 100. This in turn predicts that if comet clouds are common, there should be a significant population of repeater sources with (1) a galactic distribution, (2) space-correlated repetition, and (3) a wide range of peak luminosities and luminosity time histories. If all main sequence stars have Oort Clouds like our own, we predict approximately 4000 such repeater sources in the Milky Way at any time, each repeating on time scales of months to years. Based on estimates of the sensitivity of the CGRO/BATSE instrument and assuming isotropic gamma-ray beaming from such events, we estimate that a population of approximately 20-200 of these galactic NS-Oort Cloud gamma-ray repeater sources should be detectable by CGRO. In addition, if giant planet formation is common in the galaxy, we estimate that the accretion of isolated comets injected to the interstellar medium by giant planet formation should produce an additional source of galactic, nonrepeating, events. Comparing these estimates to the 3-4 soft gamma-ray repeater sources

  8. High Frequency Burst Firing of Granule Cells Ensures Transmission at the Parallel Fiber to Purkinje Cell Synapse at the Cost of Temporal Coding

    PubMed Central

    van Beugen, Boeke J.; Gao, Zhenyu; Boele, Henk-Jan; Hoebeek, Freek; De Zeeuw, Chris I.

    2013-01-01

    Cerebellar granule cells (GrCs) convey information from mossy fibers (MFs) to Purkinje cells (PCs) via their parallel fibers (PFs). MF to GrC signaling allows transmission of frequencies up to 1 kHz and GrCs themselves can also fire bursts of action potentials with instantaneous frequencies up to 1 kHz. So far, in the scientific literature no evidence has been shown that these high-frequency bursts also exist in awake, behaving animals. More so, it remains to be shown whether such high-frequency bursts can transmit temporally coded information from MFs to PCs and/or whether these patterns of activity contribute to the spatiotemporal filtering properties of the GrC layer. Here, we show that, upon sensory stimulation in both un-anesthetized rabbits and mice, GrCs can show bursts that consist of tens of spikes at instantaneous frequencies over 800 Hz. In vitro recordings from individual GrC-PC pairs following high-frequency stimulation revealed an overall low initial release probability of ~0.17. Nevertheless, high-frequency burst activity induced a short-lived facilitation to ensure signaling within the first few spikes, which was rapidly followed by a reduction in transmitter release. The facilitation rate among individual GrC-PC pairs was heterogeneously distributed and could be classified as either “reluctant” or “responsive” according to their release characteristics. Despite the variety of efficacy at individual connections, grouped activity in GrCs resulted in a linear relationship between PC response and PF burst duration at frequencies up to 300 Hz allowing rate coding to persist at the network level. Together, these findings support the hypothesis that the cerebellar granular layer acts as a spatiotemporal filter between MF input and PC output (D’Angelo and De Zeeuw, 2009). PMID:23734102

  9. Increase in nitric oxide and cyclic GMP of rat cerebellum by radio frequency burst-type electromagnetic field radiation.

    PubMed Central

    Miura, M; Takayama, K; Okada, J

    1993-01-01

    1. Using rat cerebellum supernatant, the effects of radio frequency (RF) burst-type electromagnetic (EM) field radiation on the production of cyclic GMP were examined under various conditions. The radiation was generated by a generator coil, and set at a 10 MHz radiation frequency, a 50% burst time, a 10 kHz burst rate and a 5 V peak-to-peak generator voltage. 2. When the cerebellum supernatant was incubated with both exogenous L-arginine (nitric oxide (NO) donor) and NADPH, and irradiated by an RF burst-type EM field, the production of cyclic GMP was increased significantly from a level of 21-22 nmol min-1 (g tissue)-1 to 25-26 nmol min-1 (g tissue)-1. By contrast, such an effect was not found when the cerebellum supernatant was irradiated by an RF volley-type EM field. 3. When neither L-arginine nor NADPH were added to the cerebellum supernatant, the production of cyclic GMP was lowered to a level of 6 nmol min-1 (g tissue)-1 and the radiation effect was not found. When the cerebellum supernatant was chelated with EDTA, the production of cyclic GMP was lowered to a level of 7 nmol min-1 (g tissue)-1 and the radiation effect was not found. 4. Incubation with Methylene Blue, a guanylate cyclase inhibitor, lowered the production of cyclic GMP to a level of 10-12 nmol min-1 (g tissue)-1, and the radiation effect did not occur. On incubation with a NO synthase inhibitor, either NG-methyl-L-arginine or N omega-nitro-L-arginine methyl ester, the production of cyclic GMP was lowered to a level of 10-12 nmol min-1 (g tissue)-1 or 5-9 nmol min-1 (g tissue)-1 respectively, and the radiation effect was not observed. 5. Using electrochemical NO probes, the production of NO in the cerebellum supernatant was detected. The concentration of NO increased gradually after the onset of the EM field radiation. The radiation effect persisted, and reached a maximum after the cessation of the radiation. 6. In an in vivo study, the arterioles of the frog web were dilated by the radiation

  10. GEOTAIL and POLAR Observations of Auroral Kilometric Radiation and Terrestrial Low Frequency Bursts and their Relationship to Energetic Particles, Auroras, and Other Substorm Phenomena

    NASA Technical Reports Server (NTRS)

    Anderson, R . R.; Gurnett, D. A.; Frank, L. A.; Thomsen, Michelle F.; Parks, G. K.; Brittnacher, M. J.; Spann, James F., Jr.; Imhoff, W. L.; Mobilia, J. H.

    1999-01-01

    Terrestrial low frequency (LF) bursts are plasma wave phenomena that appear to be a part of the low frequency end of the auroral kilometric radiation (AKR) spectrum and are observed during strong substorms, GEOTAIL and POLAR plasma wave observations from within the magnetosphere show that the AKR increases in intensity and its lower frequency limits decrease when LF bursts are observed. The first is expected as it is shows substorm onset and the latter indicates that the AKR source region is expanding to higher altitudes. Images from the POLAR VIS Earth Camera operating in the far-UV range and the POLAR UVI experiment usually feature an auroral brightening and an expansion of the aurora to higher latitudes at the time of the LF bursts. Enhanced fluxes of X-rays from precipitating electrons have also been observed by POLAR PIXIE. High resolution ground Abstract: magnetometer data from the CANOPUS and IMAGE networks show that the LF bursts occur when the expansive phase onset signatures are most intense. The ground magnetometer data and the CANOPUS meridian scanning photometer data sometimes show that during the LF burst events the expansive phase onset starts at unusually low latitudes and moves poleward. Large injections of energetic protons and electrons have also been detected by the GOES and LANL geosynchronous satellites during LF burst events. While most of the auroral brightenings and energetic particle injections associated with the LF bursts occur near local midnight, several have been observed as early as mid-afternoon. From these various measurements, we are achieving a better understanding of the plasma and particle motions during substorms that are associated with the generation and propagation of terrestrial LF bursts

  11. Cystic fibrosis in the Basque country: high frequency of mutation delta F508 in patients of Basque origin.

    PubMed

    Casals, T; Vázquez, C; Lázaro, C; Girbau, E; Giménez, F J; Estivill, X

    1992-02-01

    The Basque population is one of the oldest populations of Europe. It has been suggested that the Basques arose from a population established in western Europe during the late Paleolithic Age. The Basque language (Euskera) is a supposedly pre-Indo-European language that originates from the first settlers of Europe. The variable distribution of the major cystic fibrosis (CF) mutation (delta F508 deletion) in Europe, with higher frequencies of the mutation in northern Europe and lower frequencies in southern Europe, has suggested that the delta F508 mutation was spread by early farmers migrating from the Middle East during the Neolithic period. We have studied 45 CF families from the Basque Country, where the incidence of CF is approximately 1/4,500. The birthplaces of the parents and grandparents have been traced and are distributed according to their origin as Basque or Mixed Basque. The frequency of the delta F508 mutation in the chromosomes of Basque origin is 87%, compared with 58% in those of Mixed Basque origin. The analysis of haplotypes, both with markers closely linked to the CF gene and with intragenic markers, suggests that the delta F508 mutation was not spread by the Indo-European invasions but was already present in Europe more than 10,000 years ago, during the Paleolithic period.

  12. Gamma-ray burst constraints on the galactic frequency of extra-solar Oort clouds

    NASA Technical Reports Server (NTRS)

    Shull, J. Michael; Stern, S. Alan

    1994-01-01

    With the strong CGRO/BATSE evidence that most gamma-ray bursts do not come from galactic neutron stars, models involving the accretion of a comet onto a neutron star (NS) no longer appear to be strong contenders for explaining the majority of bursts. If this is the case, then it is worth asking whether the lack of an observed galactic gamma-ray burst population provides a useful constraint on the number of comets and comet clouds in the galaxy. Owing to the previously unrecognized structural weakness of cometary nuclei, we find the capture cross sections for comet-NS events to be much higher than previously published estimates, with tidal breakup at distances R(sub b) approximately equals to 4 x 10(exp 10) cm from the NS. As a result, impacts of comets onto field NS's penetrating the Oort Clouds of other stars are found to dominate all other galactic NS-comet capture rates by a factor of 100. This in turn predicts that if comet clouds are common, there should be a significant population of repeater sources with (1) a galactic distribution, (2) space-correlated repetition, and (3) a wide range of peak luminosities and luminosity time histories. If all main sequences stars have Oort Clouds like our own, we predict approximately 4000 such repeater sources in the Milky Way at any time, each repeating on timescales of months to years. Based on estimates of the sensitivity of the CGRO/BATSE instrument and assuming isotropic gamma-ray beaming from such events, we estimate that a population of approximately 20-200 of these galactic NS-Oort Cloud gamma-ray repeater sources should be detectable by CGRO. In addition, if giant planet formation is common in the galaxy, we estimate that the accretion of isolated comets injected to the interstellar medium by giant planet formation should produce an additional source of galactic, nonrepeating events. Comparing these estimates to the three to four soft gamma-ray repeater sources detected by BATSE, one is forced to conclude that (1

  13. The Relationship between Coronal Mass Ejections and Low Frequency Radio Bursts in the Low Corona

    NASA Astrophysics Data System (ADS)

    Gallagher, Peter; Carley, Eoin; Byrne, Jason; Long, David; Zucca, Pietro; Bloomfield, Shaun; McCauley, Joseph

    Cosmic rays and solar energetic particles may be accelerated to relativistic energies by shock waves in astrophysical plasmas. On the Sun, shocks and particle acceleration are often associated with the eruption of coronal mass ejections (CMEs). However, the physical relationship between CMEs and shock particle acceleration is not well understood. Here, we use extreme ultraviolet, radio and white-light imaging of a solar eruptive event on 22 September 2011 to show that a CME-induced shock was coincident with a coronal wave and an intense metric radio burst generated by intermittent acceleration of electrons to kinetic energies of 2-46 keV (0.1-0.4 c). Our observations show that plasmoid-driven quasiperpendicular shocks are capable of producing quasiperiodic acceleration of electrons, an effect consistent with a turbulent or rippled plasma shock surface.

  14. Heterogeneous populations of cells mediate spontaneous synchronous bursting in the developing hippocampus through a frequency-dependent mechanism.

    PubMed

    Menendez de la Prida, L; Sanchez-Andres, J V

    2000-01-01

    Under normal conditions, hippocampal slices from newborn rats and rabbits (postnatal days 0-8) show spontaneous synchronous bursts known as giant depolarizing potentials. These bursts are recorded from CA3, CA1 and the fascia dentata in both intact slices and isolated hipocampal regions. Giant depolarizing potentials are network-driven events resulting from the synergistic activation of N-methyl-D-aspartate, alpha-amino-3-hydroxy-5-methyl-4-isoxadepropionate and GABA(A) receptors, the latter playing an excitatory role. Recently, we showed that they spontaneously emerge in an all-or-none manner after the increase of synaptic and cellular activity beyond a threshold frequency [Menendez de la Prida L. and Sanchez-Andres J. V. (1999) J. Neurophysiol. 82, 202-208]. Under this framework, background levels of spontaneous activity at individual neurons build up network synchronization 100-300ms prior to the onset of giant depolarizing potentials. However, the role of distinct cellular populations and connectivity in determining the threshold frequency has not been examined. By performing simultaneous intracellular recordings from pyramidal cells, non-pyramidal cells and interneurons, we investigated their participation in the generation of giant depolarizing potentials. Electrodes containing Neurobiotin were used to examine the cellular morphology. We found that giant depolarizing potentials were not initiated from a single pacemaker cellular group; instead, they involved recurrent cooperation among these groups, which contributed differently according to their intrinsic firing capability. In all the neurons examined, the onset of these bursts took place in an all-or-none frequency-dependent manner, both spontaneously (depending on the frequency of the excitatory postsynaptic potentials) or when triggered by extracellular stimulation. The CA3 threshold of frequency was at 12Hz in both pyramidal cells and interneurons, while in the fascia dentata it was 17Hz. The

  15. The Subthalamic Nucleus becomes a Generator of Bursts in the Dopamine-Depleted State. Its High Frequency Stimulation Dramatically Weakens Transmission to the Globus Pallidus

    PubMed Central

    Ammari, Rachida; Bioulac, Bernard; Garcia, Liliana; Hammond, Constance

    2011-01-01

    Excessive burst firing in the dopamine-depleted basal ganglia correlates with severe motor symptoms of Parkinson's disease that are attenuated by high frequency electrical stimulation of the subthalamic nucleus (STN). Here we test the hypothesis that pathological bursts in dopamine-deprived basal ganglia are generated within the STN and transmitted to globus pallidus neurons. To answer this question we recorded excitatory synaptic currents and potentials from subthalamic and pallidal neurons in the basal ganglia slice (BGS) from dopamine-depleted mice while continuously blocking GABAA receptors. In control mice, a single electrical stimulus delivered to the internal capsule or the rostral pole of the STN evoked a short duration, small amplitude, monosynaptic EPSC in subthalamic neurons. In contrast, in the dopamine-depleted BGS, this monosynaptic EPSC was amplified and followed by a burst of polysynaptic EPSCs that eventually reverberated three to seven times, providing a long lasting response that gave rise to bursts of EPSCs and spikes in GP neurons. Repetitive (10–120 Hz) stimulation delivered to the STN in the dopamine-depleted BGS attenuated STN-evoked bursts of EPSCs in pallidal neurons after several minutes of stimulation but only high frequency (90–120 Hz) stimulation replaced them with small amplitude EPSCs at 20 Hz. We propose that the polysynaptic pathway within the STN amplifies subthalamic responses to incoming excitation in the dopamine-depleted basal ganglia, thereby transforming the STN into a burst generator and entraining pallidal neurons in pathogenic bursting activities. High frequency stimulation of the STN prevents the transmission of this pathological activity to globus pallidus and imposes a new glutamatergic synaptic noise on pallidal neurons. PMID:21716635

  16. Gravitational lensing, time delay, and gamma-ray bursts

    NASA Technical Reports Server (NTRS)

    Mao, Shude

    1992-01-01

    The probability distributions of time delay in gravitational lensing by point masses and isolated galaxies (modeled as singular isothermal spheres) are studied. For point lenses (all with the same mass) the probability distribution is broad, and with a peak at delta(t) of about 50 S; for singular isothermal spheres, the probability distribution is a rapidly decreasing function with increasing time delay, with a median delta(t) equals about 1/h month, and its behavior depends sensitively on the luminosity function of galaxies. The present simplified calculation is particularly relevant to the gamma-ray bursts if they are of cosmological origin. The frequency of 'recurrent' bursts due to gravitational lensing by galaxies is probably between 0.05 and 0.4 percent. Gravitational lensing can be used as a test of the cosmological origin of gamma-ray bursts.

  17. Burst Detector Sensitivity: Past, Present and Future

    NASA Technical Reports Server (NTRS)

    Band, David L.

    2005-01-01

    I compare the burst detection sensitivity of CGRO's BATSE, Swift's BAT, the GLAST Burst Monitor (GBM) and EXIST as a function of a burst s spectrum and duration. A detector's overall burst sensitivity depends on its energy sensitivity and set of accumulations times (Delta)t; these two factors shape the detected burst population. For example, relative to BATSE, the BAT s softer energy band decreases the detection rate of short, hard bursts, while the BAT s longer accumulation times increase the detection rate of long, soft bursts. Consequently, Swift is detecting long, low fluence bursts (2-3 x fainter than BATSE).

  18. Frequency of CCR5 delta-32 mutation in human immunodeficiency virus (HIV)-seropositive and HIV-exposed seronegative individuals and in general population of Medellin, Colombia.

    PubMed

    Díaz, F J; Vega, J A; Patiño, P J; Bedoya, G; Nagles, J; Villegas, C; Vesga, R; Rugeles, M T

    2000-01-01

    Repeated exposure to human immunodeficiency virus (HIV) does not always result in seroconversion. Modifications in coreceptors for HIV entrance to target cells are one of the factors that block the infection. We studied the frequency of Delta-32 mutation in ccr5 gene in Medellin, Colombia. Two hundred and eighteen individuals distributed in three different groups were analyzed for Delta-32 mutation in ccr5 gene by polymerase chain reaction (PCR): 29 HIV seropositive (SP), 39 exposed seronegative (ESN) and 150 individuals as a general population sample (GPS). The frequency of the Delta-32 mutant allele was 3.8% for ESN, 2.7% for GPS and 1.7% for SP. Only one homozygous mutant genotype (Delta-32/Delta-32) was found among the ESN (2.6%). The heterozygous genotype (ccr5/Delta-32) was found in eight GPS (5.3%), in one SP (3.4%) and in one ESN (2.6%). The differences in the allelic and genotypic frequencies among the three groups were not statistically significant. A comparison between the expected and the observed genotypic frequencies showed that these frequencies were significantly different for the ESN group, which indirectly suggests a protective effect of the mutant genotype (Delta-32/Delta-32). Since this mutant genotype explained the resistance of infection in only one of our ESN persons, different mechanisms of protection must be playing a more important role in this population.

  19. Frequencies of 32 base pair deletion of the (Delta 32) allele of the CCR5 HIV-1 co-receptor gene in Caucasians: a comparative analysis.

    PubMed

    Lucotte, Gérard

    2002-05-01

    The CCR5 gene encodes for the co-receptor for the major macrophage-tropics strains of human immunodeficiency virus (HIV-1), and a mutant allele of this gene (Delta 32) provide to homozygotes a strong resistance against infection by HIV. The frequency of the Delta 32 allele was investigated in 40 populations of 8842 non-infected subjects coming from Europe, the Middle-East and North Africa. A clear north-south decreasing gradient was evident for Delta 32 frequencies, with a significant correlation coefficient (r=0.83). The main frequency value of Delta 32 for Sweden, Norway, Denmark, Finland and Iceland (0.134) is significantly (chi(2)=63.818, P<0.001) highest than the Delta 32 mean value, indicating that probably the Vikings might have been instrumental in disseminating the Delta 32 allele during the eighth to the tenth centuries during historical times. Possibly variola virus has discriminated the Delta 32 carriers in Europe since the eighth century AD, explaining the high frequency of the Delta 32 allele in Europe today.

  20. On vortex bursting

    NASA Technical Reports Server (NTRS)

    Werle, H.

    1984-01-01

    Vortex bursting is studied by means of visualization. The physical behavior of the phenomenon is emphasized, and its similarity with boundary layer separation or wake bursting becomes apparent. The essential influence of an increasing pressure gradient on the initiation, the position and the type of bursting is clearly confirmed. The evolution of the phenomena as a function of several parameters is analyzed in the case of delta wings, alone or installed on aircraft models, and compared with the results of similar wind tunnel or flight tests.

  1. Land subsidence in the Yangtze River Delta, China revealed from multi-frequency SAR Interferometry

    NASA Astrophysics Data System (ADS)

    Li, Zhenhong; Motagh, Mahdi; Yu, Jun; Gong, Xulong; Wu, Jianqiang; Zhu, Yefei; Chen, Huogen; Zhang, Dengming; Xu, Yulin

    2014-05-01

    Land subsidence is a major worldwide hazard, and its principal causes are subsurface fluid withdrawal, drainage of organic soils, sinkholes, underground mining, hydrocompaction, thawing permafrost, and natural consolidation. Land subsidence causes many problems including: damage to public facilities such as bridges, roads, railroads, electric power lines, underground pipes; damage to private and public buildings; and in some cases of low-lying land, can increase the risk of coastal flooding from storm surges and rising sea-levels. In China, approximately 48600 km2 of land, an area roughly 30 times of the size of the Greater London, has subsided (nearly 50 cities across 16 provinces), and the annual direct economic loss is estimated to be more than RMB 100 million (~12 million). It is believed that the Suzhou-Wuxi-Changzhou region within the Yangtze River Delta is the most severely affected area for subsidence hazards in China. With its global coverage and all-weather imaging capability, Interferometric SAR (InSAR) is revolutionizing our ability to image the Earth's surface and the evolution of its shape over time. In this paper, an advanced InSAR time series technique, InSAR TS + AEM, has been employed to analysed ERS (C-band), Envisat (C-band) and TerraSAR-X (X-band) data collected over the Suzhou-Wuxi-Changzhou region during the period from 1992 to 2013. Validation with precise levelling and GPS data suggest: (1) the accuracy of the InSAR-derived mean velocity measurements is 1-3 mm/yr; (2) InSAR-derived displacements agreed with precise levelling with root mean square errors around 5 mm. It is evident that InSAR TS + AEM can be used to image the evolution of deformation patterns in the Suzhou-Wuxi-Changzhou region over time: the maximum mean velocity decreased from ~12 cm/yr during the period of 1992-1993 to ~2 cm/yr in 2003-2013. This is believed to be a result of the prohibition of groundwater use carried out by Jiangsu provincial government. The combination

  2. Evidence for recent selection of the CCR5-delta 32 deletion from differences in its frequency between Ashkenazi and Sephardi Jews.

    PubMed

    Maayan, S; Zhang, L; Shinar, E; Ho, J; He, T; Manni, N; Kostrikis, L G; Neumann, A U

    2000-08-01

    Recent studies have shown higher frequencies of the CCR5-delta 32 allele and the CCR5-delta 32/delta 32 genotype, which confers protection against HIV infection, in northern Europe as compared to Mediterranean countries. Here, we analyse the prevalence of CCR5-delta 32 in 922 HIV seronegative blood donors in Israel to verify its frequency in Jews of Ashkenazi and Sephardi origin. A significant difference (P < 0.001) was found between the CCR5-delta 32 allele frequency in Ashkenazi (13.8%) vs (4.9%) Jews. In contrast, no significant difference was observed in the frequency of the CCR2-641 mutation between Ashkenazi (9.2%) and Sephardi (13.4%) Jews. Using the Island model we calculate that a minimal genetic migration rate of 3% per generation would have been necessary if the higher CCR5-delta 32 prevalence in Ashkenazi is to be fully explained by mixing with the indigenous north-European populations. This putative migration rate is 20-fold higher than that currently estimated from other genes, and would correspond to a non-realistic minimal current admixture of 80%. Thus, our results suggest that a positive selection process for CCR5-delta 32 should have occurred in northern Europe at most a 1000 years ago, after the Ashkenazi Jews separated from their Sephardi kin and moved to north Europe.

  3. Attitudes and beliefs affect frequency of eating out in the Lower Mississippi Delta

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Attitudes and beliefs reflecting cultural values can have a positive or negative influence on eating behaviors. Eating out may negatively affect diet quality through increased fat intake and larger portion sizes. In a representative sample of the Lower Mississippi Delta (LMD) consisting of 1601 Af...

  4. Decomposing delta, theta, and alpha time–frequency ERP activity from a visual oddball task using PCA

    PubMed Central

    Bernat, Edward M.; Malone, Stephen M.; Williams, William J.; Patrick, Christopher J.; Iacono, William G.

    2008-01-01

    Objective Time–frequency (TF) analysis has become an important tool for assessing electrical and magnetic brain activity from event-related paradigms. In electrical potential data, theta and delta activities have been shown to underlie P300 activity, and alpha has been shown to be inhibited during P300 activity. Measures of delta, theta, and alpha activity are commonly taken from TF surfaces. However, methods for extracting relevant activity do not commonly go beyond taking means of windows on the surface, analogous to measuring activity within a defined P300 window in time-only signal representations. The current objective was to use a data driven method to derive relevant TF components from event-related potential data from a large number of participants in an oddball paradigm. Methods A recently developed PCA approach was employed to extract TF components [Bernat, E. M., Williams, W. J., and Gehring, W. J. (2005). Decomposing ERP time-frequency energy using PCA. Clin Neurophysiol, 116(6), 1314–1334] from an ERP dataset of 2068 17 year olds (979 males). TF activity was taken from both individual trials and condition averages. Activity including frequencies ranging from 0 to 14 Hz and time ranging from stimulus onset to 1312.5 ms were decomposed. Results A coordinated set of time–frequency events was apparent across the decompositions. Similar TF components representing earlier theta followed by delta were extracted from both individual trials and averaged data. Alpha activity, as predicted, was apparent only when time–frequency surfaces were generated from trial level data, and was characterized by a reduction during the P300. Conclusions Theta, delta, and alpha activities were extracted with predictable time-courses. Notably, this approach was effective at characterizing data from a single-electrode. Finally, decomposition of TF data generated from individual trials and condition averages produced similar results, but with predictable differences

  5. A Comparative Study of the Impact of Theta-Burst and High-Frequency Stimulation on Memory Performance

    PubMed Central

    Zhu, Yating; Wang, Rubin; Wang, Yihong

    2016-01-01

    The transformation of the information stored in the working memory into the system of long-term memory depends on the physiological mechanism, long-term potential (LTP). In a large number of experimental studies, theta-burst stimulation (TBS) and high-frequency stimulation (HFS) are LTP induction protocols. However, they have not been adapted to the model related to memory. In this paper, the improved Camperi–Wang (C–W) model with Ca2+ subsystem-induced bi-stability was adopted, and TBS and HFS were simulated to act as the initial stimuli of this working memory model. Evaluating the influence of stimuli properties (cycle, amplitude, duty ration) on memory mechanism of the model, it is found that both TBS and HFS can be adopted to activate working memory model and produce long-term memory. Moreover, the different impacts of two types of stimuli on the formation of long-term memory were analyzed as well. Thus, the importance of this study lies firstly in describing the link and interaction between working memory and long-term memory from the quantitative view, which provides a theoretical basis for the study of neural dynamics mechanism of long-term memory formation in the future. PMID:26869903

  6. A Search for Fast Radio Bursts at Low Frequencies with Murchison Widefield Array High Time Resolution Imaging

    NASA Astrophysics Data System (ADS)

    Tingay, S. J.; Trott, C. M.; Wayth, R. B.; Bernardi, G.; Bowman, J. D.; Briggs, F.; Cappallo, R. J.; Deshpande, A. A.; Feng, L.; Gaensler, B. M.; Greenhill, L. J.; Hancock, P. J.; Hazelton, B. J.; Johnston-Hollitt, M.; Kaplan, D. L.; Lonsdale, C. J.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.; Murphy, T.; Oberoi, D.; Prabu, T.; Udaya Shankar, N.; Srivani, K. S.; Subrahmanyan, R.; Webster, R. L.; Williams, A.; Williams, C. L.

    2015-12-01

    We present the results of a pilot study search for fast radio bursts (FRBs) using the Murchison Widefield Array (MWA) at low frequencies (139-170 MHz). We utilized MWA data obtained in a routine imaging mode from observations where the primary target was a field being studied for Epoch of Reionization detection. We formed images with 2 s time resolution and 1.28 MHz frequency resolution for 10.5 hr of observations, over 400 square degrees of the sky. We de-dispersed the dynamic spectrum in each of 372,100 resolution elements of 2 × 2 arcmin2, between dispersion measures of 170 and 675 pc cm-3. Based on the event rate calculations in Trott et al., which assume a standard candle luminosity of 8 × 1037 Js-1, we predict that with this choice of observational parameters, the MWA should detect (˜10, ˜2, ˜0) FRBs with spectral indices corresponding to (-2, -1, 0), based on a 7σ detection threshold. We find no FRB candidates above this threshold from our search, placing an event rate limit of \\lt 700 above 700 Jy ms per day per sky and providing evidence against spectral indices α \\lt -1.2 (S\\propto {ν }α ). We compare our event rate and spectral index limits with others from the literature. We briefly discuss these limits in light of recent suggestions that supergiant pulses from young neutron stars could explain FRBs. We find that such supergiant pulses would have to have much flatter spectra between 150 and 1400 MHz than have been observed from Crab giant pulses to be consistent with the FRB spectral index limit we derive.

  7. A Gamma-Ray Burst Trigger Toolkit

    NASA Technical Reports Server (NTRS)

    Band, David L.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    The detection rate of a gamma-ray burst detector can be increased by using a count rate trigger with many accumulation times DELTAt and energy bands DELTAE Because a burst's peak flux varies when averaged over different DELTAt and DELTAE the nominal sensitivity (the numerical value of the peak flux) of a trigger system is less important than how much fainter a burst could be at the detection threshold as DELTAt and DELTAE are changed. The relative sensitivity of different triggers can be quantified by referencing the detection threshold back to the peak flux for a fiducial value of DELTAt and DELTA E. This mapping between peak flux values for different sets of DELTAt and DELTAE varies from burst to burst. Quantitative estimates of the burst detection rate for a given detector and trigger system can be based on the observed rate at a measured peak flux value in this fiducial trigger. Predictions of a proposed trigger's burst detection rate depend on the assumed burst population, and these predictions can be wildly in error for triggers that differ significantly from previous missions. I base the fiducial rate on the BATSE observations: 550 bursts per sky above a peak flux of 0.3 ph per square centimeter per second averaged over DELTAt=1.024 sec and DELTAE=50-300 keV. Using a sample of 100 burst lightcurves I find that triggering on any value of DELTAt that is a multiple of 0.064 sec decreases the average threshold peak flux on the 1.024 sec timescale by a factor of 0.6. Extending DELTAE to lower energies includes the large flux of the X-ray background, increasing the background count rate. Consequently a low energy DELTAE is advantageous only for very soft bursts. Whether a large fraction of the population of bright bursts is soft is disputed; the new population of X-ray Flashes is soft but relatively faint.

  8. Energetic Particle Propagation in the Inner Heliosphere as Deduced from Low Frequency (less than 100 kHz) Observations of Type III Radio Bursts

    NASA Technical Reports Server (NTRS)

    Cane, H. V.; Erickson, W. C.

    2003-01-01

    Solar energetic particle (SEP) events are well-associated with solar flares. It is observed that the delay between the time of the flare and the first-arriving particles at a spacecraft increases with increasing difference between the flare longitude and the footpoint of the field line on which the spacecraft is located. This difference we call the "connection angle" and can be as large as approximately 120 deg. Recently it has been found that all SEP events are preceded by type III radio bursts. These bursts are plasma emission caused by the propagation of 2-50 keV flare electrons through the solar corona and into the solar wind. The drift of these type III radio bursts to lower and lower frequencies enables the propagation of the flare electrons to be traced from the Sun to about 1 AU. We have made an extensive analysis of the type III bursts associated with greater than 20 MeV proton events and find that, in most cases, the radio emission extends to the local plasma frequency when the energetic particles arrive within a few hours of the flare. We conclude that this emission at the lowest possible frequency is generated close to the spacecraft. We then use the time from when the burst started at the Sun to when it reached the local plasma frequency to infer the time it took the radio producing electrons to travel to the spacecraft. We find that these delay times are organized by the connection angle and correlate with the proton delay times. We also find that the differences between the radio delays at Wind and Ulysses are matched by differences in the relative arrival times of the energetic particles at the two spacecraft. The consistent timing between the relative arrival times of energetic electrons and protons and the start of the lowest frequency radio emissions suggests that the first arriving particles of both species are accelerated as part of the flare process and that they propagate to the spacecraft along trajectories similar to those of the lower

  9. Preliminary results on the apparent size of the sources of type III bursts observed at low frequencies

    NASA Technical Reports Server (NTRS)

    Alvarez, H.

    1976-01-01

    We present preliminary results on the apparent angular size of the sources of four type III bursts observed between 3500 and 50 kHz from the IMP-6 spacecraft. The observations were made with a dipole rotating in the plane of the ecliptic where the sources are assumed to be. The apparent angular sizes obtained are unexpectedly large. We discuss different explanations for the results. It seems that the scattering of radio waves by electron density inhomogeneities is the most likely cause. We report a temporal increase of the apparent angular size of the source during the burst lifetime for some bursts. From its characteristics it appears to be a real effect.

  10. The Effect of Contact Angles and Capillary Dimensions on the Burst Frequency of Super Hydrophilic and Hydrophilic Centrifugal Microfluidic Platforms, a CFD Study

    PubMed Central

    Kazemzadeh, Amin; Ganesan, Poo; Ibrahim, Fatimah; He, Shuisheng; Madou, Marc J.

    2013-01-01

    This paper employs the volume of fluid (VOF) method to numerically investigate the effect of the width, height, and contact angles on burst frequencies of super hydrophilic and hydrophilic capillary valves in centrifugal microfluidic systems. Existing experimental results in the literature have been used to validate the implementation of the numerical method. The performance of capillary valves in the rectangular and the circular microfluidic structures on super hydrophilic centrifugal microfluidic platforms is studied. The numerical results are also compared with the existing theoretical models and the differences are discussed. Our experimental and computed results show a minimum burst frequency occurring at square capillaries and this result is useful for designing and developing more sophisticated networks of capillary valves. It also predicts that in super hydrophilic microfluidics, the fluid leaks consistently from the capillary valve at low pressures which can disrupt the biomedical procedures in centrifugal microfluidic platforms. PMID:24069169

  11. Increased frequency of {gamma}{delta} T cells in cerebrospinal fluid and peripheral blood of patients with multiple sclerosis: Reactivity, cytotoxicity, and T cell receptor V gene rearrangements

    SciTech Connect

    Stinissen, P.; Vandevyver, C.; Medaer, R.

    1995-05-01

    Infiltrating {gamma}{delta} T cells are potentially involved in the central nervous system demyelination in multiple sclerosis (MS). To further study this hypothesis, we analyzed the frequency and functional properties of {gamma}{delta} T cells in peripheral blood (PB) and paired cerebrospinal fluid (CSF) of patients with MS and control subjects, including patients with other neurologic diseases (OND) and healthy individuals. The frequency analysis was performed under limiting dilution condition using rIL-2 and PHA. After PHA stimulation, a significantly increased frequency of {gamma}{delta} T cells was observed in PB and in CSF of MS patients as compared with PB and CSF of patients with OND. The frequency was represented equally in OND patients and normal individuals. Similarly, the IL-2-responsive {gamma}{delta} T cells occurred at a higher frequency in PB of MS than of control subjects. Forty-three percent of the {gamma}{delta} T cell clones isolates from PB and CSF of MS patients responded to heat shock protein (HSP70) but not HSP65, whereas only 2 of 30 control {gamma}{delta} T cell clones reacted to the HSP. The majority of the {gamma}{delta} T cell clones were able to induce non-MHC-restricted cytolysis of Daudi cells. All clones displayed a substantial reactivity to bacterial superantigens staphylococcal enterotoxin B and toxic shock syndrome toxin-1, irrespective of their {gamma}{delta} V gene usage. Furthermore, the {gamma}{delta} T cell clones expressed predominantly TCRDV2 and GV2 genes, whereas the clones derived from CSF of MS patients expressed either DV1 or DV2 genes. The obtained {gamma}{delta} clones, in general, represented rather heterogeneous clonal origins, even though a predominant clonal origin was found in a set of 10 {gamma}{delta} clones derived from one patient with MS. The present study provides new evidence supporting a possible role of {gamma}{delta} T cells in the secondary inflammatory processes in MS. 39 refs., 5 figs., 4 tabs.

  12. Propeller tone bursts

    NASA Technical Reports Server (NTRS)

    Succi, G. P.; Munro, D. H.; Ingard, K. U.

    1983-01-01

    Intense high frequency (25-38 kHz) tone bursts have been observed in acoustic tests of a scale model of a general aviation propeller. The amplitude of the tone burst is approximately equal to the amplitude of the propeller noise signature. The conditions necessary for the production of these tone bursts are described. The experiments indicate that the origin of these bursts is a periodic flow oscillation on the suction surface of the propeller blade tips which may be due to the interaction between an oscillating shock wave and a laminar boundary layer.

  13. Discovery of Nearly Coherent Oscillations with a Frequency of approximately 567 Hz During Type I X-ray Bursts of the X-ray Transient and Eclipsing Binary X1658-298

    NASA Technical Reports Server (NTRS)

    Wijnands, Rudy; Strohmayer, Tod; Franco, Lucia M.; White, Nicholas E. (Technical Monitor)

    2001-01-01

    We report the discovery of nearly coherent oscillations with a frequency of approximately 567 Hz during type I X-ray bursts from the X-ray transient and eclipsing binary X1658-298. If these oscillations are directly related to the neutron star rotation, then the spin period of the neutron star in X1658-298 is approximately 1.8 ms. The oscillations can be present during the rise or decay phase of the bursts. Oscillations during the decay phase of the bursts show an increase in frequency of approximately 0.5-1 Hz. However, in one particular burst the oscillations reappear at the end of the decay phase at about 571.5 Hz. This represents an increase in oscillation frequency of about 5 Hz, which is the largest frequency change seen so far in a burst oscillation. It is unclear if such a large change can be accommodated by present models used to explain the frequency evolution of the oscillations. The oscillations at 571.5 Hz are unusually soft compared to the oscillations found at 567 Hz. We also observed several bursts during which the oscillations are detected at much lower significance or not at all. Most of these bursts happen during periods of X-ray dipping behavior, suggesting that the X-ray dipping might decrease the amplitude of the oscillations (although several complications exist with this simple picture). We discuss our discovery in the framework of the neutron star spin interpretation.

  14. Cortical glucose metabolism correlates negatively with delta-slowing and spike-frequency in epilepsy associated with tuberous sclerosis

    PubMed Central

    Nishida, Masaaki; Asano, Eishi; Juhasz, Csaba; Muzik, Otto; Sood, Sandeep; Chugani, Harry T

    2008-01-01

    SUMMARY The mechanism of altered glucose metabolism seen on positron emission tomography (PET) in focal epilepsy is not fully understood. We determined the association between interictal glucose metabolism and interictal neuronal activity, using PET and electrocorticography (ECoG) measures derived from 865 intracranial electrode sites in 11 children with focal epilepsy associated with tuberous sclerosis complex (TSC) (age: 0.5 – 16 years) undergoing epilepsy surgery. A multiple linear regression analysis was applied to each patient, to determine whether the glucose uptake at each electrode site on interictal PET was predicted by ECoG amplitude powers and interictal spike-frequency measured in the given electrode site. The regression slopes as well as R-square values (an indicator of fitness of the regression models) were finally averaged across the 11 patients. The mean regression slope for delta amplitude power was -0.0025 (95%CI: -0.0045 to -0.0004; p=0.02 based on one-sample t-test) and that for spike frequency was -0.023 (95%CI: -0.042 to -0.0038; p=0.02). On the other hand, the mean regression slopes for the remaining ECoG amplitude powers (theta, alpha, sigma, beta and gamma activities) were not significantly different from zero. The mean R-square value was 0.39. These results suggest that increased delta-slowing and frequent spike activity were independently and additively associated with glucose hypometabolism in children with focal epilepsy associated with TSC. Association between frequent interictal spike activity and low glucose metabolism may be attributed to slow-wave components following spike discharges on ECoG recording, and a substantial proportion of the variance in regional glucose metabolism on PET could be explained by electrophysiological traits derived from conventional subdural ECoG recording. PMID:17948886

  15. Decameter Type III-Like Bursts

    NASA Astrophysics Data System (ADS)

    Melnik, V. N.; Konovalenko, A. A.; Rutkevych, B. P.; Rucker, H. O.; Dorovskyy, V. V.; Abranin, E. P.; Lecacheux, A.; Brazhenko, A. I.; Stanislavskyy, A. A.

    2007-12-01

    Starting from 1960s Type III-like bursts (Type III bursts with high drift rates) in a wide frequency range from 300 to 950MHz have been observed. These new bursts observed at certain frequency being compared to the usual Type III bursts at the same frequency show similar behaviour but feature frequency drift 2-6 times higher than the normal bursts. In this paper we report the first observations of Type III-like bursts in decameter range, carried out during summer campaigns 2002 - 2004 at UTR-2 radio telescope. The circular polarization of the bursts was measured by the radio telescope URAN-2 in 2004. The observed bursts are analyzed and compared with usual Type III bursts in the decameter range. From the analysis of over 1100 Type III-like bursts, their main parameters have been found. Characteristic feature of the observed bursts is similar to Type III-like bursts at other frequencies, i.e. measured drift rates (5-10 MHz/s) of this bursts are few times larger than that for usual Type III bursts, and their durations (1-2 s) are few times smaller than that for usual Type III bursts in this frequency band.

  16. Coronal loops diagnostics using the parameters of U-burst harmonic pair at frequencies 10-70 MHz

    NASA Astrophysics Data System (ADS)

    Dorovskyy, V. V.; Melnik, V. N.; Konovalenko, A. A.; Bubnov, I. N.; Gridin, A. A.; Shevchuk, N. V.; Rucker, H. O.; Panchenko, M.

    2013-09-01

    The results of the first observations of solar sporadic radio emission using one section of the new being currently created Giant Ukrainian Radio Telescope (GURT) are presented. The parameters of inverted U-burst with harmonic structure observed with GURT are considered. The main attention is paid to the time delay between the fundamental and harmonic components. The analytical model explaining the observed time delay is proposed.

  17. Theta-Burst LTP

    PubMed Central

    Larson, John; Munkácsy, Erin

    2014-01-01

    This review covers the spatial and temporal rules governing induction of hippocampal long-term potentiation (LTP) by theta-burst stimulation. Induction of LTP in field CA1 by high frequency stimulation bursts that resemble the burst discharges (complex-spikes) of hippocampal pyramidal neurons involves a multiple-step mechanism. A single burst is insufficient for LTP induction because it evokes both excitatory and inhibitory currents that partially cancel and limit postsynaptic depolarization. Bursts repeated at the frequency (~5 Hz) of the endogenous theta rhythm induce maximal LTP, primarily because this frequency disables feed-forward inhibition and allows sufficient postsynaptic depolarization to activate voltage-sensitive NMDA receptors. The disinhibitory process, referred to as “priming”, involves presynaptic GABA autoreceptors that inhibit GABA release. Activation of NMDA receptors allows a calcium flux into dendritic spines that serves as the proximal trigger for LTP. We include new data showing that theta-burst stimulation is more efficient than other forms of stimulation for LTP induction. In addityion, we demonstrate that associative interactions between synapses activated during theta-bursts are limited to major dendritic domains since such interactions occur within apical or basal dendritic trees but not between them. We review evidence that recordings of electrophysiological responses during theta burst stimulation can help to determine if experimental manipulations that affect LTP do so by affecting events antecedent to the induction process, such as NMDA receptor activation, or downstream signaling cascades that result from postsynaptic calcium fluxes. Finally, we argue that theta-burst LTP represents a minimal model for stable, non-decremental LTP that is more sensitive to a variety of experimental manipulations than is LTP induced by other stimulation paradigms. PMID:25452022

  18. Type III burst pair

    NASA Astrophysics Data System (ADS)

    Ning, Zongjun; Fu, Qijun; Lu, Quankang

    2000-05-01

    We present a special solar radio burst detected on 5 January 1994 using the multi-channel (50) spectrometer (1.0-2.0 GHz) of the Beijing Astronomical Observatory (BAO). Sadly, the whole event could not be recorded since it had a broader bandwidth than the limit range of the instrument. The important part was obtained, however. The event is composed of a normal drift type III burst on the lower frequency side and a reverse drift type III burst appearing almost simultaneously on the high side. We call the burst type III a burst pair. It is a typical characteristic of two type III bursts that they are morphologically symmetric about some frequency from 1.64 GHz to 1.78 GHz on the dynamic spectra records, which indicates that there are two different electron beams from the same acceleration region travelling simultaneously in opposite directions (upward and downward). A magnetic reconnection mode is a nice interpretation of type III burst pair since the plasma beta β~=0.01 is much less than 1 and the beams have velocity of about 1.07×10^8 cm s^-1 after leaving the reconnection region if we assume that the ambient magnetic field strength is about 100 G.

  19. Type III burst pair.

    NASA Astrophysics Data System (ADS)

    Zongjun, Ning; Fu, Qijun; Quankang, Lu

    2000-05-01

    Presents a special solar radio burst detected on 5 January 1994 using the multi-channel (50) spectrometer (1.0 - 2.0 GHz) of the Beijing Astronomical Observatory. Sadly, the whole event could not be recorded since it had a broader bandwidth than the limit range of the instrument. The important part was obtained, however. The event is composed of a normal drift type III burst on the lower frequency side and a reverse drift type III burst appearing almost simultaneously on the high side. The authors call the burst type III a burst pair. It is a typical characteristic of two type III bursts that they are morphologically symmetric about some frequency from 1.64 GHz to 1.78 GHz on the dynamic spectra records, which indicates that there are two different electron beams from the same acceleration region travelling simultaneously in opposite directions (upward and downward). A magnetic reconnection mode is an interpretation of type III burst pair.

  20. Pulsational frequencies in the delta Scuti stars V624 Tauri and HD 23194. Results of the STEPHI X campaign on the Pleiades cluster

    NASA Astrophysics Data System (ADS)

    Fox-Machado, L.; Álvarez, M.; Michel, E.; Li, Z. P.; Pérez Hernández, F.; Chevreton, M.; Barban, C.; Belmonte, J. A.; Dolez, N.; Fernandez, A.; Guo, J. P.; Haywood, M.; Liu, Y. Y.; Pau, S.; Planas, H.; Servan, B.

    2002-02-01

    The results of the tenth multi-site campaign of the STEPHI network are reported. The delta Scuti stars V624 Tau (HD 23156) and HD 23194, belonging to the Pleiades cluster, were observed photometrically for 34 days on three continents during 1999 November-December. An overall run of 343 hours of data was collected. Seven frequencies for V624 Tau and two frequencies for HD 23194 have been found above a 99% confidence level. These results greatly improve those found in previous studies with much less data. A preliminary comparison of observed and theoretical frequencies suggests that both stars may oscillate with radial and non-radial p modes of radial orders typical among delta Scuti stars.

  1. Jovian type III radio bursts

    NASA Technical Reports Server (NTRS)

    Kurth, W. S.; Gurnett, D. A.; Scarf, F. L.

    1989-01-01

    Radio bursts have been observed in the Voyager plasma wave data from Jupiter that bear a striking resemblance to solar type III radio bursts. The emissions lie in the frequency range near 10 kHz, have durations of a minute or so, and occur in a set of periodically spaced bursts. The spacing between primary bursts is typically 15 min, but the bursts may have additional components which recur on time scales of about 3 min. The similarity with solar type III radio bursts suggests a source mechanism involving the movement of energetic electrons through a density gradient in the plasma surrounding Jupiter. The periodicity of bursts suggests Io may be involved in the generation of waves, since the timing is similar to the Alfven wave travel time from one hemisphere to the other through the Io torus.

  2. Bursting Neurons in the Hippocampal Formation Encode Features of LFP Rhythms

    PubMed Central

    Constantinou, Maria; Gonzalo Cogno, Soledad; Elijah, Daniel H.; Kropff, Emilio; Gigg, John; Samengo, Inés; Montemurro, Marcelo A.

    2016-01-01

    Burst spike patterns are common in regions of the hippocampal formation such as the subiculum and medial entorhinal cortex (MEC). Neurons in these areas are immersed in extracellular electrical potential fluctuations often recorded as the local field potential (LFP). LFP rhythms within different frequency bands are linked to different behavioral states. For example, delta rhythms are often associated with slow-wave sleep, inactivity and anesthesia; whereas theta rhythms are prominent during awake exploratory behavior and REM sleep. Recent evidence suggests that bursting neurons in the hippocampal formation can encode LFP features. We explored this hypothesis using a two-compartment model of a bursting pyramidal neuron driven by time-varying input signals containing spectral peaks at either delta or theta rhythms. The model predicted a neural code in which bursts represented the instantaneous value, phase, slope and amplitude of the driving signal both in their timing and size (spike number). To verify whether this code is employed in vivo, we examined electrophysiological recordings from the subiculum of anesthetized rats and the MEC of a behaving rat containing prevalent delta or theta rhythms, respectively. In both areas, we found bursting cells that encoded information about the instantaneous voltage, phase, slope and/or amplitude of the dominant LFP rhythm with essentially the same neural code as the simulated neurons. A fraction of the cells encoded part of the information in burst size, in agreement with model predictions. These results provide in-vivo evidence that the output of bursting neurons in the mammalian brain is tuned to features of the LFP. PMID:28082890

  3. Neuronal Networks during Burst Suppression as Revealed by Source Analysis

    PubMed Central

    Reinicke, Christine; Moeller, Friederike; Anwar, Abdul Rauf; Mideksa, Kidist Gebremariam; Pressler, Ronit; Deuschl, Günther; Stephani, Ulrich; Siniatchkin, Michael

    2015-01-01

    Introduction Burst-suppression (BS) is an electroencephalography (EEG) pattern consisting of alternant periods of slow waves of high amplitude (burst) and periods of so called flat EEG (suppression). It is generally associated with coma of various etiologies (hypoxia, drug-related intoxication, hypothermia, and childhood encephalopathies, but also anesthesia). Animal studies suggest that both the cortex and the thalamus are involved in the generation of BS. However, very little is known about mechanisms of BS in humans. The aim of this study was to identify the neuronal network underlying both burst and suppression phases using source reconstruction and analysis of functional and effective connectivity in EEG. Material/Methods Dynamic imaging of coherent sources (DICS) was applied to EEG segments of 13 neonates and infants with burst and suppression EEG pattern. The brain area with the strongest power in the analyzed frequency (1–4 Hz) range was defined as the reference region. DICS was used to compute the coherence between this reference region and the entire brain. The renormalized partial directed coherence (RPDC) was used to describe the informational flow between the identified sources. Results/Conclusion Delta activity during the burst phases was associated with coherent sources in the thalamus and brainstem as well as bilateral sources in cortical regions mainly frontal and parietal, whereas suppression phases were associated with coherent sources only in cortical regions. Results of the RPDC analyses showed an upwards informational flow from the brainstem towards the thalamus and from the thalamus to cortical regions, which was absent during the suppression phases. These findings may support the theory that a “cortical deafferentiation” between the cortex and sub-cortical structures exists especially in suppression phases compared to burst phases in burst suppression EEGs. Such a deafferentiation may play a role in the poor neurological outcome of

  4. Relations between the frequency of the DeltaF 508 mutation and the course of pulmonary disease in cystic fibrosis patients infected with Pseudomonas aeruginosa.

    PubMed

    Rosenecker, J

    2000-08-18

    The course of pulmonary disease in cystic fibrosis is variable. There are controversial data on the impact of the type of mutation on the cystic fibrosis transmembrane conductance regulator (CFTR) gene on the course of pulmonary disease in CF. Since selected mutations of the CFTR gene appear to be associated with relatively mild disease, this study addressed the question whether the course of pulmonary disease in CF patients colonized with P. aeruginosa is influenced by the frequency of the DeltaF 508 mutation. For this study, we assessed FVC and FEV1 in 127 CF patients who attended regularly the Munich CF Center over a mean period of 43 +/- 16 (SD) months. Of these 127 patients, 69 (54.3%) were homozygous for the DeltaF 508 mutation, 42 (33.1%) were compound heterozygous for the DeltaF 508 mutation, and 16 (12.6%) did not carry the DeltaF 508 mutation on either chromosome. In homozygotes 59 (85.5%) out of 69 CF-patients were colonized with P. aeruginosa as compared with 27 (64.3%) out of 42 in heterozygotes (p <0.05). The mean age of onset of P. aeruginosa colonization was 11.0 years, and there was no difference between the three groups. The mean FVC and FEV1 values did not differ significantly between the three genotype groups when P. aeruginosa infection was disregarded. However, when only P. aeruginosa colonized patients were compared FVC and FEV1 values were lower in heterozygotes than in the other two groups both at the beginning and at the end of the study. These findings indicate that the course of pulmonary disease in CF patients is at least partially influenced by the frequency of the DeltaF 508 mutation.

  5. V(D)J recombination generates a high frequency of nonstandard TCR D[delta]-associated rearrangements in thymocytes

    SciTech Connect

    Carroll, A.M.; Slack, J.K.; Mu, Xiaochun )

    1993-03-15

    The standard products of V(D)J recombination are coding junctions, which encode Ag receptor polypeptide, and their commonly excised reciprocal products, signal junctions. Additional nonstandard products also have been detected, mostly in artificial recombination substrate studies. The occurrence of nonstandard products, including pseudonormal, hybrid, and open/shut junctions, indicates significant indeterminacy of the V(D)J recombinase. However, the incidence of nonstandard products of endogenous Ag receptor genes in vivo has not been specifically addressed. The data presented here show that for the TCR-[delta] locus, D element-associated recombination in mouse thymocytes results in a high incidence of nonstandard recombination products. D[delta]1-D[delta]2 rearrangements, both chromosome retained and excised episomal products, were studied by polymerase chain reaction amplification, cloning, and sequence analysis. The proximity of D[delta]1 and D[delta]2 elements, and the fact that both are flanked by 5[prime] and 3[prime] recombination signal sequences with 12-bp and 23-bp spacers, respectively, results in frequent pseudonormal joining. The resulting products are signal junctions retained on the chromosome. Excised episomal products include coding junctions, hybrid junctions formed in apparent violation of the 12/23 spacer rule, and standard signal junctions; some signal junctions show evidence of imprecise cleavage. Evidence for open/shut and/or oligonucleotide capture events was also seen. Similar rearrangements were detectable in thymocytes of mutant scid mice. These findings indicate a high degree of indeterminancy of V(D)J recombinase-mediated D[delta]1-D[delta]2 rearrangement in both wild-type and scid thymocytes. This indeterminacy affects the productive potential of TCR-[delta] loci. 45 refs., 4 figs.

  6. Multi-Frequency and Multi-Polarization Study on SAR-Based Coastal AReas Characterization: The Case of the Yellow River Delta

    NASA Astrophysics Data System (ADS)

    Buono, Andrea; Nunziata, Ferdinando; Migliaccio, Maurizio; Li, Xiaofeng; Shen, Dongliang; Ding, Xianwen

    2016-08-01

    The Yellow River is the most sediment-filled river and the sixth-longest one in the world. It is of paramount importance for safe navigation, local economy and environment due to the presence of floods, farms, aquacultures and pollution. Further, the Yellow River delta is characterized by several physical phenomena due to both natural and anthropogenic processes: sedimentation, erosion, floods, pollution, etc.In this study, actual partially-overlapped L-/C-band fully- polarimetric (FP) synthetic aperture radar (SAR) data are used to investigate the scattering properties of the Yellow River delta, whose very complex area is characterized by different environments as recorded by ground truth data acquired during a ship-based in-situ campaign. Preliminary results witness that multi-polarization and multi-frequency SAR measurements allow inferring more physical information in such a complex environment that can be used as starting point for developing ad hoc classification algorithms.

  7. Fast Radio Bursts

    NASA Astrophysics Data System (ADS)

    Kaspi, Victoria M.

    2017-01-01

    Fast Radio Bursts (FRBs) are a recently discovered phenomenon consisting of short (few ms) bursts of radio waves that have dispersion measures that strongly suggest an extragalactic and possibly cosmological origin. Current best estimates for the rate of FRBs is several thousand per sky per day at radio frequencies near 1.4 GHz. Even with so high a rate, to date, fewer than 20 FRBs have been reported, with one source showing repeated bursts. In this talk I will describe known FRB properties including what is known about the lone repeating source, as well as models for the origin of these mysterious events. I will also describe the CHIME radio telescope, currently under construction in Canada. Thanks to its great sensitivity and unprecedented field-of-view, CHIME promises major progress on FRBs.

  8. Frequencies of the G-protein beta3 subunit C825T polymorphism and the delta 32 mutation of the chemokine receptor-5 in patients with multiple sclerosis.

    PubMed

    Haase, Claus G; Schmidt, Stephan; Faustmann, Pedro M

    2002-09-27

    In the pathogenesis of multiple sclerosis (MS) genetic factors are known to influence autoreactive T-cell-actions like proliferation and chemotaxis across the blood-brain barrier via chemokine receptors (CCR) and G-protein coupled activating mechanisms. For the first time, we studied the frequencies of a recently described C825T polymorphism in the G-protein encoding gene for the beta3 subunit (GNB3) together with frequencies of a 32-base-pair deletion in the CCR5 gene (delta32 CCR5) in patients with MS (n = 253: relapsing-remitting (RR), n = 124 and chronic progressive course, n = 129). Apart from a trend to a reduced frequency of delta32 CCR5 and increased GNB3 825T polymorphism in primary chronic progressive patients, numbers did not reach statistical significance in any group of MS. These results could not support differences in the genetic background of MS based on that CCR5 mutation or the described GNB3 polymorphism.

  9. Frequency of the CCR5 delta 32 mutant allele in HIV-1-positive patients, female sex workers, and a normal population in Taiwan.

    PubMed

    Li, C; Yan, Y P; Shieh, B; Lee, C M; Lin, R Y; Chen, Y M

    1997-12-01

    A specific 32-nucleotide deletion mutant of the CCR5 gene (Accr5), the coreceptor gene for human immunodeficiency virus type 1 (HIV-1), can effectively suppress the transmission and pathogenesis of the virus. Individuals homozygous for the delta ccr5 allele resist primary macrophage-tropic HIV-1 infection, despite multiple high-risk sexual exposures. This gene deletion is relatively common among Caucasians but uncommon among Africans, Asians, and South Americans. We used polymerase chain reaction (PCR) technology to determine the frequency of the delta ccr5 allele in a Taiwanese population with diverse health status and social backgrounds. Subjects included 24 HIV-1-infected persons in the northern and southern parts of Taiwan; 131 HIV-1 high-risk, licensed female sex workers in the northern part of the island (21% of whom were aborigines); and 187 unrelated, healthy, HIV-1-negative individuals in southern Taiwan. PCR with primers encompassing the entire CCR5 gene was used to explore possible deletions at regions other than the 32-nucleotide area in the female sex workers. No ccr5 deletions were detected, indicating that they are rare or absent in the Taiwanese population. This finding implies that delta ccr5 is not likely to be part of the defense against the spread of HIV-1-infection in Taiwanese.

  10. X-ray observations of the burst source MXB 1728 - 34

    NASA Technical Reports Server (NTRS)

    Basinska, E. M.; Lewin, W. H. G.; Sztajno, M.; Cominsky, L. R.; Marshall, F. J.

    1984-01-01

    Where sufficient information has been obtained, attention is given to the maximum burst flux, integrated burst flux, spectral hardness, rise time, etc., of 96 X-ray bursts observed from March 1976 to March 1979. The integrated burst flux and the burst frequency appear to be correlated; the longer the burst interval, the larger the integrated burst flux, as expected on the basis of simple thermonuclear flash models. The maximum burst flux and the integrated burst flux are strongly correlated; for low flux levels their dependence is approximately linear, while for increasing values of the integrated burst flux, the flux at burst maximum saturates and reaches a plateau.

  11. Resource Sharing Controls Gene Expression Bursting.

    PubMed

    Caveney, Patrick M; Norred, S Elizabeth; Chin, Charles W; Boreyko, Jonathan B; Razooky, Brandon S; Retterer, Scott T; Collier, C Patrick; Simpson, Michael L

    2017-02-17

    Episodic gene expression, with periods of high expression separated by periods of no expression, is a pervasive biological phenomenon. This bursty pattern of expression draws from a finite reservoir of expression machinery in a highly time variant way, i.e., requiring no resources most of the time but drawing heavily on them during short intense bursts, that intimately links expression bursting and resource sharing. Yet, most recent investigations have focused on specific molecular mechanisms intrinsic to the bursty behavior of individual genes, while little is known about the interplay between resource sharing and global expression bursting behavior. Here, we confine Escherichia coli cell extract in both cell-sized microfluidic chambers and lipid-based vesicles to explore how resource sharing influences expression bursting. Interestingly, expression burst size, but not burst frequency, is highly sensitive to the size of the shared transcription and translation resource pools. The intriguing implication of these results is that expression bursts are more readily amplified than initiated, suggesting that burst formation occurs through positive feedback or cooperativity. When extrapolated to prokaryotic cells, these results suggest that large translational bursts may be correlated with large transcriptional bursts. This correlation is supported by recently reported transcription and translation bursting studies in E. coli. The results reported here demonstrate a strong intimate link between global expression burst patterns and resource sharing, and they suggest that bursting plays an important role in optimizing the use of limited, shared expression resources.

  12. Interplanetary Type IV Bursts

    NASA Astrophysics Data System (ADS)

    Hillaris, A.; Bouratzis, C.; Nindos, A.

    2016-08-01

    We study the characteristics of moving type IV radio bursts that extend to hectometric wavelengths (interplanetary type IV or type {IV}_{{IP}} bursts) and their relationship with energetic phenomena on the Sun. Our dataset comprises 48 interplanetary type IV bursts observed with the Radio and Plasma Wave Investigation (WAVES) instrument onboard Wind in the 13.825 MHz - 20 kHz frequency range. The dynamic spectra of the Radio Solar Telescope Network (RSTN), the Nançay Decametric Array (DAM), the Appareil de Routine pour le Traitement et l' Enregistrement Magnetique de l' Information Spectral (ARTEMIS-IV), the Culgoora, Hiraso, and the Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN) Radio Spectrographs were used to track the evolution of the events in the low corona. These were supplemented with soft X-ray (SXR) flux-measurements from the Geostationary Operational Environmental Satellite (GOES) and coronal mass ejections (CME) data from the Large Angle and Spectroscopic Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO). Positional information of the coronal bursts was obtained by the Nançay Radioheliograph (NRH). We examined the relationship of the type IV events with coronal radio bursts, CMEs, and SXR flares. The majority of the events (45) were characterized as compact, their duration was on average 106 minutes. This type of events was, mostly, associated with M- and X-class flares (40 out of 45) and fast CMEs, 32 of these events had CMEs faster than 1000 km s^{-1}. Furthermore, in 43 compact events the CME was possibly subjected to reduced aerodynamic drag as it was propagating in the wake of a previous CME. A minority (three) of long-lived type {IV}_{{IP}} bursts was detected, with durations from 960 minutes to 115 hours. These events are referred to as extended or long duration and appear to replenish their energetic electron content, possibly from electrons escaping from the corresponding coronal

  13. Modelling the increased frequency of extreme sea levels in the Ganges-Brahmaputra-Meghna delta due to sea level rise and other effects of climate change.

    PubMed

    Kay, S; Caesar, J; Wolf, J; Bricheno, L; Nicholls, R J; Saiful Islam, A K M; Haque, A; Pardaens, A; Lowe, J A

    2015-07-01

    Coastal flooding due to storm surge and high tides is a serious risk for inhabitants of the Ganges-Brahmaputra-Meghna (GBM) delta, as much of the land is close to sea level. Climate change could lead to large areas of land being subject to increased flooding, salinization and ultimate abandonment in West Bengal, India, and Bangladesh. IPCC 5th assessment modelling of sea level rise and estimates of subsidence rates from the EU IMPACT2C project suggest that sea level in the GBM delta region may rise by 0.63 to 0.88 m by 2090, with some studies suggesting this could be up to 0.5 m higher if potential substantial melting of the West Antarctic ice sheet is included. These sea level rise scenarios lead to increased frequency of high water coastal events. Any effect of climate change on the frequency and severity of storms can also have an effect on extreme sea levels. A shelf-sea model of the Bay of Bengal has been used to investigate how the combined effect of sea level rise and changes in other environmental conditions under climate change may alter the frequency of extreme sea level events for the period 1971 to 2099. The model was forced using atmospheric and oceanic boundary conditions derived from climate model projections and the future scenario increase in sea level was applied at its ocean boundary. The model results show an increased likelihood of extreme sea level events through the 21st century, with the frequency of events increasing greatly in the second half of the century: water levels that occurred at decadal time intervals under present-day model conditions occurred in most years by the middle of the 21st century and 3-15 times per year by 2100. The heights of the most extreme events tend to increase more in the first half of the century than the second. The modelled scenarios provide a case study of how sea level rise and other effects of climate change may combine to produce a greatly increased threat to life and property in the GBM delta by the end

  14. High-frequency depositional sequences and stratal stacking patterns in lower pliocene coastal deltas, mid-Norwegian continental shelf

    SciTech Connect

    Henriksen, S.; Weimer, P.

    1996-12-01

    Extensive deltaic and coastal progradation occurred along the mid-Norwegian continental shelf during the early Pliocene. Thirty-eight well-developed, high-frequency (fourth-order) sequences are identified within the deltaic complex on multifold seismic data. The fourth-order sequences are arranged in four oblique progradational and two sigmoid progradational sequence sets. Deposition of the high-frequency sequences and their stacking patterns probably were in response to high-frequency cycles of relative changes in sea level cycles produced by variable rates of subsidence and uplift, superimposed on ;high-frequency eustatic cycles within a lower frequency eustatic system. The mixed aggrading/prograding sequence sets are interpreted to represent increased space-added accommodation rates and deposition within third-order highstand systems tracts. Conversely, the progradational sequence sets are interpreted to represent decreasing space-added accommodation rates and deposition within the third-order low-stand systems tracts. The recognition of multiple sequence sets likely reflects the effect of long-term relative fall in sea level (tectonic uplift?) super-imposed on high-frequency eustatic cycles.

  15. Auditory Delta Event-Related Oscillatory Responses are Decreased in Alzheimer’s Disease

    PubMed Central

    Yener, G. G.; Güntekin, B.; Örken, D. Necioglu; Tülay, E.; Forta, H.; Başar, E.

    2012-01-01

    Background: Visual delta event-related (ERO) and evoked oscillations (EO) of Alzheimer patients (AD) are different than healthy. In the present study, the analysis is extented to include auditory ERO and EO in AD. The rationale is to reveal whether the auditory ERO delta responses are also reduced, and whether this is a general phenomenon in Alzheimer patients upon applying stimuli with cognitive load. Methods: Thirty-four mild AD subjects (17 de-novo and 17 medicated (cholinergic)) and seventeen healthy controls were included. Auditory oddball paradigm and sensory auditory stimuli were applied to the subjects. Oscillatory responses were analyzed by measuring maximum amplitudes in delta frequency range (0.5–3.5 Hz). Results: Auditory delta ERO (0.5–3.5 Hz) responses of healthy controls were higher than either de-novo AD or medicated AD group, without a difference between two AD subgroups. Furthermore, the auditory EO after presentation of tone bursts yielded no group difference. Conclusion: Our findings imply that delta ERO is highly unstable in AD patients in comparison to age-matched healthy controls only during the cognitive paradigm. Our results favor the hypothesis that neural delta networks are activated during cognitive tasks and that the reduced delta response is a general phenomenon in AD, due to cognitive impairment. PMID:22207418

  16. Nile Delta

    Atmospheric Science Data Center

    2013-04-15

    article title:  The Nile River Delta     View Larger Image ... of eastern Africa. At the apex of the fertile Nile River Delta is the Egyptian capital city of Cairo. To the west are the Great Pyramids ...

  17. Differential Regulation of Action Potential Shape and Burst-Frequency Firing by BK and Kv2 Channels in Substantia Nigra Dopaminergic Neurons

    PubMed Central

    Kimm, Tilia; Khaliq, Zayd M.

    2015-01-01

    pars compacta. Although both channel types participate in action potential repolarization about equally, they have contrasting and partially opposite effects in regulating neuronal firing at frequencies typical of bursting. Our analysis shows that this results from their different kinetic properties, with fast-activating BK channels serving to short-circuit activation of Kv2 channels, which tend to slow firing by producing a deep afterhyperpolarization. The cross-regulation of BK and Kv2 activation illustrates that the functional role of a channel cannot be defined in isolation but depends critically on the context of the other conductances in the cell. PMID:26674866

  18. Effects of various extremely low frequency magnetic fields on the free radical processes, natural antioxidant system and respiratory burst system activities in the heart and liver tissues.

    PubMed

    Canseven, Ayse Gulnihal; Coskun, Sule; Seyhan, Nesrin

    2008-10-01

    Magnetic fields (MFs) can affect biological systems by increasing the release of free radicals that are able to alter cell defense systems and breakdown tissue homeostasis. In the present study, the effects of extremely low frequency (ELF) electromagnetic fields (EMF) were investigated on free radical levels, natural antioxidant systems and respiratory burst system activities in heart and liver tissues of guinea pigs exposed to 50 Hz MFs of 1, 2 and 3 mT for 4 h/day and 8 h/day for 5 days by measuring malondialdehyde (MDA), nitric oxide (NO), glutathione (GSH) levels and myeloperoxidase (MPO) activity. A total of sixty-two male guinea pigs, 10-12 weeks old were studied in seven groups as control and exposure groups: Group I (control), II (1 mT, 4 h/day), III (1 mT, 8 h/day), IV (2 mT, 4 h/day), V (2 mT, 8 h/day), VI (3 mT, 4 h/day), and VII (3 mT, 8 h/day). Controls were kept under the same conditions without any exposure to MF. MDA levels increased in liver in groups II and IV, but decreased in group VII for both liver and heart tissues. NOx levels declined in heart in groups II and III and in liver in groups III, V, and VI, but increased in liver in group VII. GSH levels increased in heart in groups II, IV, V, and in liver in groups V and VI and VI, but decreased in groups II and IV in liver. MPO activity decreased in liver in groups III, IV, VI and VII with respect to controls and in heart tissues in groups II, III and IV; however, there was a significant increase MPO activity in heart in group VII. From the results, it can be concluded that the intensity and exposure duration of MFs are among the effective conditions on the formation of free radicals and behaviour of antioxidant enzymes.

  19. Solar Radio Bursts and Space Weather

    NASA Technical Reports Server (NTRS)

    Gopalswamy, Natchimuthuk,

    2012-01-01

    Radio bursts from the Sun are produced by electron accelerated to relativistic energies by physical processes on the Sun such as solar flares and coronal mass ejections (CMEs). The radio bursts are thus good indicators of solar eruptions. Three types of nonthermal radio bursts are generally associated with CMEs. Type III bursts due to accelerated electrons propagating along open magnetic field lines. The electrons are thought to be accelerated at the reconnection region beneath the erupting CME, although there is another view that the electrons may be accelerated at the CME-driven shock. Type II bursts are due to electrons accelerated at the shock front. Type II bursts are also excellent indicators of solar energetic particle (SEP) events because the same shock is supposed accelerate electrons and ions. There is a hierarchical relationship between the wavelength range of type /I bursts and the CME kinetic energy. Finally, Type IV bursts are due to electrons trapped in moving or stationary structures. The low frequency stationary type IV bursts are observed occasionally in association with very fast CMEs. These bursts originate from flare loops behind the erupting CME and hence indicate tall loops. This paper presents a summary of radio bursts and their relation to CMEs and how they can be useful for space weather predictions.

  20. Delta Scuti stars: Theory

    NASA Technical Reports Server (NTRS)

    Guzik, J. A.

    1998-01-01

    The purpose of asteroseismology is not only to derive the internal structure of individual stars from their observed oscillation frequencies, but also to test and extend one's understanding of the physics of matter under the extremes of temperature, density, and pressure found in stellar interiors. In this review, the author hopes to point out what one can learn about the Sun by studying (delta) Scuti stars, as well as what one can learn about stars more massive or evolved than the Sun. He discusses some of the difficulties in theoretical approaches to asteroseismology for (delta) Scuti stars, using FG Vir, (delta) Scuti, and CD-24(degree) 7599 as examples.

  1. Herringbone bursts associated with type II solar radio emission

    NASA Technical Reports Server (NTRS)

    Cairns, I. H.; Robinson, R. D.

    1987-01-01

    Detailed observations of the herringbone (HB) fine structure on type II solar radio bursts are presented. Data from the Culgoora radiospectrograph, radiometer and radioheliograph are analyzed. The characteristic spectral profiles, frequency drift rates and exciter velocities, fluxes, source sizes, brightness temperatures, and polarizations of individual HB bursts are determined. Correlations between individual bursts within the characteristic groups of bursts and the properties of the associated type II bursts are examined. These data are compatible with HB bursts being radiation at multiples of the plasma frequency generated by electron streams accelerated by the type II shock. HB bursts are physically distinct phenomena from type II and type III bursts, differing significantly in emission processes and/or source conditions; this conclusion indicates that many of the presently available theoretical ideas for HB bursts are incorrect.

  2. Volga Delta

    Atmospheric Science Data Center

    2013-04-17

    article title:  Volga Delta and the Caspian Sea     View ... appear reddish. A small cloud near the center of the delta separates into red, green, and blue components due to geometric parallax ... include several linear features located near the Volga Delta shoreline. These long, thin lines are artificially maintained shipping ...

  3. A joint probability approach using a 1-D hydrodynamic model for estimating high water level frequencies in the Lower Rhine Delta

    NASA Astrophysics Data System (ADS)

    Zhong, H.; van Overloop, P.-J.; van Gelder, P. H. A. J. M.

    2013-07-01

    The Lower Rhine Delta, a transitional area between the River Rhine and Meuse and the North Sea, is at risk of flooding induced by infrequent events of a storm surge or upstream flooding, or by more infrequent events of a combination of both. A joint probability analysis of the astronomical tide, the wind induced storm surge, the Rhine flow and the Meuse flow at the boundaries is established in order to produce the joint probability distribution of potential flood events. Three individual joint probability distributions are established corresponding to three potential flooding causes: storm surges and normal Rhine discharges, normal sea levels and high Rhine discharges, and storm surges and high Rhine discharges. For each category, its corresponding joint probability distribution is applied, in order to stochastically simulate a large number of scenarios. These scenarios can be used as inputs to a deterministic 1-D hydrodynamic model in order to estimate the high water level frequency curves at the transitional locations. The results present the exceedance probability of the present design water level for the economically important cities of Rotterdam and Dordrecht. The calculated exceedance probability is evaluated and compared to the governmental norm. Moreover, the impact of climate change on the high water level frequency curves is quantified for the year 2050 in order to assist in decisions regarding the adaptation of the operational water management system and the flood defense system.

  4. Hardness/intensity correlations among BATSE bursts

    NASA Technical Reports Server (NTRS)

    Paciesas, William S.; Pendleton, Geoffrey N.; Kouveliotou, Chryssa; Fishman, Gerald J.; Meegan, Charles A.; Wilson, Robert B.

    1992-01-01

    Conclusions about the nature of gamma-ray bursts derived from the size-frequency distribution may be altered if a significant correlation exists between burst intensity and spectral shape. Moreover, if gamma-ray bursts have a cosmological origin, such a correlation may be expected to result from the expansion of the universe. We have performed a rudimentary search of the BATSE bursts for hardness/intensity correlations. The range of spectral shapes was determined for each burst by computing the ratio of the intensity in the range 100-300 keV to that in 55-300 keV. We find weak evidence for the existence of a correlation, the strongest effect being present when comparing the maximum hardness ratio for each burst with its maximum rate.

  5. A Neocortical Delta Rhythm Facilitates Reciprocal Interlaminar Interactions via Nested Theta Rhythms

    PubMed Central

    Carracedo, Lucy M.; Kjeldsen, Henrik; Cunnington, Leonie; Jenkins, Alastair; Schofield, Ian; Cunningham, Mark O.; Davies, Ceri H.; Traub, Roger D.

    2013-01-01

    Delta oscillations (1–4 Hz) associate with deep sleep and are implicated in memory consolidation and replay of cortical responses elicited during wake states. A potent local generator has been characterized in thalamus, and local generators in neocortex have been suggested. Here we demonstrate that isolated rat neocortex generates delta rhythms in conditions mimicking the neuromodulatory state during deep sleep (low cholinergic and dopaminergic tone). The rhythm originated in an NMDA receptor-driven network of intrinsic bursting (IB) neurons in layer 5, activating a source of GABAB receptor-mediated inhibition. In contrast, regular spiking (RS) neurons in layer 5 generated theta-frequency outputs. In layer 2/3 principal cells, outputs from IB cells associated with IPSPs, whereas those from layer 5 RS neurons related to nested bursts of theta-frequency EPSPs. Both interlaminar spike and field correlations revealed a sequence of events whereby sparse spiking in layer 2/3 was partially reflected back from layer 5 on each delta period. We suggest that these reciprocal, interlaminar interactions may represent a “Helmholtz machine”-like process to control synaptic rescaling during deep sleep. PMID:23804097

  6. How Long does a Burst Burst?

    NASA Astrophysics Data System (ADS)

    Zhang, Bin-Bin; Zhang, Bing; Murase, Kohta; Connaughton, Valerie; Briggs, Michael S.

    2014-05-01

    Several gamma-ray bursts (GRBs) last much longer (~hours) in γ-rays than typical long GRBs (~minutes), and it has recently been proposed that these "ultra-long GRBs" may form a distinct population, probably with a different (e.g., blue supergiant) progenitor than typical GRBs. However, Swift observations suggest that many GRBs have extended central engine activities manifested as flares and internal plateaus in X-rays. We perform a comprehensive study on a large sample of Swift GRBs with X-Ray Telescope observations to investigate GRB central engine activity duration and to determine whether ultra-long GRBs are unusual events. We define burst duration t burst based on both γ-ray and X-ray light curves rather than using γ-ray observations alone. We find that t burst can be reliably measured in 343 GRBs. Within this "good" sample, 21.9% GRBs have t burst >~ 103 s and 11.5% GRBs have t burst >~ 104 s. There is an apparent bimodal distribution of t burst in this sample. However, when we consider an "undetermined" sample (304 GRBs) with t burst possibly falling in the gap between GRB duration T 90 and the first X-ray observational time, as well as a selection effect against t burst falling into the first Swift orbital "dead zone" due to observation constraints, the intrinsic underlying t burst distribution is consistent with being a single component distribution. We found that the existing evidence for a separate ultra-long GRB population is inconclusive, and further multi-wavelength observations are needed to draw a firmer conclusion. We also discuss the theoretical implications of our results. In particular, the central engine activity duration of GRBs is generally much longer than the γ-ray T 90 duration and it does not even correlate with T 90. It would be premature to make a direct connection between T 90 and the size of the progenitor star.

  7. Method and apparatus for coherent burst ranging

    DOEpatents

    Wachter, Eric A.; Fisher, Walter G.

    1998-01-01

    A high resolution ranging method is described utilizing a novel modulated waveform, hereafter referred to as coherent burst modulation. In the coherent burst method, high frequency modulation of an acoustic or electromagnetic transmitter, such as a laser, is performed at a modulation frequency. This modulation frequency is transmitted quasi-continuously in the form of interrupted bursts of radiation. Energy from the transmitter is directed onto a target, interacts with the target, and the returning energy is collected. The encoded burst pattern contained in the collected return signal is detected coherently by a receiver that is tuned so as to be principally sensitive to the modulation frequency. The receiver signal is processed to determine target range using both time-of-flight of the burst envelope and phase shift of the high frequency modulation. This approach effectively decouples the maximum unambiguous range and range resolution relationship of earlier methods, thereby allowing high precision ranging to be conducted at arbitrarily long distances using at least one burst of encoded energy. The use of a receiver tuned to the high frequency modulation contained within the coherent burst vastly improves both sensitivity in the detection of the target return signal and rejection of background interferences, such as ambient acoustic or electromagnetic noise. Simultaneous transmission at several energies (or wavelengths) is possible by encoding each energy with a separate modulation frequency or pattern; electronic demodulation at the receiver allows the return pattern for each energy to be monitored independently. Radial velocity of a target can also be determined by monitoring change in phase shift of the return signal as a function of time.

  8. Method and apparatus for coherent burst ranging

    DOEpatents

    Wachter, E.A.; Fisher, W.G.

    1998-04-28

    A high resolution ranging method is described utilizing a novel modulated waveform, hereafter referred to as coherent burst modulation. In the coherent burst method, high frequency modulation of an acoustic or electromagnetic transmitter, such as a laser, is performed at a modulation frequency. This modulation frequency is transmitted quasi-continuously in the form of interrupted bursts of radiation. Energy from the transmitter is directed onto a target, interacts with the target, and the returning energy is collected. The encoded burst pattern contained in the collected return signal is detected coherently by a receiver that is tuned so as to be principally sensitive to the modulation frequency. The receiver signal is processed to determine target range using both time-of-flight of the burst envelope and phase shift of the high frequency modulation. This approach effectively decouples the maximum unambiguous range and range resolution relationship of earlier methods, thereby allowing high precision ranging to be conducted at arbitrarily long distances using at least one burst of encoded energy. The use of a receiver tuned to the high frequency modulation contained within the coherent burst vastly improves both sensitivity in the detection of the target return signal and rejection of background interferences, such as ambient acoustic or electromagnetic noise. Simultaneous transmission at several energies (or wavelengths) is possible by encoding each energy with a separate modulation frequency or pattern; electronic demodulation at the receiver allows the return pattern for each energy to be monitored independently. Radial velocity of a target can also be determined by monitoring change in phase shift of the return signal as a function of time. 12 figs.

  9. Autaptic Connections Shift Network Excitability and Bursting

    PubMed Central

    Wiles, Laura; Gu, Shi; Pasqualetti, Fabio; Parvesse, Brandon; Gabrieli, David; Bassett, Danielle S.; Meaney, David F.

    2017-01-01

    We examine the role of structural autapses, when a neuron synapses onto itself, in driving network-wide bursting behavior. Using a simple spiking model of neuronal activity, we study how autaptic connections affect activity patterns, and evaluate if controllability significantly affects changes in bursting from autaptic connections. Adding more autaptic connections to excitatory neurons increased the number of spiking events and the number of network-wide bursts. We observed excitatory synapses contributed more to bursting behavior than inhibitory synapses. We evaluated if neurons with high average controllability, predicted to push the network into easily achievable states, affected bursting behavior differently than neurons with high modal controllability, thought to influence the network into difficult to reach states. Results show autaptic connections to excitatory neurons with high average controllability led to higher burst frequencies than adding the same number of self-looping connections to neurons with high modal controllability. The number of autapses required to induce bursting was lowered by adding autapses to high degree excitatory neurons. These results suggest a role of autaptic connections in controlling network-wide bursts in diverse cortical and subcortical regions of mammalian brain. Moreover, they open up new avenues for the study of dynamic neurophysiological correlates of structural controllability. PMID:28266594

  10. A Model-based Interpretation of Low-frequency Changes in the Carbon Cycle during the Last 120,000 years and its Implications for the Reconstruction of Atmospheric (delta) 14-C

    NASA Technical Reports Server (NTRS)

    Koehler, Peter; Muscheler, Raimund; Fischer, Hubertus

    2006-01-01

    A main caveat in the interpretation of observed changes in atmospheric (Delta)C-l4 during the last 50,000 years is the unknown variability of the carbon cycle, which together with changes in the C-14 production rates determines the C-14 dynamics. A plausible scenario explaining glacial/interglacial dynamics seen in atmospheric CO2 and (delta)C-13 was proposed recently (Kohler et al., 2005a). A similar approach that expands its interpretation to the C-14 cycle is an important step toward a deeper understanding of (Delta)C-14 variability. This approach is based on an ocean/atmosphere/biosphere box model of the global carbon cycle (BICYCLE) to reproduce low-frequency changes in atmospheric CO2 as seen in Antarctic ice cores. The model is forced forward in time by various paleoclimatic records derived from ice and sediment cores. The simulation results of our proposed scenario match a compiled CO2 record from various ice cores during the last 120,000 years with high accuracy (r(sup 2) = 0.89). We analyze scenarios with different C-14 production rates, which are either constant or based on Be-10 measured in Greenland ice cores or the recent high-resolution geomagnetic field reconstruction GLOPIS-75 and compare them with the available (Delta)C-14 data covering the last 50,000 years. Our results suggest that during the last glacial cycle in general less than 110%0o f the increased atmospheric (Delta)C-14 is based on variations in the carbon cycle, while the largest part (5/6) of the variations has to be explained by other factors. Glacial atmospheric (Delta)C-14 larger than 700% cannot not be explained within our framework, neither through carbon cycle-based changes nor through variable C-14 production. Superimposed on these general trends might lie positive anomalies in atmospheric (Delta)C-14 of approx. 50% caused by millennial-scale variability of the northern deep water production during Heinrich events and Dansgaard/Oeschger climate fluctuations. According to our

  11. Burst Oscillations: Watching Neutron Stars Spin

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2010-01-01

    It is now almost 15 years since the first detection of rotationally modulated emission from X-ray bursting neutron stars, "burst oscillations," This phenomenon enables us to see neutron stars spin, as the X-ray burst flux asymmetrically lights up the surface. It has enabled a new way to probe the neutron star spin frequency distribution, as well as to elucidate the multidimensional nature of nuclear burning on neutron stars. I will review our current observational understanding of the phenomenon, with an eye toward highlighting some of the interesting remaining puzzles, of which there is no shortage.

  12. Voyager observations of Jovian millisecond radio bursts

    NASA Technical Reports Server (NTRS)

    Alexander, J. K.; Desch, M. D.

    1984-01-01

    Voyager Planetary Radio Astronomy data collected over 30-day intervals centered on the two close encounters with Jupiter were utilized to study the characteristics of millisecond-duration radio bursts (s-bursts) at frequencies between 5 and 15 MHz. In this frequency range, s-bursts are found to occur almost independently of Central Meridian Longitude and to depend entirely on the phase of Io with respect to the observer's planetocentric line of sight. Individual bursts typically cover a total frequency range of about 1.5 to 3 MHz, and they are usually strongly circularly polarized. Most bursts in a particular s-burst storm will exhibit the same polarization sense (either right-hand or left-hand), and there is some evidence for a systematic pattern in which one polarizations sense is preferred over the other as a function of Io phase and Central Meridian Longitude. These data are all suggestive of a radio source that is located along the instantaneous Io flux tube and that extends over a linear dimension of 5000 km along the field lines in both the northern and southern Hemispheres.

  13. Control and synchronization of laser bursting and its implications in neuroscience.

    PubMed

    Arecchi, F Tito; Meucci, Riccardo; Al Naimee, Kais; Salvadori, Francesco

    2009-02-01

    We present experimental and numerical evidence of control and synchronization of burst events in modulated CO(2) lasers. Bursts appear randomly in each laser as trains of large amplitude spikes intercalated by a small amplitude chaotic regime. Experimental data and model display the frequency locking of bursts in a suitable interval of coupling strengths. The analogy with neuronal bursting will also be discussed in view of the role of bursting synchronization in cognitive functions.

  14. UWB multi-burst transmit driver for averaging receivers

    DOEpatents

    Dallum, Gregory E

    2012-11-20

    A multi-burst transmitter for ultra-wideband (UWB) communication systems generates a sequence of precisely spaced RF bursts from a single trigger event. There are two oscillators in the transmitter circuit, a gated burst rate oscillator and a gated RF burst or RF power output oscillator. The burst rate oscillator produces a relatively low frequency, i.e., MHz, square wave output for a selected transmit cycle, and drives the RF burst oscillator, which produces RF bursts of much higher frequency, i.e., GHz, during the transmit cycle. The frequency of the burst rate oscillator sets the spacing of the RF burst packets. The first oscillator output passes through a bias driver to the second oscillator. The bias driver conditions, e.g., level shifts, the signal from the first oscillator for input into the second oscillator, and also controls the length of each RF burst. A trigger pulse actuates a timing circuit, formed of a flip-flop and associated reset time delay circuit, that controls the operation of the first oscillator, i.e., how long it oscillates (which defines the transmit cycle).

  15. Characterizing Oscillatory Bursts in Single-Trial EEG Data

    NASA Technical Reports Server (NTRS)

    Knuth, K. H.; Shah, A. S.; Lakatos, P.; Schroeder, C. E.

    2004-01-01

    Oscillatory bursts in numerous bands ranging from low (theta) to high frequencies (e.g., gamma) undoubtedly play an important role in cortical dynamics. Largely because of the inadequacy of existing analytic techniques. however, oscillatory bursts and their role in cortical processing remains poorly understood. To study oscillatory bursts effectively one must be able to isolate them and characterize them in the single trial. We describe a series of straightforward analysis techniques that produce useful indices of burst characteristics. First, stimulus-evoked responses are estimated using Differentially Variable Component Analysis (dVCA), and are subtracted from the single-trial. The single-trial characteristics of the evoked responses are stored to identify possible correlations with burst activity. Time-frequency (T-F), or wavelet, analyses are then applied to the single trial residuals. While T-F plots have been used in recent studies to identify and isolate bursts, we go further by fitting each burst in the T-F plot with a two-dimensional Gaussian. This provides a set of burst characteristics, such as, center time. burst duration, center frequency. frequency dispersion. and amplitude, all of which contribute to the accurate characterization of the individual burst. The burst phase can also be estimated. Burst characteristics can be quantified with several standard techniques (e.g.. histogramming and clustering), as well as Bayesian techniques (e.g., blocking) to allow a more parametric description analysis of the characteristics of oscillatory bursts, and the relationships of specific parameters to cortical excitability and stimulus integration.

  16. Low-Speed Investigation of the Effects of Frequency and Amplitude of Oscillation in Sideslip on the Lateral Stability Derivatives of a 60 deg Delta Wing, a 45 deg Sweptback Wing and an Unswept Wing

    NASA Technical Reports Server (NTRS)

    Lichtenstein, Jacob H.; Williams, James L.

    1961-01-01

    A low-speed investigation has been conducted in the Langley stability tunnel to study the effects of frequency and amplitude of sideslipping motion on the lateral stability derivatives of a 60 deg. delta wing, a 45 deg. sweptback wing, and an unswept wing. The investigation was made for values of the reduced-frequency parameter of 0.066 and 0.218 and for a range of amplitudes from +/- 2 to +/- 6 deg. The results of the investigation indicated that increasing the frequency of the oscillation generally produced an appreciable change in magnitude of the lateral oscillatory stability derivatives in the higher angle-of-attack range. This effect was greatest for the 60 deg. delta wing and smallest for the unswept wing and generally resulted in a more linear variation of these derivatives with angle of attack. For the relatively high frequency at which the amplitude was varied, there appeared to be little effect on the measured derivatives as a result of the change in amplitude of the oscillation.

  17. Mechanisms subserving the physiological nocturnal relative hypoprolactinemia of healthy older men: dual decline in prolactin secretory burst mass and basal release with preservation of pulse duration, frequency, and interpulse interval--a General Clinical Research Center study.

    PubMed

    Iranmanesh, A; Mulligan, T; Veldhuis, J D

    1999-03-01

    Increasing age is accompanied by decrements in randomly obtained, fasting, or frequently sampled serum PRL concentrations. The precise neuroendocrine mechanisms underlying such relative hypoprolactinemia in aging are incompletely understood. In the present study, we sampled blood at 2.5-min intervals overnight in 11 young (aged 21-34 yr) and 8 older (aged 62-72 yr) healthy men for subsequent chemiluminescence-based assay of serum PRL concentrations. The mean (+/- SEM) serum PRL concentration was significantly reduced at 4.3 +/- 0.78 microg/L in older men compared with 9.5 +/- 1.2 microg/L in young volunteers (P = 0.0049). PRL concentrations correlated with serum testosterone (r = 0.473; P = 0.041), dehydroepiandrosteroen sulfate (r = +0.455, P = 0.05), and insulin-like growth factor I (r = 0.494; P = 0.032) levels. Deconvolution analysis was used to evaluate combined pulsatile and basal modes of PRL secretion. In older men, discrete PRL secretory bursts were marked by a significantly (2.4-fold) attenuated mass of hormone secreted per burst (amount of PRL secreted per unit distribution volume), viz. 1.6 +/- 0.23 (older) vs. 3.9 +/- 0.57 microg/L (young; P < 0.01). In contrast, PRL secretory burst frequency, interpulse interval, and pulse duration were invariant of age. Concomitantly, basal PRL secretion was reduced by 2-fold in older subjects, namely to 0.00030 +/- 0.00027 (older) vs. 0.00065 +/- 0.0002 microg/L/min (young; P < 0.01). The amount of total PRL secretion that was pulsatile averaged 82 +/- 5.3% in young and 99 +/- 0.13% in older men (P = 0.012), indicating preferential loss of the basal mode of PRL release in aging. Assuming that basal PRL secretion mirrors functional pituitary lactotroph cell secretory mass, whereas pulsatile PRL release reflects effective (net) intermittent hypothalamic drive to responsive lactotroph cells, then our results suggest both an attrition in lactotroph cell mass and an impoverishment of net positive hypothalamic (agonistic

  18. Observational properties of decameter type IV bursts

    NASA Astrophysics Data System (ADS)

    Melnik, Valentin; Brazhenko, Anatoly; Rucker, Helmut; Konovalenko, Alexander; Briand, Carine; Dorovskyy, Vladimir; Zarka, Philippe; Frantzusenko, Anatoly; Panchenko, Michael; Poedts, Stefan; Zaqarashvili, Teimuraz; Shergelashvili, Bidzina

    2013-04-01

    Oscillations of decameter type IV bursts were registered during observations of solar radio emission by UTR-2, URAN-2 and NDA in 2011-2012. Large majority of these bursts were accompanied by coronal mass ejections (CMEs), which were observed by SOHO and STEREO in the visible light. Only in some cases decameter type IV bursts were not associated with CMEs. The largest periods of oscillations P were some tens of minutes. There were some modes of long periods of oscillations simultaneously. Periods of oscillations in flux and in polarization profiles were close. Detailed properties of oscillations at different frequencies were analyzed on the example of two type IV bursts. One of them was observed on April 7, 2011 when a CME happened. Another one (August 1, 2011) was registered without any CME. The 7 April type IV burst had two periods in the frames 75-85 and 35-85 minutes. Interesting feature of these oscillations is decreasing periods with time. The observed decreasing rates dP/dt equaled 0.03-0.07. Concerning type IV burst observed on August 1, 2011 the period of its oscillations increases from 17 min. at 30 MHz to 44 min. at 10 MHz. Connection of type IV burst oscillations with oscillations of magnetic arches and CMEs at corresponding altitudes are discussed. The work is fulfilled in the frame of FP7 project "SOLSPANET".

  19. The GLAST Burst Monitor

    NASA Technical Reports Server (NTRS)

    Meegan, Charles; Bhat, Narayana; Connaughton, Valerie; Briggs, Michael; Diehl, Roland; Fishman, Gerald; Greiner, Jochen; Kippen, R. Marc; vonKienlin, Andreas; Kouveliotou, Chryssa; Lichti, Giselher; Paciesas, William; Preece, Robert; Steinle, Helmut; Wilson-Hodge, Colleen

    2007-01-01

    The GLAST Burst Monitor (GBM) comprises an array of NaI and BGO scintillation detectors designed to enhance the scientific return from GLAST in the study of gamma-ray bursts (GRBs). By observing in the 10 keV to 30 MeV energy range, GBM extends the spectral coverage of GRBs more than 3 decades below the LAT energy threshold. GBM computes burst locations on-board, allowing repointing of the GLAST Observatory to place strong bursts within the LAT field-of-view to observe delayed high-energy emission.

  20. Delta wing vortex manipulation using pulsed and steady blowing during ramp pitching

    NASA Technical Reports Server (NTRS)

    Moreira, J.; Johari, H.

    1995-01-01

    The effectiveness of steady and pulsed blowing as a method of controlling delta wing vortices during ramp pitching has been investigated in flow visualization experiments conducted in a water tunnel. The recessed angled spanwise blowing technique was utilized for vortex manipulation. This technique was implemented on a beveled 60 delta wing using a pair of blowing ports located beneath the vortex core at 40% chord. The flow was injected primarily in the spanwise direction but was also composed of a component normal to the wing surface. The location of vortex burst was measured as a function of blowing intensity and pulsing frequency under static conditions, and the optimum blowing case was applied at three different wing pitching rates. Experimental results have shown that, when the burst location is upstream of the blowing port, pulsed blowing delays vortex breakdown in static and dynamic cases. Dynamic tests verified the existence of a hysteresis effect and demonstrated the improvements offered by pulsed blowing over both steady blowing and no-blowing scenarios. The application of blowing, at the optimum pulsing frequency, made the vortex breakdown location comparable in static and ramp pitch-up conditions.

  1. Type III Radio Burst Duration and SEP Events

    NASA Technical Reports Server (NTRS)

    Gopalswamy, N.; Makela, P.; Xie, H.

    2010-01-01

    Long-duration (>15 min), low-frequency (<14 MHz) type III radio bursts have been reported to be indicative of solar energetic particle events. We measured the durations of type III bursts associated with large SEP events of solar cycle 23. The Type III durations are distributed symmetrically at 1 MHz yielding a mean value of approximately 33 min (median = 32 min) for the large SEP events. When the SEP events with ground level enhancement (GLE,) are considered, the distribution is essentially unchanged (mean = 32 min, median = 30 min). To test the importance of type III bursts in indicating SEP events, we considered a set of six type III bursts from the same active region (AR 10588) whose durations fit the "long duration" criterion. We analyzed the coronal mass ejections (CMEs), flares, and type II radio bursts associated with the type III bursts. The CMEs were of similar speeds and the flares are also of similar size and duration. All but one of the type III bursts was not associated with a type II burst in the metric or longer wavelength domains. The burst without type II burst also lacked a solar energetic particle (SEP) event at energies >25 MeV. The 1-MHz duration of the type III burst (28 rein) is near the median value of type III durations found for gradual SEP events and ground level enhancement (GLE) events. Yet, there was no sign of SEP events. On the other hand, two other type III bursts from the same active region had similar duration but accompanied by WAVES type 11 bursts; these bursts were also accompanied by SEP events detected by SOHO/ERNE. This study suggests that the type III burst duration may not be a good indicator of an SEP event, consistent with the statistical study of Cliver and Ling (2009, ApJ ).

  2. Neutrino bursts from gamma-ray bursts

    NASA Technical Reports Server (NTRS)

    Paczynski, Bohdan; Xu, Guohong

    1994-01-01

    If gamma-ray bursts originate at cosmological distances, as strongly indicated by the results from Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory (CGRO), then ultrarelativistic ejecta are the likely consequence of the highly super-Eddington luminosity of the sources. If the energy injection rate varies with time, then the Lorentz factor of the wind also varies, and the shells of ejected matter collide with each other. The collisions between baryons produce pions which decay into high-energy photons, electrons, electron positron pairs, and neutrino pairs. The bulk Lorentz factor of approximately 300 is required if our model is to be compatible with the observed millisecond variability. The strongest gamma-ray bursts are observed to deliver approximately 10(exp -4) ergs/sq cm in 100-200 keV photons. In our scenario more energy may be delivered in a neutrino burst. Typical neutrinos may be approximately 30 GeV if the protons have a Maxwellian energy distribution, and up to approximately TeV if the protons have a power-law distribution. Such neutrino bursts are close to the detection limit of the DUMAND II experiment.

  3. Unusual Solar Radio Burst Observed at Decameter Wavelengths

    NASA Astrophysics Data System (ADS)

    Melnik, V. N.; Brazhenko, A. I.; Konovalenko, A. A.; Rucker, H. O.; Frantsuzenko, A. V.; Dorovskyy, V. V.; Panchenko, M.; Stanislavskyy, A. A.

    2014-01-01

    An unusual solar burst was observed simultaneously by two decameter radio telescopes UTR-2 (Kharkov, Ukraine) and URAN-2 (Poltava, Ukraine) on 3 June 2011 in the frequency range of 16 - 28 MHz. The observed radio burst had some unusual properties, which are not typical for the other types of solar radio bursts. Its frequency drift rate was positive (about 500 kHz s-1) at frequencies higher than 22 MHz and negative (100 kHz s-1) at lower frequencies. The full duration of this event varied from 50 s up to 80 s, depending on the frequency. The maximum radio flux of the unusual burst reached ≈103 s.f.u. and its polarization did not exceed 10 %. This burst had a fine frequency-time structure of unusual appearance. It consisted of stripes with the frequency bandwidth 300 - 400 kHz. We consider that several accompanied radio and optical events observed by SOHO and STEREO spacecraft were possibly associated with the reported radio burst. A model that may interpret the observed unusual solar radio burst is proposed.

  4. Oscillations During Thermonuclear X-ray Bursts

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod E.; White, Nicholas E. (Technical Monitor)

    2001-01-01

    High amplitude, nearly coherent X-ray brightness oscillations during thermonuclear X-ray bursts were discovered with the Rossi X-ray Timing Explorer (RXTE) in early 1996. Spectral and timing evidence strongly supports the conclusion that these oscillations are caused by rotational modulation of the burst emission and that they reveal the spin frequency of neutron stars in low mass X-ray binaries, a long sought goal of X-ray astronomy. Studies carried out over the past year have led to the discovery of burst oscillations in four new sources, bringing to ten the number with confirmed burst oscillations. I review the status of our knowledge of these oscillations and indicate how they can be used to probe the physics of neutron stars. For a few burst oscillation sources it has been proposed that the strongest and most ubiquitous frequency is actually the first overtone of the spin frequency and hence that two nearly antipodal hot spots are present on the neutron star. This inference has important implications for both the physics of thermonuclear burning as well as the mass - radius relation for neutron stars, so its confirmation is crucial. I discuss recent attempts to confirm this hypothesis for 4U 1636-53, the source for which a signal at the putative fundamental (290Hz) has, been claimed.

  5. Superfine Structure of Jovian Millisecond Radio Bursts

    NASA Astrophysics Data System (ADS)

    Rucker, H. O.; Litvinenko, G.; Taubenschuss, U.; Leitner, M.; Lecacheux, A.; Konovalenko, A.

    2004-05-01

    Jupiter decameter (DAM) radio emission mainly consists of wide-band radio storms with time scales in seconds (L-bursts) and milliseconds (S-bursts), the latter comprising a series of short pulses with duration of a few to tens of milliseconds, and strongly controlled by the satellite Io. First in-depth analysis of the subpulse structure was made by Carr and Reyes (1999) with the discovery of successive deep envelope modulations, with time resolution better than 30 microseconds, and during these subpulse periods the discovery of phase coherence. Recent observations by means of the newly developed waveform receiver (at present unsurpassed in spectral resolution) and connected to the decameter world-largest radio telescope UTR-2 (Kharkov) yielded waveform measurements of Jovian S-bursts which have been analyzed by the wavelet analysis method. Main outcome of the present investigation is the detection of clear signatures of microsecond modulations, providing evidence of a superfine burst structure with the following parameters: a) instantaneous frequency band of one separated microsecond pulse of 100 to 300 kHz, b) time duration of one separated micropulse of 6 to 15 microseconds, and c) time interval between closest subsequent microsecond pulses of 5 to 25 microseconds. The apparent frequency drift of a millisecond burst evidently results from sequentially decreasing frequencies of subsequent subpulses, each representing an island of phase coherent gyrating electron bunches.

  6. Discovery of the Neutron Star Spin Frequency in EXO 0748-676

    NASA Technical Reports Server (NTRS)

    Villarreal, Adam R.; Strohmayer, Tod E.

    2004-01-01

    We report the results of a search for burst oscillations during thermonuclear X-ray bursts from the low mass X-ray binary (LMXB) EXO 0748-676. With the proportional counter array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE) we have detected a 45 Hz oscillation in the average power spectrum of 38 thermonuclear X-ray bursts from this source. We computed power spectra with 1 Hz frequency resolution for both the rising and decaying portions of 38 X-ray bursts from the public RXTE archive. We averaged the 1 Hz power spectra and detected a significant signal at 45 Hz in the decaying phases of the bursts. The signal is detected at a significance level of 4 x 10 (exp -8) similar signal was detected in the rising intervals. The oscillation peak is unresolved at 1 Hz frequency resolution, indicating an oscillation quality factor, Q = nu (sub 0)/Delta nu (sub fwhm) greater than 45, and the average signal amplitude is approximately equal to 3% (rms) The detection of 45 Hz burst oscillations from EXO 0748-676 provides compelling evidence that this is the neutron star spin frequency in this system. We use the inferred spin frequency to model the widths of absorption lines from the neutron star surface and show that the widths of the absorption lines from EXO 0748-676 recently reported by Cottam et al. are consistent with a 45 Hz spin frequency as long as the neutron star radius is in the range from about 9.5 - 15 km. With a known spin frequency, precise modelling of the line profiles from EXO 0748-676 holds great promise for constraining the dense matter equation of state.

  7. Characteristics of Type-II Radio Bursts Associated with Flares and CMEs

    NASA Astrophysics Data System (ADS)

    Vasanth, V.; Umapathy, S.; Vršnak, Bojan; Anna Lakshmi, M.

    2011-10-01

    We present a statistical study of the characteristics of type-II radio bursts observed in the metric (m) and deca-hectometer (DH) wavelength range during 1997-2008. The collected events are divided into two groups: Group I contains the events of m-type-II bursts with starting frequency ≥ 100 MHz, and group II contains the events with starting frequency of m-type-II radio bursts < 100 MHz. We have analyzed both samples considering three different aspects: i) statistical properties of type-II bursts, ii) statistical properties of flares and CMEs associated with type-II bursts, and iii) time delays between type-II bursts, flares, and CMEs. We find significant differences in the properties of m-type-II bursts in duration, bandwidth, drift rate, shock speed and delay between m- and DH-type-II bursts. From the timing analysis we found that the majority of m-type-II bursts in both groups occur during the flare impulsive phase. On the other hand, the DH-type-II bursts in both groups occur during the decaying phase of the associated flares. Almost all m-DH-type-II bursts are found to be associated with CMEs. Our results indicate that there are two kinds of shock in which group I (high frequency) m-type-II bursts seem to be ignited by flares whereas group II (low frequency) m-type-II bursts are CME-driven.

  8. SHEBA prompt burst dynamics

    SciTech Connect

    Kimpland, R.

    1997-12-31

    The Solution High-Energy Burst Assembly (SHEBA), located at the Los Alamos Critical Experiments Facility, is a homogeneous liquid-fueled reactor that is being prepared for prompt burst operation. As part of the preparations, a reactor safety study was performed in support of the new SHEBA experiment plan. This study looked at the maximum power, total energy yield, and maximum transient pressures that may occur in the reactor during prompt burst operation. The goal of this study is to analyze the neutronic and hydrodynamic behavior of the reactor during burst operation, and to ensure that prompt burst operation does not damage the reactor or exceed the safety envelope of the facility`s Safety Analysis Report (SAR).

  9. Gamma Ray Bursts - Observations

    NASA Technical Reports Server (NTRS)

    Gehrels, N.; Cannizzo, J. K.

    2010-01-01

    We are in an exciting period of discovery for gamma-ray bursts. The Swift observatory is detecting 100 bursts per year, providing arcsecond localizations and sensitive observations of the prompt and afterglow emission. The Fermi observatory is observing 250 bursts per year with its medium-energy GRB instrument and about 10 bursts per year with its high-energy LAT instrument. In addition, rapid-response telescopes on the ground are providing new capabilities to study optical emission during the prompt phase and spectral signatures of the host galaxies. The combined data set is enabling great advances in our understanding of GRBs including afterglow physics, short burst origin, and high energy emission.

  10. 34 First Callisto solar burst spectrometer station in Greenland

    NASA Astrophysics Data System (ADS)

    Monstein, Christian

    2016-04-01

    In mid of March 2016 a new long wavelength station in Greenland was set into operation. It is a dual circular polarization, frequency agile solar radio burst spectrometer based on two Callisto spectrometers and the Long Wavelength Array antenna. During the commissioning phase several nice radio burst observations proved that the system works as expected.

  11. Prevalence of the Extinction Burst and Its Attenuation during Treatment.

    ERIC Educational Resources Information Center

    Lerman, Dorothea C.; Iwata, Brian A.

    1995-01-01

    A commonly associated side effect of extinction as a treatment for behavior disorders is an initial increased frequency of the target response, called an "extinction burst." This study analyzed 113 sets of extinction data and found that extinction bursting occurred in only 24% of cases and was less common when extinction was combined…

  12. Mississippi Delta

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The streamers of clouds draped over the Gulf of Mexico in this true-color MODIS image from February 27, 2002, suggest that a cold, dry wind was blowing southward over the United States and began to pick up moisture over the Gulf, causing these strips of clouds. That the clouds didn't pick up until some distance from the coastline allowed MODIS to get a perfect view of the dynamic Gulf Coast environment spanning (left to right) Texas, Louisiana, Mississippi, Alabama, and Florida's Western Panhandle. The Mississippi River runs roughly down the center of the image, and is joined in Louisiana by the Red River coming in from the northwest. Over the past 7000 years, the actual delta, where the main river channel empties into the Gulf, has wandered around what we now think of as the Louisiana coast. Considering all the sediment visible in this image, it's not hard to imagine that the river carries about 2.4 billion kilograms of sediment into the Gulf each year. Deposition of some of this sediment has been building up the current delta, called the Birdfoot Delta, for obvious reasons, for about 700 years. The coastal waters are alive with microscopic organisms called phytoplankton, which contain colorful pigments, including chlorophyll, for harvesting sunlight. Beyond the sediment plume off Louisiana, the waters are very dark, which could indicate that a large amount of chlorophyll is present, absorbing lots of sunlight and causing the water to appear dark. Farther south, the waters appear bright blue, which could be a signature of coccolithophores, which use highly reflective calcium carbonate to build scaly coverings for themselves. The brighter offshore waters could also be caused by a blue-green algae called Trichodesmium, an organism that can not only harness carbon dioxide for photosynthesis, but can also take nitrogen from the air and turn it into a form that can be used by living organisms. Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC

  13. Analysis of the role of the low threshold currents IT and Ih in intrinsic delta oscillations of thalamocortical neurons

    PubMed Central

    Amarillo, Yimy; Mato, Germán; Nadal, Marcela S.

    2015-01-01

    Thalamocortical neurons are involved in the generation and maintenance of brain rhythms associated with global functional states. The repetitive burst firing of TC neurons at delta frequencies (1–4 Hz) has been linked to the oscillations recorded during deep sleep and during episodes of absence seizures. To get insight into the biophysical properties that are the basis for intrinsic delta oscillations in these neurons, we performed a bifurcation analysis of a minimal conductance-based thalamocortical neuron model including only the IT channel and the sodium and potassium leak channels. This analysis unveils the dynamics of repetitive burst firing of TC neurons, and describes how the interplay between the amplifying variable mT and the recovering variable hT of the calcium channel IT is sufficient to generate low threshold oscillations in the delta band. We also explored the role of the hyperpolarization activated cationic current Ih in this reduced model and determine that, albeit not required, Ih amplifies and stabilizes the oscillation. PMID:25999847

  14. INTEGRAL burst alert service

    NASA Technical Reports Server (NTRS)

    Pedersen, H.; Jennings, D.; Mereghetti, S.; Teegarden, B.

    1997-01-01

    The detection, accurate positioning, and spectral analysis of cosmic gamma ray bursts is an objective of the International Gamma Ray Astrophysics Laboratory (INTEGRAL) mission. Due to their unpredictable nature, gamma ray bursts can only be observed in serendipity mode. In order to allow and promote multiwavelength follow-up observations of such events, it is desirable to make the information available to the astrophysics community with a minimum delay through the use of Internet. Ideally, the data dissemination should occur within a few seconds of the start of the burst event so that follow up observations can proceed while gamma rays are still being emitted. The technical feasibility of building such a system to disseminate INTEGRAL burst alerts in real time is currently under consideration, the preliminary results of which are presented. It is concluded that such an alert service is technically feasible.

  15. Experimental measurements on an oscillating 70-degree delta wing in subsonic flow

    NASA Technical Reports Server (NTRS)

    Soltani, M. R.; Bragg, M. B.; Brandon, J. M.

    1988-01-01

    A series of low-speed wind tunnel tests on a 70-degree sharp leading-edged delta wing at both static and dynamic conditions were performed to investigate the aerodynamic forces and moments. Forces and moments were obtained from a six component internal strain gauge balance. Static results compared well with the previous experimental findings. Large amplitude dynamic motion was produced by sinusoidally oscillating the model over a range of reduced frequencies. Substantial force and moment overshoots, a delay in dynamic stall, and hysteresis loops between the values of aerodynamnic loads in upstroke and downstroke motion were observed, all of which were strong functions of the reduced frequency. The aerodynamic forces and moments were influenced by the Reynolds number. Asymmetrical vortex bursting produced by nonzero sideslip angle created a complex rolling moment variations with angle of attack.

  16. GLAST's GBM Burst Trigger

    NASA Technical Reports Server (NTRS)

    Band, D.; Briggs, M.; Connaughton, V.; Kippen, M.; Preece, R.

    2003-01-01

    The GLAST Burst Monitor (GBM) will detect and localize bursts for the GLAST mission, and provide the spectral and temporal context in the traditional 10 keV to 25 MeV band for the high energy observations by the Large Area Telescope (LAT). The GBM will use traditional rate triggers in up to three energy bands, and on a variety of timescales between 16 ms and 16 s.

  17. Mississippi Delta

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The Mississippi River delta teems with sediment deposited by the river as it flows into the Gulf of Mexico in this true-color image captured by MODIS on October 15, 2001. The sediment, which is marked by brown swirls in the Gulf, provides nutrients for the bloom of phytoplankton visible as blue-green swirls off the coastline. In the high-resolution image the city of Memphis can be seen in the southwest corner of Tennessee, which is just to left of center at the top of the image. The brown coloration that encompasses Memphis and either side of the river, as flows north to south along the left side of the image, is the river's flood plain. Also visible, in the upper-right hand corner of the image is the southern end of the Appalachian Mountains.

  18. Narrow band characteristics of Jovian L-bursts.

    NASA Technical Reports Server (NTRS)

    Barrow, C. H.

    1971-01-01

    Review of some radio observations of Jupiter made during three recent apparitions using several receivers, each tuned to a slightly different frequency close to 18 MHz. Sequences of oppositely polarized bursts have been observed and also differences in polarization mode between channels 400 kHz apart. Occasionally, isolated bursts of durations of 1 to 2 sec have been found to show real drifts in frequency, as distinct from the apparent drifts shown by changing intensity across a group of features.

  19. Meteor-Burst Communications: Is This What the Navy Needs?

    DTIC Science & Technology

    1987-06-01

    UNDERDENSE Time OVERDENSE Time Figure 5 -Underdense and Overdense Ion Trails 24 and receiver, and the action of the high altitude winds. The net effect of...experience increased fading at the lower frequencies, with attendant competing modes of propagation. As the frequency is decreased, the amount of...random occurrence of limited duration, MBC systems use a burst- mode concept. The flow of data in a burst- mode system is intermittent, transmitting only

  20. Search for the Third Harmonic of Type III Bursts Radio Emission at Decameter Wavelengths

    NASA Astrophysics Data System (ADS)

    Brazhenko, A. I.; Melnik, V. N.; Konovalenko, A. A.; Pylaev, O. S.; Frantsuzenko, A. V.; Dorovskyy, V. V.; Vashchishin, R. V.; Rucker, H. O.

    The results of observations of trio bursts consisting of type III bursts are presented in this paper. The instantaneous frequency ratio of trio components is near 1:2:3. We analyze flow, duration, frequency drift rate and polarization of trio components as well as dependencies of these characteristics on frequency.

  1. Can we identify lensed gamma-ray bursts?

    NASA Technical Reports Server (NTRS)

    Nowak, Michael A.; Grossman, Scott A.

    1994-01-01

    A gravitationally lensed gamma-ray burst (GRB) would appear as multiple bursts with identical light curves, separated in time and differing only by the scaling of their amplitudes. In reality, the detected bursts will be noisy, and therefore they may be difficult to identify as lensed images. Furthermore, faint, intrinsically similar, yet distinct light curves may be falsely identified as lensing events. In this paper we develop two statistical tests to distinguish noisy burst light curves. We use Fourier analysis techniques to analyze the signals for both intrinsic variability and variability due to noise. We are able to determine the noise level, and we compare the bursts only at frequency channels that are signal dominated. Utilizing these methods, we are able to make quantitative statements about whether two bursts are distinct. We apply these statistics to scaled versions of two subbursts of GRB 910503 -- subbursts previously investigated by Wambsganss using a different statistical test. We find that our methods are able to distinguish these bursts at slightly smaller amplitudes than those at which Wambsganss's method succeeds. We then apply our techniques to 'candidate' lensing events taken from the Burst and Transient Source Experiment (BATSE) catalog, and we find that nearly all of them, except for the very shortest ones (durations approx. less than 3 sec), are distinguishable. We therefore expect that a majority of bursts will be distinguishable from one another.

  2. Effect of burst parameters on automotive brake squeal suppression

    NASA Astrophysics Data System (ADS)

    Badertscher, Jeff; Cunefare, Kenneth A.

    2003-04-01

    Implementing a dither control signal with a 100% duty cycle is an effective means of suppressing automotive brake squeal. Dither control is a method by which high-frequency control efforts are introduced into a system to suppress a lower frequency disturbance. Dither is introduced to a brake by placing a piezoelectric stack actuator in the piston of a floating caliper brake. Burst mode dither control is characterized by duty cycles of less than 100%. A burst control signal of a specific duty cycle is also specified by the burst count and burst rate. Burst mode signals are shown to suppress brake squeal. This paper examines the nature of suppression and the effectiveness of burst mode dither control signals with varied burst parameters. An examination of the squeal response and dither control signal is used to examine the nature of suppression during bursting and dwell time. The amplitude of the control signal that is necessary to obtain full control of the system is used to assess control signal effectiveness.

  3. Could FIV zoonosis responsible of the breakdown of the pathocenosis which has reduced the European CCR5-Delta32 allele frequencies?

    PubMed Central

    Faure, Eric

    2008-01-01

    Background In Europe, the north-south downhill cline frequency of the chemokine receptor CCR5 allele with a 32-bp deletion (CCR5-Δ32) raises interesting questions for evolutionary biologists. We had suggested first that, in the past, the European colonizers, principally Romans, might have been instrumental of a progressively decrease of the frequencies southwards. Indeed, statistical analyses suggested strong negative correlations between the allele frequency and historical parameters including the colonization dates by Mediterranean civilisations. The gene flows from colonizers to native populations were extremely low but colonizers are responsible of the spread of several diseases suggesting that the dissemination of parasites in naive populations could have induced a breakdown rupture of the fragile pathocenosis changing the balance among diseases. The new equilibrium state has been reached through a negative selection of the null allele. Results Most of the human diseases are zoonoses and cat might have been instrumental in the decrease of the allele frequency, because its diffusion through Europe was a gradual process, due principally to Romans; and that several cat zoonoses could be transmitted to man. The possible implication of a feline lentivirus (FIV) which does not use CCR5 as co-receptor is discussed. This virus can infect primate cells in vitro and induces clinical signs in macaque. Moreover, most of the historical regions with null or low frequency of CCR5-Δ32 allele coincide with historical range of the wild felid species which harbor species-specific FIVs. Conclusion We proposed the hypothesis that the actual European CCR5 allelic frequencies are the result of a negative selection due to a disease spreading. A cat zoonosis, could be the most plausible hypothesis. Future studies could provide if CCR5 can play an antimicrobial role in FIV pathogenesis. Moreover, studies of ancient DNA could provide more evidences regarding the implications of

  4. Positional characteristics of meter-decameter wavelength bursts associated with hard X-ray bursts

    NASA Technical Reports Server (NTRS)

    Kundu, M. R.; Gergely, T. E.; Kane, S. R.

    1982-01-01

    Isolated and grouped type III bursts have been observed in temporal association with impulsive hard X-ray bursts in the 26-154 keV range, down to frequencies as low as 30 MHz and out to a distance of 3.1 solar radii from the disk center. The bursts occurred in regions whose electron density may have been as much as 20 times higher than that of the Newkirk-Saito model. The present observations indicate that electron acceleration/injection occurs over a region covering a wide range of magnetic field lines. It is noted that, of the two gradual hard X-ray bursts observed in association with type IV bursts, one was accompanied by a type II event, while the other was not, although both exhibited the same characteristics. It is suggested that the gradual burst associated with a type IV only involved electrons which are trapped in the plasmoid which produces the meter-decameter emission, while another fraction of the population is trapped in the low-lying loops which produce the hard X-ray and centimeter radiation.

  5. A Burst to See

    NASA Astrophysics Data System (ADS)

    2008-04-01

    On 19 March, Nature was particularly generous and provided astronomers with the wealth of four gamma-ray bursts on the same day. But that was not all: one of them is the most luminous object ever observed in the Universe. Despite being located in a distant galaxy, billions of light years away, it was so bright that it could have been seen, for a brief while, with the unaided eye. ESO PR Photo 08a/08 ESO PR Photo 08a/08 The REM Telescope and TORTORA Camera Gamma-ray bursts (GRBs) are short flashes of energetic gamma-rays lasting from less than a second to several minutes. They release a tremendous quantity of energy in this short time making them the most powerful events since the Big Bang. It is now widely accepted that the majority of the gamma-ray bursts signal the explosion of very massive, highly evolved stars that collapse into black holes. Gamma-ray bursts, which are invisible to our eyes, are discovered by telescopes in space. After releasing their intense burst of high-energy radiation, they become detectable for a short while in the optical and in the near-infrared. This 'afterglow' fades very rapidly, making detailed analysis possible for only a few hours after the gamma-ray detection. This analysis is important in particular in order to determine the GRB's distance and, hence, intrinsic brightness. The gamma-ray burst GRB 080319B was detected by the NASA/STFC/ASI Swift satellite. "It was so bright that it almost blinded the Swift instruments for a while," says Guido Chincarini, Italian principal investigator of the mission. A bright optical counterpart was soon identified in the Boötes Constellation (the "Bear Driver" or "Herdsman"). A host of ground-based telescopes reacted promptly to study this new object in the sky. In particular, the optical emission was detected by a few wide-field cameras on telescopes that constantly monitor a large fraction of the sky, including the TORTORA camera in symbiosis with the 0.6-m REM telescope located at La Silla

  6. The Glast Burst Monitor

    NASA Technical Reports Server (NTRS)

    Meegan, Charles

    2000-01-01

    The Gamma-Ray Large Area Space Telescope (GLAST) will include a secondary instrument to augment the observatory's capabilities for GRB studies. The GLAST Burst Monitor (GBK is a collaboration between Marshall Space Flight Center, the University of Huntsville, Alabama, and the Max Plank Institute for Extraterrestrial Physics. The purpose of the GBM is to extend energy coverage below the main instrument's lower limit of about 20 MeV, and to provide an on-board burst trigger and approximate location. The instrument consists of twelve NaI detectors and two BGO detectors. This combination provides energy coverage from a few keV up to about 30 MeV.

  7. The Delta 2 launcher

    NASA Astrophysics Data System (ADS)

    Ousley, Gilbert W., Sr.

    1991-12-01

    The utilization of the Delta 2 as the vehicle for launching Aristoteles into its near Sun synchronous orbit is addressed. Delta is NASA's most reliable launch vehicle and is well suited for placing the present Aristoteles spacecraft into a 400 m circular orbit. A summary of some of the Delta 2 flight parameters is presented. Diagrams of a typical Delta 2 two stage separation are included along with statistics on delta reliability and launch plans.

  8. Kilometric shock-associated events and microwave bursts

    NASA Technical Reports Server (NTRS)

    Kundu, M. R.; Macdowall, R. J.; Stone, R. G.

    1990-01-01

    The peak times of impulsive microwaves bursts are compared with those of shock-associated (SA) kilometric radio events. The first peaks in these two frequency regimes are usually well-correlated in time, but the last peaks of the SA events observed at 1 MHz occur an average of 20 min after the last impulsive microwave peaks. In some cases, the SA events overlap in time with the post-burst increases of microwave bursts; sometimes there is general correspondence in their intensity time profiles. These observations suggest that the earlier components of the SA events are usually caused by electrons accelerated in or near the microwave source region. The possibility that the later components of some SA events could be associated with nonthermal electrons responsible for microwave post-burst increases, although they have traditionally been attributed to electrons accelerated at type II burst producing shocks in the upper corona is discussed.

  9. Vibration-induced drop atomization and bursting

    NASA Astrophysics Data System (ADS)

    James, A. J.; Vukasinovic, B.; Smith, Marc K.; Glezer, A.

    2003-02-01

    A liquid drop placed on a vibrating diaphragm will burst into a fine spray of smaller secondary droplets if it is driven at the proper frequency and amplitude. The process begins when capillary waves appear on the free surface of the drop and then grow in amplitude and complexity as the acceleration amplitude of the diaphragm is slowly increased from zero. When the acceleration of the diaphragm rises above a well-defined critical value, small secondary droplets begin to be ejected from the free-surface wave crests. Then, quite suddenly, the entire volume of the drop is ejected from the vibrating diaphragm in the form of a spray. This event is the result of an interaction between the fluid dynamical process of droplet ejection and the vibrational dynamics of the diaphragm. During droplet ejection, the effective mass of the drop diaphragm system decreases and the resonance frequency of the system increases. If the initial forcing frequency is above the resonance frequency of the system, droplet ejection causes the system to move closer to resonance, which in turn causes more vigorous vibration and faster droplet ejection. This ultimately leads to drop bursting. In this paper, the basic phenomenon of vibration-induced drop atomization and drop bursting will be introduced, demonstrated, and characterized. Experimental results and a simple mathematical model of the process will be presented and used to explain the basic physics of the system.

  10. Properties of X-ray bursts from the X-ray transient 1608-522

    SciTech Connect

    Murakami, T.; Inoue, H.; Koyama, K.

    1980-09-15

    The recurrent X-ray transient 1608--522 was observed from the X-ray astronomy satellite Hakucho through the high- and low-luminosity states of its persistent flux. 1608--522 is identified to be a burst source from which 22 X-ray bursts were recorded. The burst peak intensity is found to fluctuate by a factor as large as 7. 1608--522 exhibited two distinctly different burst modes with respect to the burst profile and the peak luminosity distribution. The burst mode seems to have changed in correlation with the persistent flux, whereas the burst frequency as well as the time-averaged burst luminosity were essentially constant despite a large change in the persistent flux.

  11. The GLAST Burst Monitor

    NASA Technical Reports Server (NTRS)

    Meegan, Charles A.

    2004-01-01

    The Gamma Ray Large Area Space Telescope (GLAST) observatory, scheduled for launch in 2007, comprises the Large Area Telescope (LAT) and the GLAST Burst Monitor (GBM). spectral changes that are known to occur within GRBs. between the NASA Marshall Space Flight Center, the University of Alabama in Huntsville, and the Max Planck Institute for Extraterrestrial Physics. It consists of an array of NaI and BGO scintillation detectors operating in the 10 kev to 25 MeV range. The field of view includes the entire unocculted sky when the observatory is pointing close to the zenith. The GBM will enhance LAT observations of GRBs by extending the spectral coverage into the range of current GRB databases, and will provide a trigger for reorienting the spacecraft to observe delayed emission from bursts outside the LAT field of view. GBM is expected to trigger on about 200 bursts per year, and will provide on-board locations of strong bursts accurate to better than 10 degrees.

  12. Action potential bursts enhance transmitter release at a giant central synapse.

    PubMed

    Zhang, Bo; Sun, Liang; Yang, Yi-Mei; Huang, Hong-Ping; Zhu, Fei-Peng; Wang, Li; Zhang, Xiao-Yu; Guo, Shu; Zuo, Pan-Li; Zhang, Claire X; Ding, Jiu-Ping; Wang, Lu-Yang; Zhou, Zhuan

    2011-05-01

    Patterns of action potentials (APs), often in the form of bursts, are critical for coding and processing information in the brain. However, how AP bursts modulate secretion at synapses remains elusive. Here, using the calyx of Held synapse as a model we compared synaptic release evoked by AP patterns with a different number of bursts while the total number of APs and frequency were fixed. The ratio of total release produced by multiple bursts to that by a single burst was defined as 'burst-effect'.We found that four bursts of 25 stimuli at 100 Hz increased the totalcharge of EPSCs to 1.47 ± 0.04 times that by a single burst of 100 stimuli at the same frequency.Blocking AMPA receptor desensitization and saturation did not alter the burst-effect, indicating that it was mainly determined by presynaptic mechanisms. Simultaneous dual recordings of presynaptic membrane capacitance (Cm) and EPSCs revealed a similar burst-effect, being 1.58±0.13by Cm and 1.49±0.05 by EPSCs. Reducing presynapticCa2+ influx by lowering extracellular Ca2+concentration or buffering residual intracellular Ca2+ with EGTA inhibited the burst-effect. We further developed a computational model largely recapitulating the burst-effect and demonstrated that this effect is highly sensitive to dynamic change in availability of the releasable pool of synaptic vesicles during various patterns of activities. Taken together, we conclude that AP bursts modulate synaptic output mainly through intricate interaction between depletion and replenishment of the large releasable pool. This burst-effect differs from the somatic burst-effect previously described from adrenal chromaffin cells, which substantially depends on activity-induced accumulation of Ca2+ to facilitate release of a limited number of vesicles in the releasable pool. Hence, AP bursts may play an important role in dynamically regulating synaptic strength and fidelity during intense neuronal activity at central synapses.

  13. Time-Resolved Magneto-Optical Imaging of Y1Ba2Cu3O7-delta Thin Films in High-Frequency AC Current Regime (Postprint)

    DTIC Science & Technology

    2012-02-01

    pumped solid-state laser which provides 100 ns short pulses at 527 nm wavelength. The pulse repetition frequency (PRF) of the laser can be varied...substrate with typical dimensions of 10 mm × 5 mm [14]. The YBCO films are about 250 nm thick. The samples exhibit a critical transition temperature (Tc) of...evolution of the magnetic flux density distribution in YBa2Cu3O7−δ ( YBCO ) thin film samples is studied as a function of the phase of the applied AC current

  14. Periodic Bursts of Jovian Non-Io Decametric Radio Emission

    NASA Technical Reports Server (NTRS)

    Panchenko, M.; Rucker, H O.; Farrell, W. M.

    2013-01-01

    During the years 2000-2011 the radio instruments onboard Cassini, Wind and STEREO spacecraft have Recorded a large amount of the Jovian decametric radio emission (DAM). In this paper we report on the analysis of the new type of Jovian periodic radio bursts recently revealed in the decametric frequency range. These bursts, which are non-Io component of DAM, are characterized by a strong periodic reoccurrence over several Jovian days with a period approx. = 1:5% longer than the rotation rate of the planet's magnetosphere (System III). The bursts are typically observed between 4 and 12 MHz and their occurrence probability has been found to be significantly higher in the sector of Jovian Central Meridian Longitude between 300 deg. and 60 deg. (via 360 deg.). The stereoscopic multispacecraft observations have shown that the radio sources of the periodic bursts radiate in a non-axisymmetric hollow cone-like pattern and sub-corotate with Jupiter remaining active during several planet's rotations. The occurrence of the periodic non-Io DAM bursts is strongly correlated with pulses of the solar wind ram pressure at Jupiter. Moreover the periodic bursts exhibit a tendency to occur in groups every approx. 25 days. The polarization measurements have shown that the periodic bursts are right hand polarized radio emission associated with the Northern magnetic hemisphere of Jupiter. We suggest that periodic non-Io DAM bursts may be connected with the interchange instability in Io plasma torus triggered by the solar wind.

  15. Periodic bursts of Jovian non-Io decametric radio emission.

    PubMed

    Panchenko, M; Rucker, H O; Farrell, W M

    2013-03-01

    During the years 2000-2011 the radio instruments onboard Cassini, Wind and STEREO spacecraft have recorded a large amount of the Jovian decametric radio emission (DAM). In this paper we report on the analysis of the new type of Jovian periodic radio bursts recently revealed in the decametric frequency range. These bursts, which are non-Io component of DAM, are characterized by a strong periodic reoccurrence over several Jovian days with a period [Formula: see text] longer than the rotation rate of the planet's magnetosphere (System III). The bursts are typically observed between 4 and 12 MHz and their occurrence probability has been found to be significantly higher in the sector of Jovian Central Meridian Longitude between 300° and 60° (via 360°). The stereoscopic multispacecraft observations have shown that the radio sources of the periodic bursts radiate in a non-axisymmetric hollow cone-like pattern and sub-corotate with Jupiter remaining active during several planet's rotations. The occurrence of the periodic non-Io DAM bursts is strongly correlated with pulses of the solar wind ram pressure at Jupiter. Moreover the periodic bursts exhibit a tendency to occur in groups every [Formula: see text] days. The polarization measurements have shown that the periodic bursts are right hand polarized radio emission associated with the Northern magnetic hemisphere of Jupiter. We suggest that periodic non-Io DAM bursts may be connected with the interchange instability in Io plasma torus triggered by the solar wind.

  16. Periodic bursts of Jovian non-Io decametric radio emission

    PubMed Central

    Panchenko, M.; Rucker, H.O.; Farrell, W.M.

    2013-01-01

    During the years 2000–2011 the radio instruments onboard Cassini, Wind and STEREO spacecraft have recorded a large amount of the Jovian decametric radio emission (DAM). In this paper we report on the analysis of the new type of Jovian periodic radio bursts recently revealed in the decametric frequency range. These bursts, which are non-Io component of DAM, are characterized by a strong periodic reoccurrence over several Jovian days with a period ≈1.5% longer than the rotation rate of the planet's magnetosphere (System III). The bursts are typically observed between 4 and 12 MHz and their occurrence probability has been found to be significantly higher in the sector of Jovian Central Meridian Longitude between 300° and 60° (via 360°). The stereoscopic multispacecraft observations have shown that the radio sources of the periodic bursts radiate in a non-axisymmetric hollow cone-like pattern and sub-corotate with Jupiter remaining active during several planet's rotations. The occurrence of the periodic non-Io DAM bursts is strongly correlated with pulses of the solar wind ram pressure at Jupiter. Moreover the periodic bursts exhibit a tendency to occur in groups every ∼25 days. The polarization measurements have shown that the periodic bursts are right hand polarized radio emission associated with the Northern magnetic hemisphere of Jupiter. We suggest that periodic non-Io DAM bursts may be connected with the interchange instability in Io plasma torus triggered by the solar wind. PMID:23585696

  17. Periodic bursts of Jovian non-Io decametric radio emission

    NASA Astrophysics Data System (ADS)

    Panchenko, M.; Rucker, H. O.; Farrell, W. M.

    2013-03-01

    During the years 2000-2011 the radio instruments onboard Cassini, Wind and STEREO spacecraft have recorded a large amount of the Jovian decametric radio emission (DAM). In this paper we report on the analysis of the new type of Jovian periodic radio bursts recently revealed in the decametric frequency range. These bursts, which are non-Io component of DAM, are characterized by a strong periodic reoccurrence over several Jovian days with a period ≈1.5% longer than the rotation rate of the planet's magnetosphere (System III). The bursts are typically observed between 4 and 12 MHz and their occurrence probability has been found to be significantly higher in the sector of Jovian Central Meridian Longitude between 300° and 60° (via 360°). The stereoscopic multispacecraft observations have shown that the radio sources of the periodic bursts radiate in a non-axisymmetric hollow cone-like pattern and sub-corotate with Jupiter remaining active during several planet's rotations. The occurrence of the periodic non-Io DAM bursts is strongly correlated with pulses of the solar wind ram pressure at Jupiter. Moreover the periodic bursts exhibit a tendency to occur in groups every ∼25 days. The polarization measurements have shown that the periodic bursts are right hand polarized radio emission associated with the Northern magnetic hemisphere of Jupiter. We suggest that periodic non-Io DAM bursts may be connected with the interchange instability in Io plasma torus triggered by the solar wind.

  18. A type IV burst associated with a coronal streamer disruption event

    NASA Technical Reports Server (NTRS)

    Kundu, M. R.

    1987-01-01

    A type IV burst was observed on February 17, 1985 with the Clark Lake Radio Observatory multifrequency radioheliograph operating in the frequency range 20-125 MHz. This burst was associated with a coronal streamer disruption event. From two-dimensional images produced at 50 MHz, evidence of a type II burst and a slow moving type IV burst are shown. The observations of the moving type IV burst suggests that a plasmoid containing energetic electrons can result from the disruption of a coronal streamer.

  19. Q-Bursts: Natural ELF Radio Transients

    NASA Astrophysics Data System (ADS)

    Nickolaenko, A. P.; Hayakawa, M.; Hobara, Y.

    2010-07-01

    We overview resonance spectra and present analytical expressions for the waveforms of natural extremely low frequency transient events (Q-bursts). It is shown that model and observed waveforms are similar when a wideband receiver is used at a place with low level of industrial interference. We also describe how to detect a natural ELF transient signal embedded in the man-made noise by using the singular spectral analysis.

  20. Brown University Radio Student Telescope (BURST)

    NASA Astrophysics Data System (ADS)

    Miller, Michelle

    2017-01-01

    The Brown University Radio Student Telescope (BURST) is a rooftop low frequency radio interferometer that we hope to potentially use to observe radio transients, non-thermal radio emission from Galactic synchrotron and supernova remnants, and extragalactic radio sources. It was built by a group of Brown undergraduates this past summer. An overview of the design, ultimate installation, challenges in implementation and data acquisition will be covered in the poster.

  1. The Double Firing Burst

    NASA Astrophysics Data System (ADS)

    2008-09-01

    Astronomers from around the world combined data from ground- and space-based telescopes to paint a detailed portrait of the brightest explosion ever seen. The observations reveal that the jets of the gamma-ray burst called GRB 080319B were aimed almost directly at the Earth. Uncovering the disc ESO PR Photo 28/08 A Gamma-Ray Burst with Two Jets Read more on this illuminating blast in the additional story. GRB 080319B was so intense that, despite happening halfway across the Universe, it could have been seen briefly with the unaided eye (ESO 08/08). In a paper to appear in the 11 September issue of Nature, Judith Racusin of Penn State University, Pennsylvania (USA), and a team of 92 co-authors report observations across the electromagnetic spectrum that began 30 minutes before the explosion and followed it for months afterwards. "We conclude that the burst's extraordinary brightness arose from a jet that shot material almost directly towards Earth at almost the speed of light - the difference is only 1 part in 20 000," says Guido Chincarini, a member of the team. Gamma-ray bursts are the Universe's most luminous explosions. Most occur when massive stars run out of fuel. As a star collapses, it creates a black hole or neutron star that, through processes not fully understood, drives powerful gas jets outward. As the jets shoot into space, they strike gas previously shed by the star and heat it, thereby generating bright afterglows. The team believes the jet directed toward Earth contained an ultra-fast component just 0.4 degrees across (this is slightly smaller than the apparent size of the Full Moon). This jet is contained within another slightly less energetic jet about 20 times wider. The broad component is more typical of other bursts. "Perhaps every gamma-ray burst has a narrow jet, but astronomers miss it most of the time," says team member Stefano Covino. "We happened to view this monster down the barrel of the very narrow and energetic jet, and the chance for

  2. Burst Populations and Detector Sensitivity

    NASA Technical Reports Server (NTRS)

    Band, David L.

    2003-01-01

    The F(sub T) (peak bolometric photon flux) vs. E(sub p) (peak energy) plane is a powerful tool to compare the burst populations detected by different detectors. Detector sensitivity curves in this plane demonstrate which burst populations the detectors will detect. For example, future CZT-based detectors will show the largest increase in sensitivity for soft bursts, and will be particularly well- suited to study X-ray rich bursts and X-ray Flashes. Identical bursts at different redshifts describe a track in the F(sub T)-E(sub p) plane.

  3. RADIO FLARES FROM GAMMA-RAY BURSTS

    SciTech Connect

    Kopač, D.; Mundell, C. G.; Kobayashi, S.; Virgili, F. J.; Harrison, R.; Japelj, J.; Gomboc, A.; Guidorzi, C.; Melandri, A.

    2015-06-20

    We present predictions of centimeter and millimeter radio emission from reverse shocks (RSs) in the early afterglows of gamma-ray bursts (GRBs) with the goal of determining their detectability with current and future radio facilities. Using a range of GRB properties, such as peak optical brightness and time, isotropic equivalent gamma-ray energy, and redshift, we simulate radio light curves in a framework generalized for any circumburst medium structure and including a parameterization of the shell thickness regime that is more realistic than the simple assumption of thick- or thin-shell approximations. Building on earlier work by Mundell et al. and Melandri et al. in which the typical frequency of the RS was suggested to lie at radio rather than optical wavelengths at early times, we show that the brightest and most distinct RS radio signatures are detectable up to 0.1–1 day after the burst, emphasizing the need for rapid radio follow-up. Detection is easier for bursts with later optical peaks, high isotropic energies, lower circumburst medium densities, and at observing frequencies that are less prone to synchrotron self-absorption effects—typically above a few GHz. Given recent detections of polarized prompt gamma-ray and optical RS emission, we suggest that detection of polarized radio/millimeter emission will unambiguously confirm the presence of low-frequency RSs at early time.

  4. Delta K measurements with synthetic aperture radar data. [micirowavelength difference values

    NASA Technical Reports Server (NTRS)

    Larson, R. W.; Jackson, P. L.; Klooster, A.

    1985-01-01

    Delta K measurements are obtained from the interference of two electromagnetic waves of different frequencies. Constructive interference occurs when 2pi phase differences between the two frequencies correspond to a surface wavelength. Previous Delta K measurements have used two discrete frequencies for this purpose. Range pulses and Doppler signatures of a synthetic aperture radar system were filtered to obtain a sequence of Delta K values. Those Delta K values which correspond to the wavelengths of known surfaces show maximum constructive interference. SAR data can therefore be used for Delta K measurements, indicating the possibility of selective Delta K filtering during data gathering.

  5. A repeating fast radio burst

    NASA Astrophysics Data System (ADS)

    Spitler, L. G.; Scholz, P.; Hessels, J. W. T.; Bogdanov, S.; Brazier, A.; Camilo, F.; Chatterjee, S.; Cordes, J. M.; Crawford, F.; Deneva, J.; Ferdman, R. D.; Freire, P. C. C.; Kaspi, V. M.; Lazarus, P.; Lynch, R.; Madsen, E. C.; McLaughlin, M. A.; Patel, C.; Ransom, S. M.; Seymour, A.; Stairs, I. H.; Stappers, B. W.; van Leeuwen, J.; Zhu, W. W.

    2016-03-01

    Fast radio bursts are millisecond-duration astronomical radio pulses of unknown physical origin that appear to come from extragalactic distances. Previous follow-up observations have failed to find additional bursts at the same dispersion measure (that is, the integrated column density of free electrons between source and telescope) and sky position as the original detections. The apparent non-repeating nature of these bursts has led to the suggestion that they originate in cataclysmic events. Here we report observations of ten additional bursts from the direction of the fast radio burst FRB 121102. These bursts have dispersion measures and sky positions consistent with the original burst. This unambiguously identifies FRB 121102 as repeating and demonstrates that its source survives the energetic events that cause the bursts. Additionally, the bursts from FRB 121102 show a wide range of spectral shapes that appear to be predominantly intrinsic to the source and which vary on timescales of minutes or less. Although there may be multiple physical origins for the population of fast radio bursts, these repeat bursts with high dispersion measure and variable spectra specifically seen from the direction of FRB 121102 support an origin in a young, highly magnetized, extragalactic neutron star.

  6. A repeating fast radio burst.

    PubMed

    Spitler, L G; Scholz, P; Hessels, J W T; Bogdanov, S; Brazier, A; Camilo, F; Chatterjee, S; Cordes, J M; Crawford, F; Deneva, J; Ferdman, R D; Freire, P C C; Kaspi, V M; Lazarus, P; Lynch, R; Madsen, E C; McLaughlin, M A; Patel, C; Ransom, S M; Seymour, A; Stairs, I H; Stappers, B W; van Leeuwen, J; Zhu, W W

    2016-03-10

    Fast radio bursts are millisecond-duration astronomical radio pulses of unknown physical origin that appear to come from extragalactic distances. Previous follow-up observations have failed to find additional bursts at the same dispersion measure (that is, the integrated column density of free electrons between source and telescope) and sky position as the original detections. The apparent non-repeating nature of these bursts has led to the suggestion that they originate in cataclysmic events. Here we report observations of ten additional bursts from the direction of the fast radio burst FRB 121102. These bursts have dispersion measures and sky positions consistent with the original burst. This unambiguously identifies FRB 121102 as repeating and demonstrates that its source survives the energetic events that cause the bursts. Additionally, the bursts from FRB 121102 show a wide range of spectral shapes that appear to be predominantly intrinsic to the source and which vary on timescales of minutes or less. Although there may be multiple physical origins for the population of fast radio bursts, these repeat bursts with high dispersion measure and variable spectra specifically seen from the direction of FRB 121102 support an origin in a young, highly magnetized, extragalactic neutron star.

  7. Searching For Fast Radio Burst Counterparts with Swift's Burst Alert Telescope

    NASA Astrophysics Data System (ADS)

    Delaunay, James; Fox, Derek; AMON Team

    2017-01-01

    Fast Radio Bursts (FRBs) are millisecond-long bursts of GHz-frequency emission with Dispersion Measures large enough to be of a cosmological origin. There has yet to be a non-radio counterpart or high-confidence host galaxy detected for any FRB, leaving their true nature to be very mysterious. Using sub-threshold archival data from Swift's Burst Alert Telescope (BAT;) we searched for evidence of a gamma-ray counterpart to any of the FRBs. In this talk I will present the details and results of our search. If real-time FRB alerts are integrated into the Astrophysical Multimessenger Observatory Network (AMON;), sub-threshold FRBs can be detected through real-time spatial and temporal coincidences with other messengers. I will also talk about the real-time AMON analysis that's currently running. We gratfully acknowledge support from the Penn State Institute for Gravitation and Cosmos

  8. Feasibility of generating an artificial burst in a turbulent boundary layer

    NASA Technical Reports Server (NTRS)

    Gad-El-hak, M.

    1986-01-01

    Artificial bursts were generated in laminar and turbulent boundary layers. The burst-like events were produced by withdrawing near-wall fluid from two minute holes separated in the spanwise direction or by pitching a miniature delta wing that was flush-mounted to the wall. Either of these actions generated streamwise vorticity and a low-speed streak that resembled a naturally occurring one. The resulting sequence of events occurred at a given location and at controlled times, allowing detailed examination and comparison with natural, random bursts by means of flow visualization and fast-response probe measurement techniques.

  9. delta-Hexachlorocyclohexane (delta-HCH)

    Integrated Risk Information System (IRIS)

    delta - Hexachlorocyclohexane ( delta - HCH ) ; CASRN 319 - 86 - 8 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Ass

  10. Quasi-periodic oscillations in short recurring bursts of the soft gamma repeater J1550–5418

    SciTech Connect

    Huppenkothen, D.; D'Angelo, C.; Watts, A. L.; Heil, L.; Van der Klis, M.; Van der Horst, A. J.; Kouveliotou, C.; Baring, M. G.; Göğüş, E.; Kaneko, Y.; Granot, J.; Lin, L.; Von Kienlin, A.; Younes, G.

    2014-06-01

    The discovery of quasi-periodic oscillations (QPOs) in magnetar giant flares has opened up prospects for neutron star asteroseismology. The scarcity of giant flares makes a search for QPOs in the shorter, far more numerous bursts from soft gamma repeaters (SGRs) desirable. In Huppenkothen et al., we developed a Bayesian method for searching for QPOs in short magnetar bursts, taking into account the effects of the complicated burst structure, and have shown its feasibility on a small sample of bursts. Here we apply the same method to a much larger sample from a burst storm of 286 bursts from SGR J1550–5418. We report a candidate signal at 260 Hz in a search of the individual bursts, which is fairly broad. We also find two QPOs at ∼93 Hz, and one at 127 Hz, when averaging periodograms from a number of bursts in individual triggers, at frequencies close to QPOs previously observed in magnetar giant flares. Finally, for the first time, we explore the overall burst variability in the sample and report a weak anti-correlation between the power-law index of the broadband model characterizing aperiodic burst variability and the burst duration: shorter bursts have steeper power-law indices than longer bursts. This indicates that longer bursts vary over a broader range of timescales and are not simply longer versions of the short bursts.

  11. Delta agent (Hepatitis D)

    MedlinePlus

    ... this page: //medlineplus.gov/ency/article/000216.htm Delta agent (Hepatitis D) To use the sharing features on this page, please enable JavaScript. Delta agent is a type of virus called hepatitis ...

  12. X-ray Bursts and Oscillations: Prospects with NICER

    NASA Astrophysics Data System (ADS)

    Strohmayer, Tod E.; Mahmoodifar, Simin

    2016-04-01

    X-ray bursts (Type I) are produced by thermonuclear flashes in the accreted surface layers of some neutron stars in Low Mass X-ray Binaries (LMXBs). High frequency oscillations are observed during some of these bursts. These "burst oscillations" result from rotational modulation of an inhomogeneous temperature distribution on the neutron star surface induced by ignition and subsequent spreading of the thermonuclear flash. They provide a means to measure the spin rates of accreting neutron stars and since the burst emission arises from the neutron star surface, a unique probe of neutron star structure. To date, virtually all observations of such oscillations have been made with NASA's Rossi X-ray Timing Explorer (RXTE). We have developed a burst model employing the Schwarzschild + Doppler approximation for surface emission coupled with realistic flame spreading geometries and burst cooling to compute light curves and oscillation amplitudes for both the rising and cooling phases of X-ray bursts. We use this model to explore the capabilities for the Neutron star Interior Composition ExploreR (NICER) to detect and study burst oscillations, particularly in the energy band below 3 keV. NICER is an International Space Station attached payload (X-ray telescope) with capabilities optimized for fast timing of neutron stars in the 0.2-10 keV band. It has large collecting area (twice that of the XMM-Newton EPIC-pn camera), CCD-quality spectral resolution, and high-precision time tagging referenced to UTC through an onboard GPS receiver. NICER will begin its 18-month prime mission around the end of 2016. We will present results of simulated X-ray bursts with NICER that explore its burst oscillation detection capabilities and prospects for inferring neutron star properties from phase-resolved spectra.

  13. The Korean Solar Radio Burst Locator (KSRBL)

    NASA Astrophysics Data System (ADS)

    Dou, Yujiang; Gary, Dale E.; Liu, Zhiwei; Nita, Gelu M.; Bong, Su-Chan; Cho, Kyung-Suk; Park, Young-Deuk; Moon, Yong-Jae

    2009-05-01

    This paper describes the design and operation of the Korean Solar Radio Burst Locator (KSRBL). The KSRBL is a radio spectrometer designed to observe solar decimeter and microwave bursts over a wide band (0.245–18 GHz) as well as to detect the burst locations without interferometry or mechanical sweeping. As a prototype, it is temporarily observing at the Owens Valley Radio Observatory (OVRO), California, USA, and after commissioning will be operated at the Korea Astronomy and Space Science Institute (KASI), Daejeon, Republic of Korea. The control system can agilely choose four 500 MHz intermediate frequency (IF) bands (2 GHz instantaneous bandwidth) from the entire 0.245–18 GHz band, with a standard time resolution of 100 ms, although higher time resolution is possible subject to data-rate constraints. To cover the entire band requires 10 tunings, which are therefore completed in 1 s. Each 500 MHz band is sampled at a 1 GS s-1 (gigasample per second) rate, and 4096 time samples are Fast Fourier transformed (FFT) to 2048 subchannels for a frequency resolution of 0.24 MHz. To cover the entire range also requires two different feeds, a dual-frequency Yagi centered at 245 and 410 MHz, and a broadband spiral feed covering 0.5–18 GHz. The dynamic range is 35 dB over the 0.5–18 GHz band, and 55 dB in the 245 and 410 MHz bands, set by using switchable attenuators in steps of 5 dB. Each 500 MHz IF has a further 63 dB of settable analog attenuation. The characteristics of the spiral feed provide the ability to locate flaring sources on the Sun to typically 2‧. The KSRBL will provide a broadband view of solar bursts for the purposes of studying solar activity for basic research, and for monitoring solar activity as the source of Space Weather and solar-terrestrial effects.

  14. Connection Between the CME Velocities and Decameter Radio Bursts Parameters from URAN-4 Observations

    NASA Astrophysics Data System (ADS)

    Galanin, V. V.; Isaeva, E. A.; Kravetz, R. O.

    The paper reports the results of the research of connection between the coronal mass ejections (CME) with the IV type continual decameter bursts parameters. As the parameters characterizing the CME velocity, we used the integrated flux of the radio bursts and background intensity on 20 and 25 MHz frequencies. The analysis demonstrated that the connection between the CME velocity and IV type bursts increases, if we take into account the intensity of the radio bursts and background on two polarizations at a given frequency. In this case, the correlation coefficient is ≍ 0.75.

  15. Powerful Radio Burst Indicates New Astronomical Phenomenon

    NASA Astrophysics Data System (ADS)

    2007-09-01

    . "It was a bit of luck that the survey included some observations of the sky surrounding the clouds," Narkevic said. It was from those "flanking" observations that the mysterious radio burst appeared in the data. The burst of radio waves was strong by astronomical standards, but lasted less than five milliseconds. The signal was spread out, with higher frequencies arriving at the telescope before the lower frequencies. This effect, called dispersion, is caused by the signal passing through ionized gas in interstellar and intergalactic space. The amount of this dispersion, the astronomers said, indicates that the signal likely originated about three billion light-years from Earth. No previously-detected cosmic radio burst has the same set of characteristics. "This burst represents an entirely new astronomical phenomenon," Bailes said. The astronomers estimate on the basis of their results that hundreds of similar events should occur over the sky each day. "Few radio surveys have the necessary sensitivity to such short-duration bursts, which makes them notoriously difficult to detect with current instruments," added Crawford. The next generation of radio telescopes currently under development should be able to detect many of these bursts across the sky. Although the nature of the mysterious new object is unclear, the astronomers have some ideas of what may cause such a burst. One idea is that it may be part of the energy released when a pair of superdense neutron stars collide and merge. Such an event is thought by some scientists to be the cause of one type of gamma-ray burst, but the only radio emission seen so far from these has been from the long-lived "afterglow" that follows the original burst. Another, more exotic, candidate is a burst of energy from an evaporating black hole. Black holes, concentrations of mass so dense that not even light can escape their powerful gravity, can lose mass and energy through a process proposed by famed British physicist Stephen

  16. On the three harmonics of solar type III bursts at the decameter wavelengths

    NASA Astrophysics Data System (ADS)

    Brazhenko, Anatolii; Pylaev, Oleg; Melnik, Valentin; Konovalenko, Alexandr; Zaqarashvili, Teimuraz; Rucker, Helmut; Frantsuzenko, Anatolii; Dorovskyy, Vladimir

    2014-05-01

    Harmonic structure of type III bursts are explained in terms of plasma emission mechanism. The second harmonic emission is well known. But there are theoretical papers about the third harmonic of type III bursts. And there were observations of the third harmonic of such types of bursts as U, J, V, II. We observed triple type III bursts where frequency ratio is close to 1:2:3. They are structures where type III emission is repeated at the double and triple frequencies. Incidentally, components of triple type III bursts are not only standard type III but also type IIIb bursts. We registered 30 triple bursts during 2011 and 2012 years. Observations were made by radio telescope URAN-2, Poltava, Ukraine. It enables polarization measurements at the frequencies 8 - 32 MHz. URAN-2 allows registration of radio emission with time and frequency resolution 10 ms and 4 kHz correspondingly. We analyze properties of the components of triple bursts and their dependencies on frequency, type of burst and on the position of the component within the triplet. The main properties of the components of triple bursts such as duration and drift rate are similar to those of standard type III and IIIb bursts. We find usual for type III bursts dependencies such as follow: duration decreases with frequency, the type IIIb bursts have always smaller duration at the same frequencies, all bursts drift from high to low frequencies. But we also find the linear dependence of drift rate on frequency. All components of a trio have the same sign of polarization. Polarization of the first component is always the highest in triple bursts. It corresponds to the generally accepted viewpoint about the first harmonic emission. The second and the third components of trio have low polarization. It is typical for the second and the third harmonics according to the plasma radiation mechanism. We discuss possible emission mechanisms and theoretical aspects of observed dependencies. The most of detected regularities

  17. Type 2 and type 3 burst theory

    NASA Technical Reports Server (NTRS)

    Smith, D. F.

    1973-01-01

    The present state of the theory of type 3 bursts is reviewed by dividing the problem into the exciting agency, radiation source, and propagation of radiation between the source and the observer. In-situ measurements indicate that the excitors are electron streams of energy about 40 keV which are continuously relaxing. An investigation of neutralization of an electron stream indicates that n sub s is much less than 100,000 n sub e, where n sub s is the stream density and n sub e the coronal electron density. In situ observations are consistent with this result. An analysis of propagation of electrons in the current sheets of coronal streamers shows that such propagation at heights greater than 1 solar radius is impossible. The mechanisms for radiation are reviewed; it is shown that fundamental radiation at high frequencies (approximately 100 MHz) is highly beamed in the radial direction and that near the earth second harmonic radiation must be dominant. Because of beaming of the fundamental at high frequencies, it can often be quite weak near the limb so that the second harmonic is dominant. In considering propagation to the observer, the results of scattering of radiation are discussed. The present state of the theory of type 2 bursts is reviewed in the same manner as type 3 bursts.

  18. Swarm's Absolute Scalar Magnetometers Burst Mode Results

    NASA Astrophysics Data System (ADS)

    Coisson, P.; Vigneron, P.; Hulot, G.; Crespo Grau, R.; Brocco, L.; Lalanne, X.; Sirol, O.; Leger, J. M.; Jager, T.; Bertrand, F.; Boness, A.; Fratter, I.

    2014-12-01

    Each of the three Swarm satellites embarks an Absolute Scalar Magnetometer (ASM) to provide absolute scalar measurements of the magnetic field with high accuracy and stability. Nominal data acquisition of these ASMs is 1 Hz. But they can also run in a so-called "burst mode" and provide data at 250 Hz. During the commissioning phase of the mission, seven burst mode acquisition campaigns have been run simultaneously for all satellites, obtaining a total of ten days of burs-mode data. These campaigns allowed the identification of issues related to the operations of the piezo-electric motor and the heaters connected to the ASM, that do not impact the nominal 1 Hz scalar data. We analyze the burst mode data to identify high frequency geomagnetic signals, focusing the analysis in two regions: the low latitudes, where we seek signatures of ionospheric irregularities, and the high latitudes, to identify high frequency signals related to polar region currents. Since these campaigns have been conducted during the initial months of the mission, the three satellites where still close to each other, allowing to analyze the spatial coherency of the signals. Wavelet analysis have revealed 31 Hz signals appearing in the night-side in the equatorial region.

  19. Observation of a metric type N solar radio burst

    SciTech Connect

    Kong, Xiangliang; Chen, Yao; Feng, Shiwei; Du, Guohui; Li, Chuanyang; Koval, Artem; Vasanth, V.; Wang, Bing; Guo, Fan; Li, Gang

    2016-10-10

    Type III and type-III-like radio bursts are produced by energetic electron beams guided along coronal magnetic fields. As a variant of type III bursts, Type N bursts appear as the letter "N" in the radio dynamic spectrum and reveal a magnetic mirror effect in coronal loops. Here, we report a well-observed N-shaped burst consisting of three successive branches at metric wavelength with both fundamental and harmonic components and a high brightness temperature (>109 K). We verify the burst as a true type N burst generated by the same electron beam from three aspects of the data. First, durations of the three branches at a given frequency increase gradually and may be due to the dispersion of the beam along its path. Second, the flare site, as the only possible source of non-thermal electrons, is near the western feet of large-scale closed loops. Third, the first branch and the following two branches are localized at different legs of the loops with opposite senses of polarization. We also find that the sense of polarization of the radio burst is in contradiction to the O-mode and there exists a fairly large time delay (~3–5 s) between the fundamental and harmonic components. Possible explanations accounting for these observations are presented. Finally, assuming the classical plasma emission mechanism, we can infer coronal parameters such as electron density and magnetic field near the radio source and make diagnostics on the magnetic mirror process.

  20. Observation of a Metric Type N Solar Radio Burst

    NASA Astrophysics Data System (ADS)

    Kong, Xiangliang; Chen, Yao; Feng, Shiwei; Du, Guohui; Li, Chuanyang; Koval, Artem; Vasanth, V.; Wang, Bing; Guo, Fan; Li, Gang

    2016-10-01

    Type III and type-III-like radio bursts are produced by energetic electron beams guided along coronal magnetic fields. As a variant of type III bursts, Type N bursts appear as the letter “N” in the radio dynamic spectrum and reveal a magnetic mirror effect in coronal loops. Here, we report a well-observed N-shaped burst consisting of three successive branches at metric wavelength with both fundamental and harmonic components and a high brightness temperature (>109 K). We verify the burst as a true type N burst generated by the same electron beam from three aspects of the data. First, durations of the three branches at a given frequency increase gradually and may be due to the dispersion of the beam along its path. Second, the flare site, as the only possible source of non-thermal electrons, is near the western feet of large-scale closed loops. Third, the first branch and the following two branches are localized at different legs of the loops with opposite senses of polarization. We also find that the sense of polarization of the radio burst is in contradiction to the O-mode and there exists a fairly large time delay (˜3-5 s) between the fundamental and harmonic components. Possible explanations accounting for these observations are presented. Assuming the classical plasma emission mechanism, we can infer coronal parameters such as electron density and magnetic field near the radio source and make diagnostics on the magnetic mirror process.

  1. Optimal Burst Duration During a Facilitated Quadriceps Femoris Contraction

    PubMed Central

    McLoda, Todd A.; Carmack, Jennifer A.

    2000-01-01

    Objective: To determine the most efficient burst duty cycle for eliciting an involuntary quadriceps femoris contraction in healthy subjects. This information will allow clinicians to make an informed decision about the optimal burst duty cycle based upon a specific treatment goal. The logical goal for such a treatment choice is to enhance motor unit recruitment in an effort to maintain postoperative or postinjury strength, when voluntary contractions may be less effective. Design and Setting: Single-group and 5-measures design. All tests were performed in a university laboratory. Subjects: Forty-eight healthy subjects (27 men and 21 women; mean age, 26.4 ± 8.5 years) performed a maximal voluntary isometric contraction (MVIC) on an isokinetic device and received neuromuscular electrical stimulation (NMES) at 5 different burst duty cycles. Measurements: Subjects first performed an MVIC for knee extension on an isokinetic dynamometer at 60° of knee flexion. NMES surface electrodes were applied to the quadriceps muscle of each subject's dominant leg. The values for the NMES were 2500-Hz carrier frequency, 50-bursts-per-second treatment frequency, amplitude increased to maximum tolerance, and burst duty cycle set to each of the 5 comparison values. The peak isometric force generated by each of the 5 nonvolitional contractions was recorded, along with the maximal charge per burst tolerated by each subject. Force generated was described as percentage of MVIC. Efficiency was the amount of force per burst charge. Results: The mean MVIC achieved by the subjects was 553.8 newtons (N). The average force per burst charge generated at 10% burst duty cycle was 132.9 N; at 30%, 104.2 N; at 50%, 93.1 N; at 70%, 52.9 N; and at 90%, 41.3 N. The average efficiency (force per millicoulombs [mC]) at 10% burst duty cycle was the highest at 6.49 N/mC and at 90% was the lowest at 1.05 N/mC. Conclusions: A burst duty cycle of 10% was the most efficient ratio of burst duration to

  2. Static measurements of slender delta wing rolling moment hysteresis

    NASA Technical Reports Server (NTRS)

    Katz, Joseph; Levin, Daniel

    1991-01-01

    Slender delta wing planforms are susceptible to self-induced roll oscillations due to aerodynamic hysteresis during the limit cycle roll oscillation. Test results are presented which clearly establish that the static rolling moment hysteresis has a damping character; hysteresis tends to be greater when, due to either wing roll or side slip, the vortex burst moves back and forth over the wing trailing edge. These data are an indirect indication of the damping role of the vortex burst during limit cycle roll oscillations.

  3. Burst Mode ASIC-Based Modem

    NASA Technical Reports Server (NTRS)

    1997-01-01

    The NASA Lewis Research Center is sponsoring the Advanced Communication Technology Insertion (ACTION) for Commercial Space Applications program. The goal of the program is to expedite the development of new technology with a clear path towards productization and enhancing the competitiveness of U.S. manufacturers. The industry has made significant investment in developing ASIC-based modem technology for continuous-mode applications and has made investigations into East, reliable acquisition of burst-mode digital communication signals. With rapid advances in analog and digital communications ICs, it is expected that more functions will be integrated onto these parts in the near future. In addition custom ASIC's can also be developed to address the areas not covered by the other IC's. Using the commercial chips and custom ASIC's, lower-cost, compact, reliable, and high-performance modems can be built for demanding satellite communication application. This report outlines a frequency-hop burst modem design based on commercially available chips.

  4. PEAK FLUX DISTRIBUTIONS OF SOLAR RADIO TYPE-I BURSTS FROM HIGHLY RESOLVED SPECTRAL OBSERVATIONS

    SciTech Connect

    Iwai, K.; Masuda, S.; Miyoshi, Y.; Tsuchiya, F.; Morioka, A.; Misawa, H.

    2013-05-01

    Solar radio type-I bursts were observed on 2011 January 26 by high resolution observations with the radio telescope AMATERAS in order to derive their peak flux distributions. We have developed a two-dimensional auto burst detection algorithm that can distinguish each type-I burst element from complex noise storm spectra that include numerous instances of radio frequency interference (RFI). This algorithm removes RFI from the observed radio spectra by applying a moving median filter along the frequency axis. Burst and continuum components are distinguished by a two-dimensional maximum and minimum search of the radio dynamic spectra. The analysis result shows that each type-I burst element has one peak flux without double counts or missed counts. The peak flux distribution of type-I bursts derived using this algorithm follows a power law with a spectral index between 4 and 5.

  5. Differential behavioral state-dependence in the burst properties of CA3 and CA1 neurons.

    PubMed

    Tropp Sneider, J; Chrobak, J J; Quirk, M C; Oler, J A; Markus, E J

    2006-09-15

    Brief bursts of fast high-frequency action potentials are a signature characteristic of CA3 and CA1 pyramidal neurons. Understanding the factors determining burst and single spiking is potentially significant for sensory representation, synaptic plasticity and epileptogenesis. A variety of models suggest distinct functional roles for burst discharge, and for specific characteristics of the burst in neural coding. However, little in vivo data demonstrate how often and under what conditions CA3 and CA1 actually exhibit burst and single spike discharges. The present study examined burst discharge and single spiking of CA3 and CA1 neurons across distinct behavioral states (awake-immobility and maze-running) in rats. In both CA3 and CA1 spike bursts accounted for less than 20% of all spike events. CA3 neurons exhibited more spikes per burst, greater spike frequency, larger amplitude spikes and more spike amplitude attenuation than CA1 neurons. A major finding of the present study is that the propensity of CA1 neurons to burst was affected by behavioral state, while the propensity of CA3 to burst was not. CA1 neurons exhibited fewer bursts during maze running compared with awake-immobility. In contrast, there were no differences in burst discharge of CA3 neurons. Neurons in both subregions exhibited smaller spike amplitude, fewer spikes per burst, longer inter-spike intervals and greater spike amplitude attenuation within a burst during awake-immobility compared with maze running. These findings demonstrate that the CA1 network is under greater behavioral state-dependent regulation than CA3. The present findings should inform both theoretic and computational models of CA3 and CA1 function.

  6. Gamma Ray Bursts

    NASA Technical Reports Server (NTRS)

    Gehrels, Neil; Meszaros, Peter

    2012-01-01

    Gamma-ray bursts (GRBs) are bright flashes of gamma-rays coming from the cosmos. They occur roughly once per day ,last typically lOs of seconds and are the most luminous events in the universe. More than three decades after their discovery, and after pioneering advances from space and ground experiments, they still remain mysterious. The launch of the Swift and Fermi satellites in 2004 and 2008 brought in a trove of qualitatively new data. In this review we survey the interplay between these recent observations and the theoretical models of the prompt GRB emission and the subsequent afterglows.

  7. Analysis of variability in the burst oscillations of the accreting millisecond pulsar XTE J1814-338

    NASA Technical Reports Server (NTRS)

    Watts, Anna L.; Strohmayer, Tod E.; Markwardt, Craig B.

    2005-01-01

    The accreting millisecond pulsar XTE J1814-338 exhibits oscillations at the known spin frequency during Type I X-ray bursts. The properties of the burst oscillations reflect the nature of the thermal asymmetry on the stellar surface. We present an analysis of the variability of the burst oscillations of this source, focusing on three characteristics: fractional amplitude, harmonic content and frequency. Fractional amplitude and harmonic content constrain the size, shape and position of the emitting region, whilst variations in frequency indicate motion of the emitting region on the neutron star surface. We examine both long-term variability over the course of the outburst, and short-term variability during the bursts. For most of the bursts, fractional amplitude is consistent with that of the accretion pulsations, implying a low degree of fuel spread. There is however a population of bursts whose fractional amplitudes are substantially lower, implying a higher degree of fuel spread, possibly forced by the explosive burning front of a precursor burst. For the first harmonic, substantial differences between the burst and accretion pulsations suggest that hotspot geometry is not the only mechanism giving rise to harmonic content in the latter. Fractional amplitude variability during the bursts is low; we can only rule out the hypothesis that the fractional amplitude remains constant at the l(sigma) level for bursts that do not exhibit photospheric radius expansion (PRE). There are no significant variations in frequency in any of the bursts except for the one burst that exhibits PRE. This burst exhibits a highly significant but small (= 0.1Hz) drop in frequency in the burst rise. The timescale of the frequency shift is slower than simple burning layer expansion models predict, suggesting that other mechanisms may be at work.

  8. UWB dual burst transmit driver

    SciTech Connect

    Dallum, Gregory E; Pratt, Garth C; Haugen, Peter C; Zumstein, James M; Vigars, Mark L; Romero, Carlos E

    2012-04-17

    A dual burst transmitter for ultra-wideband (UWB) communication systems generates a pair of precisely spaced RF bursts from a single trigger event. An input trigger pulse produces two oscillator trigger pulses, an initial pulse and a delayed pulse, in a dual trigger generator. The two oscillator trigger pulses drive a gated RF burst (power output) oscillator. A bias driver circuit gates the RF output oscillator on and off and sets the RF burst packet width. The bias driver also level shifts the drive signal to the level that is required for the RF output device.

  9. An interacting loop model for solar flare bursts

    NASA Technical Reports Server (NTRS)

    Emslie, A. G.

    1981-01-01

    A schematic model is presented which attempts to explain the quasi-periodic behavior (on a timescale of less than or approximately equal to 10 s) frequency observed in solar hard X-ray bursts. It is shown how, as a result of the strong heating produced during a solar flare burst, the local gas pressure can transiently attain very large values in regions corresponding to the upper preflare chromosphere. The effectiveness of the surrounding magnetic field at confining this high pressure plasma is therefore reduced and the flaring loop becomes free to expand laterally. In so doing it may drive magnetic field lines into neighboring, non-flaring, loops in the same active region, causing magnetic reconnection to take place and triggering another flare burst. The features of this interacting loop model are found to be in good agreement with the energetics and time structure of flare-associated solar hard X-ray bursts.

  10. Microwave Type III Pair Bursts in Solar Flares

    NASA Astrophysics Data System (ADS)

    Tan, Baolin; Mészárosová, Hana; Karlický, Marian; Huang, Guangli; Tan, Chengming

    2016-03-01

    A solar microwave type III pair burst is composed of normal and reverse-sloped (RS) burst branches with oppositely fast frequency drifts. It is the most sensitive signature of the primary energy release and electron accelerations in flares. This work reports 11 microwave type III pair events in 9 flares observed by radio spectrometers in China and the Czech Republic at a frequency of 0.80-7.60 GHz during 1994-2014. These type III pairs occurred in flare impulsive and postflare phases with separate frequencies in the range of 1.08-3.42 GHz and a frequency gap of 10-1700 MHz. The frequency drift increases with the separate frequency (fx), the lifetime of each burst is anti-correlated to fx, while the frequency gap is independent of fx. In most events, the normal branches are drifting obviously faster than the RS branches. The type III pairs occurring in flare impulsive phase have lower separate frequencies, longer lifetimes, wider frequency gaps, and slower frequency drifts than that occurring in postflare phase. Also, the latter always has strong circular polarization. Further analysis indicates that near the flare energy release sites the plasma density is about {10}10{--}{10}11 cm-3 and the temperature is higher than 107 K. These results provide new constraints to the acceleration mechanism in solar flares.

  11. Comparative analysis of decametre "drift pair" bursts observed in 2002 and 2015

    NASA Astrophysics Data System (ADS)

    Volvach, Ya. S.; Stanislavsky, A. A.; Konovalenko, A. A.; Koval, A. A.; Dorovskyy, V. V.

    2016-09-01

    We report about new observations of solar "drift pair" (DP) bursts by means of the UTR-2 radio telescope at frequencies 10-30 MHz. Our experimental data include both "forward" and "reverse" bursts with high frequency and time resolution. The records of 301 bursts, observed in 10-12 July of 2015, are investigated. The main properties of these bursts (frequency bandwidth, central frequency and others) have been analysed. In this report our main attention is paid to the comparison of our observations with the similar observations of decametre DPs performed earlier during 13-15 July of 2002 in the same frequency range. Common features of DPs in the two different pieces of data samples have been found. This may indicate the possible presence of stability in the frequency-time properties of decametre DPs from one cycle of solar activity to another.

  12. EMISSION PATTERNS OF SOLAR TYPE III RADIO BURSTS: STEREOSCOPIC OBSERVATIONS

    SciTech Connect

    Thejappa, G.; Bergamo, M.; MacDowall, R. J. E-mail: mbergamo@umd.edu

    2012-02-01

    Simultaneous observations of solar type III radio bursts obtained by the STEREO A, B, and WIND spacecraft at low frequencies from different vantage points in the ecliptic plane are used to determine their directivity. The heliolongitudes of the sources of these bursts, estimated at different frequencies by assuming that they are located on the Parker spiral magnetic field lines emerging from the associated active regions into the spherically symmetric solar atmosphere, and the heliolongitudes of the spacecraft are used to estimate the viewing angle, which is the angle between the direction of the magnetic field at the source and the line connecting the source to the spacecraft. The normalized peak intensities at each spacecraft R{sub j} = I{sub j} /{Sigma}I{sub j} (the subscript j corresponds to the spacecraft STEREO A, B, and WIND), which are defined as the directivity factors are determined using the time profiles of the type III bursts. It is shown that the distribution of the viewing angles divides the type III bursts into: (1) bursts emitting into a very narrow cone centered around the tangent to the magnetic field with angular width of {approx}2 Degree-Sign and (2) bursts emitting into a wider cone with angular width spanning from {approx} - 100 Degree-Sign to {approx}100 Degree-Sign . The plots of the directivity factors versus the viewing angles of the sources from all three spacecraft indicate that the type III emissions are very intense along the tangent to the spiral magnetic field lines at the source, and steadily fall as the viewing angles increase to higher values. The comparison of these emission patterns with the computed distributions of the ray trajectories indicate that the intense bursts visible in a narrow range of angles around the magnetic field directions probably are emitted in the fundamental mode, whereas the relatively weaker bursts visible to a wide range of angles are probably emitted in the harmonic mode.

  13. Burst Firing is a Neural Code in an Insect Auditory System

    PubMed Central

    Eyherabide, Hugo G.; Rokem, Ariel; Herz, Andreas V. M.; Samengo, Inés

    2008-01-01

    Various classes of neurons alternate between high-frequency discharges and silent intervals. This phenomenon is called burst firing. To analyze burst activity in an insect system, grasshopper auditory receptor neurons were recorded in vivo for several distinct stimulus types. The experimental data show that both burst probability and burst characteristics are strongly influenced by temporal modulations of the acoustic stimulus. The tendency to burst, hence, is not only determined by cell-intrinsic processes, but also by their interaction with the stimulus time course. We study this interaction quantitatively and observe that bursts containing a certain number of spikes occur shortly after stimulus deflections of specific intensity and duration. Our findings suggest a sparse neural code where information about the stimulus is represented by the number of spikes per burst, irrespective of the detailed interspike-interval structure within a burst. This compact representation cannot be interpreted as a firing-rate code. An information-theoretical analysis reveals that the number of spikes per burst reliably conveys information about the amplitude and duration of sound transients, whereas their time of occurrence is reflected by the burst onset time. The investigated neurons encode almost half of the total transmitted information in burst activity. PMID:18946533

  14. Fine and Superfine Structure of the Decameter-Hectometer Type II Burst on 7 June 2011

    NASA Astrophysics Data System (ADS)

    Dorovskyy, V. V.; Melnik, V. N.; Konovalenko, A. A.; Brazhenko, A. I.; Panchenko, M.; Poedts, S.; Mykhaylov, V. A.

    2015-07-01

    The characteristics of a type II burst with a herringbone structure observed both with ground-based radio telescopes (UTR-2 and URAN-2) and space-borne spectrometers (STEREO-A and B) are discussed. The burst was recorded on 7 June 2011 in the frequency band 3 - 33 MHz. It was characterized by extremely rich fine structure. Statistical analysis of more than 300 herringbone sub-bursts constituting the burst was performed separately for the positively (reverse) and negatively (forward) drifting sub-bursts. The sense and the degree of circular polarization of the herringbone sub-bursts were measured in a wide frequency band (16 - 32 MHz). A second-order fine frequency structure of the herringbone sub-bursts was observed and studied for the first time. Using STEREO/COR1 and SOHO/LASCO-C2 images, we determined the direction and radial speed of the coronal mass ejection responsible for the studied type II burst. The possible location of the type II burst source on the flank of the shock was found.

  15. Swift's 500th Gamma Ray Burst

    NASA Video Gallery

    On April 13, 2010, NASA's Swift Gamma-ray Burst Explorer satellite discovered its 500th burst. Swift's main job is to quickly localize each gamma-ray burst (GRB), report its position so that others...

  16. Bursts de raios gama

    NASA Astrophysics Data System (ADS)

    Braga, J.

    2003-02-01

    Nos últimos anos, graças principalmente aos dados obtidos pelo Compton Gamma-Ray Observatory e pelo satélite ítalo-holandês BeppoSAX, grandes avanços foram obtidos no nosso conhecimento sobre os fascinantes e enigmáticos fenômenos conhecidos por "bursts"de raios gama. Neste trabalho é feita uma revisão sobre a fenomenologia desses misteriosos objetos e são apresentados os desenvolvimentos recentes nessa área palpitante da astrofísica moderna, ressaltando tanto os resultados observacionais obtidos até o momento quanto os modelos teóricos propostos para explixá-los.

  17. Quantum key based burst confidentiality in optical burst switched networks.

    PubMed

    Balamurugan, A M; Sivasubramanian, A

    2014-01-01

    The optical burst switching (OBS) is an emergent result to the technology concern that could achieve a feasible network in future. They are endowed with the ability to meet the bandwidth requirement of those applications that require intensive bandwidth. There are more domains opening up in the OBS that evidently shows their advantages and their capability to face the future network traffic. However, the concept of OBS is still far from perfection facing issues in case of security threat. The transfer of optical switching paradigm to optical burst switching faces serious downfall in the fields of burst aggregation, routing, authentication, dispute resolution, and quality of service (QoS). This paper deals with employing RC4 (stream cipher) to encrypt and decrypt bursts thereby ensuring the confidentiality of the burst. Although the use of AES algorithm has already been proposed for the same issue, by contrasting the two algorithms under the parameters of burst encryption and decryption time, end-to-end delay, it was found that RC4 provided better results. This paper looks to provide a better solution for the confidentiality of the burst in OBS networks.

  18. Quantum Key Based Burst Confidentiality in Optical Burst Switched Networks

    PubMed Central

    Balamurugan, A. M.; Sivasubramanian, A.

    2014-01-01

    The optical burst switching (OBS) is an emergent result to the technology concern that could achieve a feasible network in future. They are endowed with the ability to meet the bandwidth requirement of those applications that require intensive bandwidth. There are more domains opening up in the OBS that evidently shows their advantages and their capability to face the future network traffic. However, the concept of OBS is still far from perfection facing issues in case of security threat. The transfer of optical switching paradigm to optical burst switching faces serious downfall in the fields of burst aggregation, routing, authentication, dispute resolution, and quality of service (QoS). This paper deals with employing RC4 (stream cipher) to encrypt and decrypt bursts thereby ensuring the confidentiality of the burst. Although the use of AES algorithm has already been proposed for the same issue, by contrasting the two algorithms under the parameters of burst encryption and decryption time, end-to-end delay, it was found that RC4 provided better results. This paper looks to provide a better solution for the confidentiality of the burst in OBS networks. PMID:24578663

  19. Gamma ray bursts from extragalactic sources

    NASA Technical Reports Server (NTRS)

    Hoyle, Fred; Burbidge, Geoffrey

    1992-01-01

    The properties of gamma ray bursts of classical type are found to be explicable in terms of high speed collisions between stars. A model is proposed in which the frequency of such collisions can be calculated. The model is then applied to the nuclei of galaxies in general on the basis that galaxies, or at least some fraction of them, originate in the expulsion of stars from creation centers. Evidence that low level activity of this kind is also taking place at the center of our own Galaxy is discussed. The implications for galactic evolution are discussed and a negative view of black holes is taken.

  20. Galactic dual population models of gamma-ray bursts

    NASA Technical Reports Server (NTRS)

    Higdon, J. C.; Lingenfelter, R. E.

    1994-01-01

    We investigate in more detail the properties of two-population models for gamma-ray bursts in the galactic disk and halo. We calculate the gamma-ray burst statistical properties, mean value of (V/V(sub max)), mean value of cos Theta, and mean value of (sin(exp 2) b), as functions of the detection flux threshold for bursts coming from both Galactic disk and massive halo populations. We consider halo models inferred from the observational constraints on the large-scale Galactic structure and we compare the expected values of mean value of (V/V(sub max)), mean value of cos Theta, and mean value of (sin(exp 2) b), with those measured by Burst and Transient Source Experiment (BATSE) and other detectors. We find that the measured values are consistent with solely Galactic populations having a range of halo distributions, mixed with local disk distributions, which can account for as much as approximately 25% of the observed BATSE bursts. M31 does not contribute to these modeled bursts. We also demonstrate, contrary to recent arguments, that the size-frequency distributions of dual population models are quite consistent with the BATSE observations.

  1. Source location of the narrowbanded radio bursts at Uranus - Evidence of a cusp source

    NASA Astrophysics Data System (ADS)

    Farrell, W. M.; Desch, M. D.; Kaiser, M. L.; Kurth, W. S.

    1990-03-01

    While Voyager 2 was inbound to Uranus, radio bursts of narrow bandwidth (less than 5 kHz) were detected between 17-116 kHz. These R-X mode bursts, designated n-bursts, were of short duration, tended to occur when the north magnetic pole tipped toward the spacecraft, and increased in occurrence with increasing solar wind density. An explicit determination of the burst source location is presented, based upon fitting the region of detection at high and low frequencies to field-aligned, symmetric cones. The region of good fits was located between the north magnetic pole and the rotational pole, corresponding approximately to the northern polar cusp.

  2. Gamma-ray burst populations

    NASA Astrophysics Data System (ADS)

    Virgili, Francisco Javier

    Over the last fifty years the field of gamma-ray bursts has shown incredible growth, but the amassing of data has also left observers and theorists alike wondering about some of the basic questions surrounding these phenomena. Additionally, these events show remarkable individuality and extrema, ranging in redshift throughout the observable universe and over ten orders of magnitude in energy. This work focuses on analyzing groups of bursts that are different from the general trend and trying to understand whether these bursts are from different intrinsic populations and if so, what can be said about their progenitors. This is achieved through numerical Monte Carlo simulations and statistical inference in conjunction with current GRB observations. Chapter 1 gives a general introduction of gamma-ray burst theory and observations in a semi-historical context. Chapter 2 provides an introduction to the theory and practical issues surrounding the numerical simulations and statistics. Chapters 3--5 are each dedicated to a specific problem relating to a different type of GRB population: high-luminosity v. low-luminosity bursts, constraints from high-redshift bursts, and Type I v. Type II bursts. Chapter 6 follows with concluding remarks.

  3. Pen Branch delta expansion

    SciTech Connect

    Nelson, E.A.; Christensen, E.J.; Mackey, H.E.; Sharitz, R.R.; Jensen, J.R.; Hodgson, M.E.

    1984-02-01

    Since 1954, cooling water discharges from K Reactor ({anti X} = 370 cfs {at} 59 C) to Pen Branch have altered vegetation and deposited sediment in the Savannah River Swamp forming the Pen Branch delta. Currently, the delta covers over 300 acres and continues to expand at a rate of about 16 acres/yr. Examination of delta expansion can provide important information on environmental impacts to wetlands exposed to elevated temperature and flow conditions. To assess the current status and predict future expansion of the Pen Branch delta, historic aerial photographs were analyzed using both basic photo interpretation and computer techniques to provide the following information: (1) past and current expansion rates; (2) location and changes of impacted areas; (3) total acreage presently affected. Delta acreage changes were then compared to historic reactor discharge temperature and flow data to see if expansion rate variations could be related to reactor operations.

  4. Concept for LEU Burst Reactor

    SciTech Connect

    Klein, Steven Karl; Kimpland, Robert Herbert

    2016-03-07

    Design and performance of a proposed LEU burst reactor are sketched. Salient conclusions reached are the following: size would be ~1,500 kg or greater, depending on the size of the central cavity; internal stresses during burst require split rings for relief; the reactor would likely require multiple control and safety rods for fine control; the energy spectrum would be comparable to that of HEU machines; and burst yields and steady-state power levels will be significantly greater in an LEU reactor.

  5. The Burst of the Century

    NASA Astrophysics Data System (ADS)

    Fruchter, Andrew

    2014-09-01

    The extraordinarily bright GRB 130427A has provided a multiwavelength data set unprecedented in the history of the field. However the light curve of this burst, like that of the large majority of LAT bursts, shows a puzzling lack of a jet break (the hallmark of a collimated outflow). We propose to continue our long-term monitoring of this GRB through to the end of 2015. A detection of a jet break will give us a direct measure of the absolute energy of the burst; its absence will effectively rule out a rotating neutron star as the central engine of the GRB.

  6. Bursts of HF radio noises after irregularities of solar wind

    NASA Astrophysics Data System (ADS)

    Dudnik, O. V.; Malykhina, T. V.

    We present analyses of HF radio emission spectra of magnetospheric origin, at frequencies of 150 and 500 MHz, collected with ground-based antennae at middle latitudes ( L=2) during the second half of 1999. We discover a large occurrence of short-time-scale (1-10 s) sporadic radio bursts during active solar periods. To identify the source of these bursts, we associate their occurrence and perform correlations with solar wind parameters and energetic particle fluxes in interplanetary space and in the outer magnetosphere. Solar wind parameters and energetic ion fluxes in interplanetary space are provided by the ACE satellite. GOES8 and GOES10 satellites provide electron fluxes with energy E>2 MeV at geosynchronous orbit. These data are analyzed in order to show a correlation between particle fluxes and high amplitude radio bursts. There is a delay between the initiations of high-amplitude, short-term, sporadic radio bursts (at a frequency 150 MHz) and the arrival of high-speed solar wind streams at Earth's magnetosphere. The temporal delay of a few hours from the start of these features in the temporal distribution of electron fluxes at L=6.6 is shown, too. We suggest the possibility that the sources of radio bursts are located in the inner parts of magnetosphere.

  7. Directivity Patterns of Complex Solar Type III Radio Bursts: Stereoscopic Observations

    NASA Astrophysics Data System (ADS)

    Golla, T.; MacDowall, R. J.

    2014-12-01

    Complex solar type III-like radio bursts are a group of type III bursts that occur in association with slowly drifting type II radio bursts excited by coronal mass ejection (CME) driven shock waves. We presentsimultaneous observations of these radio bursts from the STEREO A, B and WIND spacecraft at low frequencies, located at different vantage points in the ecliptic plane. Using these stereoscopic observations, wedetermine the directivity of these complex radio bursts. We estimate the angles between the directions of the magnetic field at the sources and the lines connecting the source to the spacecraft (viewing angles) by assuming that the sources are located on the Parker spiral magnetic field lines emerging from the associated active regions into the spherically symmetric solar atmosphere. We estimate the normalized peak intensities of these bursts (directivity factors) at each spacecraft using their time profiles at each spacecraft. These observations indicate that the complex type III bursts can be divided into two groups: (1) bursts emitting into a very narrow cone centered around the tangent to the magnetic field, and (2) bursts emitting into a wider cone. We show that the bursts , which are emitted along the tangent to the spiral magnetic field lines at the source are very intense, and their intensities steadily fall as the viewing angles increase to higher values. We have developed a ray tracing code and computed the distributions of the trajectories of rays emitted at the fundamental and second harmonic of the electron plasma frequency. The comparison of the observed emission patterns with the computed distributions of the ray trajectories indicate that the intense bursts visible in a narrow range of angles around the magnetic field directions probably are emitted in the fundamental mode, whereas the relativelyweaker bursts visible to a wide range of angles are probably emitted in the harmonic mode.

  8. Delta hepatitis in Malaysia.

    PubMed

    Sinniah, M; Dimitrakakis, M; Tan, D S

    1986-06-01

    Sera from one hundred and fifty nine Malaysian individuals were screened for the prevalence of delta markers. These included 15 HBsAg positive homosexuals, 16 acute hepatitis B cases, 9 chronic hepatitis B patients, 13 healthy HBsAg carriers and 106 intravenous (i.v.) drug abusers, of whom 27 were positive for HBsAg only and the rest were anti-HBc IgG positive but HBsAg negative. The prevalence of delta markers in the homosexuals was found to be 6.7%, in the HBsAg positive drug abusers 17.8%, in acute hepatitis B cases 12.5%. No evidence of delta infection was detected in healthy HBsAg carriers, chronic hepatitis B cases and HBsAg negative i.v. drug abusers. With reference to i.v. drug abusers, the prevalence of delta markers was higher in Malays (23%) than in Chinese (7%) although the latter had a higher HBsAg carrier rate. Although the HBsAg carrier rate in the homosexuals was high, their delta prevalence rate was low as compared to drug abusers. In Malaysia, as in other non-endemic regions, hepatitis delta virus transmission appeared to occur mainly via the parenteral and sexual routes. This is the first time in Malaysia that a reservoir of delta infection has been demonstrated in certain groups of the population at high risk for hepatitis B.

  9. 30 CFR 57.3461 - Rock bursts.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Rock bursts. 57.3461 Section 57.3461 Mineral...-Underground Only § 57.3461 Rock bursts. (a) Operators of mines which have experienced a rock burst shall— (1) Within twenty four hours report to the nearest MSHA office each rock burst which: (i) Causes persons...

  10. 30 CFR 57.3461 - Rock bursts.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Rock bursts. 57.3461 Section 57.3461 Mineral...-Underground Only § 57.3461 Rock bursts. (a) Operators of mines which have experienced a rock burst shall— (1) Within twenty four hours report to the nearest MSHA office each rock burst which: (i) Causes persons...

  11. 30 CFR 57.3461 - Rock bursts.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Rock bursts. 57.3461 Section 57.3461 Mineral...-Underground Only § 57.3461 Rock bursts. (a) Operators of mines which have experienced a rock burst shall— (1) Within twenty four hours report to the nearest MSHA office each rock burst which: (i) Causes persons...

  12. 30 CFR 57.3461 - Rock bursts.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Rock bursts. 57.3461 Section 57.3461 Mineral...-Underground Only § 57.3461 Rock bursts. (a) Operators of mines which have experienced a rock burst shall— (1) Within twenty four hours report to the nearest MSHA office each rock burst which: (i) Causes persons...

  13. 30 CFR 57.3461 - Rock bursts.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Rock bursts. 57.3461 Section 57.3461 Mineral...-Underground Only § 57.3461 Rock bursts. (a) Operators of mines which have experienced a rock burst shall— (1) Within twenty four hours report to the nearest MSHA office each rock burst which: (i) Causes persons...

  14. What Can Be Interesting in the Analysis of Crowded Solar Bursts?

    NASA Astrophysics Data System (ADS)

    Stanislavsky, A. A.; Konovalenko, A. A.; Koval, A. A.; Dorovsky, V. V.; Zarka, Ph.; Rucker, H. O.

    2015-03-01

    At decameter wavelengths the radio astronomy observations reveal a wide variety of solar bursts. They are associated with solar activity manifestations such as movements of electron beams and shock waves in solar corona, flare- related events, coronal mass ejections and others. The analysis of burst features allows one to use them as probing signals which comprise useful information about solar corona parameters and their changes over time. By frequency-time measurements of different types of solar bursts occurred about the same time one can provide a comparative study of their properties, complementing the missing pieces in the complex mosaic of solar events. In this purpose we discuss features of their signal processing by the gradient filtration, as applied to quasi-periodic bursts like a zebra pattern related to Bernstein modes. The measured frequency periodicity of the bursts gives a chance to determine the magnetic field strength in upper corona around the protracted solar minimum of solar activity.

  15. Interplanetary baseline observations of type 3 solar radio bursts. [by Helios satellites

    NASA Technical Reports Server (NTRS)

    Weber, R. R.; Fitzenreiter, R. J.; Novaco, J. C.; Fainberg, J.

    1977-01-01

    Simultaneous observations of type III radio bursts using spacecraft separated by several tenths of an AU were made using the solar orbiters HELIOS-A and -B. The burst beginning at 1922 UT on March 28, 1976, was located from the intersection of the source directions measured at each spacecraft, and from the burst arrival time differences. Wide baseline observations give the radial distance of the source at each observing frequency. Consequently, coronal electron densities and exciter velocity were determined directly, without the need to assume a density model as is done with single spacecraft observations. The separation of HELIOS-A and -B also provided the first measurements of burst directivity at low frequencies. For the March 28 burst, the intensity observed from near the source longitude (HELIOS-B) was significantly greater than from 60 W of the source (HELIOS-A).

  16. Burst Oscillation Probes of Neutron Stars and Nuclear Burning with LOFT

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2012-01-01

    X-ray brightness oscillations during thermonuclear X-ray bursts--burst oscillations--have provided a new probe of neutron star spins as well as of the dependent nuclear burning processes. The frequency drift and amplitude evolution of the oscillations observed during bursts can in principle place constraints on the physics of thermonuclear flame spreading and the dynamics of the burning atmosphere. I use simulations appropriate to LOFT to explore the precision with which the time dependence of the oscillation frequency can be inferred. This can test, for example, different models for the frequency drift, such as up-lift versus geostrophic drift. I also explore the precision with which asymptotic frequencies can be constrained in order to estimate the capability for LOFT to detect the Doppler shifts induced by orbital motion of the neutron star from a sample of bursts at different orbital phases.

  17. Burst interference in TDMA radio systems

    NASA Astrophysics Data System (ADS)

    Lei, Z.; Chen, M.-X.; Feher, K.

    1985-12-01

    Burst interference is inherent in TDMA subscriber radio and satellite communications systems. Spectral and interference properties of burst modulated signals are investigated. Owing to the burst mode operation of the TDMA system its spectrum spreads; this spread increases with the increase of burst gating rate and the decrease of the burst length. A theoretical derivation of the Pe = f(Eb/N0; I) performance, computer simulation and experimental results of IJF-OQPSK and conventional QPSK burst operated systems are presented. The performance of these systems in the presence of burst mode TDMA co-channel and adjacent channel interference (I) is evaluated.

  18. Nile River Delta, Egypt

    NASA Technical Reports Server (NTRS)

    1984-01-01

    The Nile River Delta of Egypt (30.0N, 31.0E) irrigated by the Nile River and its many distributaries, is some of the richest farm land in the world and home to some 45 million people, over half of Egypt's population. The capital city of Cairo is at the apex of the delta. Just across the river from Cairo can be seen the ancient three big pyramids and sphinx at Giza and the Suez Canal is just to the right of the delta.

  19. Evidence of Transformation Bursts During Thermal Cycling of a Pu-Ga Alloy

    SciTech Connect

    Blobaum, K M; Krenn, C R; Mitchell, J N; Haslam, J J; Wall, M A; Massalski, T B; Schwartz, A J

    2005-02-09

    The thermodynamics and kinetics of the fcc (delta) to monoclinic (alpha-prime) phase transformation and its reversion in a plutonium-gallium alloy have been studied using differential scanning calorimetry, resistometry, and dilatometry. Under ambient conditions, the delta phase is metastable in a Pu-2.0 at% Ga alloy. Thermal cycling to below the ambient temperature results in a partial transformation to the alpha-prime phase; this transformation is composition-invariant and exhibits martensitic behavior. Because this transformation results in an unusually invariant large 25% volume contraction that cannot be fully accommodated by purely elastic adjustments, the transformation mode is expected to involve burst formation of individual alpha-prime particles. However, upon cooling, these individual bursts were not resolved by the above techniques, although signals corresponding to the overall accumulation of many alpha-prime particles were observed. On the other hand, upon heating, signals from differential scanning calorimetry, resistometry, and dilatometry showed a series of discrete changes occurring in periodic increments beginning at approximately 32 C. These features correspond to the cooperative reversion of many alpha-prime particles to the delta phase; they appear to be the result of an interplay between the autocatalytically driven reversion of a cascade of individual martensite units, and self-quenching caused by small changes of temperature and/or stress accompanying each individual transformation burst. The heat of the delta/alpha-prime transformation is estimated to be about + 4 kJ/mole.

  20. The Effect of Magnetic Fields on Gamma-Ray Bursts Inferred from Multi-Wavelength Observations of the Bursts of 23 January 1999

    NASA Technical Reports Server (NTRS)

    Galama, T. J.; Briggs, M. S.; Wijers, R. A. M. J.; Vreeswijk, P. M.; Rol, E.; Band, D.; vanParadijs, J.; Kouveliotou, C.; Preece, R. D.; Bremer, M.

    1999-01-01

    Gamma-ray bursts (GRBs) are thought to arise when an extremely relativistic outflow of particles from a massive explosion (the nature at which is still unclear) interacts with material surrounding the site of the explosion. Observations of the evolving changes in emission at many wavelengths allow us to investigate the origin of the photons, and so potentially determine the nature of the explosion. Here we report the results of gamma-ray, optical, infrared, submillimeter, millimeter and radio observations of the burst ORB990123 and its afterglow. Our interpretation of the data indicates that the initial and afterglow emissions are associated with three distinct regions in the fireball. The peak flux of the afterglow, one day after the burst, has a lower frequency than observed for other bursts; this explains the short-lived radio emission. We suggest that the differences between bursts reflect variations in the magnetic-field strength in the afterglow-emitting regions.

  1. LOFAR tied-array imaging and spectroscopy of solar S bursts

    NASA Astrophysics Data System (ADS)

    Morosan, D. E.; Gallagher, P. T.; Zucca, P.; O'Flannagain, A.; Fallows, R.; Reid, H.; Magdalenić, J.; Mann, G.; Bisi, M. M.; Kerdraon, A.; Konovalenko, A. A.; MacKinnon, A. L.; Rucker, H. O.; Thidé, B.; Vocks, C.; Alexov, A.; Anderson, J.; Asgekar, A.; Avruch, I. M.; Bentum, M. J.; Bernardi, G.; Bonafede, A.; Breitling, F.; Broderick, J. W.; Brouw, W. N.; Butcher, H. R.; Ciardi, B.; de Geus, E.; Eislöffel, J.; Falcke, H.; Frieswijk, W.; Garrett, M. A.; Grießmeier, J.; Gunst, A. W.; Hessels, J. W. T.; Hoeft, M.; Karastergiou, A.; Kondratiev, V. I.; Kuper, G.; van Leeuwen, J.; McKay-Bukowski, D.; McKean, J. P.; Munk, H.; Orru, E.; Paas, H.; Pizzo, R.; Polatidis, A. G.; Scaife, A. M. M.; Sluman, J.; Tasse, C.; Toribio, M. C.; Vermeulen, R.; Zarka, P.

    2015-08-01

    Context. The Sun is an active source of radio emission that is often associated with energetic phenomena ranging from nanoflares to coronal mass ejections (CMEs). At low radio frequencies (<100 MHz), numerous millisecond duration radio bursts have been reported, such as radio spikes or solar S bursts (where S stands for short). To date, these have neither been studied extensively nor imaged because of the instrumental limitations of previous radio telescopes. Aims: Here, LOw Frequency ARray (LOFAR) observations were used to study the spectral and spatial characteristics of a multitude of S bursts, as well as their origin and possible emission mechanisms. Methods: We used 170 simultaneous tied-array beams for spectroscopy and imaging of S bursts. Since S bursts have short timescales and fine frequency structures, high cadence (~50 ms) tied-array images were used instead of standard interferometric imaging, that is currently limited to one image per second. Results: On 9 July 2013, over 3000 S bursts were observed over a time period of ~8 h. S bursts were found to appear as groups of short-lived (<1 s) and narrow-bandwidth (~2.5 MHz) features, the majority drifting at ~3.5 MHz s-1 and a wide range of circular polarisation degrees (2-8 times more polarised than the accompanying Type III bursts). Extrapolation of the photospheric magnetic field using the potential field source surface (PFSS) model suggests that S bursts are associated with a trans-equatorial loop system that connects an active region in the southern hemisphere to a bipolar region of plage in the northern hemisphere. Conclusions: We have identified polarised, short-lived solar radio bursts that have never been imaged before. They are observed at a height and frequency range where plasma emission is the dominant emission mechanism, however, they possess some of the characteristics of electron-cyclotron maser emission. A movie associated to Fig. 3 is available in electronic form at http://www.aanda.org

  2. All optical binary delta-sigma modulator

    NASA Astrophysics Data System (ADS)

    Sayeh, Mohammad R.; Siahmakoun, Azad

    2005-09-01

    This paper describes a novel A/D converter called "Binary Delta-Sigma Modulator" (BDSM) which operates only with nonnegative signal with positive feedback and binary threshold. This important modification to the conventional delta-sigma modulator makes the high-speed (>100GHz) all-optical implementation possible. It has also the capability to modify its own sampling frequency as well as its input dynamic range. This adaptive feature helps designers to optimize the system performance under highly noisy environment and also manage the power consumption of the A/D converters.

  3. X-ray bursts: Observation versus theory

    NASA Technical Reports Server (NTRS)

    Lewin, W. H. G.

    1981-01-01

    Results of various observations of common type I X-ray bursts are discussed with respect to the theory of thermonuclear flashes in the surface layers of accreting neutron stars. Topics covered include burst profiles; irregular burst intervals; rise and decay times and the role of hydrogen; the accuracy of source distances; accuracy in radii determination; radius increase early in the burst; the super Eddington limit; temperatures at burst maximum; and the role of the magnetic field.

  4. Federal Funding in the Delta.

    ERIC Educational Resources Information Center

    Reeder, Richard J.; Calhoun, Samuel D.

    2002-01-01

    The Lower Mississippi Delta region, especially the rural Delta, faces many economic challenges. The rural Delta has received much federal aid in basic income support and funding for human resource development, but less for community resource programs, which are important for economic development. Federal aid to the Delta is analyzed in terms of…

  5. Compton-dragged Gamma-Ray Bursts Associated with Supernovae.

    PubMed

    Lazzati; Ghisellini; Celotti; Rees

    2000-01-20

    It is proposed that the gamma-ray photons that characterize the prompt emission of gamma-ray bursts are produced through the Compton-drag process, which is caused by the interaction of a relativistic fireball with a very dense soft photon bath. If gamma-ray bursts are indeed associated with supernovae, then the exploding star can provide enough soft photons for radiative drag to be effective. This model accounts for the basic properties of gamma-ray bursts, i.e., the overall energetics, the peak frequency of the spectrum, and the fast variability, with an efficiency that can exceed 50%. In this scenario, there is no need for particle acceleration in relativistic collisionless shocks. Furthermore, although the Poynting flux may be important in accelerating the outflow, no magnetic field is required in the gamma-ray production. The drag also naturally limits the relativistic expansion of the fireball to Gamma less, similar104.

  6. SHORT-LIVED RADIO BURSTS FROM THE CRAB PULSAR

    SciTech Connect

    Crossley, J. H.; Eilek, J. A.; Hankins, T. H.; Kern, J. S.

    2010-10-20

    Our high-time-resolution observations reveal that individual main pulses from the Crab pulsar contain one or more short-lived microbursts. Both the energy and duration of bursts measured above 1 GHz can vary dramatically in less than a millisecond. These fluctuations are too rapid to be caused by propagation through turbulence in the Crab Nebula or in the interstellar medium; they must be intrinsic to the radio emission process in the pulsar. The mean duration of a burst varies with frequency as {nu}{sup -2}, significantly different from the broadening caused by interstellar scattering. We compare the properties of the bursts to some simple models of microstructure in the radio emission region.

  7. Observation of a metric type N solar radio burst

    DOE PAGES

    Kong, Xiangliang; Chen, Yao; Feng, Shiwei; ...

    2016-10-10

    Type III and type-III-like radio bursts are produced by energetic electron beams guided along coronal magnetic fields. As a variant of type III bursts, Type N bursts appear as the letter "N" in the radio dynamic spectrum and reveal a magnetic mirror effect in coronal loops. Here, we report a well-observed N-shaped burst consisting of three successive branches at metric wavelength with both fundamental and harmonic components and a high brightness temperature (>109 K). We verify the burst as a true type N burst generated by the same electron beam from three aspects of the data. First, durations of themore » three branches at a given frequency increase gradually and may be due to the dispersion of the beam along its path. Second, the flare site, as the only possible source of non-thermal electrons, is near the western feet of large-scale closed loops. Third, the first branch and the following two branches are localized at different legs of the loops with opposite senses of polarization. We also find that the sense of polarization of the radio burst is in contradiction to the O-mode and there exists a fairly large time delay (~3–5 s) between the fundamental and harmonic components. Possible explanations accounting for these observations are presented. Finally, assuming the classical plasma emission mechanism, we can infer coronal parameters such as electron density and magnetic field near the radio source and make diagnostics on the magnetic mirror process.« less

  8. A TYPE II RADIO BURST WITHOUT A CORONAL MASS EJECTION

    SciTech Connect

    Su, W.; Cheng, X.; Ding, M. D.; Chen, P. F.; Sun, J. Q. E-mail: dmd@nju.edu.cn

    2015-05-10

    Type II radio bursts are thought to be a signature of coronal shocks. In this paper, we analyze a short-lived type II burst that started at 07:40 UT on 2011 February 28. By carefully checking white-light images, we find that the type II radio burst is not accompanied by a coronal mass ejection, only by a C2.4 class flare and narrow jet. However, in the EUV images provided by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we find a wave-like structure that propagated at a speed of ∼600 km s{sup −1} during the burst. The relationship between the type II radio burst and the wave-like structure is, in particular, explored. For this purpose, we first derive the density distribution under the wave by the differential emission measure method, which is used to restrict the empirical density model. We then use the restricted density model to invert the speed of the shock that produces the observed frequency drift rate in the dynamic spectrum. The inverted shock speed is similar to the speed of the wave-like structure. This implies that the wave-like structure is most likely a coronal shock that produces the type II radio burst. We also examine the evolution of the magnetic field in the flare-associated active region and find continuous flux emergence and cancellation taking place near the flare site. Based on these facts, we propose a new mechanism for the formation of the type II radio burst, i.e., the expansion of the strongly inclined magnetic loops after reconnecting with a nearby emerging flux acts as a piston to generate the shock wave.

  9. Heterogeneity in Short Gamma-Ray Bursts

    NASA Technical Reports Server (NTRS)

    Norris, Jay P.; Gehrels Neil; Scargle, Jeffrey D.

    2011-01-01

    We analyze the Swift/BAT sample of short gamma-ray bursts, using an objective Bayesian Block procedure to extract temporal descriptors of the bursts' initial pulse complexes (IPCs). The sample comprises 12 and 41 bursts with and without extended emission (EE) components, respectively. IPCs of non-EE bursts are dominated by single pulse structures, while EE bursts tend to have two or more pulse structures. The medians of characteristic timescales - durations, pulse structure widths, and peak intervals - for EE bursts are factors of approx 2-3 longer than for non-EE bursts. A trend previously reported by Hakkila and colleagues unifying long and short bursts - the anti-correlation of pulse intensity and width - continues in the two short burst groups, with non-EE bursts extending to more intense, narrower pulses. In addition we find that preceding and succeeding pulse intensities are anti-correlated with pulse interval. We also examine the short burst X-ray afterglows as observed by the Swift/XRT. The median flux of the initial XRT detections for EE bursts (approx 6 X 10(exp -10) erg / sq cm/ s) is approx > 20 x brighter than for non-EE bursts, and the median X-ray afterglow duration for EE bursts (approx 60,000 s) is approx 30 x longer than for non-EE bursts. The tendency for EE bursts toward longer prompt-emission timescales and higher initial X-ray afterglow fluxes implies larger energy injections powering the afterglows. The longer-lasting X-ray afterglows of EE bursts may suggest that a significant fraction explode into more dense environments than non-EE bursts, or that the sometimes-dominant EE component efficiently p()wers the afterglow. Combined, these results favor different progenitors for EE and non-EE short bursts.

  10. HETEROGENEITY IN SHORT GAMMA-RAY BURSTS

    SciTech Connect

    Norris, Jay P.; Gehrels, Neil

    2011-07-01

    We analyze the Swift/BAT sample of short gamma-ray bursts, using an objective Bayesian Block procedure to extract temporal descriptors of the bursts' initial pulse complexes (IPCs). The sample is comprised of 12 and 41 bursts with and without extended emission (EE) components, respectively. IPCs of non-EE bursts are dominated by single pulse structures, while EE bursts tend to have two or more pulse structures. The medians of characteristic timescales-durations, pulse structure widths, and peak intervals-for EE bursts are factors of {approx}2-3 longer than for non-EE bursts. A trend previously reported by Hakkila and colleagues unifying long and short bursts-the anti-correlation of pulse intensity and width-continues in the two short burst groups, with non-EE bursts extending to more intense, narrower pulses. In addition, we find that preceding and succeeding pulse intensities are anti-correlated with pulse interval. We also examine the short burst X-ray afterglows as observed by the Swift/X-Ray Telescope (XRT). The median flux of the initial XRT detections for EE bursts ({approx}6x10{sup -10} erg cm{sup -2} s{sup -1}) is {approx}>20x brighter than for non-EE bursts, and the median X-ray afterglow duration for EE bursts ({approx}60,000 s) is {approx}30x longer than for non-EE bursts. The tendency for EE bursts toward longer prompt-emission timescales and higher initial X-ray afterglow fluxes implies larger energy injections powering the afterglows. The longer-lasting X-ray afterglows of EE bursts may suggest that a significant fraction explode into denser environments than non-EE bursts, or that the sometimes-dominant EE component efficiently powers the afterglow. Combined, these results favor different progenitors for EE and non-EE short bursts.

  11. A universal characteristic of type II radio bursts

    NASA Astrophysics Data System (ADS)

    Aguilar-Rodriguez, E.; Gopalswamy, N.; MacDowall, R.; Yashiro, S.; Kaiser, M. L.

    2005-12-01

    We present a study on the spectral properties of interplanetary type II radio bursts observed by the Radio and Plasma Wave (WAVES) experiment on board the Wind spacecraft. We investigated the relative bandwidth of the type II radio bursts observed by WAVES from 1997 up to 2003. We obtained three sets of events, based on the frequency domain of occurrence: 109 events in the low-frequency domain (30 KHz to 1000 kHz, detected by the RAD1 receiver), 216 events in the high-frequency domain (1-14 MHz, observed by the RAD2 receiver), and 73 events that spanned both domains (RAD1 and RAD2). Statistical results show that the average bandwidth-to-frequency ratio (BFR) was 0.28 ± 0.15, 0.26 ± 0.16, and 0.32 ± 0.15 for RAD1, RAD2, and RAD1 + RAD2, respectively. We compared our results with those obtained for ISEE-3 type II bursts and found a difference in the average BFR, which seems to be due to a selection effect. The BFR of the WAVES type II bursts is similar to that of metric type II bursts reported in published works. This suggests that the BFR is a universal characteristic, irrespective of the spectral domain. Finally, we also studied the BFR evolution with heliocentric distance using white-light observation of the associated coronal mass ejections. We found that the BFR remains roughly constant in the SOHO/LASCO field of view (i.e., from 2.1 to 32 solar radii), while the bandwidth itself decreases.

  12. Constraining the Solar Coronal Magnetic Field Strength using Split-band Type II Radio Burst Observations

    NASA Astrophysics Data System (ADS)

    Kishore, P.; Ramesh, R.; Hariharan, K.; Kathiravan, C.; Gopalswamy, N.

    2016-11-01

    We report on low-frequency radio (85-35 MHz) spectral observations of four different type II radio bursts, which exhibited fundamental-harmonic emission and split-band structure. Each of the bursts was found to be closely associated with a whitelight coronal mass ejection (CME) close to the Sun. We estimated the coronal magnetic field strength from the split-band characteristics of the bursts, by assuming a model for the coronal electron density distribution. The choice of the model was constrained, based on the following criteria: (1) when the radio burst is observed simultaneously in the upper and lower bands of the fundamental component, the location of the plasma level corresponding to the frequency of the burst in the lower band should be consistent with the deprojected location of the leading edge (LE) of the associated CME; (2) the drift speed of the type II bursts derived from such a model should agree closely with the deprojected speed of the LE of the corresponding CMEs. With the above conditions, we find that: (1) the estimated field strengths are unique to each type II burst, and (2) the radial variation of the field strength in the different events indicate a pattern. It is steepest for the case where the heliocentric distance range over which the associated burst is observed is closest to the Sun, and vice versa.

  13. Regulation of Transcriptional Bursting by a Naturally Oscillating Signal

    PubMed Central

    Corrigan, Adam M.; Chubb, Jonathan R.

    2014-01-01

    Summary Transcription is highly stochastic, occurring in irregular bursts [1–3]. For temporal and spatial precision of gene expression, cells must somehow deal with this noisy behavior. To address how this is achieved, we investigated how transcriptional bursting is entrained by a naturally oscillating signal, by direct measurement of transcription together with signal dynamics in living cells. We identify a Dictyostelium gene showing rapid transcriptional oscillations with the same period as extracellular cAMP signaling waves. Bursting approaches antiphase to cAMP waves, with accelerating transcription cycles during differentiation. Although coupling between signal and transcription oscillations was clear at the population level, single-cell transcriptional bursts retained considerable heterogeneity, indicating that transcription is not governed solely by signaling frequency. Previous studies implied that burst heterogeneity reflects distinct chromatin states [4–6]. Here we show that heterogeneity is determined by multiple intrinsic and extrinsic cues and is maintained by a transcriptional persistence. Unusually for a persistent transcriptional behavior, the lifetime was only 20 min, with rapid randomization of transcriptional state by the response to oscillatory signaling. Linking transcription to rapid signaling oscillations allows reduction of gene expression heterogeneity by temporal averaging, providing a mechanism to generate precision in cell choices during development. PMID:24388853

  14. Solar Flares, Type III Radio Bursts, Coronal Mass Ejections, and Energetic Particles

    NASA Technical Reports Server (NTRS)

    Cane, Hilary V.; Erickson, W. C.; Prestage, N. P.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    In this correlative study between greater than 20 MeV solar proton events, coronal mass ejections (CMEs), flares, and radio bursts it is found that essentially all of the proton events are preceded by groups of type III bursts and all are preceded by CMEs. These type III bursts (that are a flare phenomenon) usually are long-lasting, intense bursts seen in the low-frequency observations made from space. They are caused by streams of electrons traveling from close to the solar surface out to 1 AU. In most events the type III emissions extend into, or originate at, the time when type II and type IV bursts are reported (some 5 to 10 minutes after the start of the associated soft X-ray flare) and have starting frequencies in the 500 to approximately 100 MHz range that often get lower as a function of time. These later type III emissions are often not reported by ground-based observers, probably because of undue attention to type II bursts. It is suggested to call them type III-1. Type III-1 bursts have previously been called shock accelerated (SA) events, but an examination of radio dynamic spectra over an extended frequency range shows that the type III-1 bursts usually start at frequencies above any type II burst that may be present. The bursts sometimes continue beyond the time when type II emission is seen and, furthermore, sometimes occur in the absence of any type II emission. Thus the causative electrons are unlikely to be shock accelerated and probably originate in the reconnection regions below fast CMEs. A search did not find any type III-1 bursts that were not associated with CMEs. The existence of low-frequency type III bursts proves that open field lines extend from within 0.5 radius of the Sun into the interplanetary medium (the bursts start above 100 MHz, and such emission originates within 0.5 solar radius of the solar surface). Thus it is not valid to assume that only closed field lines exist in the flaring regions associated with CMEs and some

  15. Cross-frequency interactions in the precedence effect.

    PubMed

    Shinn-Cunningham, B G; Zurek, P M; Durlach, N I; Clifton, R K

    1995-07-01

    This paper concerns the extent to which the precedence effect is observed when leading and lagging sounds occupy different spectral regions. Subjects, listening under headphones, were asked to match the intracranial lateral position of an acoustic pointer to that of a test stimulus composed of two binaural noise bursts with asynchronous onsets, parametrically varied frequency content, and different interaural delays. The precedence effect was measured by the degree to which the interaural delay of the matching pointer was independent of the interaural delay of the lagging noise burst in the test stimulus. The results, like those of Blauert and Divenyi [Acustica 66, 267-274 (1988)], show an asymmetric frequency effect in which the lateralization influence of a lagging high-frequency burst is almost completely suppressed by a leading low-frequency burst, whereas a lagging low-frequency burst is weighted equally with a leading high-frequency burst. This asymmetry is shown to be the result of an inherent low-frequency dominance that is seen even with simultaneous bursts. When this dominance is removed (by attenuating the low-frequency burst) the precedence effect operates with roughly equal strength both upward and downward in frequency. Within the scope of the current study (with lateralization achieved through the use of interaural time differences alone, stimuli from only two frequency bands, and only three subjects performing in all experiments), these results suggest that the precedence effect arises from a fairly central processing stage in which information is combined across frequency.

  16. Persistent Na+ current modifies burst discharge by regulating conditional backpropagation of dendritic spikes.

    PubMed

    Doiron, Brent; Noonan, Liza; Lemon, Neal; Turner, Ray W

    2003-01-01

    The estimation and detection of stimuli by sensory neurons is affected by factors that govern a transition from tonic to burst mode and the frequency characteristics of burst output. Pyramidal cells in the electrosensory lobe of weakly electric fish generate spike bursts for the purpose of stimulus detection. Spike bursts are generated during repetitive discharge when a frequency-dependent broadening of dendritic spikes increases current flow from dendrite to soma to potentiate a somatic depolarizing afterpotential (DAP). The DAP eventually triggers a somatic spike doublet with an interspike interval that falls inside the dendritic refractory period, blocking spike backpropagiation and the DAP. Repetition of this process gives rise to a rhythmic dendritic spike failure, termed conditional backpropagation, that converts cell output from tonic to burst discharge. Through in vitro recordings and compartmental modeling we show that burst frequency is regulated by the rate of DAP potentiation during a burst, which determines the time required to discharge the spike doublet that blocks backpropagation. DAP potentiation is magnified through a positive feedback process when an increase in dendritic spike duration activates persistent sodium current (I(NaP)). I(NaP) further promotes a slow depolarization that induces a shift from tonic to burst discharge over time. The results are consistent with a dynamical systems analysis that shows that the threshold separating tonic and burst discharge can be represented as a saddle-node bifurcation. The interaction between dendritic K(+) current and I(NaP) provides a physiological explanation for a variable time scale of bursting dynamics characteristic of such a bifurcation.

  17. Amplitude-Modulated Bursting: A Novel Class of Bursting Rhythms

    NASA Astrophysics Data System (ADS)

    Vo, Theodore; Kramer, Mark A.; Kaper, Tasso J.

    2016-12-01

    We report on the discovery of a novel class of bursting rhythms, called amplitude-modulated bursting (AMB), in a model for intracellular calcium dynamics. We find that these rhythms are robust and exist on open parameter sets. We develop a new mathematical framework with broad applicability to detect, classify, and rigorously analyze AMB. Here we illustrate this framework in the context of AMB in a model of intracellular calcium dynamics. In the process, we discover a novel family of singularities, called toral folded singularities, which are the organizing centers for the amplitude modulation and exist generically in slow-fast systems with two or more slow variables.

  18. DECIMETRIC TYPE III BURSTS: GENERATION AND PROPAGATION

    SciTech Connect

    Li, B.; Cairns, Iver H.; Robinson, P. A.; Yan, Y. H.

    2011-09-01

    Simulations are presented for decimetric type III radio bursts at 2f{sub p} , where f{sub p} is the local electron plasma frequency. The simulations show that 2f{sub p} radiation can be observed at Earth in two scenarios for the radiation's generation and propagation. In Scenario A, radiation is produced and propagates in warm plasmas in the lower corona that are caused by previous magnetic reconnection outflows and/or chromospheric evaporation. In Scenario B radiation is generated in normal plasmas, then due to its natural directivity pattern and refraction, radiation partly propagates into nearby regions, which are hot because of previous reconnection/evaporation. The profiles of plasma density n{sub e} (r) and electron temperature T{sub e} (r) in the lower corona (r - R{sub sun} {approx}< 100 Mm) are found to be crucial to whether radiation can be produced and escape at observable levels against the effects of free-free absorption, where r is the heliocentric distance. Significantly, the observed wide ranges of radiation properties (e.g., drift rates) require n{sub e} (r) with a large range of scale heights h{sub s} , consistent nonetheless for Scenario B with short observed EUV loops. This is relevant to problems with large h{sub s} inferred from tall EUV loops. The simulations suggest: (1) n{sub e} (r) with small h{sub s} , such as n{sub e} (r){proportional_to}(r - R{sub sun}){sup -2.38} for flaring regions, are unexpectedly common deep in the corona. This result is consistent with recent work on n{sub e} (r) for r {approx} (1.05-2)R{sub sun} extracted from observed metric type IIIs. (2) The dominance of reverse-slope bursts over normal bursts sometimes observed may originate from asymmetric reconnection/acceleration, which favors downgoing beams.

  19. Coherent delta-band oscillations between cortical areas correlate with decision making

    PubMed Central

    Nácher, Verónica; Ledberg, Anders; Deco, Gustavo; Romo, Ranulfo

    2013-01-01

    Coherent oscillations in the theta-to-gamma frequency range have been proposed as a mechanism that coordinates neural activity in large-scale cortical networks in sensory, motor, and cognitive tasks. Whether this mechanism also involves coherent oscillations at delta frequencies (1–4 Hz) is not known. Rather, delta oscillations have been associated with slow-wave sleep. Here, we show coherent oscillations in the delta frequency band between parietal and frontal cortices during the decision-making component of a somatosensory discrimination task. Importantly, the magnitude of this delta-band coherence is modulated by the different decision alternatives. Furthermore, during control conditions not requiring decision making, delta-band coherences are typically much reduced. Our work indicates an important role for synchronous activity in the delta frequency band when large-scale, distant cortical networks coordinate their neural activity during decision making. PMID:23980180

  20. A first missense mutation in the delta sarcoglycan gene associated with a severe phenotype and frequency of limb-girdle muscular dystrophy type 2F (LGMD2F) in Brazilian sarcoglycanopathies.

    PubMed Central

    Moreira, E S; Vainzof, M; Marie, S K; Nigro, V; Zatz, M; Passos-Bueno, M R

    1998-01-01

    Among the heterogeneous group of autosomal recessive limb-girdle muscular dystrophies (AR LGMDs), the sarcoglycanopathies (LGMD2C-2F) represent a subgroup characterised by defects in the gamma, alpha, beta, and delta sarcoglycan genes, respectively. Genotype-phenotype correlations in these forms of AR LGMD are important to enhance our understanding of protein function. Regarding LGMD2F, only two homozygous frameshift mutations have been reported to date in patients with a severe phenotype. In the present report, through screening 23 unrelated AR LGMD patients, we identified three subjects with LGMD2F, two with a previously reported frameshift mutation and the other homozygous for a new missense mutation in the delta sarcoglycan gene. Interestingly, this new mutation is also associated with a severe clinical course. In addition, our results suggest that this form of severe AR LGMD is not very rare in our population. Images PMID:9832045

  1. Chimera states in bursting neurons

    NASA Astrophysics Data System (ADS)

    Bera, Bidesh K.; Ghosh, Dibakar; Lakshmanan, M.

    2016-01-01

    We study the existence of chimera states in pulse-coupled networks of bursting Hindmarsh-Rose neurons with nonlocal, global, and local (nearest neighbor) couplings. Through a linear stability analysis, we discuss the behavior of the stability function in the incoherent (i.e., disorder), coherent, chimera, and multichimera states. Surprisingly, we find that chimera and multichimera states occur even using local nearest neighbor interaction in a network of identical bursting neurons alone. This is in contrast with the existence of chimera states in populations of nonlocally or globally coupled oscillators. A chemical synaptic coupling function is used which plays a key role in the emergence of chimera states in bursting neurons. The existence of chimera, multichimera, coherent, and disordered states is confirmed by means of the recently introduced statistical measures and mean phase velocity.

  2. Bursts in discontinuous Aeolian saltation

    PubMed Central

    Carneiro, M. V.; Rasmussen, K. R.; Herrmann, H. J.

    2015-01-01

    Close to the onset of Aeolian particle transport through saltation we find in wind tunnel experiments a regime of discontinuous flux characterized by bursts of activity. Scaling laws are observed in the time delay between each burst and in the measurements of the wind fluctuations at the fluid threshold Shields number θc. The time delay between each burst decreases on average with the increase of the Shields number until sand flux becomes continuous. A numerical model for saltation including the wind-entrainment from the turbulent fluctuations can reproduce these observations and gives insight about their origin. We present here also for the first time measurements showing that with feeding it becomes possible to sustain discontinuous flux even below the fluid threshold. PMID:26073305

  3. Auditory nerve spatial encoding of high-frequency pure tones: population response profiles derived from d' measure associated with nearby places along the cochlea.

    PubMed

    Kim, D O; Parham, K

    1991-03-01

    We examined a measure of discriminability in auditory nerve (AN) population responses that may underlie behavioral frequency discrimination of high-frequency pure tones in the cat. Population responses of high- (greater than = 15 spikes/s) and low- (less than 15 spikes/s) spontaneous rate (SR) AN fibers in unanesthetized decerebrate cats to 5 kHz pure tones were measured in the form of mean, mu, and standard deviation, sigma, of spike counts for 0.2 s tone bursts. The AN responses were analyzed in terms of a d'e(x, delta x) associated with adjoining cochlear places as defined in the manner of signal detection theory. We also examined sigma d'e(x, delta x), a spatial summation of the discriminability measure. The major findings are: (1) the d'e(x, delta x) function conveys information about 5 kHz pure tone frequency over a region of +/- 0.5 to 1.0 octave, or +/- 1.67 to 3.33 mm, around the characteristic place (CP), with the region being narrower at lower stimulus levels; (2) at 30 dB SPL, the integrated d'e(x, delta x) discriminability scores are similar for the apical and basal regions surrounding the CP whereas, at 70 dB SPL, the scores are higher for the apical region than for the basal region; and (3) at 50 and 70 dB SPL, the integrated d'e(x, delta x) discriminability scores of low-SR fibers were higher than those of high-SR fibers although, at 30 dB SPL, the latter were higher than the former. By using the cat cochlear frequency-place relationship and the inner hair cell (IHC) spacing, we interpret that the cat's frequency difference limen, delta f/f = 0.0088 at 4 kHz [Elliott et al., 1960, J. Acoust. Soc. Am. 32, 380-384], corresponds to a shift of cochlear excitation profile by 4.5 IHCs. From the present analysis of AN responses, we conclude that, for high-frequency pure tones, the d'e(x, delta x) code, an example of rate-place code, of frequency provides sufficient information to support the cat's behavioral frequency discrimination.

  4. MICROWAVE QUASI-PERIODIC PULSATION WITH MILLISECOND BURSTS IN A SOLAR FLARE ON 2011 AUGUST 9

    SciTech Connect

    Tan Baolin; Tan Chengming

    2012-04-10

    A peculiar microwave quasi-periodic pulsation (QPP) accompanying a hard X-ray (HXR) QPP of about 20 s duration occurred just before the maximum of an X6.9 solar flare on 2011 August 9. The most interesting aspect is that the microwave QPP consists of millisecond timescale superfine structures. Each microwave QPP pulse is made up of clusters of millisecond spike bursts or narrowband type III bursts. There are three different frequency drift rates: the global frequency drift rate of the microwave QPP pulse group, the frequency drift rate of the microwave QPP pulse, and the frequency drift rate of individual millisecond spikes or type III bursts. The physical analysis indicates that the energetic electrons accelerating from a large-scale highly dynamic magnetic reconnecting current sheet above the flaring loop propagate downward, impact the flaring plasma loop, and produce HXR bursts. The tearing-mode (TM) oscillations in the current sheet modulate HXR emission and generate HXR QPP; the energetic electrons propagating downward produce Langmuir turbulence and plasma waves, resulting in plasma emission. The modulation of TM oscillation on the plasma emission in the current-carrying plasma loop may generate microwave QPP. The TM instability produces magnetic islands in the loop. Each X-point will be a small reconnection site and will accelerate the ambient electrons. These accelerated electrons impact the ambient plasma and trigger the millisecond spike clusters or the group of type III bursts. Possibly, each millisecond spike burst or type III burst is one of the elementary bursts (EBs). A large number of such EB clusters form an intense flaring microwave burst.

  5. Interplanetary density models as inferred from solar Type III bursts

    NASA Astrophysics Data System (ADS)

    Oppeneiger, Lucas; Boudjada, Mohammed Y.; Lammer, Helmut; Lichtenegger, Herbert

    2016-04-01

    We report on the density models derived from spectral features of solar Type III bursts. They are generated by beams of electrons travelling outward from the Sun along open magnetic field lines. Electrons generate Langmuir waves at the plasma frequency along their ray paths through the corona and the interplanetary medium. A large frequency band is covered by the Type III bursts from several MHz down to few kHz. In this analysis, we consider the previous empirical density models proposed to describe the electron density in the interplanetary medium. We show that those models are mainly based on the analysis of Type III bursts generated in the interplanetary medium and observed by satellites (e.g. RAE, HELIOS, VOYAGER, ULYSSES,WIND). Those models are confronted to stereoscopic observations of Type III bursts recorded by WIND, ULYSSES and CASSINI spacecraft. We discuss the spatial evolution of the electron beam along the interplanetary medium where the trajectory is an Archimedean spiral. We show that the electron beams and the source locations are depending on the choose of the empirical density models.

  6. Polarization and position measurements of Type III bursts

    NASA Technical Reports Server (NTRS)

    Suzuki, S.; Sheridan, K. V.; Dulk, G. A.

    1980-01-01

    The positional and polarization characteristics of Type III bursts in the range 24-220 MHz as measured by the Culgoora radioheliograph, spectrograph and spectropolarimeter are reported. The study includes 997 bursts which are of two classes: fundamental-harmonic (F-H) pairs and 'structureless' bursts with no visible F-H structure, and concentrates on the polarization of the bursts and the variation of polarization from centre to limb. The observed centre-to-limb decrease in polarization approximately follows a cosine law. This decrease is not as predicted by simple theory but is consistent with other observations which imply that open field lines from an active region diverge strongly. The observed o-mode polarization of harmonic radiation implies that the wave vectors of Langmuir waves are always parallel, within about 20 deg, to the magnetic field, while the constancy of H polarization with frequency implies that the ratio of gyromagnetic to plasma frequency, the Alfven speed and the plasma beta are constant with height on the open field lines above an active region. Finally, it is inferred that some factor, in addition to the magnetic field strength, controls the polarization of F radiation.

  7. The Swift Burst Alert Telescope

    NASA Astrophysics Data System (ADS)

    Parsons, A.; Barthelmy, S.; Barbier, L.; Gehrels, N.; Palmer, D.; Tueller, J.; Fenimore, E.; BAT Engineering Team

    2000-10-01

    The Swift Gamma Ray Burst MIDEX is a multiwavelength observatory scheduled to be launched in September 2003 to study gamma-ray bursts (GRBs) and their x-ray and optical afterglow emission. Swift will exploit these newly discovered GRB afterglow characteristics to make a comprehensive study of ~ 1000 GRBs and use the afterglow phenomenon as a tool for probing their source and evolution. Swift will also be able to use GRBs to probe the early Universe. The Burst Alert Telescope (BAT), a large coded aperture instrument with a wide field-of-view (FOV), provides the gamma-ray burst triggers and locations for the Swift Mission. BAT will observe and locate hundreds of bursts per year to better than 4 arc minutes accuracy. Using this prompt burst location information, Swift can slew quickly (within 20 - 70 s) to point on-board x-ray (XRT) and optical (UVOT) instrumentation at the burst for continued afterglow studies. The BAT instrument consists of a large (5200 cm2) hard x-ray detector plane positioned one meter away from an even larger (2.6 m2) coded aperture mask. The BAT detector plane consists of 128 CdZnTe semiconductor detector modules each containing 256 individual, planar 4 mm x 4 mm x 2 mm CdZnTe detectors that are read out by a pair of XA1 Application Specific Integrated Circuits (ASICs). The BAT mask will be constructed using 5 mm x 5 mm x 1 mm lead tiles attached to a self-supporting 0.4 g/cm2 substrate fabricated from Kevlar fiber/honeycomb materials. With 4 mm square focal plane detector elements and 5 mm square mask pixels, BAT will have angular resolution better than 22 arc minutes and will determine GRB source locations to ~ 4 arc minutes for bursts detected at 5 sigma or brighter. A full description of the BAT instrument and its capabilities will be presented along with results from performance tests of prototype detector modules.

  8. Detection of artifacts from high energy bursts in neonatal EEG.

    PubMed

    Bhattacharyya, Sourya; Biswas, Arunava; Mukherjee, Jayanta; Majumdar, Arun Kumar; Majumdar, Bandana; Mukherjee, Suchandra; Singh, Arun Kumar

    2013-11-01

    Detection of non-cerebral activities or artifacts, intermixed within the background EEG, is essential to discard them from subsequent pattern analysis. The problem is much harder in neonatal EEG, where the background EEG contains spikes, waves, and rapid fluctuations in amplitude and frequency. Existing artifact detection methods are mostly limited to detect only a subset of artifacts such as ocular, muscle or power line artifacts. Few methods integrate different modules, each for detection of one specific category of artifact. Furthermore, most of the reference approaches are implemented and tested on adult EEG recordings. Direct application of those methods on neonatal EEG causes performance deterioration, due to greater pattern variation and inherent complexity. A method for detection of a wide range of artifact categories in neonatal EEG is thus required. At the same time, the method should be specific enough to preserve the background EEG information. The current study describes a feature based classification approach to detect both repetitive (generated from ECG, EMG, pulse, respiration, etc.) and transient (generated from eye blinking, eye movement, patient movement, etc.) artifacts. It focuses on artifact detection within high energy burst patterns, instead of detecting artifacts within the complete background EEG with wide pattern variation. The objective is to find true burst patterns, which can later be used to identify the Burst-Suppression (BS) pattern, which is commonly observed during newborn seizure. Such selective artifact detection is proven to be more sensitive to artifacts and specific to bursts, compared to the existing artifact detection approaches applied on the complete background EEG. Several time domain, frequency domain, statistical features, and features generated by wavelet decomposition are analyzed to model the proposed bi-classification between burst and artifact segments. A feature selection method is also applied to select the

  9. Burst Mode Receiver for 112 Gb/s DP-QPSK with parallel DSP.

    PubMed

    Thomsen, Benn C; Maher, Robert; Millar, David S; Savory, Seb J

    2011-12-12

    A burst mode 112 Gb/s DP-QPSK digital coherent optical receiver with parallel DSP suitable for implementation in a CMOS ASIC with a 218.75 MHz clock speed is presented. The receiver performance is validated in a five channel 50 GHz grid WDM burst switching experiment using a commercially available wavelength tunable laser as the local oscillator. A new equalizer initialization scheme that overcomes the degenerate convergence problem and ensures rapid convergence is introduced. We show that the performance of the tunable local oscillator is commensurate with burst mode coherent reception when differential decoding in employed and that required parallel DSP implementation does not seriously impair the polarization and frequency tracking performance of a digital coherent receiver under burst mode operation. We report a burst acquisition time of less than 200 ns.

  10. A SCENARIO FOR THE FINE STRUCTURES OF SOLAR TYPE IIIb RADIO BURSTS BASED ON ELECTRON CYCLOTRON MASER EMISSION

    SciTech Connect

    Wang, C. B.

    2015-06-10

    A scenario based on electron cyclotron maser (ECM) emission is proposed for the fine structures of solar radio emission. It is suggested that under certain conditions modulation of the ratio between the plasma frequency and electron gyro frequency by ultra-low-frequency waves, which is a key parameter for excitation of ECM instability, may lead to the intermittent emission of radio waves. As an example, the explanation for the observed fine-structure components in the solar Type IIIb bursts is discussed in detail. Three primary issues of Type IIIb bursts are addressed: (1) the physical mechanism that results in intermittent emission elements that form a chain in the dynamic spectrum of Type IIIb bursts, (2) the cause of split pairs (or double stria) and triple stria, and (3) why only IIIb–III bursts are observed in the events of fundamental harmonic pair emission whereas IIIb–IIIb or III–IIIb bursts are very rarely observed.

  11. A Scenario for the Fine Structures of Solar Type IIIb Radio Bursts Based on Electron Cyclotron Maser Emission

    NASA Astrophysics Data System (ADS)

    Wang, C. B.

    2015-06-01

    A scenario based on electron cyclotron maser (ECM) emission is proposed for the fine structures of solar radio emission. It is suggested that under certain conditions modulation of the ratio between the plasma frequency and electron gyro frequency by ultra-low-frequency waves, which is a key parameter for excitation of ECM instability, may lead to the intermittent emission of radio waves. As an example, the explanation for the observed fine-structure components in the solar Type IIIb bursts is discussed in detail. Three primary issues of Type IIIb bursts are addressed: (1) the physical mechanism that results in intermittent emission elements that form a chain in the dynamic spectrum of Type IIIb bursts, (2) the cause of split pairs (or double stria) and triple stria, and (3) why only IIIb-III bursts are observed in the events of fundamental harmonic pair emission whereas IIIb-IIIb or III-IIIb bursts are very rarely observed.

  12. Delta II Mars Pathfinder

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Final preparations for lift off of the DELTA II Mars Pathfinder Rocket are shown. Activities include loading the liquid oxygen, completing the construction of the Rover, and placing the Rover into the Lander. After the countdown, important visual events include the launch of the Delta Rocket, burnout and separation of the three Solid Rocket Boosters, and the main engine cutoff. The cutoff of the main engine marks the beginning of the second stage engine. After the completion of the second stage, the third stage engine ignites and then cuts off. Once the third stage engine cuts off spacecraft separation occurs.

  13. Cosmology: Home of a fast radio burst

    NASA Astrophysics Data System (ADS)

    Lorimer, Duncan

    2016-02-01

    Our understanding of fast radio bursts -- intense pulses of radio waves -- and their use as cosmic probes promises to be transformed now that one burst has been associated with a galaxy of known distance from Earth. See Letter p.453

  14. Type III-L Solar Radio Bursts and Their Associations with Solar Energetic Proton Events

    NASA Astrophysics Data System (ADS)

    Duffin, Robert T.; White, S. M.; Ray, P. S.; Kaiser, M. L.

    2010-05-01

    Type III-L bursts are a sub-class of type III solar radio bursts that tend to occur after the impulsive phase of flares; are longer in duration than individual type IIIs and tend to be low-frequency. There has been a proposal that type III-Ls are connected to solar energetic proton (SEP) events. Most work on this connection has started from samples of SEP events, but if type III-Ls are to be useful for prediction of SEP events, then we need to understand the properties of samples of type III-L bursts. This talk reports preliminary results from such a study. An operating definition based on previous work is used to identify type III-L events amongst M- and X-class flares from 2001; and then associations with other properties of these events are investigated, including association with SEP events. If there is an association with SEP events, one important factor that these bursts allow us to address is the question of whether acceleration takes place at an associated CME, or closer to the flare site well below the CME. Work has been developed on a type III fitting tool. A Template is chosen from a representative individual type III burst and fit to individual type III bursts and components of Complex type III bursts in order to help analyze and distinguish these bursts. This type III fitting tool can also be used to fit and distinguish Impulsive type III and type III-L bursts and help analyze various characteristics of the components of these bursts such as drift-rate and change in the duration of their intensity-time profiles with frequency. Funding for this research came from the Naval Research Laboratory where basic research in radio astronomy is funded by the Office of Naval Research, and from NASA LWS Grant FRS 526249.

  15. Delta rhythm in wakefulness: evidence from intracranial recordings in human beings.

    PubMed

    Sachdev, Robert N S; Gaspard, Nicolas; Gerrard, Jason L; Hirsch, Lawrence J; Spencer, Dennis D; Zaveri, Hitten P

    2015-08-01

    A widely accepted view is that wakefulness is a state in which the entire cortical mantle is persistently activated, and therefore desynchronized. Consequently, the EEG is dominated by low-amplitude, high-frequency fluctuations. This view is currently under revision because the 1-4 Hz delta rhythm is often evident during "quiet" wakefulness in rodents and nonhuman primates. Here we used intracranial EEG recordings to assess the occurrence of delta rhythm in 18 awake human beings. Our recordings reveal rhythmic delta during wakefulness at 10% of all recording sites. Delta rhythm could be observed in a single cortical lobe or in multiple lobes. Sites with high delta could flip between high and low delta power or could be in a persistently high delta state. Finally, these sites were rarely identified as the sites of seizure onset. Thus rhythmic delta can dominate the background operation and activity of some neocortical circuits in awake human beings.

  16. Gamma-ray burst observations

    NASA Technical Reports Server (NTRS)

    Atteia, J.-L.

    1993-01-01

    The most important observational characteristics of gamma-ray bursts are reviewed, with emphasis on X-ray and gamma-ray data. The observations are used to derive some basic properties of the sources. The sources are found to be isotropically distributed; the burster population is limited in space, and the edge of the distribution is visible.

  17. Respiratory burst oxidase of fertilization.

    PubMed Central

    Heinecke, J W; Shapiro, B M

    1989-01-01

    Partially reduced oxygen species are toxic, yet sea urchin eggs synthesize H2O2 in a "respiratory burst" at fertilization, as an extracellular oxidant to crosslink their protective surface envelopes. To study the biochemical mechanism for H2O2 production, we have isolated an NADPH-specific oxidase fraction from homogenates of unfertilized Strongylocentrotus purpuratus eggs that produces H2O2 when stimulated with Ca2+ and MgATP2-. Concentrations of free Ca2+ previously implicated in regulation of egg activation modulate the activity of the oxidase. Inhibitors were used to test the relevance of this oxidase to the respiratory burst of fertilization. Procaine, two phenothiazines, and N-ethylmaleimide (but not iodoacetamide) inhibited H2O2 production by the oxidase fraction and oxygen consumption by activated eggs. The ATP requirement suggested that protein kinase activity might regulate the respiratory burst of fertilization; consonant with this hypothesis, H-7 and staurosporine were inhibitory. The respiratory burst oxidase of fertilization is an NADPH:O2 oxidoreductase that appears to be regulated by a protein kinase; although it bears a remarkable resemblance to the neutrophil oxidase, unlike the latter it does not form O2- as its initial product. PMID:2537493

  18. Synchrotron masers and fast radio bursts

    NASA Astrophysics Data System (ADS)

    Ghisellini, G.

    2017-02-01

    Fast radio bursts, with a typical duration of 1 ms and 1 Jy flux density at gigahertz frequencies, have brightness temperatures exceeding 1033 K, requiring a coherent emission process. This can be achieved by bunching particles in volumes smaller than the typical wavelength, but this may be challenging. Maser emission is a possibility. Under certain conditions, the synchrotron-stimulated emission process can be more important than true absorption, and a synchrotron maser can be created. This occurs when the emitting electrons have a very narrow distribution of pitch angles and energies. This process overcomes the difficulties of having extremely dense bunches of particles and relaxes the light-crossing time limits, since there is no simple relation between the actual size of the source and the observed variability time-scale.

  19. The Mystery of Gamma-Ray Bursts

    NASA Technical Reports Server (NTRS)

    Fishman, Gerald J.

    1998-01-01

    Gamma-ray bursts remain on of the greatest mysteries in astrophysics in spite of recent observational advances and intense theoretical work. Although some of the basic properties of bursts were known 25 years ago, new and more detailed observations have been made by the BATSE (Burst and Transient Source Experiment) experiment on the Compton Gamma Ray Observatory in the past five years. Recent observations of bursts and some proposed models will be discussed.

  20. Soft Phonons in (delta)-Phase Plutonium Near the (delta)-(alpha)' Transition

    SciTech Connect

    Xu, R; Wong, J; Zshack, P; Hong, H; Chiang, T

    2007-09-13

    Plutonium and its alloys exhibit complex phase diagrams that imply anomalous lattice dynamics near phase stability boundaries. Specifically, the TA [111] phonon branch in Ga-stabilized {delta}-Pu at room temperature shows a pronounced soft mode at the zone boundary, which suggests a possible connection to the martensitic transformation from the fcc {delta}-phase to the monoclinic {alpha}{prime}-phase at low temperatures. This work is a study of the lattice dynamics of this system by x-ray thermal diffuse scattering. The results reveal little temperature dependence of the phonon frequencies, thus indicating that kinetic phonon softening is not responsible for this phase transition.

  1. Electron cyclotron maser emission in coronal arches and solar radio type V bursts

    SciTech Connect

    Tang, J. F.; Wu, D. J.; Tan, C. M.

    2013-12-10

    Solar radio type V bursts were classified as a special spectral class based on their moderately long duration, wide bandwidth, and sense of polarization opposite of associated type III bursts. However, type V bursts are also closely related to the preceding type III bursts. They have an approximately equal source height and the same dispersion of position with frequency. Electron cyclotron maser (ECM) instability driven by beam electrons has been used to explain type III bursts in recent years. We propose ECM emission as the physical process of type V solar radio bursts. According to the observed properties of type V and III bursts, we propose that energetic electrons in excited type V continuum are trapped in coronal loops, which are adjacent to the open field lines traced by type III electrons. With the proposed magnetic field configuration and the ECM emission mechanism, the observed properties of type V bursts, such as long duration, wide bandwidth, and opposite sense of polarization can be reasonably explained by our model.

  2. Optimal Intrinsic Dynamics for Bursting in a Three-Cell Network

    NASA Astrophysics Data System (ADS)

    Dunmyre, Justin R.; Rubin, Jonathan E.

    2010-01-01

    Previous numerical and analytical work has shown that synaptic coupling can allow a network of model neurons to synchronize despite heterogeneity in intrinsic parameter values. In particular, synchronous bursting oscillations can arise in a network with excitatory synaptic coupling, even in the absence of intrinsically bursting neurons. In this work, we explore how the intrinsic dynamics of neurons within a reduced three-cell network influence its ability to exhibit synchronous bursting and the frequency range over which such activity can occur. We establish necessary and sufficient conditions for the existence of synchronous bursting solutions and perform related numerical experiments in three-cell networks that include a quiescent cell, a tonically active cell, and a third added cell. Our results show that, in most cases, the addition of a quiescent cell is optimal for synchronous network bursting, in a variety of ways, and that intrinsically bursting cells can be detrimental to synchronous bursting, and we explain the mechanisms underlying these effects. These findings may help explain how robust synchronous oscillations arise in neuronal central pattern generators, such as the mammalian inspiratory network, despite the presence of significant cellular heterogeneity. They also support the idea that intrinsic burst capabilities of individual cells need not be central to these networks' rhythms.

  3. Decameter U-burst Harmonic Pair from a High Loop

    NASA Astrophysics Data System (ADS)

    Dorovskyy, V. V.; Melnik, V. N.; Konovalenko, A. A.; Bubnov, I. N.; Gridin, A. A.; Shevchuk, N. V.; Rucker, H. O.; Poedts, S.; Panchenko, M.

    2015-01-01

    The results of the first observations of solar sporadic radio emission within 10 - 70 MHz by the Giant Ukrainian Radio Telescope (GURT) are presented and discussed. Observations in such a wide range of frequencies considerably facilitate the registration of harmonic pairs. The solar U-burst harmonic pair observed on 8 August 2012 is analyzed. The burst key features were determined. Among them, the time delay between the fundamental and harmonic emissions was of special interest. The fundamental emission was delayed for 7 s with respect to the harmonic emission. A model for explaining the occurrence of such a delay is proposed, in which the emission source is located inside a magnetic loop containing plasma of increased density. In this case, the delay appears due to the difference in group velocities of electromagnetic waves at the fundamental and the harmonic frequencies.

  4. DELTA PHASE PLUTONIUM ALLOYS

    DOEpatents

    Cramer, E.M.; Ellinger, F.H.; Land. C.C.

    1960-03-22

    Delta-phase plutonium alloys were developed suitable for use as reactor fuels. The alloys consist of from 1 to 4 at.% zinc and the balance plutonium. The alloys have good neutronic, corrosion, and fabrication characteristics snd possess good dimensional characteristics throughout an operating temperature range from 300 to 490 deg C.

  5. Extracellular K+ in the supraoptic nucleus of the rat during reflex bursting activity by oxytocin neurones.

    PubMed Central

    Coles, J A; Poulain, D A

    1991-01-01

    1. We have investigated changes in extracellular potassium concentration [K+]o in the supraoptic nucleus of lactating rats and in particular those that occur during the intense burst of firing by the oxytocin neurones involved in the milk ejection reflex. 2. Double-barrelled K(+)-selective microelectrodes containing a highly selective sensor based on valinomycin were lowered through the exposed cortex towards the supraoptic nucleus (SON) of female rats anaesthetized with urethane. The mean resting [K+]o in the hypothalami of five rats was 2.4 mM, S.D. = 0.3 mM. 3. Where the reference barrel recorded extracellular action potentials from an oxytocin cell, the reflex burst of firing (4 s, typical maximum 50 Hz) was accompanied by a mean increase in [K+]o (delta[K+]o) of 0.22 mM (S.E.M. = 0.02 mM, fifty-seven bursts in eight cells in seven rats). The rise in [K+]o did not begin more than 0.1 s before the onset of the burst, and began to fall from its maximum during the burst. Slow field potentials, indicative of spatial buffering of K+, were undetectable (less than 50 microV). When the electrode was advanced in steps, the amplitudes of both delta[K+]o and the action potential declined steeply to about 10% over a distance of 20 microns: K+ from oxytocin cells appears to be prevented from dispersing freely through the extracellular space of the SON. 4. When the electrode recorded action potentials from a vasopressin cell, delta[K+]o during an oxytocin cell burst was very small: 0.021 mM (S.E.M. = 0.005 mM). At other sites in the SON, where antidromic stimulation evoked a field potential but no action potential, delta[K+]o was 0.047 +/- 0.005 mM. We conclude that the reason oxytocin bursts do not affect vasopressin cells is that [K+]o rises very little around vasopressin cells. A fortiori, since the increases in [K+]o were very small except where action potentials from oxytocin cells were recorded, they can make no significant contribution to synchronizing the onsets of

  6. Mixed-mode oscillations and population bursting in the pre-Bötzinger complex

    PubMed Central

    Bacak, Bartholomew J; Kim, Taegyo; Smith, Jeffrey C; Rubin, Jonathan E; Rybak, Ilya A

    2016-01-01

    This study focuses on computational and theoretical investigations of neuronal activity arising in the pre-Bötzinger complex (pre-BötC), a medullary region generating the inspiratory phase of breathing in mammals. A progressive increase of neuronal excitability in medullary slices containing the pre-BötC produces mixed-mode oscillations (MMOs) characterized by large amplitude population bursts alternating with a series of small amplitude bursts. Using two different computational models, we demonstrate that MMOs emerge within a heterogeneous excitatory neural network because of progressive neuronal recruitment and synchronization. The MMO pattern depends on the distributed neuronal excitability, the density and weights of network interconnections, and the cellular properties underlying endogenous bursting. Critically, the latter should provide a reduction of spiking frequency within neuronal bursts with increasing burst frequency and a dependence of the after-burst recovery period on burst amplitude. Our study highlights a novel mechanism by which heterogeneity naturally leads to complex dynamics in rhythmic neuronal populations. DOI: http://dx.doi.org/10.7554/eLife.13403.001 PMID:26974345

  7. Investigation of the Geoeffectiveness of CMEs Associated with IP Type II Radio Bursts

    NASA Astrophysics Data System (ADS)

    Vasanth, V.; Chen, Y.; Kong, X. L.; Wang, B.

    2015-06-01

    We perform a statistical analysis of the geoeffectiveness of coronal mass ejections (CMEs) that are associated with interplanetary (IP) type II bursts in Solar Cycle 23 during the period 1997 - 2008. About 47 % (109 out of 232) of IP type II bursts are found to be associated with geomagnetic storms. Of these 47 %, 27 % are associated with moderate, 14 % with intense, and 6 % with severe geomagnetic storms. We find that the IP type II bursts and their corresponding end frequencies can be used as indicators of CME geoeffectiveness: the lower the type II burst end frequency, the higher the possibility of having a stronger storm. In addition, we show that various combinations of CME remote-sensing and IP type II parameters can be used to improve geomagnetic storm forecasting.

  8. The stimulation of auroral kilometric radiation by type III solar radio bursts

    NASA Technical Reports Server (NTRS)

    Calvert, W.

    1981-01-01

    It has been found that the onset of auroral kilometric radiation (AKR) frequently coincides with the arrival of type III solar radio bursts. Although the AKR onsets are usually abrupt and appear to be spontaneous, they sometimes develop from a discrete frequency near the leading edge of a type III burst or sometimes occur at progressively lower frequencies following that edge. From this, and the absence of the related solar electrons in specific cases, it was concluded that the incoming type III waves were sometimes responsible for stimulating auroral kilometric radiation. It was estimated that intense, isolated type III bursts were capable of stimulating AKR roughly one third of the time, and that at least ten percent of the observed AKR onsets could be attributed to these and weaker bursts, including some barely detectable by the ISEE plasma wave receivers.

  9. Model interpretation of type III radio burst characteristics. I - Spatial aspects

    NASA Technical Reports Server (NTRS)

    Reiner, M. J.; Stone, R. G.

    1988-01-01

    The ways that the finite size of the source region and directivity of the emitted radiation modify the observed characteristics of type III radio bursts as they propagate through the interplanetary medium are investigated. A simple model that simulates the radio source region is developed to provide insight into the spatial behavior of the parameters that characterize radio bursts. The model is used to demonstrate that observed radio azimuths are systematically displaced from the geometric centroid of the exciter electron beam in such a way as to cause trajectories of the radio bursts to track back to the observer at low frequencies, rather than to follow expected Archimedean spiral-like paths. The source region model is used to investigate the spatial behavior of the peak intensities of radio bursts, and it is found that the model can qualitatively account for both the frequency dependence and the east-west asymmetry of the observed peak flux densities.

  10. Terrestrial Myriametric Radio Burst Observed by IMAGE and Geotail Satellites

    NASA Technical Reports Server (NTRS)

    Fung, Shing F.; Hashimoto, Kozo; Boardsen, Scott A.; Garcia, Leonard N.; Green, James L.; Matsumoto, Hiroshi; Reinisch, Bodo W.

    2010-01-01

    We report IMAGE and Geotail simultaneous observations of a terrestrial myriametric radio burst (TMRB) detected on August 19, 2001. The TMRB was confined in time (0830-1006 UT) and frequency (12-50 kHz), suggesting a fan beam-like emission pattern from a single discrete source. Analysis and comparisons with existing TMR radiations strongly suggest that the TMRB is a distinct emission perhaps resulting from dayside magnetic reconnection instigated by northward interplanetary field condition.

  11. The visibility of type III radio bursts originating behind the sun

    NASA Technical Reports Server (NTRS)

    Dulk, G. A.; Steinberg, J. L.; Lecacheux, A.; Hoang, S.; Macdowall, R. J.

    1985-01-01

    More than 95 percent of the solar type III bursts observed by the two Voyager spacecraft when they were in the solar hemisphere opposite the earth were also recorded by ISEE-3, and 10 of 21 type III bursts whose electron streams were directed toward the earth were recorded on the far side of the sun by Voyager. It is presently suggested that the reason for this widespread visibility is a high degree of radio wave scattering that originates at or near the local plasma frequency. Such other observed features of solar bursts as large apparent source heights may be explained by the strong scattering.

  12. Hotspot or Heatwave? Getting to Grips with Neutron Star Burst Oscillations

    NASA Technical Reports Server (NTRS)

    Watts, A.

    2005-01-01

    Many accreting neutron stars, including two of the millisecond pulsars, exhibit high frequency oscillations during Type I X-ray bursts. The properties of the burst oscillations reflect the nature of the thermal asymmetry on the stellar surface. The mechanism that gives rise to the aspzetry, however , remains unclear: possibilities include a hotspot due to uneven fuel distribution, modes of oscillation in the surface layers of the neutron star, or vortices driven by the Coriolis force. I will review some of the latest theory and observations, and present the results of a recent study of variability in the burst oscillations of the millisecond pulsar 51814-338.

  13. The Devil's in the Delta

    ERIC Educational Resources Information Center

    Luyben, William L.

    2007-01-01

    Students frequently confuse and incorrectly apply the several "deltas" that are used in chemical engineering. The deltas come in three different flavors: "out minus in", "big minus little" and "now versus then." The first applies to a change in a stream property as the stream flows through a process. For example, the "[delta]H" in an energy…

  14. The Mystery of Gamma-Ray Bursts

    NASA Technical Reports Server (NTRS)

    Fishman, Gerald J.

    2004-01-01

    Gamma-ray bursts remain one of the greatest mysteries in astrophysics. Observations of gamma-ray bursts made by the BATSE experiment on the Compton Gamma-Ray Observatory will be described. Most workers in the field now believe that they originate from cosmological distances. This view has been reinforced by observations this year of several optical afterglow counterparts to gamma-ray bursts. A summary of these recent discoveries will be presented, along with their implications for models of the burst emission mechanism and the energy source of the bursts.

  15. Narrowband Gyrosynchrotron Bursts: Probing Electron Acceleration in Solar Flares

    NASA Astrophysics Data System (ADS)

    Fleishman, Gregory D.; Nita, Gelu M.; Kontar, Eduard P.; Gary, Dale E.

    2016-07-01

    Recently, in a few case studies we demonstrated that gyrosynchrotron microwave emission can be detected directly from the acceleration region when the trapped electron component is insignificant. For the statistical study reported here, we have identified events with steep (narrowband) microwave spectra that do not show a significant trapped component and, at the same time, show evidence of source uniformity, which simplifies the data analysis greatly. Initially, we identified a subset of more than 20 radio bursts with such narrow spectra, having low- and high-frequency spectral indices larger than three in absolute value. A steep low-frequency spectrum implies that the emission is nonthermal (for optically thick thermal emission, the spectral index cannot be steeper than two), and the source is reasonably dense and uniform. A steep high-frequency spectrum implies that no significant electron trapping occurs, otherwise a progressive spectral flattening would be observed. Roughly half of these radio bursts have RHESSI data, which allow for detailed, joint diagnostics of the source parameters and evolution. Based on an analysis of radio-to-X-ray spatial relationships, timing, and spectral fits, we conclude that the microwave emission in these narrowband bursts originates directly from the acceleration regions, which have a relatively strong magnetic field, high density, and low temperature. In contrast, the thermal X-ray emission comes from a distinct loop with a smaller magnetic field, lower density, but higher temperature. Therefore, these flares likely occurred due to interaction between two (or more) magnetic loops.

  16. A turbulent burst model for boundary layer flows with pressure gradient

    NASA Astrophysics Data System (ADS)

    Thomas, L. C.; Benton, D. J.

    The object of this paper is to develop a surface renewal model of the turbulent burst phenomenon for momentum and energy transfer in the wall region for turbulent boundary layer flows with pressure gradient. In addition to obtaining inner laws for the distributions in velocity and temperature, predictions are obtained for the effect of pressure gradient on the mean burst frequency and on the turbulent Prandtl number within the wall region for slight favorable and mild adverse pressure gradients.

  17. Observations of Gamma-Ray Bursts

    NASA Technical Reports Server (NTRS)

    Fishman, G. J.

    1995-01-01

    Some basic observed properties of gamma-ray bursts are reviewed. Although some properties were known 25 years ago, new and more detailed observations have been made by the Compton Observatory in the past three years. The new observation with the greatest impact has been the observed isotropic distribution of bursts along with a deficiency of weak bursts which would be expected from a homogeneous burst distribution. This is not compatible with any known Galactic population of objects. Gamma-ray bursts show an enormous variety of burst morphologies and a wide spread in burst durations. The spectra of gamma-ray bursts are characterized by rapid variations and peak power which is almost entirely in the gamma-ray energy range. Delayed gamma-ray burst photons extending to GeV energies have been detected for the first time. A time dilation effect has also been reported to be observed in gamma-ray, bursts. The observation of a gamma-ray burst counterpart in another wavelength region has yet to be made.

  18. Do gamma-ray burst sources repeat?

    NASA Technical Reports Server (NTRS)

    Meegan, Charles A.; Hartmann, Dieter H.; Brainerd, J. J.; Briggs, Michael S.; Paciesas, William S.; Pendleton, Geoffrey; Kouveliotou, Chryssa; Fishman, Gerald; Blumenthal, George; Brock, Martin

    1995-01-01

    The demonstration of repeated gamma-ray bursts from an individual source would severely constrain burst source models. Recent reports (Quashnock and Lamb, 1993; Wang and Lingenfelter, 1993) of evidence for repetition in the first BATSE burst catalog have generated renewed interest in this issue. Here, we analyze the angular distribution of 585 bursts of the second BATSE catalog (Meegan et al., 1994). We search for evidence of burst recurrence using the nearest and farthest neighbor statistic and the two-point angular correlation function. We find the data to be consistent with the hypothesis that burst sources do not repeat; however, a repeater fraction of up to about 20% of the observed bursts cannot be excluded.

  19. DELTAS: A new Global Delta Sustainability Initiative (Invited)

    NASA Astrophysics Data System (ADS)

    Foufoula-Georgiou, E.

    2013-12-01

    Deltas are economic and environmental hotspots, food baskets for many nations, home to a large part of the world population, and hosts of exceptional biodiversity and rich ecosystems. Deltas, being at the land-water interface, are international, regional, and local transport hubs, thus providing the basis for intense economic activities. Yet, deltas are deteriorating at an alarming rate as 'victims' of human actions (e.g. water and sediment reduction due to upstream basin development), climatic impacts (e.g. sea level rise and flooding from rivers and intense tropical storms), and local exploration (e.g. sand or aggregates, groundwater and hydrocarbon extraction). Although many efforts exist on individual deltas around the world, a comprehensive global delta sustainability initiative that promotes awareness, science integration, data and knowledge sharing, and development of decision support tools for an effective dialogue between scientists, managers and policy makers is lacking. Recently, the international scientific community proposed to establish the International Year of Deltas (IYD) to serve as the beginning of such a Global Delta Sustainability Initiative. The IYD was proposed as a year to: (1) increase awareness and attention to the value and vulnerability of deltas worldwide; (2) promote and enhance international and regional cooperation at the scientific, policy, and stakeholder level; and (3) serve as a launching pad for a 10-year committed effort to understand deltas as complex socio-ecological systems and ensure preparedness in protecting and restoring them in a rapidly changing environment. In this talk, the vision for such an international coordinated effort on delta sustainability will be presented as developed by a large number of international experts and recently funded through the Belmont Forum International Opportunities Fund. Participating countries include: U.S., France, Germany, U.K., India, Japan, Netherlands, Norway, Brazil, Bangladesh

  20. QUASI-PERIODIC OSCILLATIONS AND BROADBAND VARIABILITY IN SHORT MAGNETAR BURSTS

    SciTech Connect

    Huppenkothen, Daniela; Watts, Anna L.; Uttley, Phil; Van der Horst, Alexander J.; Van der Klis, Michiel; Kouveliotou, Chryssa; Goegues, Ersin; Granot, Jonathan; Vaughan, Simon; Finger, Mark H.

    2013-05-01

    The discovery of quasi-periodic oscillations (QPOs) in magnetar giant flares has opened up prospects for neutron star asteroseismology. However, with only three giant flares ever recorded, and only two with data of sufficient quality to search for QPOs, such analysis is seriously data limited. We set out a procedure for doing QPO searches in the far more numerous, short, less energetic magnetar bursts. The short, transient nature of these bursts requires the implementation of sophisticated statistical techniques to make reliable inferences. Using Bayesian statistics, we model the periodogram as a combination of red noise at low frequencies and white noise at high frequencies, which we show is a conservative approach to the problem. We use empirical models to make inferences about the potential signature of periodic and QPOs at these frequencies. We compare our method with previously used techniques and find that although it is on the whole more conservative, it is also more reliable in ruling out false positives. We illustrate our Bayesian method by applying it to a sample of 27 bursts from the magnetar SGR J0501+4516 observed by the Fermi Gamma-ray Burst Monitor, and we find no evidence for the presence of QPOs in any of the bursts in the unbinned spectra, but do find a candidate detection in the binned spectra of one burst. However, whether this signal is due to a genuine quasi-periodic process, or can be attributed to unmodeled effects in the noise is at this point a matter of interpretation.

  1. Statistical Study of Shocks and CMEs Associated With Interplanetary Type II Bursts

    NASA Astrophysics Data System (ADS)

    Aguilar-Rodriguez, E.; Gopalswamy, N.; MacDowall, R.; Yashiro, S.; Kaiser, M. L.

    2005-05-01

    We present a study of some spectral properties associated with interplanetary Type II radio emission. Type II radio bursts are signatures of violent eruptions from the Sun that result in shock waves propagating through the corona and the interplanetary medium. We investigated the relative bandwidth of all the type II bursts observed by the Radio and Plasma Wave Experiment (WAVES) on board the Wind spacecraft from 1997 up to 2003. We obtained three sets of events, based on the frequency domain of occurrence: 109 events in the low frequency domain (30 KHz to 1000 kHz detected by the RAD1 receiver), 216 events in the high frequency domain (1-14 MHz, observed by the RAD2 receiver), and 73 events that spanned both domains (RAD1 and RAD2). We present statistical results for the bandwidth-to-frequency ratio (BFR) in the three subsets as well as a comparision of our results with the Type II solar radio bursts observed by ISEE-3 radio experiment, which is similar to WAVES/RAD1. We analyzed the bandwidth and BFR evolution with the heliocentric distance as well as an analysis of drift rate magnitude of type II radio bursts and its starting frequency. We also present some properties of shocks and coronal mass ejections associated with interplanetary type II bursts. This work is partially supported by NSF/SHINE (ATM 0204588)

  2. Investigation of all-optical gain clamped erbium-doped amplifier in the presence of variable burst traffic

    NASA Astrophysics Data System (ADS)

    Zannin, M.; Mangeni, S.; Taccheo, S.; Ennser, K.; Barlet, P.; Careglio, D.

    2011-03-01

    Optical gain clamping is an all-optical method to control the gain of optical amplifiers. Recent results show that this technique is very robust and reduces impairments in amplification of typical traffic from optical burst (and packets) switching networks, where the traffic profile is very dynamic. Nevertheless, recent results have also shown that interplay between the characteristics of the optical gain clamping optical amplifier (OGC-OA) and particular traffic profiles may induce chaotic behavior caused by resonance in the OGC-OA lasing cavity. The aim of this investigation is to assess the impact of burst duration and inter-arrival time on these chaotic behavior cases. The investigation shows that the resonating frequency in which chaotic variation of the OGC-OA gain occurs is shifted - and even reduced - when the burst duration and inter-arrival time are changed. For this investigation, continuous trains of bursts were used, with fixed burst generation frequency throughout each case considered.

  3. Understanding pesticides in California's Delta

    USGS Publications Warehouse

    Kuivila, Kathryn; Orlando, James L.

    2012-01-01

    The Sacramento-San Joaquin River Delta (Delta) is the hub of California’s water system and also an important habitat for imperiled fish and wildlife. Aquatic organisms are exposed to mixtures of pesticides that flow through the maze of Delta water channels from sources including agricultural, landscape, and urban pest-control applications. While we do not know all of the effects pesticides have on the ecosystem, there is evidence that they cause some damage to organisms in the Delta. Decades of USGS research have provided a good understanding of when, where, and how pesticides enter the Delta. However, pesticide use is continually changing. New field studies and methods are needed so that scientists can analyze which pesticides are present in the Delta, and at what concentrations, enabling them to estimate exposure and ultimate effects on organisms. Continuing research will provide resource managers and stakeholders with crucial information to manage the Delta wisely.

  4. Martian deltas: Morphology and distribution

    NASA Technical Reports Server (NTRS)

    Rice, J. W., Jr.; Scott, D. H.

    1993-01-01

    Recent detailed mapping has revealed numerous examples of Martian deltas. The location and morphology of these deltas are described. Factors that contribute to delta morphology are river regime, coastal processes, structural stability, and climate. The largest delta systems on Mars are located near the mouths of Maja, Maumee, Vedra, Ma'adim, Kasei, and Brazos Valles. There are also several smaller-scale deltas emplaced near channel mouths situated in Ismenius Lacus, Memnonia, and Arabia. Delta morphology was used to reconstruct type, quantity, and sediment load size transported by the debouching channel systems. Methods initially developed for terrestrial systems were used to gain information on the relationships between Martian delta morphology, river regime, and coastal processes.

  5. Multiple conductances cooperatively regulate spontaneous bursting in mouse olfactory bulb external tufted cells.

    PubMed

    Liu, Shaolin; Shipley, Michael T

    2008-02-13

    External tufted (ET) cells are juxtaglomerular neurons that spontaneously generate bursts of action potentials, which persist when fast synaptic transmission is blocked. The intrinsic mechanism of this autonomous bursting is unknown. We identified a set of voltage-dependent conductances that cooperatively regulate spontaneous bursting: hyperpolarization-activated inward current (I(h)), persistent Na+ current (I(NaP)), low-voltage-activated calcium current (I(L/T)) mediated by T- and/or L-type Ca2+ channels, and large-conductance Ca2+-dependent K+ current (I(BK)). I(h) is important in setting membrane potential and depolarizes the cell toward the threshold of I(NaP) and I(T/L), which are essential to generate the depolarizing envelope that is crowned by a burst of action potentials. Action potentials depolarize the membrane and induce Ca2+ influx via high-voltage-activated Ca2+ channels (I(HVA)). The combined depolarization and increased intracellular Ca2+ activates I(BK), which terminates the burst by hyperpolarizing the membrane. Hyperpolarization activates I(h) and the cycle is regenerated. A novel finding is the role of L-type Ca2+ channels in autonomous ET cells bursting. A second novel feature is the role of BK channels, which regulate burst duration. I(L) and I(BK) may go hand-in-hand, the slow inactivation of I(L) requiring I(BK)-dependent hyperpolarization to deactivate inward conductances and terminate the burst. ET cells receive monosynaptic olfactory nerve input and drive the major inhibitory interneurons of the glomerular circuit. Modulation of the conductances identified here can regulate burst frequency, duration, and spikes per burst in ET cells and thus significantly shape the impact of glomerular circuits on mitral and tufted cells, the output channels of the olfactory bulb.

  6. Delta-doping of Semiconductors

    NASA Astrophysics Data System (ADS)

    Schubert, E. F.

    2005-08-01

    Part I: 1. Introduction E. F. Schubert; Part II: 2. Electronic structure of delta-doped semiconductors C. R. Proetto; Part III: 3. Recent progress in delta-like confinement of impurities in GaAs K. H. Ploog; 4. Flow-rate modulation epitaxy (FME) of III-V semiconductors T. Makimoto and Y. Horikoshi; 5. Gas source molecular beam epitaxy (MBE) of delta-doped III-V semiconductors D. Ritter; 6. Solid phase epitaxy for delta-doping in silicon I. Eisele; 7. Low temperature MBE of silicon H.-J. Gossmann; Part IV: 8. Secondary ion mass spectrometry of delta-doped semiconductors H. S. Luftmann; 9. Capacitance-voltage profiling E. F. Schubert; 10. Redistribution of impurities in III-V semiconductors E. F. Schubert; 11. Dopant diffusion and segregation in delta-doped silicon films H.-J. Gossmann; 12. Characterisation of silicon and delta-doped structures in GaAs R. C. Newman; 13. The DX-center in silicon delta-doped GaAs and AlxGa1-xAs P. M. Koenraad; Part V: 14. Luminescence and ellipsometry spectroscopy H. Yao and E. F. Schubert; 15. Photoluminescence and Raman spectroscopy of single delta-doped III-V semiconductor heterostructures J. Wagner and D. Richards; 16. Electron transport in delta-doped quantum wells W. T. Masselink; 17. Electron mobility in delta-doped layers P. M. Koenraad; 18. Hot electrons in delta-doped GaAs M. Asche; 19. Ordered delta-doping R. L. Headrick, L. C. Feldman and B. E. Weir; Part IV: 20. Delta-doped channel III-V field effect transistors (FETs) W.-P. Hong; 21. Selectively doped heterostructure devices E. F. Schubert; 22. Silicon atomic layer doping FET K. Nakagawa and K. Yamaguchi; 23. Planar doped barrier devices R. J. Malik; 24. Silicon interband and intersubband photodetectors I. Eisele; 25. Doping superlattice devices E. F. Schubert.

  7. Origin of suppression of otoacoustic emissions evoked by two-tone bursts.

    PubMed

    Jedrzejczak, W Wiktor; Smurzynski, Jacek; Blinowska, Katarzyna J

    2008-01-01

    Otoacoustic emission (OAE) data recorded for tone bursts presented separately and as a two-tone burst complex, that had been reported previously [Yoshikawa, H., Smurzynski, J., Probst R., 2000. Suppression of tone burst evoked otoacoustic emissions in relation to frequency separation. Hear. Res. 148, 95-106], were re-processed using the method of adaptive approximations by matching pursuit (MP). Two types of stimuli were applied to record tone burst OAEs (TBOAEs): (a) cosine-windowed tone bursts of 5-ms duration with center frequencies of 1, 1.5, 2 and 3kHz, (b) complex stimuli consisting of a digital addition of the 1-kHz tone burst together with either the 1.5-, 2- or 3-kHz tone burst. The MP method allowed decomposition of signals into waveforms of defined frequency, latency, time span, and amplitude. This approach provided a high time-frequency (t-f) resolution and identified patterns of resonance modes that were characteristic for TBOAEs recorded in each individual ear. Individual responses to single-tone bursts were processed off-line to form 'sum of singles' responses. The results confirmed linear superposition behavior for a frequency separation of two-tone bursts of 2kHz (the 1-kHz and 3-kHz condition). For the 1, 1.5-kHz condition, the MP results revealed the existence of closely positioned resonance modes associated with responses recorded individually with the stimuli differing in frequency by 500Hz. Then, the differences between t-f distributions calculated for dual (two-tone bursts) and sum-of-singles conditions exhibited mutual suppression of resonance modes common to both stimuli. The degree of attenuation depended on the individual pattern of characteristic resonance modes, i.e., suppression occurred when two resonant modes excited by both stimuli overlapped. It was postulated that the suppression observed in case of dual stimuli with closely-spaced components is due to mutual attenuation of the overlapping resonance modes.

  8. Burst Oscillations: A New Spin on Neutron Stars

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2007-01-01

    Observations with NASA's Rossi X-ray Timing Explorer (RXTE) have shown that the X-ray flux during thermonuclear X-ray bursts fr-om accreting neutron stars is often strongly pulsed at frequencies as high as 620 Hz. We now know that these oscillations are produced by spin modulation of the thermonuclear flux from the neutron star surface. In addition to revealing the spin frequency, they provide new ways to probe the properties and physics of accreting neutron stars. I will briefly review our current observational and theoretical understanding of these oscillations and discuss what they are telling us about neutron stars.

  9. Delta: Data Reduction for Integrated Application Workflows.

    SciTech Connect

    Lofstead, Gerald Fredrick; Jean-Baptiste, Gregory; Oldfield, Ron A.

    2015-06-01

    Integrated Application Workflows (IAWs) run multiple simulation workflow components con- currently on an HPC resource connecting these components using compute area resources and compensating for any performance or data processing rate mismatches. These IAWs require high frequency and high volume data transfers between compute nodes and staging area nodes during the lifetime of a large parallel computation. The available network band- width between the two areas may not be enough to efficiently support the data movement. As the processing power available to compute resources increases, the requirements for this data transfer will become more difficult to satisfy and perhaps will not be satisfiable at all since network capabilities are not expanding at a comparable rate. Furthermore, energy consumption in HPC environments is expected to grow by an order of magnitude as exas- cale systems become a reality. The energy cost of moving large amounts of data frequently will contribute to this issue. It is necessary to reduce the volume of data without reducing the quality of data when it is being processed and analyzed. Delta resolves the issue by addressing the lifetime data transfer operations. Delta removes subsequent identical copies of already transmitted data during transfers and restores those copies once the data has reached the destination. Delta is able to identify duplicated information and determine the most space efficient way to represent it. Initial tests show about 50% reduction in data movement while maintaining the same data quality and transmission frequency.

  10. Detecting fast radio bursts at decametric wavelengths

    NASA Astrophysics Data System (ADS)

    Rajwade, K. M.; Lorimer, D. R.

    2017-02-01

    Fast radio bursts (FRBs) are highly dispersed, sporadic radio pulses which are likely extragalactic in nature. Here, we investigate the constraints on the source population from surveys carried out at frequencies <1 GHz. All but one FRB has so far been discovered in the 1-2 GHz band, but new and emerging instruments look set to become valuable probes of the FRB population at sub-GHz frequencies in the near future. In this paper, we consider the impacts of free-free absorption and multipath scattering in our analysis via a number of different assumptions about the intervening medium. We consider previous low-frequency surveys along with an ongoing survey with University of Technology digital backend for the Molonglo Observatory Synthesis Telescope (UTMOST) as well as future observations with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and the Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX). We predict that CHIME and HIRAX will be able to observe ∼30 or more FRBs per day, even in the most extreme scenarios where free-free absorption and scattering can significantly impact the fluxes below 1 GHz. We also show that UTMOST will detect 1-2 FRBs per month of observations. For CHIME and HIRAX, the detection rates also depend greatly on the assumed FRB distance scale. Some of the models we investigated predict an increase in the FRB flux as a function of redshift at low frequencies. If FRBs are truly cosmological sources, this effect may impact future surveys in this band, particularly if the FRB population traces the cosmic star formation rate.

  11. Fast Radio Bursts from Extragalactic Light Sails

    NASA Astrophysics Data System (ADS)

    Lingam, Manasvi; Loeb, Abraham

    2017-03-01

    We examine the possibility that fast radio bursts (FRBs) originate from the activity of extragalactic civilizations. Our analysis shows that beams used for powering large light sails could yield parameters that are consistent with FRBs. The characteristic diameter of the beam emitter is estimated through a combination of energetic and engineering constraints, and both approaches intriguingly yield a similar result that is on the scale of a large rocky planet. Moreover, the optimal frequency for powering the light sail is shown to be similar to the detected FRB frequencies. These “coincidences” lend some credence to the possibility that FRBs might be artificial in origin. Other relevant quantities, such as the characteristic mass of the light sail, and the angular velocity of the beam, are also derived. By using the FRB occurrence rate, we infer upper bounds on the rate of FRBs from extragalactic civilizations in a typical galaxy. The possibility of detecting fainter signals is briefly discussed, and the wait time for an exceptionally bright FRB event in the Milky Way is estimated.

  12. Photon mass limits from fast radio bursts

    NASA Astrophysics Data System (ADS)

    Bonetti, Luca; Ellis, John; Mavromatos, Nikolaos E.; Sakharov, Alexander S.; Sarkisyan-Grinbaum, Edward K.; Spallicci, Alessandro D. A. M.

    2016-06-01

    The frequency-dependent time delays in fast radio bursts (FRBs) can be used to constrain the photon mass, if the FRB redshifts are known, but the similarity between the frequency dependences of dispersion due to plasma effects and a photon mass complicates the derivation of a limit on mγ. The dispersion measure (DM) of FRB 150418 is known to ∼ 0.1%, and there is a claim to have measured its redshift with an accuracy of ∼ 2%, but the strength of the constraint on mγ is limited by uncertainties in the modelling of the host galaxy and the Milky Way, as well as possible inhomogeneities in the intergalactic medium (IGM). Allowing for these uncertainties, the recent data on FRB 150418 indicate that mγ ≲ 1.8 ×10-14 eVc-2 (3.2 ×10-50 kg), if FRB 150418 indeed has a redshift z = 0.492 as initially reported. In the future, the different redshift dependences of the plasma and photon mass contributions to DM can be used to improve the sensitivity to mγ if more FRB redshifts are measured. For a fixed fractional uncertainty in the extra-galactic contribution to the DM of an FRB, one with a lower redshift would provide greater sensitivity to mγ.

  13. First Radio Burst Imaging Observation From Mingantu Ultrawide Spectral Radioheliograph

    NASA Astrophysics Data System (ADS)

    Yan, Yihua; Chen, Linjie; Yu, Sijie; CSRH Team

    2015-08-01

    Radio imaging spectroscopy over wide range wavelength in dm/cm-bands will open new windows on solar flares and coronal mass ejections by tracing the radio emissions from accelerated electrons. The Chinese Spectral Radioheliograph (CSRH) with two arrays in 400MHz-2GHz /2-15GHz ranges with 64/532 frequency channels have been established in Mingantu Observing Station, Inner Mongolia of China, since 2013 and is in test observations now. CSRH is renamed as MUSER (Mingantu Ultrawide SpEctral Radioheliograph) after it's accomplishment We will introduce the progress and current status of CSRH. Some preliminary results of CSRH will be presented.On 11 Nov2014, the first burst event was registered by MUSER-I array at 400MHz-2GHz waveband. According to SGD event list there was a C-class flare peaked at 04:49UT in the disk center and the radio bursts around 04:22-04:24UT was attributed to this flare. However, MUSER-I image observation of the burst indicates that the radio burst peaked around 04:22UT was due to the eruption at the east limb of the Sun and connected to a CME appeared in that direction about 1 hour later. This demonstrate the importance of the spectroscopy observation of the solar radio burst.Acknowledgement: The CSRH team includes Wei Wang, Zhijun Chen, Fei Liu, Lihong Geng and Jian Zhang and CSRH project is supported by National Major Scientific Equipment R&D Project ZDYZ2009-3. The research was also supported by NSFC grants (11433006, 11221063), MOST grant (MOST2011CB811401), CAS Pilot-B Project (XDB09000000) and Marie Curie PIRSES- GA-295272-RADIOSUN.

  14. Fast radio burst discovered in the Arecibo pulsar ALFA survey

    SciTech Connect

    Spitler, L. G.; Freire, P. C. C.; Lazarus, P.; Lee, K. J.; Cordes, J. M.; Chatterjee, S.; Wharton, R. S.; Brazier, A.; Hessels, J. W. T.; Lorimer, D. R.; McLaughlin, M. A.; Crawford, F.; Deneva, J. S.; Kaspi, V. M.; Karako-Argaman, C.; Allen, B.; Bogdanov, S.; Camilo, F.; Jenet, F. A.; Knispel, B.; and others

    2014-08-01

    Recent work has exploited pulsar survey data to identify temporally isolated, millisecond-duration radio bursts with large dispersion measures (DMs). These bursts have been interpreted as arising from a population of extragalactic sources, in which case they would provide unprecedented opportunities for probing the intergalactic medium; they may also be linked to new source classes. Until now, however, all so-called fast radio bursts (FRBs) have been detected with the Parkes radio telescope and its 13-beam receiver, casting some concern about the astrophysical nature of these signals. Here we present FRB 121102, the first FRB discovery from a geographic location other than Parkes. FRB 121102 was found in the Galactic anti-center region in the 1.4 GHz Pulsar Arecibo L-band Feed Array (ALFA) survey with the Arecibo Observatory with a DM = 557.4 ± 2.0 pc cm{sup –3}, pulse width of 3.0 ± 0.5 ms, and no evidence of interstellar scattering. The observed delay of the signal arrival time with frequency agrees precisely with the expectation of dispersion through an ionized medium. Despite its low Galactic latitude (b = –0.°2), the burst has three times the maximum Galactic DM expected along this particular line of sight, suggesting an extragalactic origin. A peculiar aspect of the signal is an inverted spectrum; we interpret this as a consequence of being detected in a sidelobe of the ALFA receiver. FRB 121102's brightness, duration, and the inferred event rate are all consistent with the properties of the previously detected Parkes bursts.

  15. SOLAR RADIO BURSTS WITH SPECTRAL FINE STRUCTURES IN PREFLARES

    SciTech Connect

    Zhang, Yin; Tan, Baolin; Huang, Jing; Tan, Chengming; Karlický, Marian; Mészárosová, Hana; Simões, Paulo J.A.

    2015-01-20

    Good observations of preflare activities are important for us to understand the origin and triggering mechanism of solar flares, and to predict the occurrence of solar flares. This work presents the characteristics of microwave spectral fine structures as preflare activities of four solar flares observed by the Ondřejov radio spectrograph in the frequency range of 0.8-2.0 GHz. We found that these microwave bursts which occurred 1-4 minutes before the onset of flares have spectral fine structures with relatively weak intensities and very short timescales. They include microwave quasi-periodic pulsations with very short periods of 0.1-0.3 s and dot bursts with millisecond timescales and narrow frequency bandwidths. Accompanying these microwave bursts are filament motions, plasma ejection or loop brightening in the EUV imaging observations, and non-thermal hard X-ray emission enhancements observed by RHESSI. These facts may reveal certain independent, non-thermal energy releasing processes and particle acceleration before the onset of solar flares. They may help us to understand the nature of solar flares and to predict their occurrence.

  16. Frequency modulation drive for a piezoelectric motor

    DOEpatents

    Mittas, Anthony

    2001-01-01

    A piezoelectric motor has peak performance at a specific frequency f.sub.1 that may vary over a range of frequencies. A drive system is disclosed for operating such a motor at peak performance without feedback. The drive system consists of the motor and an ac source connected to power the motor, the ac source repeatedly generating a frequency over a range from f.sub.1 -.DELTA.x to f.sub.1 +.DELTA.y.

  17. Natural processes in delta restoration: application to the Mississippi Delta.

    PubMed

    Paola, Chris; Twilley, Robert R; Edmonds, Douglas A; Kim, Wonsuck; Mohrig, David; Parker, Gary; Viparelli, Enrica; Voller, Vaughan R

    2011-01-01

    Restoration of river deltas involves diverting sediment and water from major channels into adjoining drowned areas, where the sediment can build new land and provide a platform for regenerating wetland ecosystems. Except for local engineered structures at the points of diversion, restoration mainly relies on natural delta-building processes. Present understanding of such processes is sufficient to provide a basis for determining the feasibility of restoration projects through quantitative estimates of land-building rates and sustainable wetland area under different scenarios of sediment supply, subsidence, and sea-level rise. We are not yet to the point of being able to predict the evolution of a restored delta in detail. Predictions of delta evolution are based on field studies of active deltas, deltas in mine-tailings ponds, experimental deltas, and countless natural experiments contained in the stratigraphic record. These studies provide input for a variety of mechanistic delta models, ranging from radially averaged formulations to more detailed models that can resolve channels, topography, and ecosystem processes. Especially exciting areas for future research include understanding the mechanisms by which deltaic channel networks self-organize, grow, and distribute sediment and nutrients over the delta surface and coupling these to ecosystem processes, especially the interplay of topography, network geometry, and ecosystem dynamics.

  18. Coronal magnetic fields from multiple type II bursts

    NASA Astrophysics Data System (ADS)

    Honnappa, Vijayakumar; Raveesha, K. H.; Subramanian, K. R.

    Coronal magnetic fields from multiple type II bursts Vijayakumar H Doddamani1*, Raveesha K H2 and Subramanian3 1Bangalore University, Bangalore, Karnataka state, India 2CMR Institute of Technology, Bangalore, Karnataka state, India 3 Retd, Indian Institute of Astrophysics, Bangalore, Karnataka state, India Abstract Magnetic fields play an important role in the astrophysical processes occurring in solar corona. In the solar atmosphere, magnetic field interacts with the plasma, producing abundant eruptive activities. They are considered to be the main factors for coronal heating, particle acceleration and the formation of structures like prominences, flares and Coronal Mass Ejections. The magnetic field in solar atmosphere in the range of 1.1-3 Rsun is especially important as an interface between the photospheric magnetic field and the solar wind. Its structure and time dependent change affects space weather by modifying solar wind conditions, Cho (2000). Type II doublet bursts can be used for the estimation of the strength of the magnetic field at two different heights. Two type II bursts occur sometimes in sequence. By relating the speed of the type II radio burst to Alfven Mach Number, the Alfven speed of the shock wave generating type II radio burst can be calculated. Using the relation between the Alfven speed and the mean frequency of emission, the magnetic field strength can be determined at a particular height. We have used the relative bandwidth and drift rate properties of multiple type II radio bursts to derive magnetic field strengths at two different heights and also the gradient of the magnetic field in the outer corona. The magnetic field strength has been derived for different density factors. It varied from 1.2 to 2.5 gauss at a solar height of 1.4 Rsun. The empirical relation of the variation of the magnetic field with height is found to be of the form B(R) = In the present case the power law index ‘γ’ varied from -3 to -2 for variation of

  19. Stirling Colgate and Gamma-Ray Bursts

    NASA Astrophysics Data System (ADS)

    Lamb, Donald

    2014-10-01

    Even before the discovery of gamma-ray bursts (GRBs), Stirling Colgate proposed that bursts of x rays and gamma rays might be produced by a relativistic shock created in the supernova explosion of a massive star. We trace the scientific story of GRBs from their detection to the present, highlighting along the way Stirling's interest in them and his efforts to understand them. We summarize our current understanding that short, soft, repeating bursts are produced by magnetic neutron stars; short, hard bursts are produced by the mergers of neutron star-neutron star binaries; and long, hard bursts are produced by the core collapse of massive stars that have lost their hydrogen and helium envelopes. We then discuss some important open questions about GRBs and how they might be answered. We conclude by describing the recent serendipitous discovery of an x-ray burst of exactly the kind he proposed, and the insights into core collapse supernovae and GRBs that it provided.

  20. Burst interference in TDMA radio systems

    NASA Astrophysics Data System (ADS)

    Lei, Z.; Chen, M.-X.; Feher, K.

    Analytical and experimental studies show that burst interference in TDMA systems causes spectral spreading, which depends on the gating rate and duty cycle of the burst. A probability-of-error performance study of IJF (intersymbol and jitter-free) OQPSK systems in the presence of burst interference signals shows that the higher gating rate or smaller duty cycle of the burst will introduce more degradation because of increased spectral spreading. It is concluded that the transmitted power of the burst signal should be limited more strictly than that of CW signals, because the burst interference causes more degradation in the performance of the desired channel than nonburst interference with the same (C/I)mean.

  1. Transitions to Synchrony in Coupled Bursting Neurons

    NASA Astrophysics Data System (ADS)

    Dhamala, Mukeshwar; Jirsa, Viktor K.; Ding, Mingzhou

    2004-01-01

    Certain cells in the brain, for example, thalamic neurons during sleep, show spike-burst activity. We study such spike-burst neural activity and the transitions to a synchronized state using a model of coupled bursting neurons. In an electrically coupled network, we show that the increase of coupling strength increases incoherence first and then induces two different transitions to synchronized states, one associated with bursts and the other with spikes. These sequential transitions to synchronized states are determined by the zero crossings of the maximum transverse Lyapunov exponents. These results suggest that synchronization of spike-burst activity is a multi-time-scale phenomenon and burst synchrony is a precursor to spike synchrony.

  2. The 2006-2007 Active Phase Of Anomalous X-Ray Pulsar 4U 0142+61: Radiative and Timing Changes, Bursts, and Burst Spectral Features

    NASA Technical Reports Server (NTRS)

    Gavril, Fotis P.; Dib, Rim; Kaspi, Victoria M.

    2009-01-01

    After at least 6 years of quiescence, Anomalous X-ray Pulsar (AXP) 4U 0142+61 entered an active phase in 2006 March that lasted several months and included six X-ray bursts as well as many changes in the persistent X-ray emission. The bursts, the first seen from this AXP in >11 years of Rossi X-ray Timing Explorer monitoring, all occurred in the interval between 2006 April 6 and 2007 February 7. The burst durations ranged from 8-3x10(exp 3)s. The first five burst spectra are well modeled by blackbodies, with temperatures kT approx. 2 - 6 keV. However, the sixth burst had a complicated spectrum that is well characterized by a blackbody plus three emission features whose amplitude varied throughout the burst. The most prominent feature was at 14.0 keV. Upon entry into the active phase the pulsar showed a significant change in pulse morphology and a likely timing glitch. The glitch had a total frequency jump of (1.9+/-0.4)x10(exp -7) Hz, which recovered with a decay time of 17+/-2 days by more than the initial jump, implying a net spin-down of the pulsar. We discuss these events in the context of the magnetar model.

  3. TEMPORAL SPECTRAL SHIFT AND POLARIZATION OF A BAND-SPLITTING SOLAR TYPE II RADIO BURST

    SciTech Connect

    Du, Guohui; Chen, Yao; Lv, Maoshui; Kong, Xiangliang; Feng, Shiwei; Guo, Fan; Li, Gang

    2014-10-01

    In many type II solar radio bursts, the fundamental and/or the harmonic branches of the bursts can split into two almost parallel bands with similar spectral shapes and frequency drifts. However, the mechanisms accounting for this intriguing phenomenon remain elusive. In this study, we report a special band-splitting type II event in which spectral features appear systematically earlier on the upper band (with higher frequencies) than on the lower band (with lower frequencies) by several seconds. Furthermore, the emissions carried by the splitting band are moderately polarized with the left-hand polarized signals stronger than the right-hand ones. The polarization degree varies in a range of –0.3 to –0.6. These novel observational findings provide important constraints on the underlying physical mechanisms of band-splitting of type II radio bursts.

  4. Neutron starquakes and the nature of gamma-ray bursts

    NASA Technical Reports Server (NTRS)

    Madau, P.; Blaes, O.; Blandford, R. D.; Goldreich, P.

    1989-01-01

    The possibility that gamma-ray bursts originate from quakes deep in the solid crust of a neutron star is investigated. Seismic waves are radiated if shear stress is relieved by brittle fracture. However they cannot propagate directly to the surface but are temporarily trapped below a reflecting layer. The shaking of the stellar surface couples the seismic waves to Alfven waves which propagate out into the magnetosphere. The crust-magnetosphere transmission coefficient strongly increases with wave frequency and magnetic field strength. Alfven wave luminosities sufficient to power galactic gamma-ray bursts are possible if magnetic fields greater than 100 billion G cover at least part of the stellar surface. As the Alfven waves propagate out into the low density magnetosphere, they become increasingly charge starved, thereby accelerating particles to relativistic energies.

  5. Models of fast radio bursts at cosmological distances

    NASA Astrophysics Data System (ADS)

    Mottez, F.; Guépin, C.; Kotera, K.; Voisin, G.; Zarka, P.

    2016-12-01

    Fast radio bursts are isolated radio pulses of high amplitude, with a frequency / time delay relation that can be interpreted as the dispersion measure (DM) of a source at cosmological distances (several hundreds of Mpc). Up to 2015, the only known FRBs all had different locations on the sky, and different DM. Many theoretical explanations of FRBs have been proposed. Some of them are associated to unique cataclysmic events, others are compatible with the repetition of bursts from the same source. The recent publication of the repeating FRB 121102 shows that at least some of the FRB must be compatible with non-cataclysmic events. A model based on the interaction of a highly relativitic pulsar wind with a body orbiting the pulsar (planet, big asteroid, white dwarf) could explain FRBs. It is briefly compared with other models of repeating FRBs.

  6. Spectral features of solar gradual microwave bursts.

    NASA Astrophysics Data System (ADS)

    Yao, J.-X.

    The author presents data and spectral analysis of five solar gradual microwave bursts (GMB's), which are associated with the gradual hard X-ray bursts (GHB's). The durations of GMB's are about tens of minutes and are longer than that of impulsive bursts (5 min.) and the sources of GMB's are high in the corona. Therefore, one may attribute the long durations and spectral index decrease to the high radio sources.

  7. Ceramic Matrix Composite Vane Subelement Burst Testing

    NASA Technical Reports Server (NTRS)

    Brewer, David N.; Verrilli, Michael; Calomino, Anthony

    2006-01-01

    Burst tests were performed on Ceramic Matrix Composite (CMC) vane specimens, manufactured by two vendors, under the Ultra Efficient Engine Technology (UEET) project. Burst specimens were machined from the ends of 76mm long vane sub-elements blanks and from High Pressure Burner Rig (HPBR) tested specimens. The results of burst tests will be used to compare virgin specimens with specimens that have had an Environmental Barrier Coating (EBC) applied, both HPBR tested and untested, as well as a comparison between vendors.

  8. Ballerina - pirouettes in search of gamma bursts

    NASA Astrophysics Data System (ADS)

    Brandt, S.; Lund, N.; Pedersen, H.; Hjorth, J.; BALLERINA Collaboration

    1999-09-01

    The cosmological origin of gamma ray bursts has now been established with reasonable certainty. Many more bursts will need to be studied to establish the typical distance scale, and to map out the large diversity in properties which have been indicated by the first handful of events. We are proposing Ballerina, a small satellite to provide accurate positions and new data on the gamma-ray bursts. We anticipate a detection rate an order of magnitude larger than obtained from Beppo-SAX.

  9. Delta in Eberswalde

    NASA Technical Reports Server (NTRS)

    2006-01-01

    This HiRISE image covers a portion of a delta that partially fills Eberswalde crater in Margaritifer Sinus. The delta was first recognized and mapped using MOC images that revealed various features whose presence required sustained flow and deposition into a lake that once occupied the crater. The HiRISE image resolves meter-scale features that record the migration of channels and delta distributaries as the delta grew over time. Differences in grain-size of sediments within the environments on the delta enable differential erosion of the deposits. As a result, coarser channel deposits are slightly more resistant and stand in relief relative to finer-grained over-bank and more easily eroded distal delta deposits. Close examination of the relict channel deposits confirms the presence of some meter-size blocks that were likely too coarse to have been transported by water flowing within the channels. These blocks may be formed of the sand and gravel that more likely moved along the channels that was lithified and eroded. Numerous meter-scale polygonal structures are common on many surfaces, but mostly those associated with more quiescent depositional environments removed from the channels. The polygons could be the result of deposition of fine-grained sediments that were either exposed and desiccated (dried out), rich in clays that shrunk when the water was removed, turned into rock and then fractured and eroded, or some combination of these processes.

    Image PSP_001336_1560 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on November 8, 2006. The complete image is centered at -23.8 degrees latitude, 326.4 degrees East longitude. The range to the target site was 256.3 km (160.2 miles). At this distance the image scale is 25.6 cm/pixel (with 1 x 1 binning) so objects 77 cm across are resolved. The image shown here has been map-projected to 25 cm/pixel and north is up. The image was

  10. Pioneer Launch on Delta Vehicle

    NASA Technical Reports Server (NTRS)

    1969-01-01

    NASA launches the last in the series of interplanetary Pioneer spacecraft, Pioneer 10 from Cape Kennedy, Florida. The long-tank Delta launch vehicle placed the spacecraft in a solar orbit along the path of Earth's orbit. The spacecraft then passed inside and outside Earth's orbit, alternately speeding up and slowing down relative to Earth. The Delta launch vehicle family started development in 1959. The Delta was composed of parts from the Thor, an intermediate-range ballistic missile, as its first stage, and the Vanguard as its second. The first Delta was launched from Cape Canaveral on May 13, 1960 and was powerful enough to deliver a 100-pound spacecraft into geostationary transfer orbit. Delta has been used to launch civil, commercial, and military satellites into orbit. For more information about Delta, please see Chapter 3 in Roger Launius and Dennis Jenkins' book To Reach the High Frontier published by The University Press of Kentucky in 2002.

  11. Solar Micro-Type III Burst Storms and Long Dipolar Magnetic Field in the Outer Corona

    NASA Astrophysics Data System (ADS)

    Morioka, A.; Miyoshi, Y.; Iwai, K.; Kasaba, Y.; Masuda, S.; Misawa, H.; Obara, T.

    2015-08-01

    Solar micro-type III radio bursts are elements of the so-called type III storms and are characterized by short-lived, continuous, and weak emissions. Their frequency of occurrence with respect to radiation power is quite different from that of ordinary type III bursts, suggesting that the generation process is not flare-related, but due to some recurrent acceleration processes around the active region. We examine the relationship of micro-type III radio bursts with coronal streamers. We also explore the propagation channel of bursts in the outer corona, the acceleration process, and the escape route of electron beams. It is observationally confirmed that micro-type III bursts occur near the edge of coronal streamers. The magnetic field line of the escaping electron beams is tracked on the basis of the frequency drift rate of micro-type III bursts and the electron density distribution model. The results demonstrate that electron beams are trapped along closed dipolar field lines in the outer coronal region, which arise from the interface region between the active region and the coronal hole. A 22 year statistical study reveals that the apex altitude of the magnetic loop ranges from 15 to 50 RS. The distribution of the apex altitude has a sharp upper limit around 50 RS suggesting that an unknown but universal condition regulates the upper boundary of the streamer dipolar field.

  12. SOLAR MICRO-TYPE III BURST STORMS AND LONG DIPOLAR MAGNETIC FIELD IN THE OUTER CORONA

    SciTech Connect

    Morioka, A.; Misawa, H.; Obara, T.; Miyoshi, Y.; Masuda, S.; Iwai, K.; Kasaba, Y.

    2015-08-01

    Solar micro-type III radio bursts are elements of the so-called type III storms and are characterized by short-lived, continuous, and weak emissions. Their frequency of occurrence with respect to radiation power is quite different from that of ordinary type III bursts, suggesting that the generation process is not flare-related, but due to some recurrent acceleration processes around the active region. We examine the relationship of micro-type III radio bursts with coronal streamers. We also explore the propagation channel of bursts in the outer corona, the acceleration process, and the escape route of electron beams. It is observationally confirmed that micro-type III bursts occur near the edge of coronal streamers. The magnetic field line of the escaping electron beams is tracked on the basis of the frequency drift rate of micro-type III bursts and the electron density distribution model. The results demonstrate that electron beams are trapped along closed dipolar field lines in the outer coronal region, which arise from the interface region between the active region and the coronal hole. A 22 year statistical study reveals that the apex altitude of the magnetic loop ranges from 15 to 50 R{sub S}. The distribution of the apex altitude has a sharp upper limit around 50 R{sub S} suggesting that an unknown but universal condition regulates the upper boundary of the streamer dipolar field.

  13. 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.

  14. Bursts in inclined layer convection

    NASA Astrophysics Data System (ADS)

    Busse, F. H.; Clever, R. M.

    2000-08-01

    A new instability of longitudinal rolls in an inclined fluid layer heated from below is analyzed in the case of the Prandtl number P=0.71. The instability assumes the form of subharmonic undulations and evolves into a spatially chaotic pattern when the angle of inclination is of the order of 20°. The chaotic state rapidly decays and longitudinal rolls recover until the next burst of chaotic convection occurs. The theoretical findings closely correspond to recent experimental observations by Daniels et al. [Phys. Rev. Lett. (to be published)].

  15. Application of surface-acoustic-wave technology to burst-format spread-spectrum communications

    NASA Astrophysics Data System (ADS)

    Kowatsch, M.

    1984-12-01

    A hybrid direct-sequence/frequency-hopping spread-spectrum communication modem for burst-format transmission of digital data has been developed. A burst consists of a short synchronisation preamble and the data packet. Data modulation is accomplished by assignment of pairs of pseudonoise sequences with low crosscorrelation for message ones and zeros. The spreading code chip pattern is changed from bit to bit in both the preamble and the message portion of a burst. Receiver signal processing is based on the application of surface-acoustic-wave (SAW) elastic convolvers to programmable matched filtering. The performance of the system in an additive white Gaussian noise channel is analysed, measures of performance being the probability of burst loss and the bit error probability in the case of ideal synchronisation. Evaluations for a particular design are presented, and some experimental results obtained with a test system are shown for comparison.

  16. Source location of the narrowbanded radio bursts at Uranus: Evidence of a cusp source

    SciTech Connect

    Farrell, W.M.; Desch, M.D.; Kaiser, M.L. ); Kurth, W.S. )

    1990-03-01

    While Voyager 2 was inbound to Uranus, radio bursts of narrow bandwidth (< 5 kHz) were detected between 17-116 kHz by both the Planetary Radio Astronomy (PRA) and Plasma Wave (PWS) experiments. These R-X mode bursts, designated n-bursts, were of short duration (about 250 msec), tended to occur when the north magnetic pole tipped toward the spacecraft, and increased in occurrence with increasing solar wind density. In this report, the authors present an explicit determination of the burst source location based upon fitting the region of detection at high and low frequencies to field-aligned, symmetric cones. The region of good fits was located between the north magnetic pole an the rotational pole, corresponding approximately to the northern polar cusp. Based upon the emission power, it is suspected that at certain times large amounts of auroral input power may originate in this cusp.

  17. Are Fast Radio Bursts the Birthmark of Magnetars?

    NASA Astrophysics Data System (ADS)

    Lieu, Richard

    2017-01-01

    A model of fast radio bursts, which enlists young, short period extragalactic magnetars satisfying B/P > 2 × 1016 G s‑1 (1 G = 1 statvolt cm‑1) as the source, is proposed. When the parallel component {{\\boldsymbol{E}}}\\parallel of the surface electric field (under the scenario of a vacuum magnetosphere) of such pulsars approaches 5% of the critical field {E}c={m}e2{c}3/(e{\\hslash }), in strength, the field can readily decay via the Schwinger mechanism into electron–positron pairs, the back reaction of which causes {{\\boldsymbol{E}}}\\parallel to oscillate on a characteristic timescale smaller than the development of a spark gap. Thus, under this scenario, the open field line region of the pulsar magnetosphere is controlled by Schwinger pairs, and their large creation and acceleration rates enable the escaping pairs to coherently emit radio waves directly from the polar cap. The majority of the energy is emitted at frequencies ≲ 1 {GHz} where the coherent radiation has the highest yield, at a rate large enough to cause the magnetar to lose spin significantly over a timescale ≈ a few × {10}-3 s, the duration of a fast radio burst. Owing to the circumstellar environment of a young magnetar, however, the ≲1 GHz radiation is likely to be absorbed or reflected by the overlying matter. It is shown that the brightness of the remaining (observable) frequencies of ≈ 1 {GHz} and above are on a par with a typical fast radio burst. Unless some spin-up mechanism is available to recover the original high rotation rate that triggered the Schwinger mechanism, the fast radio burst will not be repeated again in the same magnetar.

  18. Near-Relativistic Solar Electrons and Type III Radio Bursts

    NASA Technical Reports Server (NTRS)

    Cane, H. V.

    2003-01-01

    Recently it has been found that the inferred injection times of greater than 25 keV electrons are up to 30 minutes later than the start times of the associated type III radio bursts at the Sun. Thus it has been suggested that the electrons that produce type III bursts do not belong to the same population as those observed above 25 keV. This paper examines the characteristics and circumstances of 79 solar electron beam events measured on the ACE spacecraft. Particular attention is paid to the very low frequency emissions of the associated radio bursts and the ambient conditions at the arrival times of the electrons at the spacecraft. It is found that the inferred greater than 25 keV electron injection delays are correlated with the times required for the associated radio bursts to drift to the lowest frequencies. This suggests that the electrons responsible for the radio emission and those observed above 25 keV are part of a single population, and that the electrons both above and below 25 keV are delayed in the interplanetary medium. Further evidence for a single population is the general correspondence between electron and local radio intensities and temporal profiles. It is found that the delays increase with the ambient solar wind density consistent with the propagation times of the electrons being determined by the characteristics of the interplanetary medium. However it is known that particle arrival times at 1 AU are a linear function of inverse particle speed. Conventionally such a relationship is taken to indicate scatter-free propagation when inferred path lengths lie close to 1.2 AU, as they do for the electron events studied here. These conflicting interpretations require further investigation.

  19. Neutron Stars and Thermonuclear X-ray Bursts

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, Supid

    2007-01-01

    This viewgraph presentation describes neutron stars and thermonuclear x ray bursts. The contents include: 1) Neutron Stars: why do we care?; 2) Thermonuclear Bursts: why do we care?; 3) Neutron Stars: Mass, Radius and Spin: a. Continuum Spectroscopy of Bursts b. Spectral Lines from Bursts c. Timing Properties of Bursts; 4) Neutron Star Atmosphere: Thermonuclear Flame Spreading; and 5) Future Prospects and Conclusions.

  20. Space Radar Image of Mississippi Delta

    NASA Technical Reports Server (NTRS)

    1999-01-01

    This is a radar image of the Mississippi River Delta where the river enters into the Gulf of Mexico along the coast of Louisiana. This multi-frequency image demonstrates the capability of the radar to distinguish different types of wetlands surfaces in river deltas. This image was acquired by the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) aboard the space shuttle Endeavour on October 2, 1995. The image is centered on latitude 29.3 degrees North latitude and 89.28 degrees West longitude. The area shown is approximately 63 kilometers by 43 kilometers (39 miles by 26 miles). North is towards the upper right of the image. As the river enters the Gulf of Mexico, it loses energy and dumps its load of sediment that it has carried on its journey through the mid-continent. This pile of sediment, or mud, accumulates over the years building up the delta front. As one part of the delta becomes clogged with sediment, the delta front will migrate in search of new areas to grow. The area shown on this image is the currently active delta front of the Mississippi. The migratory nature of the delta forms natural traps for oil and the numerous bright spots along the outside of the delta are drilling platforms. Most of the land in the image consists of mud flats and marsh lands. There is little human settlement in this area due to the instability of the sediments. The main shipping channel of the Mississippi River is the broad red stripe running northwest to southeast down the left side of the image. The bright spots within the channel are ships. The colors in the image are assigned to different frequencies and polarizations of the radar as follows: red is L-band vertically transmitted, vertically received; green is C-band vertically transmitted, vertically received; blue is X-band vertically transmitted, vertically received. Spaceborne Imaging Radar-C and X-band Synthetic Aperture Radar (SIR-C/X-SAR) is part of NASA's Mission to Planet Earth. The radars

  1. Angular Study of the III Type Solar Bursts by Ukrainian Decameter Heliograph of UTR-2

    NASA Astrophysics Data System (ADS)

    Koval, Artem; Stanislavsky, Aleksander; Konovalenko, Aleksander

    2014-05-01

    Solar radio bursts are attractive manifestations of solar activity. They contain useful information about physical processes in solar corona. The type III radio bursts are the most frequent events among many different types of solar bursts studied since middle of the last century. The type III bursts are generated by beams of fast electrons (beams velocity ~ 0.3c) ejected into the corona and propagated through coronal plasma to interplanetary medium. It is assumed that such an electron beam passing coronal plasma generates plasma waves that converse to electromagnetic waves registered as type III radio bursts. They are observed in a wide frequency range from 1 GHz to tens kHz. In particular, the decameter emission (10-30 MHz) of III type bursts arises at heights about 2-3 solar radii from the center of the Sun. In the last decades the various ground-based, satellite and spacecraft observations have provided detailed information about features of the bursts. Due to non-thermal emission mechanism their intensity can be very high that allows ones to record the bursts even by amateur radio astronomers with help of elementary antennas (for example, half-wave dipole) and simple radio equipment. At dynamic spectra the type III radio bursts are characterized by very fast frequency drifts. Usually, the analysis of such two-dimensional spectrograms reveals also duration and intensity of the events in time and frequency; if the antenna facilities permit, as well as degree of polarization. It should be noticed that the observations of angular three-dimensional structure of the burst source are also of great interest. Our knowledge about angular structure of type III radio bursts in decameter wavelengths was very restricted because of the absence of appropriate radio astronomy instruments. Recently, the difficulty has been overcome by means of the UTR-2 radio telescope (Kharkiv, Ukraine) in heliographic modes. It was successfully used for heliographic observations of solar

  2. Gravitational-wave bursts from the nuclei of distant galaxies and quasars: Proposal for detection using Doppler tracking of interplanetary spacecraft

    NASA Technical Reports Server (NTRS)

    Thorne, K. S.; Braginsky, V. B.

    1974-01-01

    Supermassive black holes which exist in the nuclei of many quasars and galaxies are examined along with the collapse which forms these holes and subsequent collisions between them which produce strong, broad-band bursts of gravitational waves. Such bursts might arrive at earth as often as 50 times per year--or as rarely as once each 300 years. The detection of such bursts with dual-frequency Doppler tracking of interplanetary spacecraft is considered.

  3. Preliminary results of a gamma-ray burst study in the Konus experiment on the Venera-11 and Venera-12 space probes

    NASA Technical Reports Server (NTRS)

    Mazets, Y. P.; Golentskiy, S. V.; Ilinskiy, V. N.; Panov, V. N.; Aptekar, R. L.; Guryan, Y. A.; Sokolov, I. A.; Sokolova, Z. Y.; Kharitonova, T. V.

    1979-01-01

    Twenty-one gamma-ray bursts and 68 solar flares in the hard X-ray range were detected on Venera-11 and Venera-12 space probes during the initial 50-day observation period. Major characteristics of the equipment used and preliminary data on the temporal structure and energy spectra of the gamma-ray bursts are considered. The pattern of gamma-ray burst frequency distribution vs. intensity, N(S), is established.

  4. Reduction in T gamma delta cell numbers and alteration in subset distribution in systemic lupus erythematosus.

    PubMed Central

    Lunardi, C; Marguerie, C; Bowness, P; Walport, M J; So, A K

    1991-01-01

    We have studied the distribution of T gamma delta cells in the peripheral blood of 35 patients with systemic lupus erythematosus (SLE) and 36 age-matched controls. The monoclonal antibodies A13, BB3 and Ti gamma A, which are specific for the V delta 1, V delta 2 and V delta 9 gene products respectively, were used to define T gamma delta cell subsets. A significantly lower frequency of T gamma delta cells was found in peripheral blood lymphocytes of SLE patients compared with normal subjects (3.2% versus 5.9%). There was a marked reduction in the V delta 2+ subset of T gamma delta cells, which resulted in a reversal of the ratio of V delta 2+/V delta 1+ cells from 4.34 to 0.56. No correlation was found with either clinical or laboratory measures of disease activity. These results suggest that the observed changed in T gamma delta subset distribution are related to the SLE itself, and not secondary to changes in disease activity. PMID:1834377

  5. Peak-Flux-Density Spectra of Large Solar Radio Bursts and Proton Emission from Flares.

    DTIC Science & Technology

    1985-08-19

    Frequency Maximum in the Deci- metric Range 20 5. Four of the Ten Events in Table I That Were Classified as U-Bursts Because of Our Decision to Favor...frequency peak at f > 1 GHz. The events in Figure 3 were on the list of Castelli and Barron5 while those in Figure 4 were not. Figure 5 contains four of...period in common from 1966 to 1976. Of the 85 previously identified U-bursts during this period (81 from CB and four 28. Zirin, H., and Tanaka, K

  6. A Stochastic Burst Follows the Periodic Morning Peak in Individual Drosophila Locomotion

    PubMed Central

    Lazopulo, Stanislav; Lopez, Juan A.; Levy, Paul; Syed, Sheyum

    2015-01-01

    Coupling between cyclically varying external light and an endogenous biochemical oscillator known as the circadian clock, modulates a rhythmic pattern with two prominent peaks in the locomotion of Drosophila melanogaster. A morning peak appears around the time lights turn on and an evening peak appears just before lights turn off. The close association between the peaks and the external 12:12 hour light/dark photoperiod means that respective morning and evening peaks of individual flies are well-synchronized in time and, consequently, feature prominently in population-averaged data. Here, we report on a brief but strong stochastic burst in fly activity that, in contrast to morning and evening peaks, is detectable only in single fly recordings. This burst was observed across 3 wild-type strains of Drosophila melanogaster. In a single fly recording, the burst is likely to appear once randomly within 0.5–5 hours after lights turn on, last for only 2–3 minutes and yet show 5 times greater activity compared to the maximum of morning peak with data binned in 3 minutes. Owing to its variable timing and short duration, the burst is virtually undetectable in population-averaged data. We use a locally-built illumination system to study the burst and find that its incidence in a population correlates with light intensity, with ~85% of control flies showing the behavior at 8000 lux (1942 μW/cm2). Consistent with that finding, several mutant flies with impaired vision show substantially reduced frequency of the burst. Additionally, we find that genetic ablation of the clock has insignificant effect on burst frequency. Together, these data suggest that the pronounced burst is likely generated by a light-activated circuit that is independent of the circadian clock. PMID:26528813

  7. Baroreflex physiology studied in healthy subjects with very infrequent muscle sympathetic bursts

    PubMed Central

    Diedrich, André; Crossman, Alexandra A.; Beightol, Larry A.; Tahvanainen, Kari U. O.; Kuusela, Tom A.; Ertl, Andrew C.

    2013-01-01

    Because it is likely that, in healthy human subjects, baroreflex mechanisms operate continuously, independent of experimental interventions, we asked the question, In what ways might study of unprovoked, very infrequent muscle sympathetic bursts inform baroreflex physiology? We closely examined arterial pressure and R-R interval responses of 11 supine healthy young subjects to arterial pressure ramps triggered by large isolated muscle sympathetic bursts. We triggered data collection sweeps on the beginnings of sympathetic bursts and plotted changes of arterial pressure (finger volume clamp or intra-arterial) and R-R intervals occurring before as well as after the sympathetic triggers. We estimated baroreflex gain from regression of R-R intervals on systolic pressures after sympathetic bursts and from the transfer function between cross-spectra of systolic pressure and R-R intervals at low frequencies. Isolated muscle sympathetic bursts were preceded by arterial pressure reductions. Baroreflex gain, calculated with linear regression of R-R intervals on systolic pressures after bursts, was virtually identical to baroreflex gain, calculated with the cross-spectral modulus [mean and (range): 24 (7–43) vs. 24 (8–45) ms/mmHg], and highly significant, according to linear regression (r2 = 0.91, P = 0.001). Our results indicate that 1) since infrequent human muscle sympathetic bursts are almost deterministically preceded by arterial pressure reductions, their occurrence likely reflects simple baroreflex physiology, and 2) the noninvasive low-frequency modulus reliably reproduces gains derived from R-R interval responses to arterial pressure ramps triggered by infrequent muscle sympathetic bursts. PMID:23195626

  8. [Delta-9-tetrahydrocannabinol pharmacokinetics].

    PubMed

    Goullé, J-P; Saussereau, E; Lacroix, C

    2008-08-01

    Delta-9-tetrahydrocannabinol (Delta-9-THC) is the main psychoactive ingredient of cannabis. Smoking is currently most common use of cannabis. The present review focuses on the pharmacokinetics of THC. The variability of THC in plant material which has significantly increased in recent years leads to variability in tissue THC levels from smoking, which is, in itself, a highly individual process. This variability of THC content has an important impact on drug pharmacokinetics and pharmacology. After smoking THC bioavailability averages 30%. With a 3.55% THC cigarette, a peak plasma level near 160 ng/mL occurs approximately 10 min after inhalation. THC is eliminated quickly from plasma in a multiphasic manner and is widely distributed to tissues, which is responsible for its pharmacologic effects. Body fat then serves as a long-term storage site. This particular pharmacokinetics explains the noncorrelation between THC blood level and clinical effects as is observed for ethanol. A major active 11-hydroxy metabolite is formed after both inhalation and oral dosing (20 and 100% of parent, respectively). The elimination of THC and its many metabolites, mainly THC-COOH, occurs via the feces and urine for several weeks. Thus, to confirm abstinence, urine THC-COOH analysis would be a useful tool. A positive result could be checked by gas chromatography-mass spectrometry THC blood analysis, indicative of a recent cannabis exposure.

  9. ENERGY-DEPENDENT GAMMA-RAY BURST PULSE WIDTH DUE TO THE CURVATURE EFFECT AND INTRINSIC BAND SPECTRUM

    SciTech Connect

    Peng, Z. Y.; Ma, L.; Zhao, X. H.; Yin, Y.; Bao, Y. Y.

    2012-06-20

    Previous studies have found that the width of the gamma-ray burst (GRB) pulse is energy dependent and that it decreases as a power-law function with increasing photon energy. In this work we have investigated the relation between the energy dependence of the pulse and the so-called Band spectrum by using a sample including 51 well-separated fast rise and exponential decay long-duration GRB pulses observed by BATSE (Burst and Transient Source Experiment on the Compton Gamma Ray Observatory). We first decompose these pulses into rise and decay phases and find that the rise widths and the decay widths also behave as a power-law function with photon energy. Then we investigate statistically the relations between the three power-law indices of the rise, decay, and total width of the pulse (denoted as {delta}{sub r}, {delta}{sub d}, and {delta}{sub w}, respectively) and the three Band spectral parameters, high-energy index ({alpha}), low-energy index ({beta}), and peak energy (E{sub p} ). It is found that (1) {alpha} is strongly correlated with {delta}{sub w} and {delta}{sub d} but seems uncorrelated with {delta}{sub r}; (2) {beta} is weakly correlated with the three power-law indices, and (3) E{sub p} does not show evident correlations with the three power-law indices. We further investigate the origin of {delta}{sub d}-{alpha} and {delta}{sub w}-{alpha}. We show that the curvature effect and the intrinsic Band spectrum could naturally lead to the energy dependence of the GRB pulse width and also the {delta}{sub d}-{alpha} and {delta}{sub w}-{alpha} correlations. Our results hold so long as the shell emitting gamma rays has a curved surface and the intrinsic spectrum is a Band spectrum or broken power law. The strong {delta}{sub d}-{alpha} correlation and inapparent correlations between {delta}{sub r} and the three Band spectral parameters also suggest that the rise and decay phases of the GRB pulses have different origins.

  10. Continuous theta burst transcranial magnetic stimulation affects brain functional connectivity.

    PubMed

    Dan Cao; Yingjie Li; Ling Wei; Yingying Tang

    2016-08-01

    Prefrontal cortex (PFC) plays an important role in the emotional processing as well as in the functional brain network. Hyperactivity in the right dorsolateral prefrontal cortex (DLPFC) would be found in anxious participants. However, it is still unclear what the role of PFC played in a resting functional network. Continuous theta burst transcranial magnetic stimulation (cTBS) is an effective tool to create virtual lesions on brain regions. In this paper, we applied cTBS over right prefrontal area, and investigated the effects of cTBS on the brain activity for functional connectivity by the method of graph theory. We recorded 64-channels EEG on thirteen healthy participants in the resting condition and emotional tasks before and after 40 s of cTBS. This work focused on the effect of cTBS on cortical activities in the resting condition by calculating the coherence between EEG channels and building functional networks before and after cTBS in the delta, theta, alpha and beta bands. Results revealed that 1) The functional connectivity after cTBS was significantly increased compared with that before cTBS in delta, theta, alpha and beta bands in the resting condition; 2) The efficiency-cost reached the maximum before and after cTBS both with the cost about 0.3 in the bands above, which meant that the information transmission of functional brain network with this cost was highly efficient; 3) the clustering coefficient and path length after cTBS was significantly increased in delta, theta and beta bands. In conclusion, cTBS over PFC indeed enhanced the functional connectivity in the resting condition. In addition, the information transmission in the resting brain network was highly efficient with the cost about 0.3.

  11. Relationship of decametric-hectometric type II radio burst, coronal mass ejections and solar flare observed during 1997-2014

    NASA Astrophysics Data System (ADS)

    Mittal, Nishant; Verma, V. K.

    2017-01-01

    In the present study we have investigated 426 DH Type II radio burst and associated CMEs events observed during the time period of 1997-2014. The starting frequency of most of associated DH type-II bursts (85%) lies in the range of 1-14 MHz (364 out of 426) with mean value of starting frequency is ∼11 MHz. The study of starting frequency (1-16 MHz) of DH type II bursts and heliocentric distance in solar radii indicate that DH type II radio bursts originate from 2.2-4.5 (RS) heliocentric distance in solar radii. We also found that the ∼ 48% DH Type II radio bursts associated CMEs are located between ± 40° of solar central disc and we also found that duration of DH type II radio bursts located at solar disc center are more than the duration of DH type II radio bursts located at solar limb. It is found that mean value for linear and initial speed of DH Type II associated CMEs are 1157 km/s and 1200 km/s, respectively. The CMEs speed are not correlated with duration of DH Type II radio bursts indicate that the durations of DH Type II radio bursts does not depend on speed of CMEs. The study also show that 426 DH type II radio bursts associated CMEs/flares occurred when there is coronal holes(CH) in nearby area and the mean distance between DH type II burst associated CMEs/ flares and boundary of coronal hole (CH) is 26°. The study also shows that there is no relation between drift velocity of DH type II radio bursts and speed of CMEs. The study also indicate that about 45% flares those associated DH Type II radio bursts have duration about 60 minutes and long duration DH Type II radio bursts are associated with X-class flares. We have also discussed that the results obtained in the present investigation in view of latest heliophysics interpretations.

  12. DNA helicases in recombination and repair: construction of a delta uvrD delta helD delta recQ mutant deficient in recombination and repair.

    PubMed Central

    Mendonca, V M; Klepin, H D; Matson, S W

    1995-01-01

    DNA helicases play pivotal roles in homologous recombination and recombinational DNA repair. They are involved in both the generation of recombinogenic single-stranded DNA ends and branch migration of synapsed Holliday junctions. Escherichia coli helicases II (uvrD), IV (helD), and RecQ (recQ) have all been implicated in the presynaptic stage of recombination in the RecF pathway. To probe for functional redundancy among these helicases, mutant strains containing single, double, and triple deletions in the helD, uvrD, and recQ genes were constructed and examined for conjugational recombination efficiency and DNA repair proficiency. We were unable to construct a strain harboring a delta recQ delta uvrD double deletion in a recBC sbcB(C) background (RecF pathway), suggesting that a delta recQ deletion mutation was lethal to the cell in a recBC sbcB(C) delta D background. However, we were able to construct a triple delta recQ delta uvrD Delta helD mutant in the recBC sbcB(C) background. This may be due to the increased mutator frequency in delta uvrD mutants which may have resulted in the fortuitous accumulation of a suppressor mutation(s). The triple helicase mutant recBC sbcB(C) delta uvrD delta recQ delta helD severely deficient in Hfr-mediated conjugational recombination and in the repair of methylmethane sulfonate-induced DNA damage. This suggests that the presence of at least one helicase--helicase II, RecQ helicase, or helicase IV--is essential for homologous recombination and recombinational DNA repair in a recBC sbcB(C) background. The triple helicase mutant was recombination and repair proficient in a rec+ background. Genetic analysis of the various double mutants unmasked additional functional redundancies with regard to conjugational recombination and DNA repair, suggesting that mechanisms of recombination depend both on the DNA substrates and on the genotype of the cell. PMID:7868608

  13. Pattern Specificity in the Effect of Prior [delta]f on Auditory Stream Segregation

    ERIC Educational Resources Information Center

    Snyder, Joel S.; Weintraub, David M.

    2011-01-01

    During repeating sequences of low (A) and high (B) tones, perception of two separate streams ("streaming") increases with greater frequency separation ([delta]f) between the A and B tones; in contrast, a prior context with large [delta]f results in less streaming during a subsequent test pattern. The purpose of the present study was to…

  14. RADIATION FROM ELECTRON PHASE SPACE HOLES AS A POSSIBLE SOURCE OF JOVIAN S-BURSTS

    SciTech Connect

    Goodrich, K. A.; Ergun, R. E.

    2015-08-10

    Radio-frequency short burst emissions (10–40 MHz), known as Jovian S-bursts, have been observed from the Jovian aurora for over fifty years. These emissions, associated with Io’s motion, have a rapidly declining frequency and an exceptionally narrow bandwidth. While it is widely believed that S-bursts are generated by the electron cyclotron maser instability, the mechanism responsible for the rapidly declining frequency and narrow bandwidth currently is not well established. We explore a hypothesis that electron phase space holes radiate or stimulate radiation in the Jovian aurora plasma environment as a possible source of S-burst emissions. Electron phase-space holes (EHs) are ubiquitous in an auroral environment and travel at the implied speeds (∼20,000 km s{sup −1}) of the structures creating the Jovian S-bursts. Furthermore, EHs have the proper physical size to create the observed bandwidth, have sufficient energy content, and can create an environment whereby X mode emissions can be excited. If verified, these findings imply that EHs may be an important source of radiation from strongly magnetized or relativistic astrophysical plasmas.

  15. DISCOVERY OF QUASI-PERIODIC OSCILLATIONS IN THE RECURRENT BURST EMISSION FROM SGR 1806-20

    SciTech Connect

    El-Mezeini, Ahmed M.; Ibrahim, Alaa I. E-mail: ai@aucegypt.ed E-mail: ai@space.mit.ed

    2010-10-01

    We present evidence for quasi-periodic oscillations (QPOs) in the recurrent outburst emission from the soft gamma repeater SGR 1806-20 using NASA's Rossi X-ray Timing Explorer (RXTE) observations. By searching a sample of 30 bursts for timing signals at the frequencies of the QPOs discovered in the 2004 December 27 giant flare from the source, we find three QPOs at 84, 103, and 648 Hz in three different bursts. The first two QPOs lie within {approx}1{sigma} from the 92 Hz QPO detected in the giant flare. The third QPO lies within {approx}9{sigma} from the 625 Hz QPO also detected in the same flare. The detected QPOs are found in bursts with different durations, morphologies, and brightness, and are vindicated by Monte Carlo simulations, which set a lower limit confidence interval {>=}4.3{sigma}. We also find evidence for candidate QPOs at higher frequencies in other bursts with lower statistical significance. The fact that we can find evidence for QPOs in the recurrent bursts at frequencies relatively close to those found in the giant flare is intriguing and can offer insight about the origin of the oscillations. We confront our finding against the available theoretical models and discuss the connection between the QPOs we report and those detected in the giant flares. The implications to the neutron star properties are also discussed.

  16. Probing X-ray burst - accretion disk interaction in low mass X-ray binaries through kilohertz quasiperiodic oscillations

    NASA Astrophysics Data System (ADS)

    Peille, P.; Olive, J.-F.; Barret, D.

    2014-07-01

    The intense radiation flux of Type I X-ray bursts is expected to interact with the accretion flow around neutron stars. High frequency quasiperiodic oscillations (kHz QPOs), observed at frequencies matching orbital frequencies at tens of gravitational radii, offer a unique probe of the innermost disk regions. In this paper, we follow the lower kHz QPOs, in response to Type I X-ray bursts, in two prototypical QPO sources, namely 4U 1636-536 and 4U 1608-522, as observed by the Proportional Counter Array of the Rossi X-ray Timing Explorer. We have selected a sample of 15 bursts for which the kHz QPO frequency can be tracked on timescales commensurable with the burst durations (tens of seconds). We find evidence that the QPOs are affected for over ~200 s during one exceptionally long burst and ~100 s during two others (although at a less significant level), while the burst emission has already decayed to a level that would enable the pre-burst QPO to be detected. On the other hand, for most of our burst-kHz QPO sample, we show that the QPO is detected as soon as the statistics allow and in the best cases, we are able to set an upper limit of ~20 s on the recovery time of the QPO. This diversity of behavior cannot be related to differences in burst peak luminosity. We discuss these results in the framework of recent findings that accretion onto the neutron star may be enhanced during Type I X-ray bursts. The subsequent disk depletion could explain the disappearance of the QPO for ~100 s, as possibly observed in two events. However, alternative scenarios would have to be invoked for explaining the short recovery timescales inferred from most bursts. Heating of the innermost disk regions would be a possibility, although we cannot exclude that the burst does not affect the QPO emission at all. Clearly the combination of fast timing and spectral information of Type I X-ray bursts holds great potential in the study of the dynamics of the inner accretion flow around neutron

  17. Halo Coronal Mass Ejections and Their Relation to DH Type-II Radio Bursts

    NASA Astrophysics Data System (ADS)

    Shanmugaraju, A.; Bendict Lawrance, M.

    2015-10-01

    A set of 88 halo CMEs observed by the Solar and Heliospheric Observatory/ Large Angle Solar Coronagraph (SOHO/LASCO) during the period 2005 to 2010 is considered to study the relationship of these halo CMEs with Type-II radio bursts in the deca-hectametric (DH) wavelength range observed by Wind/(Plasma and Radio Waves: WAVES). Among the 88 events, 39 halo CMEs are found to be associated with DH Type-II radio bursts and their characteristics are analyzed with the following results: i) The heights of the CME leading edge at the time of the starting frequencies of many of the selected DH Type-II events (74 %) are in the range (2 - 10 R_{⊙}) where the shocks are formed. ii) The mean speed of DH-associated halo CMEs (1610 km s-1) is nearly twice the mean speed (853 km s-1) of halo CMEs without DH Type-II radio bursts, implying that the peak of the Alfvén speed profile in the outer corona where DH Type-II radio bursts start might be around 800 km s-1. iii) The shock speed of DH Type-II radio bursts calculated using the heights of shock signatures of the corresponding CME events is found to be slightly higher than the CME speed. iv) The CME speed plays a major role in the determination of the ending frequency of DH Type-II radio bursts but not the starting frequency. v) The relationship between the characteristics of DH Type-II radio bursts and CMEs is explained in the context of the universal drift-rate spectrum.

  18. Air bubble bursting effect of lotus leaf.

    PubMed

    Wang, Jingming; Zheng, Yongmei; Nie, Fu-Qiang; Zhai, Jin; Jiang, Lei

    2009-12-15

    In this paper, a phenomenon of air bubbles quickly bursting within several milliseconds on a "self-cleaning" lotus leaf was described. This observation prompted the synthesis of artificial surfaces similar to that of the lotus leaf. The artificial leaf surfaces, prepared by photolithography and wet etching, showed a similar air bubble bursting effect. Smooth and rough silicon surfaces with an ordered nanostructure or patterned microstructure were utilized to study the contribution of the micro/nano hierarchical structures to this phenomenon of air bubble bursting. Air bubbles were found to burst on some superhydrophobic surfaces with microstructure (within 220 ms). However, air bubbles burst much more rapidly (within 13 ms) on similar surfaces with micro/nanostructure. The height, width, and spacing of hierarchical structures could also affect air bubble bursting, and the effect of the height was more obvious. When the height of hierarchical structures was around the height found in natural lotus papillae, the width and spacing were significant for air bubble bursting. An original model was proposed to further evaluate the reason why the micro/nano hierarchical rough structures had an excellent air bubble bursting effect, and the validity of the model was theoretically demonstrated.

  19. Backscattering of solar electron burst distributions

    NASA Astrophysics Data System (ADS)

    Skoug, R. M.; Steinberg, J. T.; Anderson, B. R.; de Koning, C. A.; Gosling, J. T.; McComas, D. J.

    2008-12-01

    Solar electron bursts are frequently observed in the ACE/SWEPAM suprathermal electron measurements at energies below 1.4 keV. Approximately 1/3 of such events show backstreaming electrons, which are typically observed after a 1-2 hour delay following burst onset and travel back towards the Sun along the magnetic field direction. These backstreaming particles are likely produced by scattering of the solar electron burst particles beyond the ~1 AU spacecraft location. Our previous studies have shown that transient solar burst electrons exhibit a greater degree of pitch angle scattering than does the steady-state solar wind electron strahl, which could result in turning back of the burst electrons. From the delays observed between the onset of the bursts and the backstreaming, we infer that burst electrons are turned back sunward at a field-aligned distance of less than 1 AU beyond the spacecraft. In this study we compare the fluxes and energy spectra of backstreaming particles with those of the outgoing burst particles. In addition, we compare the angular widths of the two electron beams. These comparisons provide an indication of the relative importance of magnetic mirroring and focusing, scattering in pitch angle, and scattering in energy for determining the character of the observed electron distributions.

  20. Astronomy: Radio burst caught red-handed

    NASA Astrophysics Data System (ADS)

    Falcke, Heino

    2017-01-01

    For almost a decade, astronomers have observed intense bursts of radio waves from the distant cosmos whose origins were unknown. The source of one such burst has now been identified, but this has only deepened the mystery. See Letter p.58

  1. The Burst Mode of Protostellar Accretion

    NASA Astrophysics Data System (ADS)

    Vorobyov, E. I.; Basu, Shantanu

    2006-10-01

    We present new numerical simulations in the thin disk approximation that characterize the burst mode of protostellar accretion. The burst mode begins upon the formation of a centrifugally balanced disk around a newly formed protostar. It comprises prolonged quiescent periods of low accretion rate (typically <~10-7 Msolar yr-1) that are punctuated by intense bursts of accretion (typically >~10-4 Msolar yr-1, with duration <~100 yr) during which most of the protostellar mass is accumulated. The accretion bursts are associated with the formation of dense protostellar/protoplanetary embryos, which are later driven onto the protostar by the gravitational torques that develop in the disk. Gravitational instability in the disk, driven by continuing infall from the envelope, is shown to be an effective means of transporting angular momentum outward and mass inward to the protostar. We show that the disk mass always remains significantly less than the central protostar's mass throughout this process. The burst phenomenon is robust enough to occur for a variety of initial values of rotation rate and frozen-in (supercritical) magnetic field and a variety of density-temperature relations. Even in cases where the bursts are nearly entirely suppressed, a moderate increase in cloud size or rotation rate can lead to vigorous burst activity. We conclude that most (if not all) protostars undergo a burst mode of evolution during their early accretion history, as inferred empirically from observations of FU Orionis variables.

  2. Physics issues of gamma ray burst emissions

    NASA Technical Reports Server (NTRS)

    Liang, Edison

    1987-01-01

    The critical physics issues in the interpretation of gamma-ray-burst spectra are reviewed. An attempt is made to define the emission-region parameter space satisfying the maximum number of observational and theoretical constraints. Also discussed are the physical mechanisms responsible for the bursts that are most consistent with the above parameter space.

  3. Burst suppression probability algorithms: state-space methods for tracking EEG burst suppression

    NASA Astrophysics Data System (ADS)

    Chemali, Jessica; Ching, ShiNung; Purdon, Patrick L.; Solt, Ken; Brown, Emery N.

    2013-10-01

    Objective. Burst suppression is an electroencephalogram pattern in which bursts of electrical activity alternate with an isoelectric state. This pattern is commonly seen in states of severely reduced brain activity such as profound general anesthesia, anoxic brain injuries, hypothermia and certain developmental disorders. Devising accurate, reliable ways to quantify burst suppression is an important clinical and research problem. Although thresholding and segmentation algorithms readily identify burst suppression periods, analysis algorithms require long intervals of data to characterize burst suppression at a given time and provide no framework for statistical inference. Approach. We introduce the concept of the burst suppression probability (BSP) to define the brain's instantaneous propensity of being in the suppressed state. To conduct dynamic analyses of burst suppression we propose a state-space model in which the observation process is a binomial model and the state equation is a Gaussian random walk. We estimate the model using an approximate expectation maximization algorithm and illustrate its application in the analysis of rodent burst suppression recordings under general anesthesia and a patient during induction of controlled hypothermia. Main result. The BSP algorithms track burst suppression on a second-to-second time scale, and make possible formal statistical comparisons of burst suppression at different times. Significance. The state-space approach suggests a principled and informative way to analyze burst suppression that can be used to monitor, and eventually to control, the brain states of patients in the operating room and in the intensive care unit.

  4. Quark nova model for fast radio bursts

    NASA Astrophysics Data System (ADS)

    Shand, Zachary; Ouyed, Amir; Koning, Nico; Ouyed, Rachid

    2016-05-01

    Fast radio bursts (FRBs) are puzzling, millisecond, energetic radio transients with no discernible source; observations show no counterparts in other frequency bands. The birth of a quark star from a parent neutron star experiencing a quark nova - previously thought undetectable when born in isolation - provides a natural explanation for the emission characteristics of FRBs. The generation of unstable r-process elements in the quark nova ejecta provides millisecond exponential injection of electrons into the surrounding strong magnetic field at the parent neutron star's light cylinder via β-decay. This radio synchrotron emission has a total duration of hundreds of milliseconds and matches the observed spectrum while reducing the inferred dispersion measure by approximately 200 cm-3 pc. The model allows indirect measurement of neutron star magnetic fields and periods in addition to providing astronomical measurements of β-decay chains of unstable neutron rich nuclei. Using this model, we can calculate expected FRB average energies (˜ 1041 erg) and spectral shapes, and provide a theoretical framework for determining distances.

  5. FRBCAT: The Fast Radio Burst Catalogue

    NASA Astrophysics Data System (ADS)

    Petroff, E.; Barr, E. D.; Jameson, A.; Keane, E. F.; Bailes, M.; Kramer, M.; Morello, V.; Tabbara, D.; van Straten, W.

    2016-09-01

    Here, we present a catalogue of known Fast Radio Burst sources in the form of an online catalogue, FRBCAT. The catalogue includes information about the instrumentation used for the observations for each detected burst, the measured quantities from each observation, and model-dependent quantities derived from observed quantities. To aid in consistent comparisons of burst properties such as width and signal-to-noise ratios, we have re-processed all the bursts for which we have access to the raw data, with software which we make available. The originally derived properties are also listed for comparison. The catalogue is hosted online as a Mysql database which can also be downloaded in tabular or plain text format for off-line use. This database will be maintained for use by the community for studies of the Fast Radio Burst population as it grows.

  6. Backstreaming Electrons Associated With Solar Electron Bursts

    NASA Astrophysics Data System (ADS)

    Skoug, R. M.; Steinberg, J. T.; de Koning, C. A.; Gosling, J. T.; McComas, D. J.

    2007-12-01

    Solar electron bursts are frequently observed in the ACE/SWEPAM suprathermal electron measurements at energies below 1.4 keV. A significant fraction of such events show backscattered electrons, beginning after the burst onset and traveling back towards the Sun along the magnetic field direction. Such backscattered particles imply a scattering mechanism beyond the spacecraft location. Some bursts also show backstreaming conic distributions, implying mirroring at magnetic field enhancements beyond the spacecraft. Here we present a study of these backstreaming particles during solar electron events. We examine the occurrence of backstreaming electrons and their relationship to other burst characteristics such as pitch angle width, duration, and energy range. We also investigate the time delay between burst onset and the appearance of backscattered electrons, including energy and pitch-angle dispersion. We examine the pitch angle distribution and energy dependence of backstreaming electrons, and consider possible origins of these electron distributions and their relationship to solar wind structure beyond the spacecraft.

  7. Ginga Gamma-Ray Burst Line Occurrence

    NASA Technical Reports Server (NTRS)

    Band, David

    1998-01-01

    The purpose of this project is the statistical evaluation of the occurrence of spectral lines in the gamma-ray burst spectra detected by the Ginga burst detector, and the comparison of the Ginga results to the BATSE observations. Two significant line features were detected in the Ginga bursts, but thus far none have been detected in the bursts BATSE detected. These line features may indicate the presence of strong magnetic fields in bursts, and therefore are important physical diagnostics of the conditions in the plasma which radiates the observed gamma-rays. The issue is whether there is a discrepancy between the Ginga and BATSE results; the potential discrepancy must be evaluated statistically. Even if BATSE line detections are announced, the statistical methodology we have developed can be used to estimate the rate at which different types of spectral features occur.

  8. Gamma ray bursts: a 1983 overview

    SciTech Connect

    Cline, T.L.

    1983-10-01

    Gamma ray burst observations are reviewed with mention of new gamma-ray and optical transient measurements and with discussions of the controversial, contradictory and unresolved issues that have recently emerged: burst spectra appear to fluctuate in time as rapidly as they are measured, implying that any one spectrum may be incorrect. Energy spectra can be obligingly fitted to practically any desired shape, implying, in effect, that no objective spectral resolution exists at all. Burst fluxes and temporal quantities, including the total event energy, are characterized very differently with differing instruments, implying that even elementary knowledge of their properties is instrumentally subjective. Finally, the log N-log S determinations are deficient in the weak bursts, while there is no detection of a source direction anisotropy, implying that Ptolemy was right or that burst source distance estimates are basically guesswork. These issues may remain unsolved until vastly improved instruments are flown.

  9. Gamma Ray Bursts: a 1983 Overview

    NASA Technical Reports Server (NTRS)

    Cline, T. L.

    1983-01-01

    Gamma ray burst observations are reviewed with mention of new gamma-ray and optical transient measurements and with discussions of the controversial, contradictory and unresolved issues that have recently emerged: burst spectra appear to fluctuate in time as rapidly as they are measured, implying that any one spectrum may be incorrect; energy spectra can be obligingly fitted to practically any desired shape, implying, in effect, that no objective spectral resolution exists at all; burst fluxes and temporal quantities, including the total event energy, are characterized very differently with differing instruments, implying that even elementary knowledge of their properties is instrumentally subjective; finally, the log N-log S determinations are deficient in the weak bursts, while there is no detection of a source direction anisotropy, implying that Ptolemy was right or that burst source distance estimates are basically guesswork. These issues may remain unsolved until vastly improved instruments are flown.

  10. Microsecond flares in gamma-ray bursts

    NASA Technical Reports Server (NTRS)

    Schaefer, Bradley E.; Cohen, Justin; Teegarden, Bonnard J.; Cline, Thomas L.; Fishman, Gerald J.; Meegan, Charles A.; Wilson, Robert B.; Paciesas, William S.; Pendleton, Geoffrey N.; Matteson, James L.

    1993-01-01

    It has been suggested that gamma-ray burst light curves may consist of many superposed flares with a duration shorter than 30/microsec. If true, the implications for the interpretation of burst data are enormous. With the launch of the Compton Gamma-Ray Observatory, four predictions of Mitrofanov's (1989) suggestion can be tested. Our results which contradict this suggestion are (1) the photon arrival times are not correlated between independent detectors, (2) the spectral hardness and intensity does not depend on the detector area, (3) the bursts seen by detectors which measure photon positions do not see microsecond flares, and (4) burst positions deduced from detectors with different projected areas are close to the positions deduced from time-of-flight differences between separated spacecraft. We conclude, therefore, that gamma-ray bursts are not composed of microsecond flares.

  11. Mackenzie River Delta, Canada

    NASA Technical Reports Server (NTRS)

    2007-01-01

    The Mackenzie River in the Northwest Territories, Canada, with its headstreams the Peace and Finley, is the longest river in North America at 4241 km, and drains an area of 1,805,000 square km. The large marshy delta provides habitat for migrating Snow Geese, Tundra Swans, Brant, and other waterfowl. The estuary is a calving area for Beluga whales. The Mackenzie (previously the Disappointment River) was named after Alexander Mackenzie who travelled the river while trying to reach the Pacific in 1789.

    The image was acquired on August 4, 2005, covers an area of 55.8 x 55.8 km, and is located at 68.6 degrees north latitude, 134.7 degrees west longitude.

    The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate.

  12. Colorado River Delta

    NASA Technical Reports Server (NTRS)

    2008-01-01

    The Colorado River ends its 2330 km journey in the Gulf of Mexico in Baja California. The heavy use of the river as an irrigation source for the Imperial Valley has dessicated the lower course of the river in Mexico such that it no longer consistently reaches the sea. Prior to the mid 20th century, the Colorado River Delta provided a rich estuarine marshland that is now essentially desiccated, but nonetheless is an important ecological resource.

    The image was acquired May 29, 2006, covers an area of 44.3 x 57.5 km, and is located at 32.1 degrees north latitude, 115.1 degrees west longitude.

    The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate.

  13. Flutter analysis of highly swept delta wings by conventional methods

    NASA Technical Reports Server (NTRS)

    Gibbons, M. D.; Soistmann, D. L.; Bennett, R. M.

    1988-01-01

    The flutter boundaries of six thin highly-swept delta-platform wings have been calculated. Comparisons are made between experimental data and results using several aerodynamic methods. The aerodynamic methods used include a subsonic and supersonic kernel function, second order piston theory, and a transonic small disturbance code. The dynamic equations of motion are solved using analytically calculated mode shapes and frequencies.

  14. Up to 400 GHz burst-mode pulse generation from a hybrid harmonic mode-locked Er-doped fibre laser

    NASA Astrophysics Data System (ADS)

    Wang, Sheng-Min; Lai, Yinchieh

    2017-02-01

    By inserting a birefringence filter with FSR  =  100 GHz inside a hybrid mode-locked Er-doped fibre laser, we successfully generate ps to sub-ps optical burst pulses with the intra-burst pulse rate up to 400 GHz. Multiplication of the intra-burst pulse rate is attributed to a new effect analogous to rational harmonic mode-locking, which occurs due to the relative alignment of the cavity harmonic frequencies, the external phase modulation induced frequencies, and the filter-selected frequencies.

  15. Spatiotemporal chaos from bursting dynamics

    SciTech Connect

    Berenstein, Igal; De Decker, Yannick

    2015-08-14

    In this paper, we study the emergence of spatiotemporal chaos from mixed-mode oscillations, by using an extended Oregonator model. We show that bursting dynamics consisting of fast/slow mixed mode oscillations along a single attractor can lead to spatiotemporal chaotic dynamics, although the spatially homogeneous solution is itself non-chaotic. This behavior is observed far from the Hopf bifurcation and takes the form of a spatiotemporal intermittency where the system locally alternates between the fast and the slow phases of the mixed mode oscillations. We expect this form of spatiotemporal chaos to be generic for models in which one or several slow variables are coupled to activator-inhibitor type of oscillators.

  16. Burst Firing in a Motion-Sensitive Neural Pathway Correlates with Expansion Properties of Looming Objects that Evoke Avoidance Behaviors

    PubMed Central

    McMillan, Glyn A.; Gray, John R.

    2015-01-01

    The locust visual system contains a well-defined motion-sensitive pathway that transfers visual input to motor centers involved in predator evasion and collision avoidance. One interneuron in this pathway, the descending contralateral movement detector (DCMD), is typically described as using rate coding; edge expansion of approaching objects causes an increased rate of neuronal firing that peaks after a certain retinal threshold angle is exceeded. However, evidence of intrinsic DCMD bursting properties combined with observable oscillations in mean firing rates and tight clustering of spikes in raw traces, suggest that bursting may be important for motion detection. Sensory neuron bursting provides important timing information about dynamic stimuli in many model systems, yet no studies have rigorously investigated if bursting occurs in the locust DCMD during object approach. We presented repetitions of 30 looming stimuli known to generate behavioral responses to each of 20 locusts in order to identify and quantify putative bursting activity in the DCMD. Overall, we found a bimodal distribution of inter-spike intervals (ISI) with peaks of more frequent and shorter ISIs occurring from 1–8 ms and longer less frequent ISIs occurring from 40–50 ms. Subsequent analysis identified bursts and isolated single spikes from the responses. Bursting frequency increased in the latter phase of an approach and peaked at the time of collision, while isolated spiking was predominant during the beginning of stimulus approach. We also found that the majority of inter-burst intervals (IBIs) occurred at 40–50 ms (or 20–25 bursts/s). Bursting also occurred across varied stimulus parameters and suggests that burst timing may be a key component of looming detection. Our findings suggest that the DCMD uses two modes of coding to transmit information about looming stimuli and that these modes change dynamically with a changing stimulus at a behaviorally-relevant time. PMID:26696845

  17. A DS/FH burst communication modem based on SAW elastic convolvers

    NASA Astrophysics Data System (ADS)

    Kowatsch, M.; Lafferl, J. T.; Seifert, F. J.

    This paper presents a burst-type spread spectrum communication modem with binary orthogonal code shift keying (CSK) employed for data modulation. A burst consists of an 8-bit synchronization preamble followed by a block of 1000 message bits, transmitted at 84 kbit/s. The spread spectrum modulation scheme is direct sequence (DS) combined with noncoherent frequency hopping (FH). Each bit of both the preamble and the message portion of a burst is encoded by a different 255-chip Kasami sequence with a chip rate of 21.4 MHz. The hop rate of the carrier is equal to the data rate, the number of frequencies being 13. The total transmission bandwidth is 300 MHz. Receiver signal processing is based on the application of two SAW elastic convolvers to programmable matched filtering. Performance measurements in a simulated communications channel show good agreement with theory.

  18. A storm of type 3 bursts observed by RAE-1 in August 1968

    NASA Technical Reports Server (NTRS)

    Howard, E. G.

    1973-01-01

    Curves of the number of type 3 bursts as a function of time are presented for six fixed frequencies (2.8, 1.65, 1.31, 0.995, 0.700, and 0.54 MHz). The curves peak at approximately 0500 UT August 20, 1968, and are symmetrical on both sides. Sakurai (1971) has shown that this time correlates well with the CMP of the McMath Region 9597. The maximum rate of bursts is approximately 150 per hour at the higher frequency of 2.8 MHz. Over 20,000 bursts were counted during the 15-day period from August 13 to August 27 when the active region was visible to the earth. A least-squares normal curve has been fitted to the observational data and calculations of variance and standard deviation are given.

  19. Tracking Type III Radio Burst Sources in the Solar Corona by Heliographic Means

    NASA Astrophysics Data System (ADS)

    Koval, A. A.; Stanislavsky, A. A.; Konovalenko, A. A.; Volvach, Ya. S.

    We present the preliminary results of heliographic measurements of solar type III radio bursts in the low-frequency range (16.5-33 MHz) using the UTR-2 radio heliograph. The radio astronomy tools permit us to obtain two-dimensional spatial structures of burst sources in dependence of frequency and time. Each heliogram consists of 40 pixels (beams) as a result of the serial sweep in UV-plane wherein signals of each beam are recorded in a dynamic spectrum with both high temporal (˜ 2.482 ms) and top spectral (˜ 4 kHz) resolutions. The rate of output heliograph is one image per 3 seconds. Over a session in April, 2013 many type III radio and IIIb-III bursts were observed. On the heliograms the source motion direction in the upper corona is clearly detectable. The heliogram features are discussed.

  20. Erosion Between Two Delta Fronts, the Mekong Delta Case

    NASA Astrophysics Data System (ADS)

    Unverricht, D.; Heinrich, C.; Nguyen, T. C.; Szczucinski, W.; Schwarzer, K.; Stattegger, K.

    2013-12-01

    Human activities, like embanking, sand mining, groundwater extraction and deforestation lead to strong changes of the deltaic environment. Especially, mangrove cutting influences strongly the coastal erosion along large areas of the southern Mekong delta coast. However, all currently published data document erosion from subaerial areas excluding the subaqueous Mekong delta. Our study fills this gap along the subaqueous Mekong Delta between the Bassac River mouth and the Gulf of Thailand. Hydroacoustic profiles and sediment coring were carried out during two cruises in 2007 and 2008. Analyses of ADCP measurements provide valuable information of current direction and velocity during the inter-monsoon season. Fine sediment dynamics including SPM were analyzed applying laser in situ scattering and Transmissiometry (LISST) at vertical profiles. Two delta fronts were found more than 200 km apart, one in front of the main Mekong river distributaries and the other around Ca Mau Cape, the south-western most spit of the Mekong River Delta. Although the delta front around Ca Mau Cape is not directly supplied by the main distributaries of the Mekong River, it is the fastest prograding region of the subaqueous Mekong delta. Alongshore sediment transport takes place from the north-eastern main distributaries towards south-west (Ca Mau Cape). Between both delta fronts, a large scale alternating sand-ridge-system, at least 120 km long and 6 to 10 km wide (ridge crest distance), has developed where erosional channels separate two sand-ridge bodies. The origin of the sand-ridge system is situated at the delta slope off Ganh Hao around water depths between 10 and 18 m. Here, the delta slope consists mainly of fine sand in the upper layer (up to 20 cm thickness) and is separated by an erosional hiatus from the lower muddy layer. The mangroves and sandy beaches at the coast in this region are also under erosion. It is assumed that the eroded beach sand feeds the sand-ridge-system. The

  1. Review of evoked and event-related delta responses in the human brain.

    PubMed

    Güntekin, Bahar; Başar, Erol

    2016-05-01

    In the last decade, the brain's oscillatory responses have invaded the literature. The studies on delta (0.5-3.5Hz) oscillatory responses in humans upon application of cognitive paradigms showed that delta oscillations are related to cognitive processes, mainly in decision making and attentional processes. The present manuscript comprehensively reviews the studies on delta oscillatory responses upon cognitive stimulation in healthy subjects and in different pathologies, namely Alzheimer's disease, Mild Cognitive Impairment (MCI), bipolar disorder, schizophrenia and alcoholism. Further delta oscillatory response upon presentation of faces, facial expressions, and affective pictures are reviewed. The relationship between pre-stimulus delta activity and post-stimulus evoked and event-related responses and/or oscillations is discussed. Cross-frequency couplings of delta oscillations with higher frequency windows are also included in the review. The conclusion of this review includes several important remarks, including that delta oscillatory responses are involved in cognitive and emotional processes. A decrease of delta oscillatory responses could be a general electrophysiological marker for cognitive dysfunction (Alzheimer's disease, MCI, bipolar disorder, schizophrenia and alcoholism). The pre-stimulus activity (phase or amplitude changes in delta activity) has an effect on post-stimulus EEG responses.

  2. Wave-wave interactions in solar type III radio bursts

    SciTech Connect

    Thejappa, G.; MacDowall, R. J.

    2014-02-11

    The high time resolution observations from the STEREO/WAVES experiment show that in type III radio bursts, the Langmuir waves often occur as localized magnetic field aligned coherent wave packets with durations of a few ms and with peak intensities well exceeding the strong turbulence thresholds. Some of these wave packets show spectral signatures of beam-resonant Langmuir waves, down- and up-shifted sidebands, and ion sound waves, with frequencies, wave numbers, and tricoherences satisfying the resonance conditions of the oscillating two stream instability (four wave interaction). The spectra of a few of these wave packets also contain peaks at f{sub pe}, 2f{sub pe} and 3 f{sub pe} (f{sub pe} is the electron plasma frequency), with frequencies, wave numbers and bicoherences (computed using the wavelet based bispectral analysis techniques) satisfying the resonance conditions of three wave interactions: (1) excitation of second harmonic electromagnetic waves as a result of coalescence of two oppositely propagating Langmuir waves, and (2) excitation of third harmonic electromagnetic waves as a result of coalescence of Langmuir waves with second harmonic electromagnetic waves. The implication of these findings is that the strong turbulence processes play major roles in beam stabilization as well as conversion of Langmuir waves into escaping radiation in type III radio bursts.

  3. Solar Type II Radio Bursts and IP Type II Events

    NASA Technical Reports Server (NTRS)

    Cane, H. V.; Erickson, W. C.

    2005-01-01

    We have examined radio data from the WAVES experiment on the Wind spacecraft in conjunction with ground-based data in order to investigate the relationship between the shocks responsible for metric type II radio bursts and the shocks in front of coronal mass ejections (CMEs). The bow shocks of fast, large CMEs are strong interplanetary (IP) shocks, and the associated radio emissions often consist of single broad bands starting below approx. 4 MHz; such emissions were previously called IP type II events. In contrast, metric type II bursts are usually narrowbanded and display two harmonically related bands. In addition to displaying complete dynamic spectra for a number of events, we also analyze the 135 WAVES 1 - 14 MHz slow-drift time periods in 2001-2003. We find that most of the periods contain multiple phenomena, which we divide into three groups: metric type II extensions, IP type II events, and blobs and bands. About half of the WAVES listings include probable extensions of metric type II radio bursts, but in more than half of these events, there were also other slow-drift features. In the 3 yr study period, there were 31 IP type II events; these were associated with the very fastest CMEs. The most common form of activity in the WAVES events, blobs and bands in the frequency range between 1 and 8 MHz, fall below an envelope consistent with the early signatures of an IP type II event. However, most of this activity lasts only a few tens of minutes, whereas IP type II events last for many hours. In this study we find many examples in the radio data of two shock-like phenomena with different characteristics that occur simultaneously in the metric and decametric/hectometric bands, and no clear example of a metric type II burst that extends continuously down in frequency to become an IP type II event. The simplest interpretation is that metric type II bursts, unlike IP type II events, are not caused by shocks driven in front of CMEs.

  4. Spin Down of Pulsations in the Cooling Tail of an X-ray Burst from 4U 1636-53

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod E.

    1999-01-01

    We report the discovery with the proportional counter array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE) of a decrease in the frequency of X-ray brightness oscillations in the cooling tail of an X-ray burst from 4U 1636-53. This is the first direct evidence for a spin down of the pulsations seen during thermonuclear bursts. We find that the spin down episode is correlated with the appearance in this burst of an extended tail of emission with a decay timescale much longer than is seen in other bursts from 4U 1636-53 in the same set of observations. We present both time resolved energy and variability spectra during this burst and compare them with results from a second burst which shows neither a spin down episode nor an extended tail. A spectral evolution study of the "spin down" burst reveals a secondary signature of weak radius expansion, not seen in other bursts, and correlated with the spin down episode, which may indicate a secondary thermonuclear energy release. We interpret the spin down episode in the context of an angular momentum conserving shell, which is reexpanded and therefore spun down by an additional thermonuclear energy release which could also explain the extended X-ray tail.

  5. Unveiling the population of orphan γ-ray bursts

    NASA Astrophysics Data System (ADS)

    Ghirlanda, G.; Salvaterra, R.; Campana, S.; Vergani, S. D.; Japelj, J.; Bernardini, M. G.; Burlon, D.; D'Avanzo, P.; Melandri, A.; Gomboc, A.; Nappo, F.; Paladini, R.; Pescalli, A.; Salafia, O. S.; Tagliaferri, G.

    2015-06-01

    Gamma-ray bursts (GRBs) are detectable in the γ-ray band if their jets are oriented toward the observer. However, for each GRB with a typical θjet, there should be ~2/θ2jet bursts whose emission cone is oriented elsewhere in space. These off-axis bursts can eventually be detected when, due to the deceleration of their relativistic jets, the beaming angle becomes comparable to the viewing angle. Orphan afterglows (OAs) should outnumber the current population of bursts detected in the γ-ray band even if they have not been conclusively observed so far at any frequency. We compute the expected flux of the population of orphan afterglows in the mm, optical, and X-ray bands through a population synthesis code of GRBs and the standard afterglow emission model. We estimate the detection rate of OAs with ongoing and forthcoming surveys. The average duration of OAs as transients above a given limiting flux is derived and described with analytical expressions: in general OAs should appear as daily transients in optical surveys and as monthly/yearly transients in the mm/radio band. We find that ~2 OA yr-1 could already be detected by Gaia and up to 20 OA yr-1 could be observed by the ZTF survey. A larger number of 50 OA yr-1 should be detected by LSST in the optical band. For the X-ray band, ~26 OA yr-1 could be detected by the eROSITA. For the large population of OA detectable by LSST, the X-ray and optical follow up of the light curve (for the brightest cases) and/or the extensive follow up of their emission in the mm and radio band could be the key to disentangling their GRB nature from other extragalactic transients of comparable flux density.

  6. Observing a Burst with Sunglasses

    NASA Astrophysics Data System (ADS)

    2003-11-01

    Unique Five-Week VLT Study of the Polarisation of a Gamma-Ray Burst Afterglow "Gamma-ray bursts (GRBs)" are certainly amongst the most dramatic events known in astrophysics. These short flashes of energetic gamma-rays, first detected in the late 1960's by military satellites, last from less than one second to several minutes. GRBs have been found to be situated at extremely large ("cosmological") distances. The energy released in a few seconds during such an event is larger than that of the Sun during its entire lifetime of more than 10,000 million years. The GRBs are indeed the most powerful events since the Big Bang known in the Universe, cf. ESO PR 08/99 and ESO PR 20/00. During the past years circumstantial evidence has mounted that GRBs signal the collapse of extremely massive stars, the so-called hypernovae. This was finally demonstrated some months ago when astronomers, using the FORS instrument on ESO's Very Large Telescope (VLT), documented in unprecedented detail the changes in the spectrum of the light source ("the optical afterglow") of the gamma-ray burst GRB 030329 (cf. ESO PR 16/03). A conclusive and direct link between cosmological gamma-ray bursts and explosions of very massive stars was provided on this occasion. Gamma-Ray Burst GRB 030329 was discovered on March 29, 2003 by NASA's High Energy Transient Explorer spacecraft. Follow-up observations with the UVES spectrograph at the 8.2-m VLT KUEYEN telescope at the Paranal Observatory (Chile) showed the burst to have a redshift of 0.1685 [1]. This corresponds to a distance of about 2,650 million light-years, making GRB 030329 the second-nearest long-duration GRB ever detected. The proximity of GRB 030329 resulted in very bright afterglow emission, permitting the most extensive follow-up observations of any afterglow to date. A team of astronomers [2] led by Jochen Greiner of the Max-Planck-Institut für extraterrestrische Physik (Germany) decided to make use of this unique opportunity to study the

  7. The 2006-2007 Active Phase of Anomalous X-Ray Pulsar 4U 0142+61: Radiative and Timing Changes, Bursts,and Burst Spectral Features

    NASA Technical Reports Server (NTRS)

    Gavriil, Fotis P.; Dib, Rim; Kaspi, Victoria M.

    2011-01-01

    After at least 6 years of quiescence, Anomalous X-ray Pulsar (AXP) 4U 0142+61 entered an active phase in 2006 March that lasted several months and included six X-ray bursts as well as many changes in the persistent X-ray emission. The bursts, the first seen from this AXP in > 11 years of Rossi X-ray Timing Explorer monitoring, all occurred in the interval between 2006 April 6 and 2007 February 7. The burst durations ranged from 0.4 - 1.8 x 10(exp 3) s. The first five burst spectra are well modeled by blackbodies, with temperatures kT approx 2 - 9 keV. However, the sixth burst had a complicated spectrum that is well characterized by a blackbody plus two emission features whose amplitude varied throughout the burst. The most prominent feature was at 14.0 keV. Upon entry into the active phase the pulsar showed a significant change in pulse morphology and a likely timing glitch. The glitch had a total frequency jump of (1.9+/-0.4) x 10(exp -7) Hz, which recovered with a decay time of 17+/-2 days by more than the initial jump, implying a net spin-down of the pulsar. Within the framework of the magnetar model, the net spin-down of the star could be explained by regions of the superfluid that rotate. slower than the rest. The bursts, flux enhancements, and pulse morphology changes can be explained as arising from crustal deformations due to stresses imposed by the highly twisted internal magnetic field. However, unlike other AXP outbursts, we cannot account for a major twist being implanted in the magnetosphere.

  8. Cortical source of blink-related delta oscillations and their correlation with levels of consciousness.

    PubMed

    Bonfiglio, Luca; Olcese, Umberto; Rossi, Bruno; Frisoli, Antonio; Arrighi, Pieranna; Greco, Giovanni; Carozzo, Simone; Andre, Paolo; Bergamasco, Massimo; Carboncini, Maria Chiara

    2013-09-01

    Recently, blink-related delta oscillations (delta BROs) have been observed in healthy subjects during spontaneous blinking at rest. Delta BROs have been linked with continuous gathering of information from the surrounding environment, which is classically attributed to the precuneus. Furthermore, fMRI studies have shown that precuneal activity is reduced or missing when consciousness is low or absent. We therefore hypothesized that the source of delta BROs in healthy subjects could be located in the precuneus and that delta BROs could be absent or reduced in patients with disorders of consciousness (DOC). To test these hypotheses, electroencephalographic (EEG) activity at rest was recorded in 12 healthy controls and nine patients with DOC (four vegetative states, and five minimally conscious states). Three-second-lasting EEG epochs centred on each blink instance were analyzed in both time- (BROs) and frequency domains (event-related spectral perturbation or ERSP and intertrial coherence or ITC). Cortical sources of the maximum blink-related delta power, corresponding to the positive peak of the delta BROs, were estimated by standardized Low Resolution Electromagnetic Tomography. In control subjects, as expected, the source of delta BROs was located in the precuneus, whereas in DOC patients, delta BROs were not recognizable and no precuneal localization was possible. Furthermore, we observed a direct relationship between spectral indexes and levels of cognitive functioning in all subjects participating in the study. This reinforces the hypothesis that delta BROs reflect neural processes linked with awareness of the self and of the environment.

  9. The Case of the Disappearing Spindle Burst

    PubMed Central

    Tiriac, Alexandre; Blumberg, Mark S.

    2016-01-01

    Sleep spindles are brief cortical oscillations at 10–15 Hz that occur predominantly during non-REM (quiet) sleep in adult mammals and are thought to contribute to learning and memory. Spindle bursts are phenomenologically similar to sleep spindles, but they occur predominantly in early infancy and are triggered by peripheral sensory activity (e.g., by retinal waves); accordingly, spindle bursts are thought to organize neural networks in the developing brain and establish functional links with the sensory periphery. Whereas the spontaneous retinal waves that trigger spindle bursts in visual cortex are a transient feature of early development, the myoclonic twitches that drive spindle bursts in sensorimotor cortex persist into adulthood. Moreover, twitches—and their associated spindle bursts—occur exclusively during REM (active) sleep. Curiously, despite the persistence of twitching into adulthood, twitch-related spindle bursts have not been reported in adult sensorimotor cortex. This raises the question of whether such spindle burst activity does not occur in adulthood or, alternatively, occurs but has yet to be discovered. If twitch-related spindle bursts do occur in adults, they could contribute to the calibration, maintenance, and repair of sensorimotor systems. PMID:27119028

  10. Spectral evolution of gamma-ray bursts

    NASA Technical Reports Server (NTRS)

    Band, D.; Matteson, J.; Ford, L.; Schaefer, B.; Teegarden, B.; Cline, T.; Paciesas, W.; Pendleton, G.; Fishman, G.; Meegan, C.

    1992-01-01

    BATSE's Spectral Detectors provide a series of high resolution spectra over the duration of a gamma-ray burst; fits to these spectra show the evolution of the continuum as the burst progresses. The burst continuum can usually be fit by the spectral form AE sup alpha exp(-E/kT) from around 25 keV to more than 3 MeV, with varying trends in the value and evolution of the spectral parameters. As a result of limited statistics for E greater than 1 - 2 MeV in the individual spectra, a high energy power law is not required. Only long duration strong bursts can be studied by fitting a series of spectra, and therefore our conclusions concern only this class of burst. The bursts we analyzed tend to be characterized by a hard-to-soft trend both for individual intensity spikes and for the burst as a whole: the hardness leads the count rate in spectra which resolve the temporal variations, while the hardness of successive spikes decreases. We also summarize the performance of the Spectral Detectors and the development of analysis tools to date.

  11. The Relation Between Large-Scale Coronal Propagating Fronts and Type II Radio Bursts

    NASA Astrophysics Data System (ADS)

    Nitta, Nariaki V.; Liu, Wei; Gopalswamy, Nat; Yashiro, Seiji

    2014-12-01

    Large-scale, wave-like disturbances in extreme-ultraviolet (EUV) and type II radio bursts are often associated with coronal mass ejections (CMEs). Both phenomena may signify shock waves driven by CMEs. Taking EUV full-disk images at an unprecedented cadence, the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory has observed the so-called EIT waves or large-scale coronal propagating fronts (LCPFs) from their early evolution, which coincides with the period when most metric type II bursts occur. This article discusses the relation of LCPFs as captured by AIA with metric type II bursts. We show examples of type II bursts without a clear LCPF and fast LCPFs without a type II burst. Part of the disconnect between the two phenomena may be due to the difficulty in identifying them objectively. Furthermore, it is possible that the individual LCPFs and type II bursts may reflect different physical processes and external factors. In particular, the type II bursts that start at low frequencies and high altitudes tend to accompany an extended arc-shaped feature, which probably represents the 3D structure of the CME and the shock wave around it, and not just its near-surface track, which has usually been identified with EIT waves. This feature expands and propagates toward and beyond the limb. These events may be characterized by stretching of field lines in the radial direction and may be distinct from other LCPFs, which may be explained in terms of sudden lateral expansion of the coronal volume. Neither LCPFs nor type II bursts by themselves serve as necessary conditions for coronal shock waves, but these phenomena may provide useful information on the early evolution of the shock waves in 3D when both are clearly identified in eruptive events.

  12. Cell type-specific synaptic dynamics of synchronized bursting in the juvenile CA3 rat hippocampus.

    PubMed

    Aradi, Ildiko; Maccaferri, Gianmaria

    2004-10-27

    Spontaneous synchronous bursting of the CA3 hippocampus in vitro is a widely studied model of physiological and pathological network synchronization. The role of inhibitory conductances during network bursting is not understood in detail, despite the fact that several antiepileptic drugs target GABA(A) receptors. Here, we show that the first manifestation of a burst event is a cell type-specific flurry of GABA(A) receptor-mediated inhibitory input to pyramidal cells, but not to stratum oriens horizontal interneurons. Moreover, GABA(A) receptor-mediated synaptic input is proportionally smaller in these interneurons compared with pyramidal cells. Computational models and dynamic-clamp studies using experimentally derived conductance waveforms indicate that both these factors modulate spike timing during synchronized activity. In particular, the different kinetics and the larger strength of GABAergic input to pyramidal cells defer action potential initiation and contribute to the observed delay of firing, so that the interneuronal activity leads the burst cycle. In contrast, excitatory inputs to both neuronal populations during a burst are kinetically similar, as required to maintain synchronicity. We also show that the natural pattern of activation of inhibitory and excitatory conductances during a synchronized burst cycle is different within the same neuronal population. In particular, GABA(A) receptor-mediated currents activate earlier and outlast the excitatory components driving the bursts. Thus, cell type-specific balance and timing of GABA(A) receptor-mediated input are critical to set the appropriate spike timing in pyramidal cells and interneurons and coordinate additional neurotransmitter release modulating burst strength and network frequency.

  13. Artificial delta growth

    NASA Astrophysics Data System (ADS)

    Mikeš, Daniel

    2010-05-01

    A deltaic sedimentary system has a point source; sediment is carried over the delta plain by distributary channels away from the point source and deposited at the delta front by distributary mouth bars. The established methods to describe such a sedimentary system are "bedding analysis", "facies analysis", and "basin analysis". We shall call the ambient conditions "input" and the rock record "output". There exist a number of methods to deduce input from output, e.g. "Sequence stratigraphy" (a.o. Vail et al. 1977, Catuneanu et al. 2009), "Shoreline trajectory" (a.o. Helland-Hansen & Martinsen 1996, Helland-Hansen & Hampson 2009) on the one hand and the complex use of established techniques on the other (a.o. Miall & Miall 2001, Miall & Miall 2002). None of these deductive methods seems to be sufficient. I claim that the common errors in all these attempts are the following: (1) a sedimentary system is four-dimensional (3+1) and a lesser dimensional analysis is insufficient; (2) a sedimentary system is complex and any empirical/deductive analysis is non-unique. The proper approach to the problem is therefore the theoretical/inductive analysis. To that end we performed six scenarios of a scaled version of a passive margin delta in a flume tank. The scenarios have identical stepwise tectonic subsidence and semi-cyclic sealevel, but different supply curves, i.e. supply is: constant, highly-frequent, proportional to sealevel, inversely proportional to sealevel, lagging to sealevel, ahead of sealevel. The preliminary results are indicative. Lobe-switching occurs frequently and hence locally sedimentation occurs shortly and hiatuses are substantial; therefore events in 2D (+1) cross-sections don't correlate temporally. The number of sedimentary cycles disequals the number of sealevel cycles. Lobe-switching and stepwise tectonic subsidence cause onlap/transgression. Erosional unconformities are local diachronous events, whereas maximum flooding surfaces are regional

  14. Development report for dual-burst disks

    SciTech Connect

    Fusco, A.M.

    1996-11-01

    Burst disks, commonly used in pressure relief applications, were studied as single-use valves. A dual-burst disk design was chosen for primary investigation for systems involving separation of gases of two significantly different pressures. The two disks are used to seal either end of a piston cavity that has a different cross-sectional area on each side. Different piston surface areas are used to maintain hydrostatic equilibrium, P{sub 1}A{sub 1} = P{sub 2}A{sub 2}. The single-use valve functions when the downstream pressure is reduced to approximately atmospheric pressure, creating a pressure differential that causes the burst disks to fail. Several parameters were studied to determine the optimum design of the burst disk. These parameters include thickness, diameter, area/pressure ratio, scoring, and disk geometry. The disk material was limited to 304L stainless steel. Factors that were considered essential to the optimization of the design were robustness, manufacturability, and burst pressure variability. The thicknesses of the disks that were studied range from 0.003 in. to 0.010 in. A model for predicting burst pressures of the burst disks was derived. The model combines membrane stress theory with force/displacement data to predict the burst pressure of various designs to within {+-}10%. This model results from studies that characterize the behavior of individual small and large disks. Welding techniques used to join the dual-disk assembly are discussed. Laser welds are used to join and seal the disks to the bulkhead. These welds were optimized for repeatability and robustness. Resistance upset welding is suggested for joining the dual-disk assembly to the pressure vessel body. Resistance upset weld parameters were developed for this particular design so as to minimize the side effects on the burst-disk performance and to provide high-quality welds.

  15. Hydraulic Geometry of a tidally influenced delta channel network: the Mahakam Delta, East Kalimantan, Indonesia

    NASA Astrophysics Data System (ADS)

    Sassi, M.; Hoitink, A.; de Brye, B.; Deleersnijder, E.

    2011-12-01

    Hydraulic Geometry (HG) refers to relations between the characteristics of channels in a network, including mean depth, width, and bed slope, and the discharge conveyed by the channel during bank-full conditions. HG relations are of fundamental importance to water management in channel networks, and they bear an interesting relation with geomorphology. River delta channel networks typically scale according to HG relations such as log(A) ~ p*log(Q), where A is channel cross sectional area, Q water discharge, and the exponent p is in between 0.8 and 1.2. In tidal networks, the tidal prism or tidal discharge can be used, instead of a discharge with a constant frequency of occurrence. In the tidal case, the exponent often shows the same range of variation. Tidal rivers are intrinsically complex, as tidal propagation is influenced by river discharge and vice-versa. Consequently, channel geometry in tidally influenced river deltas may show a mixed scaling behavior of river and tidal channel networks, as the channel forming discharges may both be of river and tidal origin. In tidal regions, the tidal dynamics may lead to a cyclic variation in water discharge distribution at bifurcations, readily affecting HG relations. We present results from the Mahakam delta channel network in Indonesia, a tide-river dominated delta which has been prograding for 60 km over the last 5000 years. Bathymetric surveys were conducted over the distributary network and connected tidal channels. Based on a geomorphic analysis of the present distributary network, we show that channel geometry of the fluvial distributary network scales with bifurcation order. The bifurcation order does not feature a clear relation with bifurcate branch length or bifurcate width ratio, as in the case of river deltas. HG relations of the area of selected cross-sections are well represented by the tidal prism or by the river discharge, when scaled with the bifurcation order. Numerical simulations show that river

  16. Eddy current technique for predicting burst pressure

    DOEpatents

    Petri, Mark C.; Kupperman, David S.; Morman, James A.; Reifman, Jaques; Wei, Thomas Y. C.

    2003-01-01

    A signal processing technique which correlates eddy current inspection data from a tube having a critical tubing defect with a range of predicted burst pressures for the tube is provided. The method can directly correlate the raw eddy current inspection data representing the critical tubing defect with the range of burst pressures using a regression technique, preferably an artificial neural network. Alternatively, the technique deconvolves the raw eddy current inspection data into a set of undistorted signals, each of which represents a separate defect of the tube. The undistorted defect signal which represents the critical tubing defect is related to a range of burst pressures utilizing a regression technique.

  17. Transcriptional bursting explains the noise–versus–mean relationship in mRNA and protein levels

    SciTech Connect

    Dar, Roy; Shaffer, Sydney M.; Singh, Abhyudai; Razooky, Brandon S.; Simpson, Michael L.; Raj, Arjun; Weinberger, Leor S.

    2016-07-28

    Recent analysis demonstrates that the HIV-1 Long Terminal Repeat (HIV LTR) promoter exhibits a range of possible transcriptional burst sizes and frequencies for any mean-expression level. However, these results have also been interpreted as demonstrating that cell-tocell expression variability (noise) and mean are uncorrelated, a significant deviation from previous results. Here, we re-examine the available mRNA and protein abundance data for the HIV LTR and find that noise in mRNA and protein expression scales inversely with the mean along analytically predicted transcriptional burst-size manifolds. We then experimentally perturb transcriptional activity to test a prediction of the multiple burst-size model: that increasing burst frequency will cause mRNA noise to decrease along given burst-size lines as mRNA levels increase. In conclusion, the data show that mRNA and protein noise decrease as mean expression increases, supporting the canonical inverse correlation between noise and mean.

  18. Transcriptional bursting explains the noise–versus–mean relationship in mRNA and protein levels

    DOE PAGES

    Dar, Roy; Shaffer, Sydney M.; Singh, Abhyudai; ...

    2016-07-28

    Recent analysis demonstrates that the HIV-1 Long Terminal Repeat (HIV LTR) promoter exhibits a range of possible transcriptional burst sizes and frequencies for any mean-expression level. However, these results have also been interpreted as demonstrating that cell-tocell expression variability (noise) and mean are uncorrelated, a significant deviation from previous results. Here, we re-examine the available mRNA and protein abundance data for the HIV LTR and find that noise in mRNA and protein expression scales inversely with the mean along analytically predicted transcriptional burst-size manifolds. We then experimentally perturb transcriptional activity to test a prediction of the multiple burst-size model: thatmore » increasing burst frequency will cause mRNA noise to decrease along given burst-size lines as mRNA levels increase. In conclusion, the data show that mRNA and protein noise decrease as mean expression increases, supporting the canonical inverse correlation between noise and mean.« less

  19. Fanning the Flames: X-ray Burst Probes of Nuclear Burning

    NASA Astrophysics Data System (ADS)

    Mahmoodifar, Simin; Strohmayer, Tod

    2015-04-01

    Type I X-ray bursts are thermonuclear explosions observed in many accreting neutron stars (NSs) that result from rapid unstable burning of hydrogen and helium accreted onto the surface of the star. During an X-ray burst the X-ray flux rapidly rises by a factor of 10-20 in a couple of seconds and then decays on a longer timescale as the surface of the star cools. Oscillations have been detected during the rise and/or decay of some of these X-ray bursts that have frequencies within a few Hz of the stellar spin frequency and must be due to nonuniform emission from the stellar surface. Here I discuss the results of simulations of the rise and decay of a typical X-ray burst light curve and the evolution of their fractional oscillation amplitudes. We generate light curves using a physical model for a spreading hot spot, taking into account the effect of the Coriolis force (latitude-dependent flame spreading speed), as well as relativistic effects. I will explain how the combination of the light curve and fractional amplitude evolution can constrain the properties of the flame spreading, such as ignition latitude, which would be important for measuring NSs masses and radii using X-ray burst oscillations. I discuss the prospects for future X-ray missions such as ESA's LOFT in this area.

  20. The search for neutrino bursts from supernovae with Baksan underground scintillation telescope

    NASA Astrophysics Data System (ADS)

    Novoseltseva, R. V.; Boliev, M. M.; Dzaparova, I. M.; Kochkarov, M. M.; Novoseltsev, Yu. F.; Petkov, V. B.; Volchenko, V. I.; Volchenko, G. V.; Yanin, A. F.

    2016-11-01

    The current status of the experiment on recording neutrino bursts from core collapse stars is presented. The actual observational time is 29.76 years. An upper bound of the mean frequency of core collapse supernovae in our Galaxy is f col < 0.077 year-1 (90% CL).

  1. Distribution of the mutated delta 32 allele of the CCR5 gene in a Sicilian population.

    PubMed

    Sidoti, A; D'Angelo, R; Rinaldi, C; De Luca, G; Pino, F; Salpietro, C; Giunta, D E; Saltalamacchia, F; Amato, A

    2005-06-01

    The CCR5 gene encodes a cell-surface chemokine receptor molecule that serves as a co-receptor for macrophage-tropic strains of human immunodeficiency virus type 1 (HIV-1). A mutation in this gene may alter the expression or the function of the protein product, thereby altering chemokine binding and/or signalling or HIV-1 infection of cells that normally express CCR5 protein. Individuals homozygous for a 32-bp deletion allele of CCR5 (CCR5 delta32), heritable as a Mendelian trait, are relatively resistant to HIV-1 infection. The CCR5 delta32 mutation is present in the Caucasian population at different frequencies. The aim of this study was to investigate the frequency of truncated alleles of the CCR5 delta32 gene in a Sicilian population, as the interpopulation variation in CCR5 delta32 frequency may be a significant factor in the prediction of AIDS endemicity in future studies. We examined 901 healthy individuals from several Sicilian provinces. We found a mean (+/- standard deviation) delta32 allele frequency (fr) of 0.04 +/- 0.012. The highest value was observed in the province of Messina, with a mean delta32 allele frequency of 0.06 +/- 0.024, where we collected samples from a cohort of 114 HIV-1-infected individuals. The observed frequency amongst these patients was quite low (fr = 0.03 +/- 0.031) compared to the healthy population, although the difference was not statistically significant.

  2. A self-adapting approach for the detection of bursts and network bursts in neuronal cultures.

    PubMed

    Pasquale, Valentina; Martinoia, Sergio; Chiappalone, Michela

    2010-08-01

    Dissociated networks of neurons typically exhibit bursting behavior, whose features are strongly influenced by the age of the culture, by chemical/electrical stimulation or by environmental conditions. To help the experimenter in identifying the changes possibly induced by specific protocols, we developed a self-adapting method for detecting both bursts and network bursts from electrophysiological activity recorded by means of micro-electrode arrays. The algorithm is based on the computation of the logarithmic inter-spike interval histogram and automatically detects the best threshold to distinguish between inter- and intra-burst inter-spike intervals for each recording channel of the array. An analogous procedure is followed for the detection of network bursts, looking for sequences of closely spaced single-channel bursts. We tested our algorithm on recordings of spontaneous as well as chemically stimulated activity, comparing its performance to other methods available in the literature.

  3. Reliability of spike and burst firing in thalamocortical relay cells.

    PubMed

    Zeldenrust, Fleur; Chameau, Pascal J P; Wadman, Wytse J

    2013-12-01

    The reliability and precision of the timing of spikes in a spike train is an important aspect of neuronal coding. We investigated reliability in thalamocortical relay (TCR) cells in the acute slice and also in a Morris-Lecar model with several extensions. A frozen Gaussian noise current, superimposed on a DC current, was injected into the TCR cell soma. The neuron responded with spike trains that showed trial-to-trial variability, due to amongst others slow changes in its internal state and the experimental setup. The DC current allowed to bring the neuron in different states, characterized by a well defined membrane voltage (between -80 and -50 mV) and by a specific firing regime that on depolarization gradually shifted from a predominantly bursting regime to a tonic spiking regime. The filtered frozen white noise generated a spike pattern output with a broad spike interval distribution. The coincidence factor and the Hunter and Milton measure were used as reliability measures of the output spike train. In the experimental TCR cell as well as the Morris-Lecar model cell the reliability depends on the shape (steepness) of the current input versus spike frequency output curve. The model also allowed to study the contribution of three relevant ionic membrane currents to reliability: a T-type calcium current, a cation selective h-current and a calcium dependent potassium current in order to allow bursting, investigate the consequences of a more complex current-frequency relation and produce realistic firing rates. The reliability of the output of the TCR cell increases with depolarization. In hyperpolarized states bursts are more reliable than single spikes. The analytically derived relations were capable to predict several of the experimentally recorded spike features.

  4. Supersonic aerodynamics of delta wings

    NASA Technical Reports Server (NTRS)

    Wood, Richard M.

    1988-01-01

    Through the empirical correlation of experimental data and theoretical analysis, a set of graphs has been developed which summarize the inviscid aerodynamics of delta wings at supersonic speeds. The various graphs which detail the aerodynamic performance of delta wings at both zero-lift and lifting conditions were then employed to define a preliminary wing design approach in which both the low-lift and high-lift design criteria were combined to define a feasible design space.

  5. Activation of group I metabotropic glutamate receptors enhances persistent sodium current and rhythmic bursting in main olfactory bulb external tufted cells

    PubMed Central

    Ennis, Matthew

    2013-01-01

    Rhythmically bursting olfactory bulb external tufted (ET) cells are thought to play a key role in synchronizing glomerular network activity to respiratory-driven sensory input. Whereas spontaneous bursting in these cells is intrinsically generated by interplay of several voltage-dependent currents, bursting strength and frequency can be modified by local intrinsic and centrifugal synaptic input. Activation of metabotropic glutamate receptors (mGluRs) engages a calcium-dependent cation current (ICAN) that increases rhythmic bursting, but mGluRs may also modulate intrinsic mechanisms involved in bursting. Here, we used patch-clamp electrophysiology in rat olfactory bulb slices to investigate whether mGluRs modulate two key intrinsic currents involved in ET cell burst initiation: persistent sodium (INaP) and hyperpolarization-activated cation (Ih) currents. Using a BAPTA-based internal solution to block ICAN, we found that the mGluR1/5 agonist DHPG enhanced INaP but did not alter Ih. INaP enhancement consisted of increased current at membrane potentials between −60 and −50 mV and a hyperpolarizing shift in activation threshold. Both effects would be predicted to shorten the interburst interval. In agreement, DHPG modestly depolarized (∼3.5 mV) ET cells and increased burst frequency without effect on other major burst parameters. This increase was inversely proportional to the basal burst rate such that slower ET cells exhibited the largest increases. This may enable ET cells with slow intrinsic burst rates to pace with faster sniff rates. Taken with other findings, these results indicate that multiple neurotransmitter mechanisms are engaged to fine-tune rhythmic ET cell bursting to context- and state-dependent changes in sniffing frequency. PMID:24225539

  6. Bursting the Taylor cone bubble

    NASA Astrophysics Data System (ADS)

    Pan, Zhao; Truscott, Tadd

    2014-11-01

    A soap bubble fixed on a surface and placed in an electric field will take on the shape of a cone rather than constant curvature (dome) when the electrical field is not present. The phenomenon was introduced by J. Zeleny (1917) and studied extensively by C.T. Wilson & G.I. Taylor (1925). We revisit the Taylor cone problem by studying the deformation and bursting of soap bubbles in a point charge electric field. A single bubble takes on the shape of a cone in the electric field and a high-speed camera equipped with a micro-lens is used to observe the unsteady dynamics at the tip. Rupture occurs as a very small piece of the tip is torn away from the bubble toward the point charge. Based on experiments, a theoretical model is developed that predicts when rupture should occur. This study may help in the design of foam-removal techniques in engineering and provide a better understanding of an electrified air-liquid interface.

  7. Gamma-Ray Burst Progenitors

    NASA Astrophysics Data System (ADS)

    Levan, Andrew; Crowther, Paul; de Grijs, Richard; Langer, Norbert; Xu, Dong; Yoon, Sung-Chul

    2016-12-01

    We review our current understanding of the progenitors of both long and short duration gamma-ray bursts (GRBs). Constraints can be derived from multiple directions, and we use three distinct strands; (i) direct observations of GRBs and their host galaxies, (ii) parameters derived from modelling, both via population synthesis and direct numerical simulation and (iii) our understanding of plausible analog progenitor systems observed in the local Universe. From these joint constraints, we describe the likely routes that can drive massive stars to the creation of long GRBs, and our best estimates of the scenarios that can create compact object binaries which will ultimately form short GRBs, as well as the associated rates of both long and short GRBs. We further discuss how different the progenitors may be in the case of black hole engine or millisecond-magnetar models for the production of GRBs, and how central engines may provide a unifying theme between many classes of extremely luminous transient, from luminous and super-luminous supernovae to long and short GRBs.

  8. Gamma-ray burst cosmology

    NASA Astrophysics Data System (ADS)

    Wang, F. Y.; Dai, Z. G.; Liang, E. W.

    2015-08-01

    Gamma-ray bursts (GRBs) are the most luminous electromagnetic explosions in the Universe, which emit up to 8.8 × 1054 erg isotropic equivalent energy in the hard X-ray band. The high luminosity makes them detectable out to the largest distances yet explored in the Universe. GRBs, as bright beacons in the deep Universe, would be the ideal tool to probe the properties of high-redshift universe: including the cosmic expansion and dark energy, star formation rate, the reionization epoch and the metal enrichment history of the Universe. In this article, we review the luminosity correlations of GRBs, and implications for constraining the cosmological parameters and dark energy. Observations show that the progenitors of long GRBs are massive stars. So it is expected that long GRBs are tracers of star formation rate. We also review the high-redshift star formation rate derived from GRBs, and implications for the cosmic reionization history. The afterglows of GRBs generally have broken power-law spectra, so it is possible to extract intergalactic medium (IGM) absorption features. We also present the capability of high-redshift GRBs to probe the pre-galactic metal enrichment and the first stars.

  9. Overview Animation of Gamma-ray Burst

    NASA Video Gallery

    Gamma-ray bursts are the most luminous explosions in the cosmos. Astronomers think most occur when the core of a massive star runs out of nuclear fuel, collapses under its own weight, and forms a b...

  10. POPULATION SYNTHESIS AND GAMMA RAY BURST PROGENITORS

    SciTech Connect

    C. L. FREYER

    2000-12-11

    Population synthesis studies of binaries are always limited by a myriad of uncertainties from the poorly understood effects of binary mass transfer and common envelope evolution to the many uncertainties that still remain in stellar evolution. But the importance of these uncertainties depends both upon the objects being studied and the questions asked about these objects. Here I review the most critical uncertainties in the population synthesis of gamma-ray burst progenitors. With a better understanding of these uncertainties, binary population synthesis can become a powerful tool in understanding, and constraining, gamma-ray burst models. In turn, as gamma-ray bursts become more important as cosmological probes, binary population synthesis of gamma-ray burst progenitors becomes an important tool in cosmology.

  11. Expected Performance of the GLAST Burst Monitor

    NASA Technical Reports Server (NTRS)

    Meegan, Charles; Fishman, Gerald; Kouveliotou, Chryssa; Wilson-Hodge, Colleen; Paciesas, William; Preece, Robert; Briggs, Michael; Bhat, Narayana; Connaughton, Valerie; Greiner, Jochen; vonKienlin, Andreas; Diehl, Roland; Steinle, Helmut; Bissaldi, Elisabetta; Kippen, R. Marc

    2007-01-01

    The GLAST Burst Monitor (GBM) will enhance LAT observations of GRBs by extending the spectral coverage from the LAT threshold down to approx. 8 kev, and will provide a trigger for re-orienting the spacecraft to observe delayed emission from selected bursts outside the LAT field of view. GBM consists of twelve NaI scintillation detectors operating in the 8 kev to 1 MeV energy range and two BGO scintillation detectors operating in the 150 keV to 30 MeV energy range. Detector resolution, effective area, and angular response have been determined by calibrations. Analyses indicate that the on-board burst threshold will be approx. 0.7 photon/cm2/s and the on-board burst localization accuracy will typically be better than 8 degrees.

  12. Impulsive solar X-ray bursts

    NASA Technical Reports Server (NTRS)

    Crannell, C. J.; Frost, K. J.; Maetzler, C.; Ohki, K.; Saba, J. L.

    1977-01-01

    A set of 22 simple, impulsive solar flares, identified in the OSO-5 hard X-ray data, were analyzed together with coincident microwave and meterwave radio observations. The rise times and fall times of the X-ray bursts are found to be highly correlated and effectively equal, strongly suggesting a flare energizing mechanism that is reversible. The good time resolution available for these observations reveals that the microwave emission is influenced by an additional process, evident in the tendency of the microwave emission to peak later and decay more slowly than the symmetric X-ray bursts. Meterwave emission is observed in coincidence with the 5 events which show the strongest time correlation between the X-ray and microwave burst structure. This meterwave emission is characterized by U-burst radiation, indicating confinement of the flare source.

  13. The Gamma-Ray Burst Next Door

    NASA Technical Reports Server (NTRS)

    Wanjek, Christopher

    2003-01-01

    I hesitate to spawn a thousand bad sci-fi flicks, but here it goes: Scientists now say that some gamma-ray bursts, the most powerful explosions in the universe, originate in nearby galaxy clusters. If one were to occur nearby, it could wipe out life on Earth. Fortunately, the chances of mass extinction are slimmer than the Chicago Cubs meeting the Boston Red Sox in the World Series (. . . and the Red Sox winning). But a new analysis of over 1400 archived gamma-ray bursts reveals that about 100 bursts originated within 325 million light-years of Earth, and not billions of light-years away as previously thought. If so, there's no reason why a burst couldn't go off in our galaxy.

  14. NASA's Swift Sees 'Dual Personality' Burst

    NASA Video Gallery

    These animations illustrate two wildly different explanations for GRB 101225A, better known as the "Christmas burst." First, a solitary neutron star in our own galaxy shreds and accretes an approac...

  15. GLAST Burst Monitor Trigger Classification Algorithm

    NASA Technical Reports Server (NTRS)

    Perrin, D. J.; Sidman, E. D.; Meegan, C. A.; Briggs, M. S.; Connaughton, V.

    2004-01-01

    The Gamma Ray Large Area Space Telescope (GLAST), currently set for launch in the first quarter of 2007, will consist of two instruments, the GLAST Burst Monitor (GBM) and the Large Area Telescope (LAT). One of the goals of the GBM is to identify and locate gamma-ray bursts using on-board software. The GLAST observatory can then be re-oriented to allow observations by the LAT. A Bayesian analysis will be used to distinguish gamma-ray bursts from other triggering events, such as solar flares, magnetospheric particle precipitation, soft gamma repeaters (SGRs), and Cygnus X-1 flaring. The trigger parameters used in the analysis are the burst celestial coordinates, angle from the Earth's horizon, spectral hardness, and the spacecraft geomagnetic latitude. The algorithm will be described and the results of testing will be presented.

  16. Transverse Bursts in Inclined Layer Convection: Experiment

    NASA Astrophysics Data System (ADS)

    Daniels, Karen; Wiener, Richard; Bodenschatz, Eberhard

    2002-03-01

    We report experimental results on inclined layer convection in a fluid of Prandtl number σ ≈ 1. A codimension-two point divides regions of buoyancy-driven convection (longitudinal rolls) at lower angles from shear-driven convection (transverse rolls) at higher angles (Daniels et al. PRL 84: 5320, 2000). In the region of buoyancy-driven convection, near the codimension-two point, we observe longitudinal rolls with intermittent, localized, subharmonic transverse bursts. The patterns are spatiotemporally chaotic. With increasing temperature difference the bursts increase in duration and number. We examine the details of the bursting process (e.g. the energy of longitudinal, transverse, and mixed modes) and compare our results to bursting processes in other systems. This work is supported by the National Science Foundation under grant DMR-0072077 and the IGERT program in nonlinear systems, grant DGE-9870631.

  17. Optimal Codes for the Burst Erasure Channel

    NASA Technical Reports Server (NTRS)

    Hamkins, Jon

    2010-01-01

    Deep space communications over noisy channels lead to certain packets that are not decodable. These packets leave gaps, or bursts of erasures, in the data stream. Burst erasure correcting codes overcome this problem. These are forward erasure correcting codes that allow one to recover the missing gaps of data. Much of the recent work on this topic concentrated on Low-Density Parity-Check (LDPC) codes. These are more complicated to encode and decode than Single Parity Check (SPC) codes or Reed-Solomon (RS) codes, and so far have not been able to achieve the theoretical limit for burst erasure protection. A block interleaved maximum distance separable (MDS) code (e.g., an SPC or RS code) offers near-optimal burst erasure protection, in the sense that no other scheme of equal total transmission length and code rate could improve the guaranteed correctible burst erasure length by more than one symbol. The optimality does not depend on the length of the code, i.e., a short MDS code block interleaved to a given length would perform as well as a longer MDS code interleaved to the same overall length. As a result, this approach offers lower decoding complexity with better burst erasure protection compared to other recent designs for the burst erasure channel (e.g., LDPC codes). A limitation of the design is its lack of robustness to channels that have impairments other than burst erasures (e.g., additive white Gaussian noise), making its application best suited for correcting data erasures in layers above the physical layer. The efficiency of a burst erasure code is the length of its burst erasure correction capability divided by the theoretical upper limit on this length. The inefficiency is one minus the efficiency. The illustration compares the inefficiency of interleaved RS codes to Quasi-Cyclic (QC) LDPC codes, Euclidean Geometry (EG) LDPC codes, extended Irregular Repeat Accumulate (eIRA) codes, array codes, and random LDPC codes previously proposed for burst erasure

  18. Delta-opioid receptors mediate unique plasticity onto parvalbumin-expressing interneurons in area CA2 of the hippocampus.

    PubMed

    Piskorowski, Rebecca A; Chevaleyre, Vivien

    2013-09-04

    Inhibition is critical for controlling information transfer in the brain. However, the understanding of the plasticity and particular function of different interneuron subtypes is just emerging. Using acute hippocampal slices prepared from adult mice, we report that in area CA2 of the hippocampus, a powerful inhibitory transmission is acting as a gate to prevent CA3 inputs from driving CA2 neurons. Furthermore, this inhibition is highly plastic, and undergoes a long-term depression following high-frequency 10 Hz or theta-burst induction protocols. We describe a novel form of long-term depression at parvalbumin-expressing (PV+) interneuron synapses that is dependent on delta-opioid receptor (DOR) activation. Additionally, PV+ interneuron transmission is persistently depressed by DOR activation in area CA2 but only transiently depressed in area CA1. These results provide evidence for a differential temporal modulation of PV+ synapses between two adjacent cortical circuits, and highlight a new function of PV+ cells in controlling information transfer.

  19. A Non-Triggered Burst Supplement to the BATSE Gamma-Ray Burst Catalogs

    NASA Technical Reports Server (NTRS)

    Kommers, J.; Lewin, W. H.; Kouveliotou, C.; vanParadijs, J.; Pendleton, G. N.; Meegan, C. A.; Fishman, G. J.

    1998-01-01

    The Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory detects gamma-ray bursts (GRBs) with a real-time burst detection (or "trigger") system running onboard the spacecraft. Under some circumstances, however, a GRB may not activate the onboard burst trigger. For example, the burst may be too faint to exceed the onboard detection threshold, or it may occur while the onboard burst trigger is disabled for technical reasons. This paper is a catalog of such "non-triggered" GRBs that were detected in a search of the archival continuous data from BATSE. It lists 873 non-triggered bursts that were recorded between 1991 December 9.0 and 1997 December 17.0. For each burst, the catalog gives an estimated source direction, duration, peak flux, and fluence. Similar data are presented for 50 additional bursts of unknown origin that were detected in the 25-50 keV range; these events may represent the low-energy "tail" of the GRB spectral distribution. This catalog increases the number of GRBs detected with BATSE by 48% during the time period covered by the search.

  20. QoS-guaranteed burst transmission for VoIP service over optical burst switching networks

    NASA Astrophysics Data System (ADS)

    Tachibana, Takuji; Kasahara, Shoji

    2007-08-01

    We propose a burst transmission method that guarantees the voice over Internet protocol (VoIP) service. The proposed method consists of three techniques: round-robin burst assembly with slotted scheduling, priority control with void filling, and hop-based preemption. Each technique is utilized so that the burst loss probability and the burst transmission delay satisfy VoIP quality of service (QoS). We evaluate by simulation the performance of the proposed method in NSFNET with 14 nodes. Numerical examples show that our proposed method is effective for guaranteeing the VoIP QoS while accommodating a large number of VoIP users.

  1. Progress Report: Pressure Vessel Burst Test Study

    DTIC Science & Technology

    1994-08-01

    report is provided on a program developed to study through test and analysis, the characteristics of blast waves and fragmentation generated by ruptured ...vessels were composite overwrapped pressure vessels ( COPV ) and were cut with a shaped charge (no groove) around its center. The burst location on the...and the shaped charge cut area (shown with dotted lines). BURST INITIATION Longitudinal stress in the circumferential grooves (for developing axial

  2. Localizing the Fast Radio Burst 121102

    NASA Astrophysics Data System (ADS)

    Chatterjee, Shami; Wharton, Robert; Law, Casey J.; Hessels, Jason; Burke-Spolaor, Sarah; Bower, Geoffrey C.; Abruzzo, Matthew W.; Bassa, Cees; Butler, Bryan J.; Cordes, James M.; Paul, Demorest; Kaspi, Victoria M.; McLaughlin, Maura; Ransom, Scott M.; Scholz, Paul; Seymour, Andrew; Spitler, Laura; Tendulkar, Shriharsh P.; PALFA Survey Team; VLA+AO FRB121102 Simultaneous Campaign Team; EVN FRB121102 Campaign Team

    2017-01-01

    The precise localization of a fast radio burst and the identification of its host counterpart would allow constraints on their distances and energetics, and enable us to discriminate between various origin scenarios, from the local and mundane to the cosmological and exotic. Here we report on the results of an ongoing localization campaign on the repeating fast radio burst source, FRB 121102, with the VLA, Arecibo, and other telescopes.

  3. Gamma-Ray Burst Class Properties

    NASA Technical Reports Server (NTRS)

    Hakkila, Jon; Haglin, David J.; Pendleton, Geoffrey N.; Mallozzi, Robert S.; Meegan, Charles A.; Roiger, Richard J.

    2000-01-01

    Guided by the supervised pattern recognition algorithm C4.5 developed by Quinlan in 1986, we examine the three gamma-ray burst classes identified by Mukherjee et al. in 1998. C4.5 provides strong statistical support for this classification. However, with C4.5 and our knowledge of the Burst and Transient Source Experiment (BATSE) instrument, we demonstrate that class 3 (intermediate fluence, intermediate duration, soft) does not have to be a distinct source population: statistical/systematic errors in measuring burst attributes combined with the well-known hardness/intensity correlation can cause low peak flux class 1 (high fluence, long, intermediate hardness) bursts to take on class 3 characteristics naturally. Based on our hypothesis that the third class is not a distinct one, we provide rules so that future events can be placed in either class 1 or class 2 (low fluence, short, hard). We find that the two classes are relatively distinct on the basis of Band's work in 1993 on spectral parameters alpha, beta, and E (sub peak) alone. Although this does not indicate a better basis for classification, it does suggest that different physical conditions exist for class 1 and class 2 bursts. In the process of studying burst class characteristics, we identify a new bias affecting burst fluence and duration measurements. Using a simple model of how burst duration can be underestimated, we show how this fluence duration bias can affect BATSE measurements and demonstrate the type of effect it can have on the BATSE fluence versus peak flux diagram.

  4. Variable Protostellar Accretion with Episodic Bursts

    NASA Astrophysics Data System (ADS)

    Vorobyov, Eduard I.; Basu, Shantanu

    2015-06-01

    We present the latest development of the disk gravitational instability and fragmentation model, originally introduced by us to explain episodic accretion bursts in the early stages of star formation. Using our numerical hydrodynamics model with improved disk thermal balance and star-disk interaction, we computed the evolution of protostellar disks formed from the gravitational collapse of prestellar cores. In agreement with our previous studies, we find that cores of higher initial mass and angular momentum produce disks that are more favorable to gravitational instability and fragmentation, while a higher background irradiation and magnetic fields moderate the disk tendency to fragment. The protostellar accretion in our models is time-variable, thanks to the nonlinear interaction between different spiral modes in the gravitationally unstable disk, and can undergo episodic bursts when fragments migrate onto the star owing to the gravitational interaction with other fragments or spiral arms. Most bursts occur in the partly embedded Class I phase, with a smaller fraction taking place in the deeply embedded Class 0 phase and a few possible bursts in the optically visible Class II phase. The average burst duration and mean luminosity are found to be in good agreement with those inferred from observations of FUors. The model predicts the existence of two types of bursts: the isolated ones, showing well-defined luminosity peaks separated with prolonged periods (˜ {{10}4} yr) of quiescent accretion, and clustered ones, demonstrating several bursts occurring one after another during just a few hundred years. Finally, we estimate that 40%-70% of the star-forming cores can display bursts after forming a star-disk system.

  5. Search for absorption edges in superexpansion bursts

    NASA Astrophysics Data System (ADS)

    in't Zand, Jean

    2013-09-01

    Our goal is to measure with the LETGS a series of bright type-I X-ray bursts with strong photospheric radius expansion ('superexpansion') to search for absorption edges due to the ashes of nuclear burning. We request a quick TOO, to be triggered by ISS-MAXI and Swift-BAT, with a total exposure time of 100 ks to obtain the detection of about 10 bursts.

  6. GAMCIT: A gamma ray burst detector

    NASA Technical Reports Server (NTRS)

    Surka, Derek M.; Grunsfeld, John M.; Warneke, Brett A.

    1992-01-01

    The origin of celestial gamma ray bursts remains one of the great mysteries of modern astrophysics. The GAMCIT Get-Away-Special payload is designed to provide new and unique data in the search for the sources of gamma ray bursts. GAMCIT consists of three gamma ray detectors, an optical CCD camera, and an intelligent electronics system. This paper describes the major components of the system, including the electronics and structural designs.

  7. Supernovae and gamma-ray bursts connection

    SciTech Connect

    Valle, Massimo Della

    2015-12-17

    I’ll review the status of the Supernova/Gamma-Ray Burst connection. Several pieces of evidence suggest that long duration Gamma-ray Bursts are associated with bright SNe-Ic. However recent works suggest that GRBs might be produced in tight binary systems composed of a massive carbon-oxygen cores and a neutron star companion. Current estimates of the SN and GRB rates yield a ratio GRB/SNe-Ibc in the range ∼ 0.4% − 3%.

  8. Further observations of the burst source MXB 1728-34

    NASA Technical Reports Server (NTRS)

    Hoffman, J. A.; Lewin, W. H. G.; Doty, J.

    1977-01-01

    MXB 1728-34 has been observed by the SAS 3 observatory on eight occasions. It was bursting 95-100 per cent of the time, with burst intervals from 4 to 8 hr. The burst intervals were not correlated with the burst intensities. Seven relatively hard bursts occurring in July 1976 were all observed at energies up to about 30 keV. Following each of these bursts, enhanced X-ray emission was observed for several minutes, with a much softer spectrum than that of the bursts themselves. No periodic pulsations were observed from the associated steady source.

  9. High resolution observations with Artemis-IV and the NRH. I. Type IV associated narrow-band bursts

    NASA Astrophysics Data System (ADS)

    Bouratzis, C.; Hillaris, A.; Alissandrakis, C. E.; Preka-Papadema, P.; Moussas, X.; Caroubalos, C.; Tsitsipis, P.; Kontogeorgos, A.

    2016-02-01

    Context. Narrow-band bursts appear on dynamic spectra from microwave to decametric frequencies as fine structures with very small duration and bandwidth. They are believed to be manifestations of small scale energy release through magnetic reconnection. Aims: We analyzed 27 metric type IV events with embedded narrow-band bursts, which were observed by the ARTEMIS-IV radio spectrograph from 30 June 1999 to 1 August 2010. We examined the morphological characteristics of isolated narrow-band structures (mostly spikes) and groups or chains of structures. Methods: The events were recorded with the SAO high resolution (10 ms cadence) receiver of ARTEMIS-IV in the 270-450 MHz range. We measured the duration, spectral width, and frequency drift of ~12 000 individual narrow-band bursts, groups, and chains. Spike sources were imaged with the Nançay radioheliograph (NRH) for the event of 21 April 2003. Results: The mean duration of individual bursts at fixed frequency was ~100 ms, while the instantaneous relative bandwidth was ~2%. Some bursts had measurable frequency drift, either positive or negative. Quite often spikes appeared in chains, which were closely spaced in time (column chains) or in frequency (row chains). Column chains had frequency drifts similar to type-IIId bursts, while most of the row chains exhibited negative frequently drifts with a rate close to that of fiber bursts. From the analysis of NRH data, we found that spikes were superimposed on a larger, slowly varying, background component. They were polarized in the same sense as the background source, with a slightly higher degree of polarization of ~65%, and their size was about 60% of their size in total intensity. Conclusions: The duration and bandwidth distributions did not show any clear separation in groups. Some chains tended to assume the form of zebra, lace stripes, fiber bursts, or bursts of the type-III family, suggesting that such bursts might be resolved in spikes when viewed with high

  10. Physics of Gamma Ray Burst Sources

    NASA Technical Reports Server (NTRS)

    Meszaros, Peter

    2004-01-01

    During this grant period, the physics of gamma-ray bursts was investigated. A number of new results have emerged. The importance of pair formation in high compactness burst spectra may help explain x-ray flashes; a universal jet shape is a likely explanation for the distribution of jet break times; gravitational waves may be copiously produced both in short bursts from compact mergers and in long bursts arising from collapsars; x-ray iron lines are likely to be due to interaction with the stellar atmosphere of the progenitor; prompt optical flashes from reverse shocks will give diagnostics on the Lorentz factor and the environment; GeV and TeV emission from bursts may be expected in the external shock; etc. The group working with the PI included postdocs Dr. Bing Zhang (now assistant professor at University of Nevada); Dr. Shiho Kobayashi; graduate student Lijun Gou; collaborators Drs. Tim Kallman and Martin Rees. Meszaros shared with Rees and Dr. Bohan Paczynsky the AAS Rossi Prize in 2000 for their work on the theory of gamma ray bursts. The refereed publications and conference proceedings resulting from this research are summarized below. The PI gave a number of invited talks at major conferences, also listed.

  11. Phase analysis method for burst onset prediction

    NASA Astrophysics Data System (ADS)

    Stellino, Flavio; Mazzoni, Alberto; Storace, Marco

    2017-02-01

    The response of bursting neurons to fluctuating inputs is usually hard to predict, due to their strong nonlinearity. For the same reason, decoding the injected stimulus from the activity of a bursting neuron is generally difficult. In this paper we propose a method describing (for neuron models) a mechanism of phase coding relating the burst onsets with the phase profile of the input current. This relation suggests that burst onset may provide a way for postsynaptic neurons to track the input phase. Moreover, we define a method of phase decoding to solve the inverse problem and estimate the likelihood of burst onset given the input state. Both methods are presented here in a unified framework, describing a complete coding-decoding procedure. This procedure is tested by using different neuron models, stimulated with different inputs (stochastic, sinusoidal, up, and down states). The results obtained show the efficacy and broad range of application of the proposed methods. Possible applications range from the study of sensory information processing, in which phase-of-firing codes are known to play a crucial role, to clinical applications such as deep brain stimulation, helping to design stimuli in order to trigger or prevent neural bursting.

  12. Observational clues to the energy release process in impulsive solar bursts

    NASA Technical Reports Server (NTRS)

    Batchelor, David

    1990-01-01

    The nature of the energy release process that produces impulsive bursts of hard X-rays and microwaves during solar flares is discussed, based on new evidence obtained using the method of Crannell et al. (1978). It is shown that the hard X-ray spectral index gamma is negatively correlated with the microwave peak frequency, suggesting a common source for the microwaves and X-rays. The thermal and nonthermal models are compared. It is found that the most straightforward explanations for burst time behavior are shock-wave particle acceleration in the nonthermal model and thermal conduction fronts in the thermal model.

  13. Bayesian reconstruction of gravitational wave bursts using chirplets

    NASA Astrophysics Data System (ADS)

    Millhouse, Margaret; Cornish, Neil; Littenberg, Tyson

    2017-01-01

    The BayesWave algorithm has been shown to accurately reconstruct unmodeled short duration gravitational wave bursts and to distinguish between astrophysical signals and transient noise events. BayesWave does this by using a variable number of sine-Gaussian (Morlet) wavelets to reconstruct data in multiple interferometers. While the Morlet wavelets can be summed together to produce any possible waveform, there could be other wavelet functions that improve the performance. Because we expect most astrophysical gravitational wave signals to evolve in frequency, modified Morlet wavelets with linear frequency evolution - called chirplets - may better reconstruct signals with fewer wavelets. We compare the performance of BayesWave using Morlet wavelets and chirplets on a variety of simulated signals.

  14. Deltas of the Lake Malawi rift, east Africa: Seismic expression and exploration implications

    SciTech Connect

    Scholz, C.A.

    1995-11-01

    High-resolution, air-gun-sourced seismic reflection surveys over the offshore regions of five river deltas in Lake Malawi in the East African rift system reveal considerable variability in acoustic facies and stratigraphic architecture. This variability can largely be attributed to the influences of different structural settings, and to a lesser degree to high-amplitude (100-400 m) and high-frequency (1000 to 100,000 yr) fluctuations in lake level. Deltas on flexural and axial margins in the rift lake show well-developed progradational geometries. In contrast, a delta on a steep, accommodation zone margin distributes coarse sediments over a broad depositional apron, rather than concentrating sediment in discrete progradational lobes as on the other deltas. A large border fault margin river delta displays the most complex tectonic and stratigraphic architecture of all the deltas studied. It contains several delta-associated facies, including prograding clinoform packages, fan deltas stacked against a boundary fault, and extensive subaqueous fans. Flexural margin lowstand deltas may be the most prospective for hydrocarbon exploration due to their large, internally well-organized, progradational lobes and their close proximity to deep-water, high total organic carbon lacustrine source facies.

  15. Search for gravitational waves associated with the gamma ray burst GRB030329 using the LIGO detectors

    SciTech Connect

    Abbott, B.; Anderson, S.B.; Araya, M.; Armandula, H.; Asiri, F.; Barish, B.C.; Barnes, M.; Barton, M.A.; Bhawal, B.; Billingsley, G.; Black, E.; Blackburn, K.; Bogue, L.; Bork, R.; Busby, D.; Cardenas, L.; Chandler, A.; Chapsky, J.; Charlton, P.; Coyne, D.

    2005-08-15

    We have performed a search for bursts of gravitational waves associated with the very bright gamma ray burst GRB030329, using the two detectors at the LIGO Hanford Observatory. Our search covered the most sensitive frequency range of the LIGO detectors (approximately 80--2048 Hz), and we specifically targeted signals shorter than {approx_equal}150 ms. Our search algorithm looks for excess correlated power between the two interferometers and thus makes minimal assumptions about the gravitational waveform. We observed no candidates with gravitational-wave signal strength larger than a predetermined threshold. We report frequency-dependent upper limits on the strength of the gravitational waves associated with GRB030329. Near the most sensitive frequency region, around {approx_equal}250 Hz, our root-sum-square (RSS) gravitational-wave strain sensitivity for optimally polarized bursts was better than h{sub RSS}{approx_equal}6x10{sup -21} Hz{sup -1/2}. Our result is comparable to the best published results searching for association between gravitational waves and gamma ray bursts.

  16. Bursting phenomena as well as the bifurcation mechanism in a coupled BVP oscillator with periodic excitation

    NASA Astrophysics Data System (ADS)

    Xiaofang, Zhang; Lei, Wu; Qinsheng, Bi

    2016-07-01

    We explore the complicated bursting oscillations as well as the mechanism in a high-dimensional dynamical system. By introducing a periodically changed electrical power source in a coupled BVP oscillator, a fifth-order vector field with two scales in frequency domain is established when an order gap exists between the natural frequency and the exciting frequency. Upon the analysis of the generalized autonomous system, bifurcation sets are derived, which divide the parameter space into several regions associated with different types of dynamical behaviors. Two typical cases are focused on as examples, in which different types of bursting oscillations such as subHopf/subHopf burster, subHopf/fold-cycle burster, and double-fold/fold burster can be observed. By employing the transformed phase portraits, the bifurcation mechanism of the bursting oscillations is presented, which reveals that different bifurcations occurring at the transition between the quiescent states (QSs) and the repetitive spiking states (SPs) may result in different forms of bursting oscillations. Furthermore, because of the inertia of the movement, delay may exist between the locations of the bifurcation points on the trajectory and the bifurcation points obtained theoretically. Project supported by the National Natural Science Foundation of China (Grant No. 21276115).

  17. Modeling gamma-ray bursts

    NASA Astrophysics Data System (ADS)

    Maxham, Amanda

    Discovered serendipitously in the late 1960s, gamma-ray bursts (GRBs) are huge explosions of energy that happen at cosmological distances. They provide a grand physical playground to those who study them, from relativistic effects such as beaming, jets, shocks and blastwaves to radiation mechanisms such as synchrotron radiation to galatic and stellar populations and history. Through the Swift and Fermi space telescopes dedicated to observing GRBs over a wide range of energies (from keV to GeV), combined with accurate pinpointing that allows ground based follow-up observations in the optical, infrared and radio, a rich tapestry of GRB observations has emerged. The general picture is of a mysterious central engine (CE) probably composed of a black hole or neutron star that ejects relativistic shells of matter into intense magnetic fields. These shells collide and combine, releasing energy in "internal shocks" accounting for the prompt emission and flaring we see and the "external shock" or plowing of the first blastwave into the ambient surrounding medium has well-explained the afterglow radiation. We have developed a shell model code to address the question of how X-ray flares are produced within the framework of the internal shock model. The shell model creates randomized GRB explosions from a central engine with multiple shells and follows those shells as they collide, merge and spread, producing prompt emission and X-ray flares. We have also included a blastwave model, which can constrain X-ray flares and explain the origin of high energy (GeV) emission seen by the Fermi telescope. Evidence suggests that gamma-ray prompt emission and X-ray flares share a common origin and that at least some flares can only be explained by long-lasting central engine activity. We pay special attention to the time history of central engine activity, internal shocks, and observed flares. We calculate the gamma-ray (Swift/BAT band) and X-ray (Swift/XRT band) lightcurves for arbitrary

  18. Review of delta wing space shuttle vehicle dynamics

    NASA Technical Reports Server (NTRS)

    Reding, J. P.; Ericsson, L. E.

    1971-01-01

    The unsteady aerodynamics of the proposed delta planform, high cross range, shuttle orbiters, are investigated. It is found that these vehicles are subject to five unsteady-flow phenomena that could compromise the flight dynamics. The phenomena are as follows: (1) leeside shock-induced separation, (2) sudden leading-edge stall, (3) vortex burst, (4)bow shock-flap shock interaction, and (5) forebody vorticity. Trajectory shaping is seen as the most powerful means of avoiding deterimental effects of the stall phenomena; however, stall must be fixed or controlled when traversing the stall region. Other phenomana may be controlled by carefully programmed control deflections and some configuration modifications. Ways to alter the occurrence of the various flow conditions are explored.

  19. Dynamics of bow-tie shaped bursting: Forced pendulum with dynamic feedback

    NASA Astrophysics Data System (ADS)

    Hongray, Thotreithem; Balakrishnan, Janaki

    2016-12-01

    A detailed study is performed on the parameter space of the mechanical system of a driven pendulum with damping and constant torque under feedback control. We report an interesting bow-tie shaped bursting oscillatory behaviour, which is exhibited for small driving frequencies, in a certain parameter regime, which has not been reported earlier in this forced system with dynamic feedback. We show that the bursting oscillations are caused because of a transition of the quiescent state to the spiking state by a saddle-focus bifurcation, and because of another saddle-focus bifurcation, which leads to cessation of spiking, bringing the system back to the quiescent state. The resting period between two successive bursts (Trest) is estimated analytically.

  20. Dynamics of bow-tie shaped bursting: Forced pendulum with dynamic feedback.

    PubMed

    Hongray, Thotreithem; Balakrishnan, Janaki

    2016-12-01

    A detailed study is performed on the parameter space of the mechanical system of a driven pendulum with damping and constant torque under feedback control. We report an interesting bow-tie shaped bursting oscillatory behaviour, which is exhibited for small driving frequencies, in a certain parameter regime, which has not been reported earlier in this forced system with dynamic feedback. We show that the bursting oscillations are caused because of a transition of the quiescent state to the spiking state by a saddle-focus bifurcation, and because of another saddle-focus bifurcation, which leads to cessation of spiking, bringing the system back to the quiescent state. The resting period between two successive bursts (Trest) is estimated analytically.

  1. All-Sky Monitoring with the Fermi Gamma Ray Burst Monitor

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.

    2010-01-01

    We are currently monitoring the transient hard X-ray/soft gamma ray sky using the Gamma Ray Burst Monitor (GBM) on-board Fermi. The twelve GBM NaI detectors span 8 keV to 1MeV, while the two GBM BGO detectors span about 150 keV to 40 MeV. With GBM, we detect transient events on multiple timescales. Brief events, such as Gamma Ray Bursts, Solar flares, and magnetar bursts are detected with on-board triggers. On longer timescales, we use the Earth occultation technique to monitor a number of sources, including X-ray binaries, AGN, and solar flaring activity. To date we have detected 7 sources above 100 keV. Transient activity from accretion-powered pulsars is monitored using epoch-folding techniques. With GBM we track the pulsed flux and frequency for a number of pulsars. We will present highlights of GBM observations on various timescales.

  2. A Decameter Stationary Type IV Burst in Imaging Observations on 2014 September 6

    NASA Astrophysics Data System (ADS)

    Koval, Artem; Stanislavsky, Aleksander; Chen, Yao; Feng, Shiwei; Konovalenko, Aleksander; Volvach, Yaroslav

    2016-08-01

    First-of-its-kind radio imaging of a decameter solar stationary type IV radio burst has been presented in this paper. On 2014 September 6 the observations of type IV burst radio emission were carried out with the two-dimensional heliograph based on the Ukrainian T-shaped radio telescope (UTR-2), together with other telescope arrays. Starting at ˜09:55 UT and for ˜3 hr, the radio emission was kept within the observational session of UTR-2. The interesting observation covered the full evolution of this burst, “from birth to death.” During the event lifetime, two C-class solar X-ray flares with peak times 11:29 UT and 12:24 UT took place. The time profile of this burst in radio has a double-humped shape that can be explained by injection of energetic electrons, accelerated by the two flares, into the burst source. According to the heliographic observations, we suggest that the burst source was confined within a high coronal loop, which was part of a relatively slow coronal mass ejection. The latter has been developed for several hours before the onset of the event. Through analysis of about 1.5 × 106 heliograms (3700 temporal frames with 4096 images in each frame that correspond to the number of frequency channels), the radio burst source imaging shows a fascinating dynamical evolution. Both space-based (GOES, SDO, SOHO, STEREO) data and various ground-based instrumentation (ORFEES, NDA, RSTO, NRH) records have been used for this study.

  3. A biomechanical study on burst mechanisms of plant fruit: stress analysis of pericarps before bursting.

    PubMed

    Endo, Yasuhiro; Sakamoto, Jiro; Kashiwano, Yuki; Yokota, Hideo; Nakamura, Sakiko; Kinoshita, Eichiro

    2010-10-01

    Bursting of fruit is a very interesting biomechanical phenomenon because its mechanism is directly related to the plant's reproduction. A plant that produces fruit that bursts powerfully and spreads the seeds widely has the advantage of reproduction without relying on other mechanisms such as transportation of fruit by insects. The structures of many types of fruit have likely been optimized by evolution, although the structure itself appears rather simplistic. Strain energy is stored in each pericarp because of growth deformation, swelling or desiccation just before bursting. Throughout these changes, the mechanical stress of the pericarps is at equilibrium. At the instant of bursting, the stored strain energy is released very rapidly. Quick and wide motion of the pericarps in a certain direction is advantageous for throwing the seed a long distance. The motion and deformation of bursting pericarps depend on their tissue structure and mechanical stress condition just before the burst. We tracked the bursting motion by using a high-speed camera. Then we calculated the pre-burst stress generated in a pericarp of Impatiens by using the finite-element method. The boundary condition obtained by experiments using a high-speed video camera is given, and the stress was calculated using reverse deformation analysis. The stress distribution of the pericarp is effective in causing the pericarp motion to throw the seeds far away.

  4. A Nontriggered Burst Supplement to the BATSE Gamma-Ray Burst Catalogs

    NASA Technical Reports Server (NTRS)

    Kommers, Jefferson M.; Lewin, Walter H. G.; Kouveliotou, Chryssa; vanParadijs, Jan; Pendleton, Geoffrey N.; Meegan, Charles A.; Fishman, Gerald J.

    2001-01-01

    The Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory detects gamma-ray bursts (GRBs) with a real-time burst detection (or "trigger") system running onboard the spacecraft. Under some circumstances, however, a GRB may not activate the on-board burst trigger. For example, the burst may be too faint to exceed the on-board detection threshold, or it may occur while the on-board burst trigger is disabled for technical reasons. This paper describes a catalog of 873 "nontriggered" GRBs that were detected in a search of the archival continuous data from BATSE recorded between 1991 December 9.0 and 1997 December 17.0. For each burst, the catalog gives an estimated source direction, duration, peak flux, and fluence. Similar data are presented for 50 additional bursts of unknown origin that were detected in the 25-50 keV range; these events may represent the low-energy "tail" of the GRB spectral distribution. This catalog increases the number of GRBs detected with BATSE by 48% during the time period covered by the search.

  5. Spiky Fine Structure of Type III-like Radio Bursts in Absorption

    NASA Astrophysics Data System (ADS)

    Chernov, G. P.; Yan, Y. H.; Tan, C. M.; Chen, B.; Fu, Q. J.

    2010-03-01

    An uncommon fine structure in the radio spectrum consisting of bursts in absorption was observed with the Chinese Solar Broadband Radiospectrometer (SBRS) in the frequency range of 2.6 - 3.8 GHz during an X3.4/4B flare on 13 December 2006 in active region NOAA 10930 (S05W33). Usual fine structures in emission such as spikes, zebra stripes, and drifting fibers were observed at the peak of every new flare brightening. Within an hour at the decay phase of the event we observed bursts consisting of spikes in absorption, which pulsated periodically in frequency. Their instantaneous frequency bandwidths were found to be in the 75 MHz range. Moreover, in the strongest Type III-like bursts in absorption, the spikes showed stripes of the zebra-pattern (ZP) that drifted to higher frequencies. All spikes had the duration as short as down to the limit of the instrument resolution of ≈8 ms. The TRACE 195 Å images indicate that the magnetic reconnection at this moment occurred in the western edge of the flare loop arcade. Taking into account the presence of the reverse-drifting bursts in emission, in the course of the restoration of the magnetic structures in the corona, the acceleration of the beams of fast particles must have occurred both upward and downward at different heights. The upward beams will be captured by the magnetic trap, where the loss-cone distribution of fast particles (responsible for the emission of continuum and ZP) were formed. An additional injection of fast particles will fill the loss-cone later, breaking the loss-cone distribution. Therefore, the generation of continuum will be quenched at these moments, which was evidenced by the formation of bursts in absorption.

  6. The DELTA Synchrotron Light Interferometer

    SciTech Connect

    Berges, U.

    2004-05-12

    Synchrotron radiation sources like DELTA, the Dortmund Electron Accelerator, a third generation synchrotron light source, need an optical monitoring system to measure the beam size at different points of the ring with high resolution and accuracy. These measurements also allow an investigation of the emittance of the storage ring, an important working parameter for the efficiency of working beamlines with experiments using the synchrotron radiation. The resolution limits of the different types of optical synchrotron light monitors at DELTA are investigated. The minimum measurable beamsize with the normal synchrotron light monitor using visible light at DELTA is about 80 {mu}m. Due to this a synchrotron light interferometer was built up and tested at DELTA. The interferometer uses the same beamline in the visible range. The minimum measurable beamsize is with about 8 {mu}m one order of magnitude smaller. This resolution is sufficient for the expected small vertical beamsizes at DELTA. The electron beamsize and emittance were measured with both systems at different electron beam energies of the storage ring. The theoretical values of the present optics are smaller than the measured emittance. So possible reasons for beam movements are investigated.

  7. The capability of the existing network of installations for detecting the antineutrino burst from collapsing stars

    NASA Technical Reports Server (NTRS)

    Khalchukov, F. F.; Ryassny, V. G.; Ryazhskaya, O. G.; Zatsepin, G. T.

    1985-01-01

    As the neutrino fluxes can bring information from the internal layers of the collapsing star, the problem of the neutrino burst detection is of importance for both the direct registering of the collapse itself and the investigation of its dynamics. The main characteristics of the neutrino fluxes have been obtained by simulations. The total neutrino flux energy is estimated as 2.5 x 10 to the 53 to 1.4 x 10 to the 54 erg, the energy of NU sub E flux being 10 to the 53 erg. Predictions on neutrino energy spectra are quite different. Two models of the collapse will be used: the model by Bowers and Wilson, hereafter BW, and the model by Nadyozhin and Otroschenko (NO). The NU sub e spectrum in the BW-model reaches the maximum at E max sub NU = 8 MeV. Average energy of NU sub E E sub nu approx. = 10 MeV. The NO-model gives E max sub Nu = 10.5 MeV and E sub nu = 12.6 MeV. The NU sub E-burst duration is DELTA tau sub NU = 20s for the NO-model. As the black hole formation is the result of the star collapse in the BW-model, DELTA tau sub nu is taken to be 5s.

  8. The capability of the existing network of installations for detecting the antineutrino burst from collapsing stars

    NASA Astrophysics Data System (ADS)

    Khalchukov, F. F.; Ryassny, V. G.; Ryazhskaya, O. G.; Zatsepin, G. T.

    1985-08-01

    As the neutrino fluxes can bring information from the internal layers of the collapsing star, the problem of the neutrino burst detection is of importance for both the direct registering of the collapse itself and the investigation of its dynamics. The main characteristics of the neutrino fluxes have been obtained by simulations. The total neutrino flux energy is estimated as 2.5 x 10 to the 53 to 1.4 x 10 to the 54 erg, the energy of NUE flux being 10 to the 53 erg. Predictions on neutrino energy spectra are quite different. Two models of the collapse will be used: the model by Bowers and Wilson, hereafter BW, and the model by Nadyozhin and Otroschenko (NO). The NUe spectrum in the BW-model reaches the maximum at E maxNU = 8 MeV. Average energy of NUE Enu approx. = 10 MeV. The NO-model gives E maxNu = 10.5 MeV and Enu = 12.6 MeV. The NUE-burst duration is DELTA tauNU = 20s for the NO-model. As the black hole formation is the result of the star collapse in the BW-model, DELTA taunu is taken to be 5s.

  9. Type II Radio Bursts as an Indicator of CME Location

    NASA Astrophysics Data System (ADS)

    Quirk, C. A.; St Cyr, O. C.; Henning, C.; Xie, H.; Gilbert, H. R.; Orlove, M.; Gopalswamy, N.; Odstrcil, D.

    2011-12-01

    We examined a subset of nine low-frequency radio events with type II radio bursts that drifted below 2 megahertz and were detected by the WAVES investigation on the WIND spacecraft. For each event, we identified the associated coronal mass ejection (CME) and derived the electron density using a model of solar wind plasma frequency (fp ≈ 9 * ne1/2, where fp is plasma frequency in kHz and ne is electron density in cm-3) . We also used the pb_inverter program in SolarSoft developed by Howard and Hayes to examine the electron density structure. Expanding on the Van De Hulst process of inverting polarized brightness measurements, the program inverts total brightness measurements from SOHO LASCO images to extract electron density information. From the electron density inferred from radio spectra, we derived the location of the CME using five standard electron density to height models (Leblanc, 1996; Saito, 1977; Bougeret, 1984; Alvarez, 1973; and Fainberg, 1971). Using images from the LASCO instrument on SOHO and the SECCHI instrument on STEREO, we extracted locations of the leading edge of the CME and compared the heights and velocities to those found using the frequency data. For the lowest frequency events, we also compared our results to the outputs of ENLIL, a time-dependent, three-dimensional, MHD model of the heliosphere hosted by the Community Coordinated Modeling Center (CCMC) at NASA Goddard Space Flight Center.

  10. QKD-Based Secured Burst Integrity Design for Optical Burst Switched Networks

    NASA Astrophysics Data System (ADS)

    Balamurugan, A. M.; Sivasubramanian, A.; Parvathavarthini, B.

    2016-03-01

    The field of optical transmission has undergone numerous advancements and is still being researched mainly due to the fact that optical data transmission can be done at enormous speeds. It is quite evident that people prefer optical communication when it comes to large amount of data involving its transmission. The concept of switching in networks has matured enormously with several researches, architecture to implement and methods starting with Optical circuit switching to Optical Burst Switching. Optical burst switching is regarded as viable solution for switching bursts over networks but has several security vulnerabilities. However, this work exploited the security issues associated with Optical Burst Switching with respect to integrity of burst. This proposed Quantum Key based Secure Hash Algorithm (QKBSHA-512) with enhanced compression function design provides better avalanche effect over the conventional integrity algorithms.

  11. FRB121102: statistics of burst properties compared to the fast radio burst population

    NASA Astrophysics Data System (ADS)

    Seymour, Andrew; Michilli, Daniele; McLaughlin, Maura; Chatterjee, Shami; Hessel, Jason; Spolaor, Sarah; Paul, Demorest; Scholz, Paul; Spitler, Laura; Tendulkar, Shriharsh P.; PALFA Survey Team; VLA+AO FRB121102 Simultaneous Campaign Team; EVN FRB121102 Campaign Team

    2017-01-01

    Fast Radio Bursts (FRBs) are millisecond-long radio events with dispersion measures that exceed that expected from our Galaxy. Therefore the FRB source is anticipated to be extragalactic and highly energetic. Until recently, these were only observed as one-off events. This was until multiple bursts were observed at the Arecibo Observatory from FRB 121102. I will present the most recent burst statistics from FRB 121102's follow-up observations. Understanding the distribution of all burst characteristics can eliminate some of the proposed mechanisms to FRB 121102’s burst events. Not only that, comparing these values to the rest of the FRB population can give insight as to whether FRB 121102 is distinct from the rest of the FRB population.

  12. DEMETER observations of bursty MF emissions and their relation to ground-level auroral MF burst

    NASA Astrophysics Data System (ADS)

    Broughton, M. C.; LaBelle, J.; Parrot, M.

    2014-12-01

    A survey of medium frequency (MF) electric field data from selected orbits of the Detection of Electro-Magnetic Emissions Transmitted from Earthquakes (DEMETER) spacecraft reveals 68 examples of a new type of bursty MF emissions occurring at high latitudes associated with auroral phenomena. These resemble auroral MF burst, a natural radio emission observed at ground level near local substorm onsets. Similar to MF burst, the bursty MF waves observed by DEMETER have broadband, impulsive frequency structure covering 1.5-3.0 MHz, amplitudes of 50-100 μV/m, an overall occurrence rate of ˜0.76% with higher occurrence during active times, and strong correlation with auroral hiss. The magnetic local time distribution of the MF waves observed by DEMETER shows peak occurrence rate near 18 MLT, somewhat earlier than the equivalent peak in the occurrence rate of ground level MF burst, though propagation effects and differences in the latitudes sampled by the two techniques may explain this discrepancy. Analysis of solar wind and SuperMAG data suggests that while the bursty MF waves observed by DEMETER are associated with enhanced auroral activity, their coincidence with substorm onset may not be as exact as that of ground level MF burst. One conjunction occurs in which MF burst is observed at Churchill, Manitoba, within 8 min of MF emissions detected by DEMETER on field lines approximately 1000 km southeast of Churchill. These observations may plausibly be associated with the same auroral event detected by ground level magnetometers at several Canadian observatories. Although it is uncertain, the balance of the evidence suggests that the bursty MF waves observed with DEMETER are the same phenomenon as the ground level MF burst. Hence, theories of MF burst generation in the ionosphere, such as beam-generated Langmuir waves excited over a range of altitudes or strong Langmuir turbulence generating a range of frequencies within a narrow altitude range, need to be revisited to

  13. Dynamical structure of solar radio burst type III as evidence of energy of solar flares

    NASA Astrophysics Data System (ADS)

    Hamidi, Zety Sharizat Binti

    2013-11-01

    Observations of low frequency solar type III radio bursts associated with the ejection of plasma oscillations localized disturbance is due to excitation atoms in the plasma frequency incoherent radiations play a dominant role at the meter and decimeter wavelengths. Here, we report the results of the dynamical structure of solar flare type III that occurred on 9th March 2012 at National Space Centre, Sg Lang, Selangor, Malaysia by using the CALLISTO system. These bursts are associated with solar flare type M6 which suddenly ejected in the active region AR 1429 starting at 03:32 UT and ending at 05:00 UT with the peak at 04:12 UT. The observation showed an initial strong burst occurred due to strong signal at the beginning of the phase. We also found that both solar burst and flares tend to be a numerous on the same day and probability of chance coincidence is high. It is clearly seen that an impulsive lace burst was detected at 4:24 UT and it is more plausible that the energies are confined to the top of the loop when we compared with X-ray results. Associated with this event was type II with velocities 1285 km/s and type IV radio sweeps along with a full halo Coronal Mass Ejections (CMEs) first seen in SOHO/LASCO C2 imagery at 09/0426 Z. We concluded that the significance of study solar burst type III lies in the fact that the emission at decimetric wavelength comes from the role of magnetic field in active region that may provide the key to the energy release mechanism in a flare.

  14. Statistics of MF-Burst Emissions: Analysis of Data from South Pole Station and from Multiple Northern Hemisphere Stations

    NASA Astrophysics Data System (ADS)

    Labelle, J.; Jackson, E.; Tantiwiwat, M.; Linder, J.; Ye, S.; Weatherwax, A.

    2004-05-01

    Medium-frequency burst (MF-burst) is a broadband impulsive emission at 1-5 MHz observed at ground level during auroral substorm onsets [Weatherwax et al., 1994; LaBelle et al., 1997; review by LaBelle and Treumann, 2002]. Its amplitude is comparable to that of auroral hiss, with which it often coincides. Polarization measurements indicate that MF-burst propagates in the LO mode in the ionosphere [Shepherd et al., 1997], but aside from that its generation mechanism is unknown. In order to measure MF-burst and related auroral emissions, Dartmouth College operates LF/MF/HF radio receivers at South Pole Station and at various northern hemisphere observatories. South Pole is one of the best sites worldwide for observing MF-burst, because of the low level of man-made and natural noise in the 1-5 MHz band. This low noise level allows easy identification of events and semi-automatic data analysis; exploiting these, we present statistics of MF-burst amplitudes, frequencies, dates and local times of occurrence, etc., for one full year of data collected in 2003. To complement this single-station statistical study, we examine MF-burst data from 1997-8 when simultaneous data from up to five northern hemisphere stations, separated by 200-400 km north-south, exist. 80--90% of the MF-burst events occur at a single station; however, some events occur on up to four of the five stations simultaneously. In MF-burst emissions which occur at multiple stations, the onset of the emission often shifts poleward as the substorm onset progresses. We examine the statistics of this poleward shift in comparison to other substorm diagnostics. References: Weatherwax, A.T., J. LaBelle, and M.L. Trimpi, A new type of auroral radio emission at 1.4-3.7 MHz observed from the ground, Geophys. Res. Lett., 21, 2753, 1994. LaBelle, J., S.G. Shepherd, and M.L. Trimpi, Observations of auroral medium frequency burst emissions, J. Geophys. Res., 102, 22221, 1997. Shepherd, S.G., J. LaBelle, and M.L. Trimpi

  15. Serotonin-dependent kinetics of feeding bursts underlie a graded response to food availability in C. elegans.

    PubMed

    Lee, Kyung Suk; Iwanir, Shachar; Kopito, Ronen B; Scholz, Monika; Calarco, John A; Biron, David; Levine, Erel

    2017-02-01

    Animals integrate physiological and environmental signals to modulate their food uptake. The nematode C. elegans, whose food uptake consists of pumping bacteria from the environment into the gut, provides excellent opportunities for discovering principles of conserved regulatory mechanisms. Here we show that worms implement a graded feeding response to the concentration of environmental bacteria by modulating a commitment to bursts of fast pumping. Using long-term, high-resolution, longitudinal recordings of feeding dynamics under defined conditions, we find that the frequency and duration of pumping bursts increase and the duration of long pauses diminishes in environments richer in bacteria. The bioamine serotonin is required for food-dependent induction of bursts as well as for maintaining their high rate of pumping through two distinct mechanisms. We identify the differential roles of distinct families of serotonin receptors in this process and propose that regulation of bursts is a conserved mechanism of behaviour and motor control.

  16. Serotonin-dependent kinetics of feeding bursts underlie a graded response to food availability in C. elegans

    PubMed Central

    Lee, Kyung Suk; Iwanir, Shachar; Kopito, Ronen B.; Scholz, Monika; Calarco, John A.; Biron, David; Levine, Erel

    2017-01-01

    Animals integrate physiological and environmental signals to modulate their food uptake. The nematode C. elegans, whose food uptake consists of pumping bacteria from the environment into the gut, provides excellent opportunities for discovering principles of conserved regulatory mechanisms. Here we show that worms implement a graded feeding response to the concentration of environmental bacteria by modulating a commitment to bursts of fast pumping. Using long-term, high-resolution, longitudinal recordings of feeding dynamics under defined conditions, we find that the frequency and duration of pumping bursts increase and the duration of long pauses diminishes in environments richer in bacteria. The bioamine serotonin is required for food-dependent induction of bursts as well as for maintaining their high rate of pumping through two distinct mechanisms. We identify the differential roles of distinct families of serotonin receptors in this process and propose that regulation of bursts is a conserved mechanism of behaviour and motor control. PMID:28145493

  17. Simultaneous radio and X-ray observations of the X-ray burst source MXB 1636-53

    NASA Technical Reports Server (NTRS)

    Thomas, R. M.; Duldig, M. L.; Haynes, R. F.; Simons, L. W.; Murdin, P.; Hoffman, J. A.; Lewin, W. H. G.; Wheaton, W. A.; Doty, J.

    1979-01-01

    On June 17, 1977, the X-ray burst source MXB 1636-53 was simultaneously monitored for about 4 hr with the Parkes 64-m radio telescope at a frequency of 14.7 GHz and the SAS 3 X-ray satellite (1.3-12 keV). One X-ray burst was observed; an upper limit (2 sigmas) of 200 mJy is reported for any radio burst coincident with the X-ray event. During the X-ray burst the radio/X-ray time-integrated flux ratio was no more than 375 with a 90 percent confidence. An upper limit (2 sigmas) of 22 mJy was determined for any steady 14.7-GHz source coincident with the X-ray position.

  18. Transverse Bursts in Inclined Layer Convection: Theory

    NASA Astrophysics Data System (ADS)

    Bodenschatz, Eberhard; Brink, Jeandrew; Pesch, Werner

    2002-03-01

    We report theoretical and computational results on thermally driven inclined layer convection. For small Prandtl number fluids, experiments have reported bursting phenomena at both small angles, strong driving and high angles, weak driving (Daniels et al. PRL 84: 5320, 2000). Theoretically, the small angle, strong driving case was described by Clever and Busse (Physics of Fluids 12: 2137, 2000) and was connected to a subharmonic instability. At large angles, close to the codimension-two point, intermittent, localized, transverse subharmonic bursts occur at weak driving. Qualitatively, the bursts draw energy from the roll modes, exhaust them while growing, and die out when they are unable to find a new attractor. We investigate a connection between the small- and large-angle bursts. Using Galerkin methods and direct simulations of the underlying Boussinesq equations, we examine the extent to which they are related to a linear instability of the roll pattern. We address a possible connection to the shear flow turbulent bursts observed in Taylor-Couette flow. In addition, we present a theoretical analysis of the small Prandtl number case, for which the codimension-two point moves to zero angle. This work is supported by a Cornell Graduate Student Fellowship and by the National Science Foundation under grant DMR-0072077.

  19. GRB Catalog: Bursts from Vela to Swift

    NASA Technical Reports Server (NTRS)

    Angelini, L.

    2008-01-01

    Gamma ray burst (GRB) astronomy started when the first event was recorded on July 2, 1967 by Vela 4a and 4b. Since then many missions have flown experiments capable of detecting GRBs. The events collected by these older experiments are mostly available in paper copy, each containing a few ten to a few hundred bursts. No systematic effort in cataloging of these bursts has been available. In some cases the information is unpublished and in others difficult to retrieve. The first major GRB catalog was obtained by GRO with the BATSE experiment. It contains more than 2000 bursts and includes homogeneous information for each of the bursts. With the launch of Swift, the first Gamma-ray/X-ray mission dedicated to the study of GRBs and their afterglows, a wealth of information is collected by the Swift instrument as well as from ground-based telescopes. This talk will describe the efforts to create a comprehensive GRBCAT and its current status and future prospective.

  20. A proto-Okavango Delta?

    NASA Astrophysics Data System (ADS)

    Podgorski, J. E.; Kgotlhang, L.; Ngwisanyi, T.; Ploug, C.; Auken, E.; Kinzelbach, W. K.; Green, A. G.

    2010-12-01

    The Okavango Delta within the Kalahari Desert of northwestern Botswana is one of the world's largest inland deltas and the largest wetland in southern Africa. An annual flood originating from the Okavango River in the northwest passes through the upper panhandle region of the delta before inundating the 150 km x 150 km fan where most water is lost to evapotranspiration. The fan occupies an active graben at the southwestern end of the East Africa rift zone. The focus of faulting is along the fan’s southeastern end where the Kunyere-Thamalakane faults show 200-300 m of dip-slip offset, forming a backstop to the movement of water and sediments. An airborne TEM survey was flown over the entire delta in 2007 with 2 km line spacing. A preliminary inversion of the entire data set has been undertaken using a quasi-2D inversion scheme that includes resistivity, layer thickness, and transmitter height as parameters. Tests with a many-layer model indicate that a four-layer model explains the data. Inversion results are corroborated by limited borehole data. The TEM model includes significant lateral and vertical variations in electrical resistivity. In the central region of the fan, a near-surface high resistivity layer is underlain sequentially by a more conductive layer (about 100 m depth) and a more resistive half-space (about 160 m depth), the latter of which could be a fresh water aquifer. This resistive feature has a fan-like form. A plausible evolutionary scenario that explains the TEM data includes a proto-Okavango Delta (highly resistive half-space ) and a lake (intermediate-depth conductive layer). During a climatic episode similar to today’s, a proto-Okavango Delta sequence would have been deposited against a fault, much as the Kunyere-Thamalakane faults today delineate the southeastern margin of the present Okavango Delta. This region would have then been flooded by a Pleistocene lake system that inundated much of northern Botswana and was the source of

  1. New decoding methods of interleaved burst error-correcting codes

    NASA Astrophysics Data System (ADS)

    Nakano, Y.; Kasahara, M.; Namekawa, T.

    1983-04-01

    A probabilistic method of single burst error correction, using the syndrome correlation of subcodes which constitute the interleaved code, is presented. This method makes it possible to realize a high capability of burst error correction with less decoding delay. By generalizing this method it is possible to obtain probabilistic method of multiple (m-fold) burst error correction. After estimating the burst error positions using syndrome correlation of subcodes which are interleaved m-fold burst error detecting codes, this second method corrects erasure errors in each subcode and m-fold burst errors. The performance of these two methods is analyzed via computer simulation, and their effectiveness is demonstrated.

  2. The first BATSE gamma-ray burst catalog

    NASA Technical Reports Server (NTRS)

    Fishman, Gerald J.; Meegan, Charles A.; Wilson, Robert B.; Brock, Martin N.; Horack, John M.; Kouveliotou, Chryssa; Howard, Sethanne; Paciesas, William S.; Briggs, Michael S.; Pendleton, Geoffrey N.

    1994-01-01

    The Burst and Transient Source Experiment on the Compton Gamma-Ray Observatory detected 260 cosmic gamma-ray bursts during the period 19 Apr 1991 to 5 Mar 1992. This paper presents the occurrence times, locations, peak count rates, peak fluxes, fluences, durations, and plots of time histories for these bursts. The angular distribution is consistent with isotropy. The intensity distribution shows a deficit in the number of weak bursts, which is not consistent with a homogeneous distribution of burst sources in Euclidean space. The duration distribution shows evidence for a separate class of bursts with durations less than about 2 seconds.

  3. A continuum model of transcriptional bursting

    PubMed Central

    Corrigan, Adam M; Tunnacliffe, Edward; Cannon, Danielle; Chubb, Jonathan R

    2016-01-01

    Transcription occurs in stochastic bursts. Early models based upon RNA hybridisation studies suggest bursting dynamics arise from alternating inactive and permissive states. Here we investigate bursting mechanism in live cells by quantitative imaging of actin gene transcription, combined with molecular genetics, stochastic simulation and probabilistic modelling. In contrast to early models, our data indicate a continuum of transcriptional states, with a slowly fluctuating initiation rate converting the gene between different levels of activity, interspersed with extended periods of inactivity. We place an upper limit of 40 s on the lifetime of fluctuations in elongation rate, with initiation rate variations persisting an order of magnitude longer. TATA mutations reduce the accessibility of high activity states, leaving the lifetime of on- and off-states unchanged. A continuum or spectrum of gene states potentially enables a wide dynamic range for cell responses to stimuli. DOI: http://dx.doi.org/10.7554/eLife.13051.001 PMID:26896676

  4. Arc burst pattern analysis fault detection system

    NASA Technical Reports Server (NTRS)

    Russell, B. Don (Inventor); Aucoin, B. Michael (Inventor); Benner, Carl L. (Inventor)

    1997-01-01

    A method and apparatus are provided for detecting an arcing fault on a power line carrying a load current. Parameters indicative of power flow and possible fault events on the line, such as voltage and load current, are monitored and analyzed for an arc burst pattern exhibited by arcing faults in a power system. These arcing faults are detected by identifying bursts of each half-cycle of the fundamental current. Bursts occurring at or near a voltage peak indicate arcing on that phase. Once a faulted phase line is identified, a comparison of the current and voltage reveals whether the fault is located in a downstream direction of power flow toward customers, or upstream toward a generation station. If the fault is located downstream, the line is de-energized, and if located upstream, the line may remain energized to prevent unnecessary power outages.

  5. Gamma-Ray Burst Intensity Distributions

    NASA Technical Reports Server (NTRS)

    Band, David L.; Norris, Jay P.; Bonnell, Jerry T.

    2004-01-01

    We use the lag-luminosity relation to calculate self-consistently the redshifts, apparent peak bolometric luminosities L(sub B1), and isotropic energies E(sub iso) for a large sample of BATSE bursts. We consider two different forms of the lag-luminosity relation; for both forms the median redshift, for our burst database is 1.6. We model the resulting sample of burst energies with power law and Gaussian dis- tributions, both of which are reasonable models. The power law model has an index of a = 1.76 plus or minus 0.05 (95% confidence) as opposed to the index of a = 2 predicted by the simple universal jet profile model; however, reasonable refinements to this model permit much greater flexibility in reconciling predicted and observed energy distributions.

  6. Unveiling the secrets of gamma ray bursts

    NASA Astrophysics Data System (ADS)

    Gomboc, Andreja

    2012-07-01

    Gamma Ray Bursts are unpredictable and brief flashes of gamma rays that occur about once a day in random locations in the sky. Since gamma rays do not penetrate the Earth's atmosphere, they are detected by satellites, which automatically trigger ground-based telescopes for follow-up observations at longer wavelengths. In this introduction to Gamma Ray Bursts we review how building a multi-wavelength picture of these events has revealed that they are the most energetic explosions since the Big Bang and are connected with stellar deaths in other galaxies. However, in spite of exceptional observational and theoretical progress in the last 15 years, recent observations raise many questions which challenge our understanding of these elusive phenomena. Gamma Ray Bursts therefore remain one of the hottest topics in modern astrophysics.

  7. Prompt Radio Emission from Gamma Ray Bursts

    NASA Astrophysics Data System (ADS)

    Gotthardt, Noelle

    2010-02-01

    Gamma-ray bursts have been observed, but these enigmatic objects are yet unexplained. These short duration events are undoubtedly due to high-energy events. Fading optical emission and even radio emission has been observed from such events, but prompt radio emission from these events would be very useful in pinning down the physics of the bursts, the nature of the progenitor object,and possibly the medium in which it occurs. If these phenomena occur at large redshifts, there is the possibility that the observations could probe the Epoch of Reionization, or the intergalactic medium. A number of models have been proposed to explain the gamma-ray bursts, ranging from compact object mergers, to maser-like coherent emission. These models are not well constrained by current observations. Prompt radio emission may be detected by a transient radio array. I will discuss a planned search for such signals by the Eight-meter-wavelength Transient Array (ETA). )

  8. Fuzzy correlations of gamma-ray bursts

    NASA Technical Reports Server (NTRS)

    Hartmann, Dieter H.; Linder, Eric V.; Blumenthal, George R.

    1991-01-01

    The origin of gamma-ray bursts is not known, both in the sense of the nature of the source emitting the radiation and literally, the position of the burst on the sky. Lacking unambiguously identified counterparts in any wavelength band studied to date, statistical approaches are required to determine the burster distance scale. Angular correlation analysis is one of the most powerful tools in this regard. However, poor detector resolution gives large localization errors, effectively beam smearing the positions. The resulting fuzzy angular correlation function is investigated and the generic isotropization that smearing induces on any intrinsic clustering is discussed. In particular, the extent to which gamma-ray burst observations by the BATSE detector aboard the Gamma-Ray Observatory might recover an intrinsic source correlation is investigated.

  9. Theory of type IIIb solar radio bursts

    NASA Technical Reports Server (NTRS)

    Smith, R. A.; De La Noe, J.

    1976-01-01

    During the initial space-time evolution of an electron beam injected into the corona, the strong beam-plasma interaction occurs at the head of the beam, leading to the amplification of a quasi-monochromatic large-amplitude plasma wave that stabilizes by trapping the beam particles. Oscillation of the trapped particles in the wave troughs amplifies sideband electrostatic waves. The sidebands and the main wave subsequently decay to observable transverse electromagnetic waves through the parametric decay instability. This process gives rise to the elementary striation bursts. Owing to velocity dispersion in the beam and the density gradient of the corona, the entire process may repeat at a finite number of discrete plasma levels, producing chains of elementary bursts. All the properties of the type IIIb bursts are accounted for in the context of the theory.

  10. Interaction function of coupled bursting neurons

    NASA Astrophysics Data System (ADS)

    Xia, Shi; Jiadong, Zhang

    2016-06-01

    The interaction functions of electrically coupled Hindmarsh-Rose (HR) neurons for different firing patterns are investigated in this paper. By applying the phase reduction technique, the phase response curve (PRC) of the spiking neuron and burst phase response curve (BPRC) of the bursting neuron are derived. Then the interaction function of two coupled neurons can be calculated numerically according to the PRC (or BPRC) and the voltage time course of the neurons. Results show that the BPRC is more and more complicated with the increase of the spike number within a burst, and the curve of the interaction function oscillates more and more frequently with it. However, two certain things are unchanged: ϕ = 0, which corresponds to the in-phase synchronization state, is always the stable equilibrium, while the anti-phase synchronization state with ϕ = 0.5 is an unstable equilibrium. Project supported by the National Natural Science Foundation of China (Grant Nos. 11272065 and 11472061).

  11. Swift Burst Alert Telescope (BAT) Instrument Response

    NASA Technical Reports Server (NTRS)

    Parsons, A.; Hullinger, D.; Markwardt, C.; Barthelmy, S.; Cummings, J.; Gehrels, N.; Krimm, H.; Tueller, J.; Fenimore, E.; Palmer, D.

    2004-01-01

    The Burst Alert Telescope (BAT), a large coded aperture instrument with a wide field-of-view (FOV), provides the gamma-ray burst triggers and locations for the Swift Gamma-Ray Burst Explorer. In addition to providing this imaging information, BAT will perform a 15 keV - 150 keV all-sky hard x-ray survey based on the serendipitous pointings resulting from the study of gamma-ray bursts and will also monitor the sky for transient hard x-ray sources. For BAT to provide spectral and photometric information for the gamma-ray bursts, the transient sources and the all-sky survey, the BAT instrument response must be determined to an increasingly greater accuracy. In this talk, we describe the BAT instrument response as determined to an accuracy suitable for gamma-ray burst studies. We will also discuss the public data analysis tools developed to calculate the BAT response to sources at different energies and locations in the FOV. The level of accuracy required for the BAT instrument response used for the hard x-ray survey is significantly higher because this response must be used in the iterative clean algorithm for finding fainter sources. Because the bright sources add a lot of coding noise to the BAT sky image, fainter sources can be seen only after the counts due to the bright sources are removed. The better we know the BAT response, the lower the noise in the cleaned spectrum and thus the more sensitive the survey. Since the BAT detector plane consists of 32768 individual, 4 mm square CZT gamma-ray detectors, the most accurate BAT response would include 32768 individual detector response functions to separate mask modulation effects from differences in detector efficiencies! We describe OUT continuing work to improve the accuracy of the BAT instrument response and will present the current results of Monte Carlo simulations as well as BAT ground calibration data.

  12. Investigation of primordial black hole bursts using interplanetary network gamma-ray bursts

    DOE PAGES

    Ukwatta, Tilan Niranjan; Hurley, Kevin; MacGibbon, Jane H.; ...

    2016-07-25

    The detection of a gamma-ray burst (GRB) in the solar neighborhood would have very important implications for GRB phenomenology. The leading theories for cosmological GRBs would not be able to explain such events. The final bursts of evaporating primordial black holes (PBHs), however, would be a natural explanation for local GRBs. We present a novel technique that can constrain the distance to GRBs using detections from widely separated, non-imaging spacecraft. This method can determine the actual distance to the burst if it is local. We applied this method to constrain distances to a sample of 36 short-duration GRBs detected bymore » the Interplanetary Network (IPN) that show observational properties that are expected from PBH evaporations. These bursts have minimum possible distances in the 1013–1018 cm (7–105 au) range, which are consistent with the expected PBH energetics and with a possible origin in the solar neighborhood, although none of the bursts can be unambiguously demonstrated to be local. Furthermore, assuming that these bursts are real PBH events, we estimate lower limits on the PBH burst evaporation rate in the solar neighborhood.« less

  13. Investigation of primordial black hole bursts using interplanetary network gamma-ray bursts

    SciTech Connect

    Ukwatta, Tilan Niranjan; Hurley, Kevin; MacGibbon, Jane H.; Svinkin, D. S.; Aptekar, R. L.; Golenetskii, S. V.; Frederiks, D. D.; Pal'Shin, V. D.; Goldsten, J.; Boynton, W.; Kozyrev, A. S.; Rau, A.; von Kienlin, A.; Zhang, X.; Connaughton, V.; Yamaoka, K.; Ohno, M.; Ohmori, N.; Feroci, M.; Cline, T.; Gehrels, N.; Krimm, H. A.; McTiernan, J.

    2016-07-25

    The detection of a gamma-ray burst (GRB) in the solar neighborhood would have very important implications for GRB phenomenology. The leading theories for cosmological GRBs would not be able to explain such events. The final bursts of evaporating primordial black holes (PBHs), however, would be a natural explanation for local GRBs. We present a novel technique that can constrain the distance to GRBs using detections from widely separated, non-imaging spacecraft. This method can determine the actual distance to the burst if it is local. We applied this method to constrain distances to a sample of 36 short-duration GRBs detected by the Interplanetary Network (IPN) that show observational properties that are expected from PBH evaporations. These bursts have minimum possible distances in the 1013–1018 cm (7–105 au) range, which are consistent with the expected PBH energetics and with a possible origin in the solar neighborhood, although none of the bursts can be unambiguously demonstrated to be local. Furthermore, assuming that these bursts are real PBH events, we estimate lower limits on the PBH burst evaporation rate in the solar neighborhood.