BLAZAR SPECTRAL PROPERTIES AT 74 MHz

Energy Technology Data Exchange (ETDEWEB)

Massaro, F.; Funk, S. [SLAC National Laboratory and Kavli Institute for Particle Astrophysics and Cosmology, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States); Giroletti, M. [INAF Istituto di Radioastronomia, via Gobetti 101, I-40129 Bologna (Italy); Paggi, A.; D' Abrusco, R. [Harvard-Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Tosti, G. [Dipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia (Italy)

2013-10-01

Blazars are the most extreme class of active galactic nuclei. Despite a previous investigation at 102 MHz for a small sample of BL Lac objects and our recent analysis of blazars detected in the Westerbork Northern Sky Survey, a systematic study of the blazar spectral properties at frequencies below 100 MHz has been never carried out. In this paper, we present the first analysis of the radio spectral behavior of blazars based on the recent Very Large Array Low-frequency Sky Survey (VLSS) at 74 MHz. We search for blazar counterparts in the VLSS catalog, confirming that they are detected at 74 MHz. We then show that blazars present radio-flat spectra (i.e., radio spectral indices of ∼0.5) when evaluated, which also about an order of magnitude in frequency lower than previous analyses. Finally, we discuss the implications of our findings in the context of the blazars-radio galaxies connection since the low-frequency radio data provide a new diagnostic tool to verify the expectations of the unification scenario for radio-loud active galaxies.

Effective spectral index properties for Fermi blazars

Science.gov (United States)

Yang, JiangHe; Fan, JunHui; Liu, Yi; Zhang, YueLian; Tuo, ManXian; Nie, JianJun; Yuan, YuHai

2018-05-01

Blazars are a special subclass of active galactic nuclei with extreme observation properties. This subclass can be divided into two further subclasses of flat spectrum radio quasars (FSRQs) and BL Lacertae objects (BL Lacs) according to their emission line features. To compare the spectral properties of FSRQs and BL Lacs, the 1.4 GHz radio, optical R-band, 1 keV X-ray, and 1 GeV γ-ray flux densities for 1108 Fermi blazars are calculated to discuss the properties of the six effective spectral indices of radio to optical ( α RO), radio to X-ray ( α RX), radio to γ ray ( α Rγ), optical to X-ray ( α OX), optical to γ ray ( α Oγ), and X-ray to γ ray ( α Xγ). The main results are as follows: For the averaged effective spectral indices, \\overline {{α _{OX}}} > \\overline {{α _{Oγ }}} > \\overline {{α _{Xγ }}} > \\overline {{α _{Rγ }}} > \\overline {{α _{RX}}} > \\overline {{α _{RO}}} for samples of whole blazars and BL Lacs; \\overline {{α _{Xγ }}} ≈ \\overline {{α _{Rγ }}} ≈ \\overline {{α _{RX}}} for FSRQs and low-frequency-peaked BL Lacs (LBLs); and \\overline {{α _{OX}}} ≈ \\overline {{α _{Oγ }}} ≈ \\overline {{α _{Xγ }}} for high-synchrotron-frequency-peaked BL Lacs (HBLs). The distributions of the effective spectral indices involving optical emission ( α RO, α OX, and α Oγ) for LBLs are different from those for FSRQs, but if the effective spectral index does not involve optical emission ( α RX, α Rγ, and α Xγ), the distributions for LBLs and FSRQs almost come from the same parent population. X-ray emissions from blazars include both synchrotron and inverse Compton (IC) components; the IC component for FSRQs and LBLs accounts for a larger proportion than that for HBLs; and the radiation mechanism for LBLs is similar to that for FSRQs, but the radiation mechanism for HBLs is different from that for both FSRQs and LBLs in X-ray bands. The tendency of α Rγ decreasing from LBLs to HBLs suggests that the synchrotron self

Discovery and characterization of the first low-peaked and intermediate-peaked BL Lacertae objects in the very high energy {gamma}-ray regime

Energy Technology Data Exchange (ETDEWEB)

Berger, Karsten

2009-12-19

20 years after the discovery of the Crab Nebula as a source of very high energy {gamma}-rays, the number of sources newly discovered above 100 GeV using ground-based Cherenkov telescopes has considerably grown, at the time of writing of this thesis to a total of 81. The sources are of different types, including galactic sources such as supernova remnants, pulsars, binary systems, or so-far unidentified accelerators and extragalactic sources such as blazars and radio galaxies. The goal of this thesis work was to search for {gamma}-ray emission from a particular type of blazars previously undetected at very high {gamma}-ray energies, by using the MAGIC telescope. Those blazars previously detected were all of the same type, the so-called high-peaked BL Lacertae objects. The sources emit purely non-thermal emission, and exhibit a peak in their radio-to-X-ray spectral energy distribution at X-ray energies. The entire blazar population extends from these rare, low-luminosity BL Lacertae objects with peaks at X-ray energies to the much more numerous, high-luminosity infrared-peaked radio quasars. Indeed, the low-peaked sources dominate the source counts obtained from space-borne observations at {gamma}-ray energies up to 10 GeV. Their spectra observed at lower {gamma}-ray energies show power-law extensions to higher energies, although theoretical models suggest them to turn over at energies below 100 GeV. This opened the quest for MAGIC as the Cherenkov telescope with the currently lowest energy threshold. In the framework of this thesis, the search was focused on the prominent sources BL Lac, W Comae and S5 0716+714, respectively. Two of the sources were unambiguously discovered at very high energy {gamma}-rays with the MAGIC telescope, based on the analysis of a total of about 150 hours worth of data collected between 2005 and 2008. The analysis of this very large data set required novel techniques for treating the effects of twilight conditions on the data quality

Discovery and characterization of the first low-peaked and intermediate-peaked BL Lacertae objects in the very high energy γ-ray regime

International Nuclear Information System (INIS)

Berger, Karsten

2009-01-01

20 years after the discovery of the Crab Nebula as a source of very high energy γ-rays, the number of sources newly discovered above 100 GeV using ground-based Cherenkov telescopes has considerably grown, at the time of writing of this thesis to a total of 81. The sources are of different types, including galactic sources such as supernova remnants, pulsars, binary systems, or so-far unidentified accelerators and extragalactic sources such as blazars and radio galaxies. The goal of this thesis work was to search for γ-ray emission from a particular type of blazars previously undetected at very high γ-ray energies, by using the MAGIC telescope. Those blazars previously detected were all of the same type, the so-called high-peaked BL Lacertae objects. The sources emit purely non-thermal emission, and exhibit a peak in their radio-to-X-ray spectral energy distribution at X-ray energies. The entire blazar population extends from these rare, low-luminosity BL Lacertae objects with peaks at X-ray energies to the much more numerous, high-luminosity infrared-peaked radio quasars. Indeed, the low-peaked sources dominate the source counts obtained from space-borne observations at γ-ray energies up to 10 GeV. Their spectra observed at lower γ-ray energies show power-law extensions to higher energies, although theoretical models suggest them to turn over at energies below 100 GeV. This opened the quest for MAGIC as the Cherenkov telescope with the currently lowest energy threshold. In the framework of this thesis, the search was focused on the prominent sources BL Lac, W Comae and S5 0716+714, respectively. Two of the sources were unambiguously discovered at very high energy γ-rays with the MAGIC telescope, based on the analysis of a total of about 150 hours worth of data collected between 2005 and 2008. The analysis of this very large data set required novel techniques for treating the effects of twilight conditions on the data quality. This was successfully achieved

Compact high voltage, high peak power, high frequency transformer for converter type modulator applications.

Science.gov (United States)

Reghu, T; Mandloi, V; Shrivastava, Purushottam

2016-04-01

The design and development of a compact high voltage, high peak power, high frequency transformer for a converter type modulator of klystron amplifiers is presented. The transformer has been designed to operate at a frequency of 20 kHz and at a flux swing of ±0.6 T. Iron (Fe) based nanocrystalline material has been selected as a core for the construction of the transformer. The transformer employs a specially designed solid Teflon bobbin having 120 kV insulation for winding the high voltage secondary windings. The flux swing of the core has been experimentally found by plotting the hysteresis loop at actual operating conditions. Based on the design, a prototype transformer has been built which is per se a unique combination of high voltage, high frequency, and peak power specifications. The transformer was able to provide 58 kV (pk-pk) at the secondary with a peak power handling capability of 700 kVA. The transformation ratio was 1:17. The performance of the transformer is also presented and discussed.

Signature of inverse Compton emission from blazars

Science.gov (United States)

Gaur, Haritma; Mohan, Prashanth; Wierzcholska, Alicja; Gu, Minfeng

2018-01-01

Blazars are classified into high-, intermediate- and low-energy-peaked sources based on the location of their synchrotron peak. This lies in infra-red/optical to ultra-violet bands for low- and intermediate-peaked blazars. The transition from synchrotron to inverse Compton emission falls in the X-ray bands for such sources. We present the spectral and timing analysis of 14 low- and intermediate-energy-peaked blazars observed with XMM-Newton spanning 31 epochs. Parametric fits to X-ray spectra help constrain the possible location of transition from the high-energy end of the synchrotron to the low-energy end of the inverse Compton emission. In seven sources in our sample, we infer such a transition and constrain the break energy in the range 0.6-10 keV. The Lomb-Scargle periodogram is used to estimate the power spectral density (PSD) shape. It is well described by a power law in a majority of light curves, the index being flatter compared to general expectation from active galactic nuclei, ranging here between 0.01 and 1.12, possibly due to short observation durations resulting in an absence of long-term trends. A toy model involving synchrotron self-Compton and external Compton (EC; disc, broad line region, torus) mechanisms are used to estimate magnetic field strength ≤0.03-0.88 G in sources displaying the energy break and infer a prominent EC contribution. The time-scale for variability being shorter than synchrotron cooling implies steeper PSD slopes which are inferred in these sources.

The Study on the Physical Properties of Blazar Jets

Science.gov (United States)

Kang, S. J.

2017-09-01

of LSP blazars is the same as that of FR IIs, we find that it is an electron-positron pair dominated leptonic jet in these blazars, and the number density of electron-positron pairs is several times higher than that of electron-proton pairs, but the jet power is still dominated by protons. For the high-synchrotron-peaked (HSP) BL Lac PKS 1424+240, the SED fitting with the synchrotron self-Compton (SSC) model gave unreasonable fitting parameters (e.g., a very large Doppler factor δ). In this work, we take into account the possible external soft photon field, and then fit the multi-waveband SEDs of blazar PKS 1424+240 with one-zone leptonic jet models in both states. We find the SSC+external-Compton (EC) model can give a better fitting result if the EC process is included. However, the needed energy density of external soft photon field (U_{ext}) is much lower than the typical value. This result is consistent with the results of some other BL Lacs, where the BLR or torus is very weak or disappearing. It means that there is evolution of the energy density of external soft photon field with decreasing of the luminosity of blazars (the flat spectrum radio quasars (FSRQs)-BL Lac: low energy peaked BL Lac (LBL)-intermediate energy peaked BL Lac (IBL)-high energy peaked BL Lac (HBL)). And on this basis, in the chapter 5, we further explore the possible evolution of the external soft photon field of blazars based on the EC process. We employ the one-zone homogeneous leptonic jet model and χ2 procedure to fit simultaneously or quasi-simultaneously multi-waveband SEDs for a sample of blazars with a wide distribution of luminosities. In our model, we set Uext as a free parameter. Studying the energy density of the external photon field in different subclasses of blazars, we find: (1) the Uext of the high luminosity blazar (FSRQs and LBLs) keeps roughly as a constant, which is, however, smaller than that constrained from BLR observations. Assuming IR as the source of soft

BLAZAR ANTI-SEQUENCE OF SPECTRAL VARIATION WITHIN INDIVIDUAL BLAZARS: CASES FOR MRK 501 AND 3C 279

Energy Technology Data Exchange (ETDEWEB)

Zhang, Jin; Zhang, Shuang-Nan; Liang, En-Wei, E-mail: zhang.jin@hotmail.com [National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

2013-04-10

The jet properties of Mrk 501 and 3C 279 are derived by fitting broadband spectral energy distributions (SEDs) with lepton models. The derived {gamma}{sub b} (the break Lorenz factor of the electron distribution) is 10{sup 4}-10{sup 6} for Mrk 501 and 200 {approx} 600 for 3C 279. The magnetic field strength (B) of Mrk 501 is usually one order of magnitude lower than that of 3C 279, but their Doppler factors ({delta}) are comparable. A spectral variation feature where the peak luminosity is correlated with the peak frequency, which is opposite from the blazar sequence, is observed in the two sources. We find that (1) the peak luminosities of the two bumps in the SEDs for Mrk 501 depend on {gamma}{sub b} in both the observer and co-moving frames, but they are not correlated with B and {delta} and (2) the luminosity variation of 3C 279 is dominated by the external Compton (EC) peak and its peak luminosity is correlated with {gamma}{sub b} and {delta}, but anti-correlated with B. These results suggest that {gamma}{sub b} may govern the spectral variation of Mrk 501 and {delta} and B would be responsible for the spectral variation of 3C 279. The narrow distribution of {gamma}{sub b} and the correlation of {gamma}{sub b} and B in 3C 279 would be due to the cooling from the EC process and the strong magnetic field. Based on our brief discussion, we propose that this spectral variation feature may originate from the instability of the corona but not from the variation of the accretion rate as does the blazar sequence.

Core shift effect in blazars

Science.gov (United States)

Agarwal, A.; Mohan, P.; Gupta, Alok C.; Mangalam, A.; Volvach, A. E.; Aller, M. F.; Aller, H. D.; Gu, M. F.; Lähteenmäki, A.; Tornikoski, M.; Volvach, L. N.

2017-07-01

We studied the pc-scale core shift effect using radio light curves for three blazars, S5 0716+714, 3C 279 and BL Lacertae, which were monitored at five frequencies (ν) between 4.8 and 36.8 GHz using the University of Michigan Radio Astronomical Observatory (UMRAO), the Crimean Astrophysical Observatory (CrAO) and Metsähovi Radio Observatory for over 40 yr. Flares were Gaussian fitted to derive time delays between observed frequencies for each flare (Δt), peak amplitude (A) and their half width. Using A ∝ να, we infer α in the range of -16.67-2.41 and using Δ t ∝ ν ^{1/k_r}, we infer kr ∼ 1, employed in the context of equipartition between magnetic and kinetic energy density for parameter estimation. From the estimated core position offset (Ωrν) and the core radius (rcore), we infer that opacity model may not be valid in all cases. The mean magnetic field strengths at 1 pc (B1) and at the core (Bcore) are in agreement with previous estimates. We apply the magnetically arrested disc model to estimate black hole spins in the range of 0.15-0.9 for these blazars, indicating that the model is consistent with expected accretion mode in such sources. The power-law-shaped power spectral density has slopes -1.3 to -2.3 and is interpreted in terms of multiple shocks or magnetic instabilities.

The broadband spectral energy distributions of SDSS blazars

Science.gov (United States)

Li, Huai-Zhen; Chen, Luo-En; Jiang, Yun-Guo; Yi, Ting-Feng

2015-07-01

We compiled the radio, optical and X-ray data of blazars from the Sloan Digital Sky Survey database, and presented the distribution of luminosities and broadband spectral indices. The distribution of luminosities shows that the averaged luminosity of flat spectrum radio quasars (FSRQs) is larger than that of BL Lacertae (BL Lac) objects. On the other hand, the broadband spectral energy distribution reveals that FSRQs and low energy peaked BL Lac objects have similar spectral properties, but high energy peaked BL Lac objects have a distinct spectral property. This may be due to the fact that different subclasses of blazars have different intrinsic environments and are at different cooling levels. Even so, a unified scheme is also revealed from the color-color diagram, which hints that there are similar physical processes operating in all objects under a range of intrinsic physical conditions or beaming parameters. Supported by the National Natural Science Foundation of China.

THE SPECTRAL INDEX PROPERTIES OF FERMI BLAZARS

Energy Technology Data Exchange (ETDEWEB)

Fan, J. H.; Yang, J. H.; Yuan, Y. H.; Wang, J.; Gao, Y., E-mail: jhfan_cn@yahoo.com.cn [Center for Astrophysics, Guangzhou University, Guangzhou 510006 (China)

2012-12-20

In this paper, a sample of 451 blazars (193 flat spectrum radio quasars (FSRQs), 258 BL Lacertae objects) with corresponding X-ray and Fermi {gamma}-ray data is compiled to investigate the correlation both between the X-ray spectral index and the {gamma}-ray spectral index and between the spectral index and the luminosity, and to compare the spectral indexes {alpha}{sub X}, {alpha}{sub {gamma}}, {alpha}{sub X{gamma}}, and {alpha}{sub {gamma}X{gamma}} for different subclasses. We also investigated the correlation between the X-ray and the {gamma}-ray luminosity. The following results have been obtained. Our analysis indicates that an anti-correlation exists between the X-ray and the {gamma}-ray spectral indexes for the whole sample. However, when we considered the subclasses of blazars (FSRQs, the low-peaked BL Lacertae objects (LBLs) and the high-peaked BL Lacertae objects (HBLs)) separately, there is not a clear relationship for each subclass. Based on the Fermi-detected sources, we can say that the HBLs are different from FSRQs, while the LBLs are similar to FSRQs.

Comparisons of Jet Properties between GeV Radio Galaxies and Blazars

Science.gov (United States)

Xue, Zi-Wei; Zhang, Jin; Cui, Wei; Liang, En-Wei; Zhang, Shuang-Nan

2017-09-01

We compile a sample of spectral energy distributions (SEDs) of 12 GeV radio galaxies (RGs), including eight FR I RGs and four FR II RGs. These SEDs can be represented with the one-zone leptonic model. No significant unification, as expected in the unification model, is found for the derived jet parameters between FR I RGs and BL Lacertae objects (BL Lacs) and between FR II RGs and flat spectrum radio quasars (FSRQs). However, on average FR I RGs have a larger {γ }{{b}} (break Lorentz factor of electrons) and lower B (magnetic field strength) than FR II RGs, analogous to the differences between BL Lacs and FSRQs. The derived Doppler factors (δ) of RGs are on average smaller than those of blazars, which is consistent with the unification model such that RGs are the misaligned parent populations of blazars with smaller δ. On the basis of jet parameters from SED fits, we calculate their jet powers and the powers carried by each component, and compare their jet compositions and radiation efficiencies with blazars. Most of the RG jets may be dominated by particles, like BL Lacs, not FSRQs. However, the jets of RGs with higher radiation efficiencies tend to have higher jet magnetization. A strong anticorrelation between synchrotron peak frequency and jet power is observed for GeV RGs and blazars in both the observer and co-moving frames, indicating that the “sequence” behavior among blazars, together with the GeV RGs, may be intrinsically dominated by jet power.

SPECTRAL PROPERTIES OF BRIGHT FERMI-DETECTED BLAZARS IN THE GAMMA-RAY BAND

International Nuclear Information System (INIS)

Abdo, A. A.; Ackermann, M.; Ajello, M.; Bechtol, K.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Borgland, A. W.; Bouvier, A.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Bellazzini, R.; Bregeon, J.; Brez, A.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bonamente, E.; Brigida, M.

2010-01-01

The gamma-ray energy spectra of bright blazars of the LAT Bright AGN Sample (LBAS) are investigated using Fermi-LAT data. Spectral properties (hardness, curvature, and variability) established using a data set accumulated over 6 months of operation are presented and discussed for different blazar classes and subclasses: flat spectrum radio quasars (FSRQs), low-synchrotron peaked BLLacs (LSP-BLLacs), intermediate-synchrotron peaked BLLacs (ISP-BLLacs), and high-synchrotron peaked BLLacs (HSP-BLLacs). The distribution of photon index (Γ, obtained from a power-law fit above 100 MeV) is found to correlate strongly with blazar subclass. The change in spectral index from that averaged over the 6 months observing period is < 0.2-0.3 when the flux varies by about an order of magnitude, with a tendency toward harder spectra when the flux is brighter for FSRQs and LSP-BLLacs. A strong departure from a single power-law spectrum appears to be a common feature for FSRQs. This feature is also present for some high-luminosity LSP-BLLacs, and a small number of ISP-BLLacs. It is absent in all LBAS HSP-BLLacs. For 3C 454.3 and AO 0235+164, the two brightest FSRQ source and LSP-BLLac source, respectively, a broken power law (BPL) gives the most acceptable of power law, BPL, and curved forms. The consequences of these findings are discussed.

Relationships between electroencephalographic spectral peaks across frequency bands

Directory of Open Access Journals (Sweden)

Sacha Jennifer Van Albada

2013-03-01

Full Text Available The degree to which electroenencephalographic (EEG spectral peaks are independent, and the relationships between their frequencies have been debated. A novel fitting method was used to determine peak parameters in the range 2–35 Hz from a large sample of eyes-closed spectra, and their interrelationships were investigated. Findings were compared with a mean-field model of thalamocortical activity, which predicts near-harmonic relationships between peaks. The subject set consisted of 1424 healthy subjects from the Brain Resource International Database. Peaks in the theta range occurred on average near half the alpha peak frequency, while peaks in the beta range tended to occur near twice and three times the alpha peak frequency on an individual-subject basis. Moreover, for the majority of subjects, alpha peak frequencies were significantly positively correlated with frequencies of peaks in the theta and low and high beta ranges. Such a harmonic progression agrees semiquantitatively with theoretical predictions from the mean-field model. These findings indicate a common or analogous source for different rhythms, and help to define appropriate individual frequency bands for peak identification.

Relationships between Electroencephalographic Spectral Peaks Across Frequency Bands

Science.gov (United States)

van Albada, S. J.; Robinson, P. A.

2013-01-01

The degree to which electroencephalographic spectral peaks are independent, and the relationships between their frequencies have been debated. A novel fitting method was used to determine peak parameters in the range 2–35 Hz from a large sample of eyes-closed spectra, and their interrelationships were investigated. Findings were compared with a mean-field model of thalamocortical activity, which predicts near-harmonic relationships between peaks. The subject set consisted of 1424 healthy subjects from the Brain Resource International Database. Peaks in the theta range occurred on average near half the alpha peak frequency, while peaks in the beta range tended to occur near twice and three times the alpha peak frequency on an individual-subject basis. Moreover, for the majority of subjects, alpha peak frequencies were significantly positively correlated with frequencies of peaks in the theta and low and high beta ranges. Such a harmonic progression agrees semiquantitatively with theoretical predictions from the mean-field model. These findings indicate a common or analogous source for different rhythms, and help to define appropriate individual frequency bands for peak identification. PMID:23483663

UNVEILING THE NATURE OF THE UNIDENTIFIED GAMMA-RAY SOURCES. III. GAMMA-RAY BLAZAR-LIKE COUNTERPARTS AT LOW RADIO FREQUENCIES

Energy Technology Data Exchange (ETDEWEB)

Massaro, F.; Funk, S. [SLAC National Laboratory and Kavli Institute for Particle Astrophysics and Cosmology, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States); D' Abrusco, R.; Paggi, A. [Harvard-Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Giroletti, M. [INAF Istituto di Radioastronomia, via Gobetti 101, I-40129 Bologna (Italy); Masetti, N. [INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna, via Gobetti 101, I-40129 Bologna (Italy); Tosti, G. [Dipartimento di Fisica, Universita degli Studi di Perugia, I-06123 Perugia (Italy); Nori, M. [Department of Physics and Astronomy, University of Bologna, viale Berti Pichat 6/2, I-40127 Bologna (Italy)

2013-07-01

About one-third of the {gamma}-ray sources listed in the second Fermi Large Area Telescope catalog (2FGL) have no firmly established counterpart at lower energies and so are classified as unidentified gamma-ray sources (UGSs). Here, we propose a new approach to find candidate counterparts for the UGSs based on the 325 MHz radio survey performed with the Westerbork Synthesis Radio Telescope in the northern hemisphere. First, we investigate the low-frequency radio properties of blazars, the largest known population of {gamma}-ray sources; then we search for sources with similar radio properties combining the information derived from the Westerbork Northern Sky Survey (WENSS) with those of the NRAO Very Large Array Sky Survey. We present a list of candidate counterparts for 32 UGSs with at least one counterpart in the WENSS. We also performed an extensive research in the literature to look for infrared and optical counterparts of the {gamma}-ray blazar candidates selected using the low-frequency radio observations to confirm their nature. On the basis of our multifrequency research, we identify 23 new {gamma}-ray blazar candidates out of the 32 UGSs investigated. Comparison with previous results on the UGSs is also presented. Finally, we speculate on the advantages of using low-frequency radio observations to associate UGSs and to search for {gamma}-ray pulsar candidates.

OPTICAL SPECTROSCOPIC OBSERVATIONS OF GAMMA-RAY BLAZAR CANDIDATES. IV. RESULTS OF THE 2014 FOLLOW-UP CAMPAIGN

International Nuclear Information System (INIS)

Ricci, F.; Massaro, F.; Landoni, M.; D’Abrusco, R.; Milisavljevic, D.; Paggi, A.; Smith, Howard A.; Stern, D.; Masetti, N.; Tosti, G.

2015-01-01

The extragalactic γ-ray sky is dominated by the emission arising from blazars, one of the most peculiar classes of radio-loud active galaxies. Since the launch of Fermi several methods were developed to search for blazars as potential counterparts of unidentified γ-ray sources (UGSs). To confirm the nature of the selected candidates, optical spectroscopic observations are necessary. In 2013 we started a spectroscopic campaign to investigate γ-ray blazar candidates selected according to different procedures. The main goals of our campaign are: (1) to confirm the nature of these candidates, and (2) whenever possible, determine their redshifts. Optical spectroscopic observations will also permit us to verify the robustness of the proposed associations and check for the presence of possible source class contaminants to our counterpart selection. This paper reports the results of observations carried out in 2014 in the northern hemisphere with Kitt Peak National Observatory and in the southern hemisphere with the Southern Astrophysical Research telescopes. We also report three sources observed with the Magellan and Palomar telescopes. Our selection of blazar-like sources that could be potential counterparts of UGSs is based on their peculiar infrared colors and on their combination with radio observations both at high and low frequencies (i.e., above and below ∼1 GHz) in publicly available large radio surveys. We present the optical spectra of 27 objects. We confirm the blazar-like nature of nine sources that appear to be potential low-energy counterparts of UGSs. Then we present new spectroscopic observations of 10 active galaxies of uncertain type associated with Fermi sources, classifying all of them as blazars. In addition, we present the spectra for five known γ-ray blazars with uncertain redshift estimates and three BL Lac candidates that were observed during our campaign. We also report the case for WISE J173052.85−035247.2, candidate counterpart of the

OPTICAL SPECTROSCOPIC OBSERVATIONS OF GAMMA-RAY BLAZAR CANDIDATES. IV. RESULTS OF THE 2014 FOLLOW-UP CAMPAIGN

Energy Technology Data Exchange (ETDEWEB)

Ricci, F. [Dipartimento di Matematica e Fisica, Università Roma Tre, via della Vasca Navale 84, I-00146, Roma (Italy); Massaro, F. [Dipartimento di Fisica, Università degli Studi di Torino, via Pietro Giuria 1, I-10125 Torino (Italy); Landoni, M. [INAF-Osservatorio Astronomico di Brera, Via Emilio Bianchi 46, I-23807 Merate (Italy); D’Abrusco, R.; Milisavljevic, D.; Paggi, A.; Smith, Howard A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Stern, D. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Mail Stop 169-221, Pasadena, CA 91109 (United States); Masetti, N. [INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna, via Gobetti 101, I-40129, Bologna (Italy); Tosti, G., E-mail: riccif@fis.uniroma3.it [Dipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia (Italy)

2015-05-15

The extragalactic γ-ray sky is dominated by the emission arising from blazars, one of the most peculiar classes of radio-loud active galaxies. Since the launch of Fermi several methods were developed to search for blazars as potential counterparts of unidentified γ-ray sources (UGSs). To confirm the nature of the selected candidates, optical spectroscopic observations are necessary. In 2013 we started a spectroscopic campaign to investigate γ-ray blazar candidates selected according to different procedures. The main goals of our campaign are: (1) to confirm the nature of these candidates, and (2) whenever possible, determine their redshifts. Optical spectroscopic observations will also permit us to verify the robustness of the proposed associations and check for the presence of possible source class contaminants to our counterpart selection. This paper reports the results of observations carried out in 2014 in the northern hemisphere with Kitt Peak National Observatory and in the southern hemisphere with the Southern Astrophysical Research telescopes. We also report three sources observed with the Magellan and Palomar telescopes. Our selection of blazar-like sources that could be potential counterparts of UGSs is based on their peculiar infrared colors and on their combination with radio observations both at high and low frequencies (i.e., above and below ∼1 GHz) in publicly available large radio surveys. We present the optical spectra of 27 objects. We confirm the blazar-like nature of nine sources that appear to be potential low-energy counterparts of UGSs. Then we present new spectroscopic observations of 10 active galaxies of uncertain type associated with Fermi sources, classifying all of them as blazars. In addition, we present the spectra for five known γ-ray blazars with uncertain redshift estimates and three BL Lac candidates that were observed during our campaign. We also report the case for WISE J173052.85−035247.2, candidate counterpart of the

HIGH-ENERGY NEUTRINOS FROM RECENT BLAZAR FLARES

Energy Technology Data Exchange (ETDEWEB)

Halzen, Francis; Kheirandish, Ali [Wisconsin IceCube Particle Astrophysics Center and Department of Physics, University of Wisconsin, Madison, WI 53706 (United States)

2016-11-01

The energy density of cosmic neutrinos measured by IceCube matches the one observed by Fermi in extragalactic photons that predominantly originate in blazars. This has inspired attempts to match Fermi sources with IceCube neutrinos. A spatial association combined with a coincidence in time with a flaring source may represent a smoking gun for the origin of the IceCube flux. In 2015 June, the Fermi Large Area Telescope observed an intense flare from blazar 3C 279 that exceeded the steady flux of the source by a factor of 40 for the duration of a day. We show that IceCube is likely to observe neutrinos, if indeed hadronic in origin, in data that are still blinded at this time. We also discuss other opportunities for coincident observations that include a recent flare from blazar 1ES 1959+650 that previously produced an intriguing coincidence with AMANDA observations.

The RINGO2 and DIPOL optical polarization catalogue of blazars

Science.gov (United States)

Jermak, H.; Steele, I. A.; Lindfors, E.; Hovatta, T.; Nilsson, K.; Lamb, G. P.; Mundell, C.; Barres de Almeida, U.; Berdyugin, A.; Kadenius, V.; Reinthal, R.; Takalo, L.

2016-11-01

We present ˜2000 polarimetric and ˜3000 photometric observations of 15 γ-ray bright blazars over a period of 936 days (2008-10-11 to 2012-10-26) using data from the Tuorla blazar monitoring program (KVA DIPOL) and Liverpool Telescope (LT) RINGO2 polarimeters (supplemented with data from SkyCamZ (LT) and Fermi-LAT γ-ray data). In 11 out of 15 sources we identify a total of 19 electric vector position angle (EVPA) rotations and 95 flaring episodes. We group the sources into subclasses based on their broad-band spectral characteristics and compare their observed optical and γ-ray properties. We find that (1) the optical magnitude and γ-ray flux are positively correlated, (2) EVPA rotations can occur in any blazar subclass, four sources show rotations that go in one direction and immediately rotate back, (3) we see no difference in the γ-ray flaring rates in the sample; flares can occur during and outside of rotations with no preference for this behaviour, (4) the average degree of polarization (DoP), optical magnitude and γ-ray flux are lower during an EVPA rotation compared with during non-rotation and the distribution of the DoP during EVPA rotations is not drawn from the same parent sample as the distribution outside rotations, (5) the number of observed flaring events and optical polarization rotations are correlated, however we find no strong evidence for a temporal association between individual flares and rotations and (6) the maximum observed DoP increases from ˜10 per cent to ˜30 per cent to ˜40 per cent for subclasses with synchrotron peaks at high, intermediate and low frequencies, respectively.

Extragalactic Peaked-spectrum Radio Sources at Low Frequencies

Energy Technology Data Exchange (ETDEWEB)

Callingham, J. R.; Gaensler, B. M.; Sadler, E. M.; Lenc, E. [Sydney Institute for Astronomy (SIfA), School of Physics, The University of Sydney, NSW 2006 (Australia); Ekers, R. D.; Bell, M. E. [CSIRO Astronomy and Space Science (CASS), Marsfield, NSW 2122 (Australia); Line, J. L. B.; Hancock, P. J.; Kapińska, A. D.; McKinley, B.; Procopio, P. [ARC Centre of Excellence for All-Sky Astrophysics (CAASTRO) (Australia); Hurley-Walker, N.; Tingay, S. J.; Franzen, T. M. O.; Morgan, J. [International Centre for Radio Astronomy Research (ICRAR), Curtin University, Bentley, WA 6102 (Australia); Dwarakanath, K. S. [Raman Research Institute (RRI), Bangalore 560080 (India); For, B.-Q. [International Centre for Radio Astronomy Research (ICRAR), The University of Western Australia, Crawley, WA 6009 (Australia); Hindson, L.; Johnston-Hollitt, M. [School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington 6140 (New Zealand); Offringa, A. R., E-mail: joseph.callingham@sydney.edu.au [Netherlands Institute for Radio Astronomy (ASTRON), Dwingeloo (Netherlands); and others

2017-02-20

We present a sample of 1483 sources that display spectral peaks between 72 MHz and 1.4 GHz, selected from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. The GLEAM survey is the widest fractional bandwidth all-sky survey to date, ideal for identifying peaked-spectrum sources at low radio frequencies. Our peaked-spectrum sources are the low-frequency analogs of gigahertz-peaked spectrum (GPS) and compact-steep spectrum (CSS) sources, which have been hypothesized to be the precursors to massive radio galaxies. Our sample more than doubles the number of known peaked-spectrum candidates, and 95% of our sample have a newly characterized spectral peak. We highlight that some GPS sources peaking above 5 GHz have had multiple epochs of nuclear activity, and we demonstrate the possibility of identifying high-redshift ( z > 2) galaxies via steep optically thin spectral indices and low observed peak frequencies. The distribution of the optically thick spectral indices of our sample is consistent with past GPS/CSS samples but with a large dispersion, suggesting that the spectral peak is a product of an inhomogeneous environment that is individualistic. We find no dependence of observed peak frequency with redshift, consistent with the peaked-spectrum sample comprising both local CSS sources and high-redshift GPS sources. The 5 GHz luminosity distribution lacks the brightest GPS and CSS sources of previous samples, implying that a convolution of source evolution and redshift influences the type of peaked-spectrum sources identified below 1 GHz. Finally, we discuss sources with optically thick spectral indices that exceed the synchrotron self-absorption limit.

Intra-night Optical Variability Monitoring of Fermi Blazars: First Results from 1.3 m J. C. Bhattacharya Telescope

Energy Technology Data Exchange (ETDEWEB)

Paliya, Vaidehi S.; Ajello, M.; Kaur, A. [Department of Physics and Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC 29634-0978 (United States); Stalin, C. S., E-mail: vpaliya@g.clemson.edu [Indian Institute of Astrophysics, Block II, Koramangala, Bangalore-560034 (India)

2017-07-20

We report the first results obtained from our campaign to characterize the intra-night-optical variability (INOV) properties of Fermi detected blazars, using the observations from the recently commissioned 1.3 m J. C. Bhattacharya telescope (JCBT). During the first run, we were able to observe 17 blazars in the Bessel R filter for ∼137 hr. Using C- and scaled F -statistics, we quantify the extent of INOV and derive the duty cycle (DC), which is the fraction of time during which a source exhibits a substantial flux variability. We find a high DC of 40% for BL Lac objects and the flat spectrum radio quasars are relatively less variable (DC ∼ 15%). However, when estimated for blazars sub-classes, a high DC of ∼59% is found in low synchrotron peaked (LSP) blazars, whereas, intermediate and high synchrotron peaked objects have a low DC of ∼11% and 13%, respectively. We find evidence of the association of the high amplitude INOV with the γ -ray flaring state. We also notice a high polarization during the elevated INOV states (for the sources that have polarimetric data available), thus supporting the jet based origin of the observed variability. We plan to enlarge the sample and utilize the time availability from the small telescopes, such as 1.3 m JCBT, to strengthen/verify the results obtained in this work and those existing in the literature.

Jets, black holes and disks in blazars

Directory of Open Access Journals (Sweden)

Ghisellini Gabriele

2013-12-01

Full Text Available The Fermi and Swift satellites, together with ground based Cherenkov telescopes, has greatly improved our knowledge of blazars, namely Flat Spectrum Radio Quasars and BL Lac objects, since all but the most powerful emit most of their electro–magnetic output at γ–ray energies, while the very powerful blazars emit mostly in the hard X–ray region of the spectrum. Often they show coordinated variability at different frequencies, suggesting that in these cases the same population of electrons is at work, in a single zone of the jet. The location of this region along the jet is a matter of debate. The jet power correlates with the mass accretion rate, with jets existing at all values of disk luminosities, measured in Eddington units, sampled so far. The most powerful blazars show clear evidence of the emission from their disks, and this has revived methods of finding the black hole mass and accretion rate by modelling a disk spectrum to the data. Being so luminous, blazars can be detected also at very high redshift, and therefore are a useful tool to explore the far universe. One interesting line of research concerns how heavy are their black holes at high redshifts. If we associate the presence of a relativistic jets with a fastly spinning black hole, then we naively expect that the accretion efficiency is larger than for non–spinning holes. As a consequence, the black hole mass in jetted systems should grow at a slower rate. In turn, this would imply that, at high redshifts, the heaviest black holes should be in radio–quiet quasars. We instead have evidences of the opposite, challenging our simple ideas of how a black hole grows.

Passive radio frequency peak power multiplier

Science.gov (United States)

Farkas, Zoltan D.; Wilson, Perry B.

1977-01-01

Peak power multiplication of a radio frequency source by simultaneous charging of two high-Q resonant microwave cavities by applying the source output through a directional coupler to the cavities and then reversing the phase of the source power to the coupler, thereby permitting the power in the cavities to simultaneously discharge through the coupler to the load in combination with power from the source to apply a peak power to the load that is a multiplication of the source peak power.

THE WISE BLAZAR-LIKE RADIO-LOUD SOURCES: AN ALL-SKY CATALOG OF CANDIDATE γ-RAY BLAZARS

Energy Technology Data Exchange (ETDEWEB)

D' Abrusco, R.; Paggi, A.; Smith, H. A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Massaro, F. [Dipartimento di Fisica, Università degli Studi di Torino, via Pietro Giuria 1, I-10125 Torino (Italy); Masetti, N. [INAF/IASF di Bologna, via Gobetti 101, I-40129 Bologna (Italy); Landoni, M. [INAF/Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (Italy); Tosti, G. [Dipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia (Italy)

2014-11-01

We present a catalog of radio-loud candidate γ-ray emitting blazars with WISE mid-infrared colors similar to the colors of confirmed γ-ray blazars. The catalog is assembled from WISE sources detected in all four WISE filters, with colors compatible with the three-dimensional locus of the WISE γ-ray emitting blazars, and which can be spatially cross-matched with radio sources from one of the three radio surveys: NVSS, FIRST, and/or SUMSS. Our initial WISE selection uses a slightly modified version of previously successful algorithms. We then select only the radio-loud sources using a measure of the radio-to-IR flux, the q {sub 22} parameter, which is analogous to the q {sub 24} parameter known in the literature but which instead uses the WISE band-four flux at 22 μm. Our final catalog contains 7855 sources classified as BL Lacs, FSRQs, or mixed candidate blazars; 1295 of these sources can be spatially re-associated as confirmed blazars. We describe the properties of the final catalog of WISE blazar-like radio-loud sources and consider possible contaminants. Finally, we discuss why this large catalog of candidate γ-ray emitting blazars represents a new and useful resource to address the problem of finding low-energy counterparts to currently unidentified high-energy sources.

The classification of flaring states of blazars

Science.gov (United States)

Resconi, E.; Franco, D.; Gross, A.; Costamante, L.; Flaccomio, E.

2009-08-01

Aims: The time evolution of the electromagnetic emission from blazars, in particular high-frequency peaked sources (HBLs), displays irregular activity that has not yet been understood. In this work we report a methodology capable of characterizing the time behavior of these variable objects. Methods: The maximum likelihood blocks (MLBs) is a model-independent estimator that subdivides the light curve into time blocks, whose length and amplitude are compatible with states of constant emission rate of the observed source. The MLBs yield the statistical significance in the rate variations and strongly suppresses the noise fluctuations in the light curves. We applied the MLBs for the first time on the long term X-ray light curves (RXTE/ASM) of Mkn 421, Mkn 501, 1ES 1959+650, and 1ES 2155-304, more than 10 years of observational data (1996-2007). Using the MLBs interpretation of RXTE/ASM data, the integrated time flux distribution is determined for each single source considered. We identify in these distributions the characteristic level, as well as the flaring states of the blazars. Results: All the distributions show a significant component at negative flux values, most probably caused by an uncertainty in the background subtraction and by intrinsic fluctuations of RXTE/ASM. This effect concerns in particular short time observations. To quantify the probability that the intrinsic fluctuations give rise to a false identification of a flare, we study a population of very faint sources and their integrated time-flux distribution. We determine duty cycle or fraction of time a source spent in the flaring state of the source Mkn 421, Mkn 501, 1ES 1959+650 and 1ES 2155-304. Moreover, we study the random coincidences between flares and generic sporadic events such as high-energy neutrinos or flares in other wavelengths.

Observations Of Gamma-ray Loud Blazars With The VLBA At 5 GHz

Science.gov (United States)

Linford, Justin; Taylor, G. B.; Romani, R.; Readhead, A. C. S.; Reeves, R.; Richards, J. L.; Helmboldt, J. F.

2011-01-01

The Fermi Gamma-ray Space Telescope has been scanning the sky for more than a year. About half of the sources detected by Fermi's Large Area Telesope (LAT) are active galactic nuclei (AGN). Nearly all of these gamma-ray loud AGN are blazars; strong, compact radio emitters that exhibit variability in their flux and apparent superluminal motion in their jets. Several groups are currently monitoring the radio properties of these gamma-ray loud blazars. We present results from both archival and contemporaneous observations of 200 LAT-detected blazars using the Very Long Baseline Array (VLBA) at a frequency of 5 GHz (wavelength of 6 cm). Our large, flux-limited sample provides unique insights into the mechanism that produces strong gamma-ray emissions. We explore the parsec-scale properties of the cores and jets of these highly energetic objects, including core polarization. We compare the gamma-ray loud blazars to their gamma-ray quiet counterparts in the VLBA Imaging and Polarimetry Survey (VIPS). We also investigate the differences between the BL Lacertae objects (BL Lacs) and flat-spectrum radio quasars (FSRQs).

Radio variability of the blazar AO 0235 + 164

International Nuclear Information System (INIS)

O'dell, S.L.; Dennison, B.; Broderick, J.J.; Altschuler, D.R.; Condon, J.J.; Payne, H.E.; Mitchell, K.J.

1988-01-01

The high-redshift blazar A0 0235 + 164 exhibits flux-density variations which are primarily of the less common variety in which low-frequency flux-density variations track the high-frequency variations but are delayed and of smaller amplitude. Observational results based on five years of monitoring are presented which are correlated over at least a factor of 50 frequency range in the sense expected for an expanding synchrotron component: outbursts propagating toward lower frequencies with diminishing amplitudes. A simple, semiempirical jet model is developed which accounts reasonably well for the radio properties of the object. The predictions of the model are compared with observations, examining the radio flux-density histories, the radio spectral evolution, the radio structure, and evidence for relativistic bulk motion. 59 references

BROADBAND OBSERVATIONS OF HIGH REDSHIFT BLAZARS

Energy Technology Data Exchange (ETDEWEB)

Paliya, Vaidehi S. [Department of Physics and Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC 29634-0978 (United States); Parker, M. L.; Fabian, A. C. [Institute of Astronomy, Madingley Road, Cambridge CB3 0HA (United Kingdom); Stalin, C. S., E-mail: vpaliya@g.clemson.edu [Indian Institute of Astrophysics, Block II, Koramangala, Bangalore-560034 (India)

2016-07-01

We present a multi-wavelength study of four high redshift blazars, S5 0014+81 ( z = 3.37), CGRaBS J0225+1846 ( z = 2.69), BZQ J1430+4205 ( z = 4.72), and 3FGL J1656.2−3303 ( z = 2.40) using quasi-simultaneous data from the Swift , Nuclear Spectroscopic Telescope Array ( NuSTAR ) and the Fermi -Large Area Telescope (LAT) and also archival XMM-Newton observations. Other than 3FGL J1656.2−3303, none of the sources were known as γ -ray emitters, and our analysis of ∼7.5 yr of LAT data reveals the first time detection of statistically significant γ -ray emission from CGRaBS J0225+1846. We generate the broadband spectral energy distributions (SED) of all the objects, centering at the epoch of NuSTAR observations and reproduce them using a one-zone leptonic emission model. The optical−UV emission in all the objects can be explained by radiation from the accretion disk, whereas the X-ray to γ -ray windows of the SEDs are found to be dominated by inverse Compton scattering off the broad line region photons. All of them host black holes that are billions of solar masses. Comparing the accretion disk luminosity and the jet power of these sources with a large sample of blazars, we find them to occupy a high disk luminosity–jet power regime. We also investigate the X-ray spectral properties of the sources in detail with a major focus on studying the causes of soft X-ray deficit, a feature generally seen in high redshift radio-loud quasars. We summarize that this feature could be explained based on the intrinsic curvature in the jet emission rather than being due to the external effects predicted in earlier studies, such as host galaxy and/or warm absorption.

TIME-DEPENDENT ELECTRON ACCELERATION IN BLAZAR TRANSIENTS: X-RAY TIME LAGS AND SPECTRAL FORMATION

Energy Technology Data Exchange (ETDEWEB)

Lewis, Tiffany R.; Becker, Peter A. [Department of Physics and Astronomy, George Mason University, Fairfax, VA 22030-4444 (United States); Finke, Justin D., E-mail: pbecker@gmu.edu, E-mail: tlewis13@gmu.edu, E-mail: justin.finke@nrl.navy.mil [U.S. Naval Research Laboratory, Code 7653, 4555 Overlook Avenue SW, Washington, DC 20375-5352 (United States)

2016-06-20

Electromagnetic radiation from blazar jets often displays strong variability, extending from radio to γ -ray frequencies. In a few cases, this variability has been characterized using Fourier time lags, such as those detected in the X-rays from Mrk 421 using Beppo SAX. The lack of a theoretical framework to interpret the data has motivated us to develop a new model for the formation of the X-ray spectrum and the time lags in blazar jets based on a transport equation including terms describing stochastic Fermi acceleration, synchrotron losses, shock acceleration, adiabatic expansion, and spatial diffusion. We derive the exact solution for the Fourier transform of the electron distribution and use it to compute the Fourier transform of the synchrotron radiation spectrum and the associated X-ray time lags. The same theoretical framework is also used to compute the peak flare X-ray spectrum, assuming that a steady-state electron distribution is achieved during the peak of the flare. The model parameters are constrained by comparing the theoretical predictions with the observational data for Mrk 421. The resulting integrated model yields, for the first time, a complete first-principles physical explanation for both the formation of the observed time lags and the shape of the peak flare X-ray spectrum. It also yields direct estimates of the strength of the shock and the stochastic magnetohydrodynamical wave acceleration components in the Mrk 421 jet.

MULTIWAVELENGTH VARIABILITY OF THE BLAZARS Mrk 421 AND 3C 454.3 IN THE HIGH STATE

Energy Technology Data Exchange (ETDEWEB)

Gaur, Haritma; Gupta, Alok C. [Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital 263129 (India); Wiita, Paul J., E-mail: haritma@aries.res.in [Department of Physics, College of New Jersey, P.O. Box 7718, Ewing, NJ 08628 (United States)

2012-01-15

We report the results of photometric observations of the blazars Mrk 421 and 3C 454.3 designed to search for intraday variability (IDV) and short-term variability (STV). Optical photometric observations were spread over 18 nights for Mrk 421 and 7 nights for 3C 454.3 during our observing run in 2009-2010 at the 1.04 m telescope at Aryabhatta Research Institute of Observational Sciences, India. Genuine IDV is found for the source 3C 454.3 but not for Mrk 421. Genuine STV is found for both sources. Mrk 421 was revealed by the Monitor of All-sky X-ray Image (MAXI) X-ray detector on the International Space Station to be in an exceptionally high flux state in 2010 January-February. We performed a correlation between the X-ray and optical bands to search for time delays and found a weak correlation with higher frequencies leading the lower frequencies by about 10 days. The blazar 3C 454.3 was found to be in a high flux state in 2009 November-December. We performed correlations in optical observations made at three telescopes, along with X-ray data from the MAXI camera and public release {gamma}-ray data from the Fermi space telescope. We found strong correlations between the {gamma}-ray and optical bands at a time lag of about four days, but the X-ray flux is not correlated with either. We briefly discuss the possible reasons for the time delays between these bands within the framework of existing models for X-ray and {gamma}-ray emission mechanisms.

Extended radio emission and the nature of blazars

International Nuclear Information System (INIS)

Antonucci, R.R.J.; Ulvestad, J.S.

1985-01-01

The VLA has been used at 20 cm to map all 23 of the 54 confirmed blazars listed in the Angel and Stockman review paper that had not been mapped before at high resolution. (Blazars include BL Lac objects and optically violently variable quasars.) In addition, data on most of the previously mapped blazars have been reprocessed in order to achieve higher dynamic range. Extended emission has been detected associated with 49 of the 54 objects. The extended radio emission has been used to test the hypothesis that blazars are normal radio galaxies and radio quasars viewed along the jet axes. We find that blazars have substantial extended power, consistent with this hypothesis. Many have extended powers as high as the luminous Fanaroff-Riley class 2 radio doubles. The projected linear sizes are small, as expected from foreshortening of the extended sources, and many blazars have the expected core-halo morphology. There are also several small doubles, a head-tail source, and some one-sided sources, and these could be in cases where the line of sight is slightly off the jet axis, or projections of asymmetrical radio galaxies and quasars. The ratio of core to extended radio emission has been studied as a possible indicator of viewing aspect or beaming intensity. It is found to correlate with optical polarization, optical and radio core variability, and one-sided radio morphology. We can go beyond these consistency checks and work toward a proof of the hypothesis under discussion. The flux from the extended emission alone is sufficient in some blazars to qualify them for inclusion in the 3C and 4C catalogs. Suppose that the radio core emission is anisotropic, but the extended emission is predominantly isotropic. The isotropy of the extended emission implies that these blazars would be in the catalogs even if viewed from the side

Multi-Frequency Observations of Gamma-Ray Blazar 1633+382 SG ...

Indian Academy of Sciences (India)

Gamma-rays—quasars: 1633+382(4C+38.41)—radio jets— polarization. 1. Introduction. Blazars are the most numerous objects in the γ-ray sky (Abdo et al. 2010). They show dramatic variability across the electromagnetic spectrum (e.g., Jorstad et al. 2010; Marscher et al. 2010). Both these properties (strong γ-ray emission.

Optical spectroscopic observations of blazars and γ-ray blazar candidates in the sloan digital sky survey data release nine

Energy Technology Data Exchange (ETDEWEB)

Massaro, F.; Masetti, N.; D' Abrusco, R.; Paggi, A.; Funk, S.

2014-09-09

We present an analysis of the optical spectra available in the Sloan Digital Sky Survey data release nine (SDSS DR9) for the blazars listed in the ROMA-BZCAT and for the γ-ray blazar candidates selected according to their IR colors. First, we adopt a statistical approach based on Monte Carlo simulations to find the optical counterparts of the blazars listed in the ROMA-BZCAT catalog. Then, we crossmatched the SDSS spectroscopic catalog with our selected samples of blazars and γ-ray blazar candidates, searching for those with optical spectra available to classify our blazar-like sources and, whenever possible, to confirm their redshifts. Our main objectives are to determine the classification of uncertain blazars listed in the ROMA-BZCAT and to discover new gamma-ray blazars. For the ROMA-BZCAT sources, we investigated a sample of 84 blazars, confirming the classification for 20 of them and obtaining 18 new redshift estimates. For the γ-ray blazars, indicated as potential counterparts of unassociated Fermi sources or with uncertain nature, we established the blazar-like nature of 8 out of the 27 sources analyzed and confirmed 14 classifications.

Probing the Diffuse Optical-IR Background with TeV Blazars Detected with the MAGIC Telescopes

Energy Technology Data Exchange (ETDEWEB)

Prandini, Elisa [Dipartimento di Fisica e Astronomia “G. Galilei”, University of Padova, Padua (Italy); Domínguez, Alberto [Departamento de Física Atómica, Universidad Complutense, Madrid (Spain); Fallah Ramazani, Vandad [Tuorla observatory, University of Turku, Turku (Finland); Hassan, Tarek [IFAE, The Barcelona Institute of Science and Technology, Bellaterra (Spain); Mazin, Daniel [Max Planck Institute for Physics, Munich (Germany); Institute for Cosmic Ray Research, University of Tokyo, Tokyo (Japan); Moralejo, Abelardo [IFAE, The Barcelona Institute of Science and Technology, Bellaterra (Spain); Nievas Rosillo, Mireia [Departamento de Física Atómica, Universidad Complutense, Madrid (Spain); Vanzo, Gaia; Vazquez Acosta, Monica, E-mail: prandini@pd.infn.it [Instituto de Astrofísica de Canarias, Tenerife (Spain); Departamento de Astrofisica, Universidad de La Laguna, Tenerife (Spain)

2017-11-22

Blazars are radio loud quasars whose jet points toward the observer. The observed emission is mostly non-thermal, dominated by the jet emission, and in some cases extends up to the very high energy gamma rays (VHE; E > 100 GeV). To date, more than 60 blazars have been detected at VHE mainly with ground-based imaging atmospheric Cherenkov telescopes (IACTs) such as MAGIC, H.E.S.S., and VERITAS. Energetic photons from a blazar may interact with the diffuse optical and IR background (the extragalactic background light, EBL) leaving an imprint on the blazar energy spectrum. This effect can be used to constrain the EBL, with basic assumptions on the intrinsic energy spectrum. Current generation of IACTs is providing valuable measurements of the EBL density and energy spectrum from optical to infrared frequencies. In this contribution, we present the latest results obtained with the data taken with the MAGIC telescopes: using 32 spectra from 12 blazars, the scale factor of the optical density predicted by the EBL model from Domínguez et al. (2011) is constrained to be 0.95 (+0.11, −0.12){sub stat} (+0.16, −0.07){sub sys}, where a value of 1 means the perfect match with the model.

Probing the Diffuse Optical-IR Background with TeV Blazars Detected with the MAGIC Telescopes

Directory of Open Access Journals (Sweden)

Elisa Prandini

2017-11-01

Full Text Available Blazars are radio loud quasars whose jet points toward the observer. The observed emission is mostly non-thermal, dominated by the jet emission, and in some cases extends up to the very high energy gamma rays (VHE; E > 100 GeV. To date, more than 60 blazars have been detected at VHE mainly with ground-based imaging atmospheric Cherenkov telescopes (IACTs such as MAGIC, H.E.S.S., and VERITAS. Energetic photons from a blazar may interact with the diffuse optical and IR background (the extragalactic background light, EBL leaving an imprint on the blazar energy spectrum. This effect can be used to constrain the EBL, with basic assumptions on the intrinsic energy spectrum. Current generation of IACTs is providing valuable measurements of the EBL density and energy spectrum from optical to infrared frequencies. In this contribution, we present the latest results obtained with the data taken with the MAGIC telescopes: using 32 spectra from 12 blazars, the scale factor of the optical density predicted by the EBL model from Domínguez et al. (2011 is constrained to be 0.95 (+0.11, −0.12stat (+0.16, −0.07sys, where a value of 1 means the perfect match with the model.

Multiwavelength Study of Gamma-Ray Bright Blazars

Science.gov (United States)

Morozova, Daria; Larionov, V. M.; Hagen-Thorn, V. A.; Jorstad, S. G.; Marscher, A. P.; Troitskii, I. S.

2011-01-01

We investigate total intensity radio images of 6 gamma-ray bright blazars (BL Lac, 3C 279, 3C 273, W Com, PKS 1510-089, and 3C 66A) and their optical and gamma-ray light curves to study connections between gamma-ray and optical brightness variations and changes in the parsec-scale radio structure. We use high-resolution maps obtained by the BU group at 43 GHz with the VLBA, optical light curves constructed by the St.Petersburg State U. (Russia) team using measurements with the 0.4 m telescope of St.Petersburg State U. (LX200) and the 0.7 m telescope of the Crimean Astrophysical Observatory (AZT-8), and gamma-ray light curves, which we have constructed with data provided by the Fermi Large Area Telescope. Over the period from August 2008 to November 2009, superluminal motion is found in all 6 objects with apparent speed ranging from 2c to 40c. The blazars with faster apparent speeds, 3C 273, 3C 279, PKS 1510-089, and 3C 66A, exhibit stronger variability of the gamma-ray emission. There is a tendency for sources with sharply peaked gamma-ray flares to have faster jet speed than sources with gamma-ray light curves with no sharp peaks. Gamma-ray light curves with sharply peaked gamma-ray flares possess a stronger gamma-ray/optical correlations. The research at St.Petersburg State U. was funded by the Minister of Education and Science of the Russian Federation (state contract N#P123). The research at BU was funded in part by NASA Fermi Guest Investigator grant NNX08AV65G and by NSF grant AST-0907893. The VLBA is an instrument of the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

X-Ray Intraday Variability of Five TeV Blazars with NuSTAR

Energy Technology Data Exchange (ETDEWEB)

Pandey, Ashwani; Gupta, Alok C. [Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital 263002 (India); Wiita, Paul J., E-mail: ashwanitapan@gmail.com, E-mail: acgupta30@gmail.com, E-mail: wiitap@tcnj.edu [Department of Physics, The College of New Jersey, 2000 Pennington Road, Ewing, NJ 08628-0718 (United States)

2017-06-01

We have examined 40 Nuclear Spectroscopic Telescope Array ( NuSTAR ) light curves (LCs) of five TeV emitting high synchrotron peaked blazars: 1ES 0229+200, Mrk 421, Mrk 501, 1ES 1959+650, and PKS 2155−304. Four of the blazars showed intraday variability in the NuSTAR energy range of 3–79 keV. Using an autocorrelation function analysis we searched for intraday variability timescales in these LCs and found indications of several between 2.5 and 32.8 ks in eight LCs of Mrk 421, a timescale around 8.0 ks for one LC of Mrk 501, and timescales of 29.6 and 57.4 ks in two LCs of PKS 2155-304. The other two blazars’ LCs do not show any evidence for intraday variability timescales shorter than the lengths of those observations; however, the data were both sparser and noisier for them. We found positive correlations with zero lag between soft (3–10 keV) and hard (10–79 keV) bands for most of the LCs, indicating that their emissions originate from the same electron population. We examined spectral variability using a hardness ratio analysis and noticed a general “harder-when-brighter” behavior. The 22 LCs of Mrk 421 observed between 2012 July and 2013 April show that this source was in a quiescent state for an extended period of time and then underwent an unprecedented double-peaked outburst while monitored on a daily basis during 2013 April 10–16. We briefly discuss models capable of explaining these blazar emissions.

A Search for QPOs in the Blazar OJ287: Preliminary Results from the 2015/2016 Observing Campaign

Directory of Open Access Journals (Sweden)

S. Zola

2016-10-01

Full Text Available We analyse the light curve in the R band of the blazar OJ287, gathered during the 2015/2016 observing season. We did a search for quasi-periodic oscillations (QPOs using several methods over a wide range of timescales. No statistically significant periods were found in the high-frequency domain both in the ground-based data and in Kepler observations. In the longer-period domain, the Lomb–Scargle periodogram revealed several peaks above the 99% significance level. The longest one—about 95 days—corresponds to the innermost stable circular orbit (ISCO period of the more massive black hole. The 43-day period could be an alias, or it can be attributed to accretion in the form of a two-armed spiral wave.

OPTICAL SPECTROSCOPIC OBSERVATIONS OF GAMMA-RAY BLAZAR CANDIDATES. V. TNG, KPNO, AND OAN OBSERVATIONS OF BLAZAR CANDIDATES OF UNCERTAIN TYPE IN THE NORTHERN HEMISPHERE

Energy Technology Data Exchange (ETDEWEB)

Álvarez Crespo, N.; Massaro, F. [Dipartimento di Fisica, Università degli Studi di Torino, via Pietro Giuria 1, I-10125 Torino (Italy); Masetti, N. [INAF—Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna, via Gobetti 101, I-40129, Bologna (Italy); Ricci, F.; La Franca, F. [Dipartimento di Matematica e Fisica, Università Roma Tre, via della Vasca Navale 84, I-00146, Roma (Italy); Landoni, M. [INAF-Osservatorio Astronomico di Brera, Via Emilio Bianchi 46, I-23807 Merate (Italy); Patiño-Álvarez, V.; Chavushyan, V.; Torrealba, J. [Instituto Nacional de Astrofisica, Óptica y Electrónica, Apartado Postal 51-216, 72000 Puebla, México (Mexico); D’Abrusco, R.; Paggi, A.; Smith, Howard A. [Harvard—Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Jiménez-Bailón, E. [Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 877, Ensenada, 22800 Baja California, México (Mexico); Latronico, L. [Istituto Nazionale di Fisica Nucleare, Sezione di Torino, I-10125 Torino (Italy); Tosti, G. [Dipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia (Italy)

2016-02-15

The extragalactic γ-ray sky is dominated by emission from blazars, a peculiar class of active galactic nuclei. Many of the γ-ray sources included in the Fermi-Large Area Telescope Third Source catalog (3FGL) are classified as blazar candidates of uncertain type (BCUs) because there are no optical spectra available in the literature to confirm their nature. In 2013, we started a spectroscopic campaign to look for the optical counterparts of the BCUs and of the unidentified γ-ray sources to confirm their blazar nature. Whenever possible we also determine their redshifts. Here, we present the results of the observations carried out in the northern hemisphere in 2013 and 2014 at the Telescopio Nazionale Galileo, Kitt Peak National Observatory, and Observatorio Astronómico Nacional in San Pedro Mártir. In this paper, we describe the optical spectra of 25 sources. We confirmed that all of the 15 BCUs observed in our campaign and included in our sample are blazars and we estimated the redshifts for three of them. In addition, we present the spectra for three sources classified as BL Lacs in the literature but with no optical spectra available to date. We found that one of them is a quasar (QSO) at a redshift of z = 0.208 and the other two are BL Lacs. Moreover, we also present seven new spectra for known blazars listed in the Roma-BZCAT that have an uncertain redshift or are classified as BL Lac candidates. We found that one of them, 5BZB J0724+2621, is a “changing look” blazar. According to the spectrum available in the literature, it was classified as a BL Lac, but in our observation we clearly detected a broad emission line that led us to classify this source as a QSO at z = 1.17.

DETECTION OF VERY HARD γ -RAY SPECTRUM FROM THE TEV BLAZAR MRK 501

Energy Technology Data Exchange (ETDEWEB)

Shukla, A.; Chitnis, V. R.; Acharya, B. S. [Department of High Energy Physics, Tata Institute of Fundamental Research, Mumbai 400005 (India); Mannheim, K.; Dorner, D. [Institute for Theoretical Physics and Astrophysics, Universität Würzburg, D-97074 Würzburg (Germany); Roy, J. [UM-DAE Center for Excellence in Basic Sciences, Mumbai 400098 (India); Hughes, G.; Biland, A. [ETH Zurich, Institute for Particle Physics, Otto-Stern-Weg 5, 8093 Zurich (Switzerland)

2016-12-01

The occasional hardening of the GeV-to-TeV spectrum observed from the blazar Mrk 501 has reopened the debate on the physical origin of radiation and particle acceleration processes in TeV blazars. We have used the ∼7 years of Fermi -LAT data to search for the time intervals with unusually hard spectra from the nearby TeV blazar Mrk 501. We detected hard spectral components above 10 GeV with photon index <1.5 at a significance level of more than 5 sigma on 17 occasions, each with 30 day integration time. The photon index of the hardest component reached a value of 0.89 ± 0.29. We interpret these hard spectra as signatures of intermittent injection of sharply peaked and localized particle distributions from the base of the jet.

Twin peak high-frequency quasi-periodic oscillations as a spectral imprint of dual oscillation modes of accretion tori

Science.gov (United States)

Bakala, P.; Goluchová, K.; Török, G.; Šrámková, E.; Abramowicz, M. A.; Vincent, F. H.; Mazur, G. P.

2015-09-01

Context. High-frequency (millisecond) quasi-periodic oscillations (HF QPOs) are observed in the X-ray power-density spectra of several microquasars and low-mass X-ray binaries. Two distinct QPO peaks, so-called twin peak QPOs, are often detected simultaneously exhibiting their frequency ratio close or equal to 3:2. A widely discussed class of proposed QPOs models is based on oscillations of accretion toroidal structures orbiting in the close vicinity of black holes or neutron stars. Aims: Following the analytic theory and previous studies of observable spectral signatures, we aim to model the twin peak QPOs as a spectral imprint of specific dual oscillation regime defined by a combination of the lowest radial and vertical oscillation mode of slender tori. We consider the model of an optically thick slender accretion torus with constant specific angular momentum. We examined power spectra and fluorescent Kα iron line profiles for two different simulation setups with the mode frequency relations corresponding to the epicyclic resonance HF QPOs model and modified relativistic precession QPOs model. Methods: We used relativistic ray-tracing implemented in the parallel simulation code LSDplus. In the background of the Kerr spacetime geometry, we analyzed the influence of the distant observer inclination and the spin of the central compact object. Relativistic optical projection of the oscillating slender torus is illustrated by images in false colours related to the frequency shift. Results: We show that performed simulations yield power spectra with the pair of dominant peaks that correspond to the frequencies of radial and vertical oscillation modes and with the peak frequency ratio equal to the proper value 3:2 on a wide range of inclinations and spin values. We also discuss exceptional cases of a very low and very high inclination, as well as unstable high spin relativistic precession-like configurations that predict a constant frequency ratio equal to 1:2. We

IDENTIFICATION OF NEW GAMMA-RAY BLAZAR CANDIDATES WITH MULTIFREQUENCY ARCHIVAL OBSERVATIONS

Energy Technology Data Exchange (ETDEWEB)

Cowperthwaite, Philip S. [Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States); Massaro, F. [SLAC National Laboratory and Kavli Institute for Particle Astrophysics and Cosmology, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States); D' Abrusco, R.; Paggi, A.; Smith, Howard A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Tosti, G., E-mail: pcowpert@umd.edu [Dipartimento di Fisica, Università Degli Studi di Perugia, I-06123 Perugia (Italy)

2013-11-01

Blazars are a highly variable, radio-loud subclass of active galactic nuclei. In order to better understand such objects we must be able to easily identify candidate blazars from the growing population of unidentified sources. Working toward this goal, we attempt to identify new gamma-ray blazar candidates from a sample of 102 previously unidentified sources. These sources are selected from The Astronomer's Telegram and the literature on the basis of non-periodic variability and multi-wavelength behavior. We then attempt to associate these objects to an IR counterpart in the Wide-field Infrared Survey Explorer all-sky survey. We are able to identify 16 candidate sources whose IR colors are consistent with those of the blazar population. Of those, 13 sources have IR colors indicative of being gamma-ray emitting blazar candidates. These sources all possess archival multi-wavelength observations that support their blazar-like nature.

Holographic wavefront characterization of a frequency-tripled high-peak-power neodymium:glass laser

International Nuclear Information System (INIS)

Kessler, T.J.

1984-01-01

Near-field amplitude and phase distributions from a high-peak-power, frequency converted Nd:glass laser (lambda = 351 nm) have been holographically recorded on silver-halide emulsions. Conventionally, the absence of a suitable reference beam forces one to use some type of shearing interferometry to obtain phasefront information, while the near-field and far-field distributions are recorded as intensity profiles. In this study, a spatially filtered, locally generated reference beam was created to holographically store the complex amplitude distribution of the pulsed laser beam, while reconstruction of the original wavefront was achieved with a continuous-wave laser. Reconstructed near-field and quasi-far-field intensity distributions closely resembled those obtained from conventional techniques, and accurate phasefront reconstruction was achieved. Furthermore, several two-beam interferometric techniques, not practicable with a high-peak-power laser, have been successfully implemented on a continuous-wave reconstruction of the pulsed laser beam. 46 refs., 40 figs., 1 tab

Multi-Frequency Blazar Micro-Variability as a Tool to Investigate Relativistic Jets

Directory of Open Access Journals (Sweden)

James R. Webb

2016-08-01

Full Text Available For the past 12 years we have been studying optical micro-variability of a sample of 15 Blazars. We summarize the results of this study and draw some basic conclusions about the characteristics of micro-variability. The intermittency, the stochastic nature, and the similar profile shapes seen in micro-variations at different times and in different objects have led us to a possible model to explain the observed micro-variations. The model is based on a strong shock propagating down a relativistic jet and encountering turbulence which causes density or magnetic field enhancements. We use the theory of Kirk, Reiger, and Mastichiadis (1998 to describe the pulse of synchrotron emission emanating from individual density enhancements energized by the shock. By fitting these “pulses” to micro-variability observations, we obtain excellent fits to actual micro-variations. The model predicts that the spectral index changes as a function of pulse duration. This effect should be observable in multi-frequency micro-variability data. We present the theoretical model, model fits of our micro-variability light curves, and preliminary multi-frequency micro-variability observations that support this model. A further test that has yet to be carried out involves observing polarization changes in different pulses.

Blazar origin of some IceCube events

Energy Technology Data Exchange (ETDEWEB)

Miranda, Luis Salvador; Leon, Alberto Rosales de; Sahu, Sarira [Universidad Nacional Autonoma de Mexico, Circuito Exterior, C.U., Instituto de Ciencias Nucleares, Mexico, DF (Mexico)

2016-07-15

Recently the ANTARES collaboration presented a time dependent analysis of a selected number of flaring blazars to look for upward going muon events produced from the charge current interaction of the muon neutrinos. We use the same list of flaring blazars to look for a possible positional correlation with the IceCube neutrino events. In the context of the photohadronic model we propose that the neutrinos are produced within the nuclear region of the blazar where Fermi accelerated high energy protons interact with the background synchrotron/SSC photons. Although we found that some objects from the ANTARES list are within the error circles of a few IceCube events, the statistical analysis shows that none of these sources have a significant correlation. (orig.)

Blazar Variability from Turbulence in Jets Launched by Magnetically Arrested Accretion Flows

International Nuclear Information System (INIS)

Riordan, Michael O’; Pe’er, Asaf; McKinney, Jonathan C.

2017-01-01

Blazars show variability on timescales ranging from minutes to years, the former being comparable to and in some cases even shorter than the light-crossing time of the central black hole. The observed γ -ray light curves can be described by a power-law power density spectrum (PDS), with a similar index for both BL Lacs and flat-spectrum radio quasars. We show that this variability can be produced by turbulence in relativistic jets launched by magnetically arrested accretion flows (MADs). We perform radiative transport calculations on the turbulent, highly magnetized jet launching region of a MAD with a rapidly rotating supermassive black hole. The resulting synchrotron and synchrotron self-Compton emission, originating from close to the black hole horizon, is highly variable. This variability is characterized by PDS, which is remarkably similar to the observed power-law spectrum at frequencies less than a few per day. Furthermore, turbulence in the jet launching region naturally produces fluctuations in the plasma on scales much smaller than the horizon radius. We speculate that similar turbulent processes, operating in the jet at large radii (and therefore a high bulk Lorentz factor), are responsible for blazar variability over many decades in frequency, including on minute timescales.

Blazar Variability from Turbulence in Jets Launched by Magnetically Arrested Accretion Flows

Energy Technology Data Exchange (ETDEWEB)

Riordan, Michael O’; Pe’er, Asaf [Physics Department, University College Cork, Cork (Ireland); McKinney, Jonathan C., E-mail: michael_oriordan@umail.ucc.ie [Department of Physics and Joint Space-Science Institute, University of Maryland, College Park, MD 20742 (United States)

2017-07-10

Blazars show variability on timescales ranging from minutes to years, the former being comparable to and in some cases even shorter than the light-crossing time of the central black hole. The observed γ -ray light curves can be described by a power-law power density spectrum (PDS), with a similar index for both BL Lacs and flat-spectrum radio quasars. We show that this variability can be produced by turbulence in relativistic jets launched by magnetically arrested accretion flows (MADs). We perform radiative transport calculations on the turbulent, highly magnetized jet launching region of a MAD with a rapidly rotating supermassive black hole. The resulting synchrotron and synchrotron self-Compton emission, originating from close to the black hole horizon, is highly variable. This variability is characterized by PDS, which is remarkably similar to the observed power-law spectrum at frequencies less than a few per day. Furthermore, turbulence in the jet launching region naturally produces fluctuations in the plasma on scales much smaller than the horizon radius. We speculate that similar turbulent processes, operating in the jet at large radii (and therefore a high bulk Lorentz factor), are responsible for blazar variability over many decades in frequency, including on minute timescales.

Radio core dominance of Fermi blazars

Science.gov (United States)

Pei, Zhi-Yuan; Fan, Jun-Hui; Liu, Yi; Yuan, Yi-Hai; Cai, Wei; Xiao, Hu-Bing; Lin, Chao; Yang, Jiang-He

2016-07-01

During the first 4 years of mission, Fermi/LAT detected 1444 blazars (3FGL) (Ackermann et al. in Astrophys. J. 810:14, 2015). Fermi/LAT observations of blazars indicate that Fermi blazars are luminous and strongly variable with variability time scales, for some cases, as short as hours. Those observations suggest a strong beaming effect in Fermi/LAT blazars. In the present work, we will investigate the beaming effect in Fermi/LAT blazars using a core-dominance parameter, R = S_{core}/ S_{ext.}, where S_{core} is the core emission, while S_{ext.} is the extended emission. We compiled 1335 blazars with available core-dominance parameter, out of which 169 blazars have γ-ray emission (from 3FGL). We compared the core-dominance parameters, log R, between the 169 Fermi-detected blazars (FDBs) and the rest non-Fermi-detected blazars (non-FDBs), and we found that the averaged values are R+(2.25±0.10), suggesting that a source with larger log R has larger V.I. value. Thirdly, we compared the mean values of radio spectral index for FDBs and non-FDBs, and we obtained < α_{radio}rangle =0.06±0.35 for FDBs and < α_{radio}rangle =0.57±0.46 for non-FDBs. If γ-rays are composed of two components like radio emission (core and extended components), then we can expect a correlation between log R and the γ-ray spectral index. When we used the radio core-dominance parameter, log R, to investigate the relationship, we found that the spectral index for the core component is α_{γ}|_{core} = 1.11 (a photon spectral index of α_{γ}^{ph}|_{core} = 2.11) and that for the extended component is α_{γ}|_{ext.} = 0.70 (a photon spectral index of α_{γ}^{ph}|_{ext.} = 1.70). Some discussions are also presented.

The Ringo2 Optical Polarisation Catalogue of 13 High-Energy Blazars

Science.gov (United States)

Barres de Almeida, Ulisses; Jermak, Helen; Mundell, Carole; Lindfors, Elina; Nilsson, Kari; Steele, Iain

2015-08-01

We present the findings of the Ringo2 3-year survey of 13 blazars (3 FSRQs and 10 BL Lacs) with regular coverage and reasonably fast cadence of one to three observations a week. Ringo2 was installed on the Liverpool Robotic Telescope (LT) on the Canary Island of La Palma between 2009 and 2012 and monitored thirteen high-energy-emitting blazars in the northern sky. The objects selected as well as the observational strategy were tuned to maximise the synergies with high-energy X- to gamma-ray observations. Therefore this sample stands out as a well-sampled, long-term view of high-energy AGN jets in polarised optical light. Over half of the sources exhibited an increase in optical flux during this period and almost a quarter were observed in outburst. We compare the optical data to gamma (Fermi/LAT) and X-ray data during these periods of outburst. In this talk we present the data obtained for all sources over the lifetime of Ringo2 with additional optical data from the KVA telescope and the SkyCamZ wide-field camera (on the LT), we explore the relationship between the change in polarisation angle as a function of time (dEVPA/dMJD), flux and polarisation degree along with cross correlation comparisons of optical and high-energy flux.

Exploring the Variability of the Fermi LAT Blazar Population

Science.gov (United States)

Macomb, Daryl J.; Shrader, C. R.

2014-01-01

The flux variability of the approximately 2000 point sources cataloged by the Fermi Gamma-Ray Space Telescope provide important clues to population characteristics. This is particularly true of the more than 1100 source that are likely AGN. By characterizing the intrinsic flux variability and distinguishing this variability from flaring behavior, we can better address questions of flare amplitudes, durations, recurrence times, and temporal profiles. A better understanding of the responsible physical environments, such as the scale and location of jet structures responsible for the high-energy emission, may emerge from such studies. Assessing these characteristics as a function of blazar sub-class is a further goal in order to address questions about the fundamentals of blazar AGN physics. Here we report on progress made in categorizing blazar flare behavior, and correlate these behaviors with blazar sub-type and other source parameters.

New Gener. High-Energy Spectra of the Blazar 3C 279 with XMM-Newton and GLAST

Science.gov (United States)

Collmar, Werner

2007-10-01

We propose two 20 ksec XMM-Newton observations of the X-ray bright gamma-ray blazar 3C~279 simultaneous with GLAST/LAT. The main goal is to measure its X-ray properties (spectrum, variability) in order to (1) improve our knowledge on the X-ray emission of the blazar, and (2) to supplement and correlate them to simultaneous GLAST/LAT Gamma-ray observations (30 MeV-300 GeV). Simultaneous GLAST observations of 3C 279 are guaranteed (assuming proper operation then). The high-energy data will be supplemented by ground-based measurements, adding finally up to multifrequency spectra which have unprecedented accuracy and will extend up to high-energy gamma-rays. Such high-quality SEDs will provide severe constraints on their modeling and have the potential to discriminate among models.

Bifurcation and chaos in high-frequency peak current mode Buck converter

Science.gov (United States)

Chang-Yuan, Chang; Xin, Zhao; Fan, Yang; Cheng-En, Wu

2016-07-01

Bifurcation and chaos in high-frequency peak current mode Buck converter working in continuous conduction mode (CCM) are studied in this paper. First of all, the two-dimensional discrete mapping model is established. Next, reference current at the period-doubling point and the border of inductor current are derived. Then, the bifurcation diagrams are drawn with the aid of MATLAB. Meanwhile, circuit simulations are executed with PSIM, and time domain waveforms as well as phase portraits in i L-v C plane are plotted with MATLAB on the basis of simulation data. After that, we construct the Jacobian matrix and analyze the stability of the system based on the roots of characteristic equations. Finally, the validity of theoretical analysis has been verified by circuit testing. The simulation and experimental results show that, with the increase of reference current I ref, the corresponding switching frequency f is approaching to low-frequency stage continuously when the period-doubling bifurcation happens, leading to the converter tending to be unstable. With the increase of f, the corresponding I ref decreases when the period-doubling bifurcation occurs, indicating the stable working range of the system becomes smaller. Project supported by the National Natural Science Foundation of China (Grant No. 61376029), the Fundamental Research Funds for the Central Universities, China, and the College Graduate Research and Innovation Program of Jiangsu Province, China (Grant No. SJLX15_0092).

Detecting new γ-ray sources based on multi-frequency data the case of 1WHSPJ031423.9+061956

Science.gov (United States)

Arsioli, Bruno; Chang, Yu Ling

2015-12-01

We use the Fermi Science Tools in an attempt to unveil faint γ-ray blazars that may be above the threshold for detectability with Fermi-LAT and are not identified by automated methods. Our search for new sources in the 100MeV-300GeV band is mainly driven by the 1/2WHSP catalogs, which list high synchrotron peaked blazars expected to be emitters of VHE photons. Here we present the γ-ray detection of 1WHSP J031423.9+061956, modelling its high energy spectrum as a power law. We describe an example where multi-frequency selection, performed at much lower energies (from radio to X-ray), helps to pin-point a high energy source. The 1/2WHSP catalogs are built with the aim of providing a list of TeV targets for the VHE arrays of Cherenkov telescopes. Moreover, these catalogs provide useful seeds for identifying new high energy sources within the raw-data from Fermi. With the aid of multi-frequency data, we can explore the very high energy domain in greater details, improving the description of the γ-ray sky.

Automatic Locking of Laser Frequency to an Absorption Peak

Science.gov (United States)

Koch, Grady J.

2006-01-01

An electronic system adjusts the frequency of a tunable laser, eventually locking the frequency to a peak in the optical absorption spectrum of a gas (or of a Fabry-Perot cavity that has an absorption peak like that of a gas). This system was developed to enable precise locking of the frequency of a laser used in differential absorption LIDAR measurements of trace atmospheric gases. This system also has great commercial potential as a prototype of means for precise control of frequencies of lasers in future dense wavelength-division-multiplexing optical communications systems. The operation of this system is completely automatic: Unlike in the operation of some prior laser-frequency-locking systems, there is ordinarily no need for a human operator to adjust the frequency manually to an initial value close enough to the peak to enable automatic locking to take over. Instead, this system also automatically performs the initial adjustment. The system (see Figure 1) is based on a concept of (1) initially modulating the laser frequency to sweep it through a spectral range that includes the desired absorption peak, (2) determining the derivative of the absorption peak with respect to the laser frequency for use as an error signal, (3) identifying the desired frequency [at the very top (which is also the middle) of the peak] as the frequency where the derivative goes to zero, and (4) thereafter keeping the frequency within a locking range and adjusting the frequency as needed to keep the derivative (the error signal) as close as possible to zero. More specifically, the system utilizes the fact that in addition to a zero crossing at the top of the absorption peak, the error signal also closely approximates a straight line in the vicinity of the zero crossing (see Figure 2). This vicinity is the locking range because the linearity of the error signal in this range makes it useful as a source of feedback for a proportional + integral + derivative control scheme that

GAMMA-RAY OBSERVATIONAL PROPERTIES OF TeV-DETECTED BLAZARS

International Nuclear Information System (INIS)

Şentürk, G. D.; Errando, M.; Mukherjee, R.; Böttcher, M.

2013-01-01

The synergy between the Fermi-LAT and ground-based Cherenkov telescope arrays gives us the opportunity for the first time to characterize the high-energy emission from blazars over 5 decades in energy, from 100 MeV to 10 TeV. In this study, we perform a Fermi-LAT spectral analysis for TeV-detected blazars and combine it with archival TeV data. We examine the observational properties in the γ-ray band of our sample of TeV-detected blazars and compare the results with X-ray and GeV-selected populations. The spectral energy distributions (SEDs) that result from combining Fermi-LAT and ground-based spectra are studied in detail. Simple parameterizations such as a power-law function do not always reproduce the high-energy SEDs, where spectral features that could indicate intrinsic absorption are observed.

Multiwavelength Observations of the Blazar BL Lacertae: A New Fast TeV Gamma-Ray Flare

Science.gov (United States)

Abeysekara, A. U.; Benbow, W.; Bird, R.; Brantseg, T.; Brose, R.; Buchovecky, M.; Buckley, J. H.; Bugaev, V.; Connolly, M. P.; Cui, W.; Daniel, M. K.; Falcone, A.; Feng, Q.; Finley, J. P.; Fortson, L.; Furniss, A.; Gillanders, G. H.; Gunawardhana, I.; Hütten, M.; Hanna, D.; Hervet, O.; Holder, J.; Hughes, G.; Humensky, T. B.; Johnson, C. A.; Kaaret, P.; Kar, P.; Kertzman, M.; Krennrich, F.; Lang, M. J.; Lin, T. T. Y.; McArthur, S.; Moriarty, P.; Mukherjee, R.; O’Brien, S.; Ong, R. A.; Otte, A. N.; Park, N.; Petrashyk, A.; Pohl, M.; Pueschel, E.; Quinn, J.; Ragan, K.; Reynolds, P. T.; Richards, G. T.; Roache, E.; Rulten, C.; Sadeh, I.; Santander, M.; Sembroski, G. H.; Shahinyan, K.; Wakely, S. P.; Weinstein, A.; Wells, R. M.; Wilcox, P.; Williams, D. A.; Zitzer, B.; The VERITAS Collaboration; Jorstad, S. G.; Marscher, A. P.; Lister, M. L.; Kovalev, Y. Y.; Pushkarev, A. B.; Savolainen, T.; Agudo, I.; Molina, S. N.; Gómez, J. L.; Larionov, V. M.; Borman, G. A.; Mokrushina, A. A.; Tornikoski, M.; Lähteenmäki, A.; Chamani, W.; Enestam, S.; Kiehlmann, S.; Hovatta, T.; Smith, P. S.; Pontrelli, P.

2018-04-01

Combined with measurements made by very-long-baseline interferometry, the observations of fast TeV gamma-ray flares probe the structure and emission mechanism of blazar jets. However, only a handful of such flares have been detected to date, and only within the last few years have these flares been observed from lower-frequency-peaked BL Lac objects and flat-spectrum radio quasars. We report on a fast TeV gamma-ray flare from the blazar BL Lacertae observed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS). with a rise time of ∼2.3 hr and a decay time of ∼36 min. The peak flux above 200 GeV is (4.2 ± 0.6) × 10‑6 photon m‑2 s‑1 measured with a 4-minute-binned light curve, corresponding to ∼180% of the flux that is observed from the Crab Nebula above the same energy threshold. Variability contemporaneous with the TeV gamma-ray flare was observed in GeV gamma-ray, X-ray, and optical flux, as well as in optical and radio polarization. Additionally, a possible moving emission feature with superluminal apparent velocity was identified in Very Long Baseline Array observations at 43 GHz, potentially passing the radio core of the jet around the time of the gamma-ray flare. We discuss the constraints on the size, Lorentz factor, and location of the emitting region of the flare, and the interpretations with several theoretical models that invoke relativistic plasma passing stationary shocks.

Peak alpha frequency is a neural marker of cognitive function across the autism spectrum.

Science.gov (United States)

Dickinson, Abigail; DiStefano, Charlotte; Senturk, Damla; Jeste, Shafali Spurling

2018-03-01

Cognitive function varies substantially and serves as a key predictor of outcome and response to intervention in autism spectrum disorder (ASD), yet we know little about the neurobiological mechanisms that underlie cognitive function in children with ASD. The dynamics of neuronal oscillations in the alpha range (6-12 Hz) are associated with cognition in typical development. Peak alpha frequency is also highly sensitive to developmental changes in neural networks, which underlie cognitive function, and therefore, it holds promise as a developmentally sensitive neural marker of cognitive function in ASD. Here, we measured peak alpha band frequency under a task-free condition in a heterogeneous sample of children with ASD (N = 59) and age-matched typically developing (TD) children (N = 38). At a group level, peak alpha frequency was decreased in ASD compared to TD children. Moreover, within the ASD group, peak alpha frequency correlated strongly with non-verbal cognition. As peak alpha frequency reflects the integrity of neural networks, our results suggest that deviations in network development may underlie cognitive function in individuals with ASD. By shedding light on the neurobiological correlates of cognitive function in ASD, our findings lay the groundwork for considering peak alpha frequency as a useful biomarker of cognitive function within this population which, in turn, will facilitate investigations of early markers of cognitive impairment and predictors of outcome in high risk infants. © 2017 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

The Gamma-Ray Blazar Content of the Northern Sky

Energy Technology Data Exchange (ETDEWEB)

Michelson, Peter

2003-07-16

Using survey data, we have re-evaluated the correlation of flat spectrum radio sources with EGRET sources in the Northern sky. An analysis incorporating the radio and X-ray properties and the {gamma}-ray source localization is used to gauge the reliability of associations and to search for counterparts of previously unidentified EGRET sources. Above |b|=10{sup o}, where the classification is complete, we find that 70% of the Northern EGRET sources have counterparts similar to the bright EGRET blazars. For several of these we identify known blazar counterparts more likely than the earlier proposed 3EG association; for {approx}20 we have new identifications. Spectroscopic confirmation of these candidates is in progress and we have found flat spectrum radio quasars and BL Lac counterparts with redshifts as high as 4. We also find strong evidence for a set of 28 objects with no plausible counterpart like the known EGRET blazars. These thus represent either a new extragalactic population or a population of Galactic objects with a large scale height. The survey has been extended into the plane, where we find several new blazar candidates; the bulk of the sources are, however, Galactic. Looking ahead to the GLAST era, we predict that several of the present 3EG sources are composite and that higher resolution data will break these into multiple blazar IDs.

Methods for the Quasi-Periodic Variability Analysis in Blazars Y. Liu ...

Indian Academy of Sciences (India)

the variability analysis in blazars in optical and radio bands, to search for possible quasi-periodic signals. 2. Power spectral density (PSD). In statistical signal processing and physics, the power spectral density (PSD) is a positive real function of a frequency variable associated with a stationary stochas- tic process. Intuitively ...

CLUSTERING OF γ-RAY-SELECTED 2LAC FERMI BLAZARS

Energy Technology Data Exchange (ETDEWEB)

Allevato, V.; Finoguenov, A. [Department of Physics, University of Helsinki, Gustaf Hällströmin katu 2a, FI-00014 Helsinki (Finland); Cappelluti, N. [University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250 (United States)

2014-12-20

We present the first measurement of the projected correlation function of 485 γ-ray-selected blazars, divided into 175 BL Lacertae (BL Lacs) and 310 flat-spectrum radio quasars (FSRQs) detected in the 2 year all-sky survey by the Fermi-Large Area Telescope. We find that Fermi BL Lacs and FSRQs reside in massive dark matter halos (DMHs) with log M{sub h} = 13.35{sub −0.14}{sup +0.20} and log M{sub h} = 13.40{sub −0.19}{sup +0.15} h {sup –1} M {sub ☉}, respectively, at low (z ∼ 0.4) and high (z ∼ 1.2) redshift. In terms of clustering properties, these results suggest that BL Lacs and FSRQs are similar objects residing in the same dense environment typical of galaxy groups, despite their different spectral energy distributions, power, and accretion rates. We find no difference in the typical bias and hosting halo mass between Fermi blazars and radio-loud active galactic nuclei (AGNs), supporting the unification scheme simply equating radio-loud objects with misaligned blazar counterparts. This similarity in terms of the typical environment they preferentially live in, suggests that blazars tend to occupy the center of DMHs, as already pointed out for radio-loud AGNs. This implies, in light of several projects looking for the γ-ray emission from DM annihilation in galaxy clusters, a strong contamination from blazars to the expected signal from DM annihilation.

Spectral properties of blazars. I. Objects observed in the far-ultraviolet. II. An X-ray observed sample

International Nuclear Information System (INIS)

Ghisellini, G.; Maraschi, L.; Treves, A.; Tanzi, E. G.; Milano Universita, Italy; CNR, Istituto di Fisica Cosmica, Milan, Italy)

1986-01-01

All blazars observed with the IUE are studied and shown to form a well-defined subgroup according to their spectral properties. These properties are discussed with respect to theoretical models and are compared with those of quasars. Radio, ultraviolet, and X-ray fluxes are used to construct composite spectral indices, and systematic differences between X-ray selected and otherwise selected objects are discussed. It is confirmed that X-ray selected objects have flatter overall spectra, and are therefore weaker radio emitters relative to their X-ray emission than objects selected otherwise. It is found that X-ray selected blazars have the same average X-ray luminosity as blazars selected otherwise and are underluminous at UV and radio frequencies. This finding is used to argue that the radio-weak, X-ray selected BL Lac objects are, in terms of space density, the dominant members of the blazar population. The results are interpreted in the framework of synchrotron emission models involving relativistic plasma jets. 134 references

Spectral properties of blazars. I. Objects observed in the far-ultraviolet. II. An X-ray observed sample

Energy Technology Data Exchange (ETDEWEB)

Ghisellini, G.; Maraschi, L.; Treves, A.; Tanzi, E. G.

1986-11-01

All blazars observed with the IUE are studied and shown to form a well-defined subgroup according to their spectral properties. These properties are discussed with respect to theoretical models and are compared with those of quasars. Radio, ultraviolet, and X-ray fluxes are used to construct composite spectral indices, and systematic differences between X-ray selected and otherwise selected objects are discussed. It is confirmed that X-ray selected objects have flatter overall spectra, and are therefore weaker radio emitters relative to their X-ray emission than objects selected otherwise. It is found that X-ray selected blazars have the same average X-ray luminosity as blazars selected otherwise and are underluminous at UV and radio frequencies. This finding is used to argue that the radio-weak, X-ray selected BL Lac objects are, in terms of space density, the dominant members of the blazar population. The results are interpreted in the framework of synchrotron emission models involving relativistic plasma jets. 134 references.

Identification of the OGLE Blazars behind the Large and Small Magellanic Clouds

Directory of Open Access Journals (Sweden)

Natalia Żywucka

2017-11-01

Full Text Available We report the selection of blazar candidates behind the Large and Small Magellanic Clouds. Both flat spectrum radio quasar and BL Lacreate objects were selected based on the long-term, multi-colour Optical Gravitational Lensing Experiment photometric data. We cross-correlated the Magellanic Quasar Survey catalogue of spectroscopically confirmed quasars and quasar candidates located behind the Magellanic Clouds with the radio data at six frequencies from 0.8 to 20 GHz. Among the 1654 objects visible in optical range, we identified a sample of 44 newly selected blazar candidates, including 27 flat spectrum radio quasars and 17 BL Lacs. We examined selected objects with respect to their radio, optical, and mid-infrared properties.

MULTIFREQUENCY PHOTO-POLARIMETRIC WEBT OBSERVATION CAMPAIGN ON THE BLAZAR S5 0716+714: SOURCE MICROVARIABILITY AND SEARCH FOR CHARACTERISTIC TIMESCALES

International Nuclear Information System (INIS)

Bhatta, G.; Stawarz, Ł.; Ostrowski, M.; Markowitz, A.; Akitaya, H.; Arkharov, A. A.; Bachev, R.; Benítez, E.; Borman, G. A.; Carosati, D.; Cason, A. D.; Chanishvili, R.; Damljanovic, G.; Dhalla, S.; Frasca, A.; Hiriart, D.; Hu, S-M.

2016-01-01

Here we report on the results of the Whole Earth Blazar Telescope photo-polarimetric campaign targeting the blazar S5 0716+71, organized in 2014 March to monitor the source simultaneously in BVRI and near-IR filters. The campaign resulted in an unprecedented data set spanning ∼110 hr of nearly continuous, multiband observations, including two sets of densely sampled polarimetric data mainly in the R filter. During the campaign, the source displayed pronounced variability with peak-to-peak variations of about 30% and “bluer-when-brighter” spectral evolution, consisting of a day-timescale modulation with superimposed hour-long microflares characterized by ∼0.1 mag flux changes. We performed an in-depth search for quasi-periodicities in the source light curve; hints for the presence of oscillations on timescales of ∼3 and ∼5 hr do not represent highly significant departures from a pure red-noise power spectrum. We observed that, at a certain configuration of the optical polarization angle (PA) relative to the PA of the innermost radio jet in the source, changes in the polarization degree (PD) led the total flux variability by about 2 hr; meanwhile, when the relative configuration of the polarization and jet angles altered, no such lag could be noted. The microflaring events, when analyzed as separate pulse emission components, were found to be characterized by a very high PD (>30%) and PAs that differed substantially from the PA of the underlying background component, or from the radio jet positional angle. We discuss the results in the general context of blazar emission and energy dissipation models.

MULTIFREQUENCY PHOTO-POLARIMETRIC WEBT OBSERVATION CAMPAIGN ON THE BLAZAR S5 0716+714: SOURCE MICROVARIABILITY AND SEARCH FOR CHARACTERISTIC TIMESCALES

Energy Technology Data Exchange (ETDEWEB)

Bhatta, G.; Stawarz, Ł.; Ostrowski, M. [Astronomical Observatory of Jagiellonian University, ul. Orla 171, 30-244 Krakow (Poland); Markowitz, A. [Center for Astrophysics and Space Sciences, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0424 (United States); Akitaya, H. [Hiroshima Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Arkharov, A. A. [Main (Pulkovo) Astronomical Observatory of RAS, Pulkovskoye shosse, 60, 196140 St. Petersburg (Russian Federation); Bachev, R. [Institute of Astronomy, Bulgarian Academy of Sciences, 72, Tsarigradsko Shosse Blvd., 1784 Sofia (Bulgaria); Benítez, E. [Instituto de Astronomía, Universidad Nacional Autónoma de México, Mexico DF (Mexico); Borman, G. A. [Crimean Astrophysical Observatory, P/O Nauchny, Crimea, 298409 (Russian Federation); Carosati, D. [EPT Observatories, Tijarafe, La Palma (Spain); Cason, A. D. [Private address, 105 Glen Pine Trail, Dawnsonville, GA 30534 (United States); Chanishvili, R. [Abastumani Observatory, Mt. Kanobili, 0301 Abastumani, Georgia (United States); Damljanovic, G. [Astronomical Observatory, Volgina 7, 11060 Belgrade (Serbia); Dhalla, S. [Florida International University, Miami, FL 33199 (United States); Frasca, A. [INAF—Osservatorio Astrofisico di Catania (Italy); Hiriart, D. [Instituto de Astronomía, Universidad Nacional Autónoma de México, Ensenada (Mexico); Hu, S-M., E-mail: gopalbhatta716@gmail.com [Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University at Weihai, 264209 Weihai (China); and others

2016-11-01

Here we report on the results of the Whole Earth Blazar Telescope photo-polarimetric campaign targeting the blazar S5 0716+71, organized in 2014 March to monitor the source simultaneously in BVRI and near-IR filters. The campaign resulted in an unprecedented data set spanning ∼110 hr of nearly continuous, multiband observations, including two sets of densely sampled polarimetric data mainly in the R filter. During the campaign, the source displayed pronounced variability with peak-to-peak variations of about 30% and “bluer-when-brighter” spectral evolution, consisting of a day-timescale modulation with superimposed hour-long microflares characterized by ∼0.1 mag flux changes. We performed an in-depth search for quasi-periodicities in the source light curve; hints for the presence of oscillations on timescales of ∼3 and ∼5 hr do not represent highly significant departures from a pure red-noise power spectrum. We observed that, at a certain configuration of the optical polarization angle (PA) relative to the PA of the innermost radio jet in the source, changes in the polarization degree (PD) led the total flux variability by about 2 hr; meanwhile, when the relative configuration of the polarization and jet angles altered, no such lag could be noted. The microflaring events, when analyzed as separate pulse emission components, were found to be characterized by a very high PD (>30%) and PAs that differed substantially from the PA of the underlying background component, or from the radio jet positional angle. We discuss the results in the general context of blazar emission and energy dissipation models.

Extended Radio Emission in MOJAVE Blazars: Challenges to Unification

Science.gov (United States)

Kharb, P.; Lister, M. L.; Cooper, N. J.

2010-02-01

We present the results of a study on the kiloparsec-scale radio emission in the complete flux density limited MOJAVE sample, comprising 135 radio-loud active galactic nuclei. New 1.4 GHz Very Large Array (VLA) radio images of six quasars and previously unpublished images of 21 blazars are presented, along with an analysis of the high-resolution (VLA A-array) 1.4 GHz emission for the entire sample. While extended emission is detected in the majority of the sources, about 7% of the sources exhibit only radio core emission. We expect more sensitive radio observations, however, to detect faint emission in these sources, as we have detected in the erstwhile "core-only" source, 1548+056. The kiloparsec-scale radio morphology varies widely across the sample. Many BL Lac objects exhibit extended radio power and kiloparsec-scale morphology typical of powerful FRII jets, while a substantial number of quasars possess radio powers intermediate between FRIs and FRIIs. This poses challenges to the simple radio-loud unified scheme, which links BL Lac objects to FRIs and quasars to FRIIs. We find a significant correlation between extended radio emission and parsec-scale jet speeds: the more radio powerful sources possess faster jets. This indicates that the 1.4 GHz (or low-frequency) radio emission is indeed related to jet kinetic power. Various properties such as extended radio power and apparent parsec-scale jet speeds vary smoothly between different blazar subclasses, suggesting that, at least in terms of radio jet properties, the distinction between quasars and BL Lac objects, at an emission-line equivalent width of 5 Å, is essentially an arbitrary one. While the two blazar subclasses display a smooth continuation in properties, they often reveal differences in the correlation test results when considered separately. This can be understood if, unlike quasars, BL Lac objects do not constitute a homogeneous population, but rather include both FRI and FRII radio galaxies for

EXTENDED RADIO EMISSION IN MOJAVE BLAZARS: CHALLENGES TO UNIFICATION

International Nuclear Information System (INIS)

Kharb, P.; Lister, M. L.; Cooper, N. J.

2010-01-01

We present the results of a study on the kiloparsec-scale radio emission in the complete flux density limited MOJAVE sample, comprising 135 radio-loud active galactic nuclei. New 1.4 GHz Very Large Array (VLA) radio images of six quasars and previously unpublished images of 21 blazars are presented, along with an analysis of the high-resolution (VLA A-array) 1.4 GHz emission for the entire sample. While extended emission is detected in the majority of the sources, about 7% of the sources exhibit only radio core emission. We expect more sensitive radio observations, however, to detect faint emission in these sources, as we have detected in the erstwhile 'core-only' source, 1548+056. The kiloparsec-scale radio morphology varies widely across the sample. Many BL Lac objects exhibit extended radio power and kiloparsec-scale morphology typical of powerful FRII jets, while a substantial number of quasars possess radio powers intermediate between FRIs and FRIIs. This poses challenges to the simple radio-loud unified scheme, which links BL Lac objects to FRIs and quasars to FRIIs. We find a significant correlation between extended radio emission and parsec-scale jet speeds: the more radio powerful sources possess faster jets. This indicates that the 1.4 GHz (or low-frequency) radio emission is indeed related to jet kinetic power. Various properties such as extended radio power and apparent parsec-scale jet speeds vary smoothly between different blazar subclasses, suggesting that, at least in terms of radio jet properties, the distinction between quasars and BL Lac objects, at an emission-line equivalent width of 5 A, is essentially an arbitrary one. While the two blazar subclasses display a smooth continuation in properties, they often reveal differences in the correlation test results when considered separately. This can be understood if, unlike quasars, BL Lac objects do not constitute a homogeneous population, but rather include both FRI and FRII radio galaxies for

Automated Blazar Light Curves Using Machine Learning

Energy Technology Data Exchange (ETDEWEB)

Johnson, Spencer James [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2017-07-27

This presentation describes a problem and methodology pertaining to automated blazar light curves. Namely, optical variability patterns for blazars require the construction of light curves and in order to generate the light curves, data must be filtered before processing to ensure quality.

BLAZAR OPTICAL VARIABILITY IN THE PALOMAR-QUEST SURVEY

International Nuclear Information System (INIS)

Bauer, Anne; Baltay, Charles; Coppi, Paolo; Ellman, Nancy; Jerke, Jonathan; Rabinowitz, David; Scalzo, Richard

2009-01-01

We study the ensemble optical variability of 276 flat-spectrum radio quasars (FSRQs) and 86 BL Lacs in the Palomar-QUEST Survey with the goal of searching for common fluctuation properties, examining the range of behavior across the sample, and characterizing the appearance of blazars in such a survey so that future work can more easily identify such objects. The survey, which covers 15,000 deg 2 multiple times over 3.5 years, allows for the first ensemble blazar study of this scale. Variability amplitude distributions are shown for the FSRQ and BL Lac samples for numerous time lags, and also studied through structure function analyses. Individual blazars show a wide range of variability amplitudes, timescales, and duty cycles. Of the best-sampled objects, 35% are seen to vary by more than 0.4 mag; for these, the fraction of measurements contributing to the high-amplitude variability ranges constantly from about 5% to 80%. Blazar variability has some similarities to that of type I quasi-stellar objects (QSOs) but includes larger amplitude fluctuations on all timescales. FSRQ variability amplitudes are particularly similar to those of QSOs on timescales of several months, suggesting significant contributions from the accretion disk to the variable flux at these timescales. Optical variability amplitudes are correlated with the maximum apparent velocities of the radio jet for the subset of FSRQs with MOJAVE Very Long Baseline Array measurements, implying that the optically variable flux's strength is typically related to that of the radio emission. We also study CRATES radio-selected FSRQ candidates, which show similar variability characteristics to known FSRQs; this suggests a high purity for the CRATES sample.

SYSTEMATIC STUDY OF GAMMA-RAY-BRIGHT BLAZARS WITH OPTICAL POLARIZATION AND GAMMA-RAY VARIABILITY

Energy Technology Data Exchange (ETDEWEB)

Itoh, Ryosuke; Fukazawa, Yasushi; Kanda, Yuka; Shiki, Kensei; Kawabata, Miho; Nakaoka, Tatsuya; Takaki, Katsutoshi; Takata, Koji; Ui, Takahiro [Department of Physical Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Nalewajko, Krzysztof; Madejski, Greg M. [Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, Stanford University, 2575 Sand Hill Road M/S 29, Menlo Park, CA 94025 (United States); Uemura, Makoto; Tanaka, Yasuyuki T.; Kawabata, Koji S.; Akitaya, Hiroshi; Ohsugi, Takashi [Hiroshima Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Schinzel, Frank K. [Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87131 (United States); Moritani, Yuki [Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, The University of Tokyo, Kashiwa, Chiba 277-8583 (Japan); Sasada, Mahito [Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States); Yamanaka, Masayuki, E-mail: itoh@hep01.hepl.hiroshima-u.ac.jp, E-mail: itoh@hp.phys.titech.ac.jp [Department of Physics, Faculty of Science and Engineering, Konan University, Okamoto, Kobe, Hyogo 658-8501 (Japan); and others

2016-12-10

Blazars are highly variable active galactic nuclei that emit radiation at all wavelengths from radio to gamma rays. Polarized radiation from blazars is one key piece of evidence for synchrotron radiation at low energies, and it also varies dramatically. The polarization of blazars is of interest for understanding the origin, confinement, and propagation of jets. However, even though numerous measurements have been performed, the mechanisms behind jet creation, composition, and variability are still debated. We performed simultaneous gamma-ray and optical photopolarimetry observations of 45 blazars between 2008 July and 2014 December to investigate the mechanisms of variability and search for a basic relation between the several subclasses of blazars. We identify a correlation between the maximum degree of optical linear polarization and the gamma-ray luminosity or the ratio of gamma-ray to optical fluxes. Since the maximum polarization degree depends on the condition of the magnetic field (chaotic or ordered), this result implies a systematic difference in the intrinsic alignment of magnetic fields in parsec-scale relativistic jets between different types of blazars (flat-spectrum radio quasars vs. BL Lacs) and consequently between different types of radio galaxies (FR I versus FR II).

Impact of seeing and host galaxy into the analysis of photo-polarimetric microvariability in blazars. Case study of the nearby blazars 1ES 1959+650 and HB89 2201+044

Science.gov (United States)

Sosa, M. S.; von Essen, C.; Andruchow, I.; Cellone, S. A.

2017-11-01

Blazars, a type of Active Galactic Nuclei, present a particular orientation of their jets close to the line of sight. Their radiation is thus relativistically beamed, giving rise to extreme behaviors, specially strong variability on very short timescales (I.e., microvariability). Here we present simultaneous photometric and polarimetric observations of two relatively nearby blazars, 1ES 1959+650 and HB89 2201+044, that were obtained using the Calar Alto Faint Object Spectrograph mounted at the 2.2 m telescope in Calar Alto, Spain. An outstanding characteristic of these two blazars is the presence of well resolved host galaxies. This particular feature allows us to produce a study of their intrinsic polarization, a measurement of the polarization state of the galactic nucleus unaffected by the host galaxy. To carry out this work, we computed photometric fluxes from which we calculated the degree and orientation of the blazars polarization. Then, we analyzed the depolarizing effect introduced by the host galaxy with the main goal to recover the intrinsic polarization of the galactic nucleus, carefully taking into consideration the spurious polarimetric variability introduced by changes in seeing along the observing nights. We find that the two blazars do not present intra-night photo-polarimetric variability, although we do detect a significant inter-night variability. Comparing polarimetric values before and after accounting for the host galaxies, we observe a significant difference in the polarization degree of about 1% in the case of 1ES 1959+650, and 0.3% in the case of HB89 2201+044, thus evidencing the non-negligible impact introduced by the host galaxies. We note that this host galaxy effect depends on the waveband, and varies with changing seeing conditions, so it should be particularly considered when studying frequency-dependent polarization in blazars. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated

Redshift measurement of Fermi blazars for the Cherenkov telescope array

Science.gov (United States)

Pita, S.; Goldoni, P.; Boisson, C.; Cotter, G.; Lefaucheur, J.; Lenain, J.-P.; Lindfors, E.; Williams, D. A.

2017-01-01

Blazars are active galactic nuclei, and the most numerous High Energy (HE) and Very High Energy (VHE) γ-ray emitters. Their optical emission is often dominated by non-thermal, and, in the case of BL Lacs, featureless continuum radiation. This makes the determination of their redshift extremely difficult. Indeed, as of today only about 50% of γ-ray blazars have a measured spectroscopic redshift. The knowledge of redshift is fundamental because it allows the precise modeling of the VHE emission and also of its interaction with the extragalactic background light (EBL). The beginning of the Cherenkov Telescope Array (CTA) operations in the near future will allow the detection of several hundreds of new blazars. Using the Fermi catalogue of sources above 50 GeV (2FHL), we performed simulations which indicate that a significant fraction of the 2FHL blazars detectable by CTA will not have a measured redshift. As a matter of fact, the organization of observing campaigns to measure the redshift of these blazars has been recognized as a necessary support for the AGN Key Science Project of CTA. We are planning such an observing campaign. In order to optimize our chances of success, we will perform preliminary deep imaging observations aimed at detecting or setting upper limits to the host galaxy. We will then take spectra of the candidates with the brightest host galaxies. Taking advantage of the recent success of an X-shooter GTO observing campaign, these observations will be different with respect to previous ones due to the use of higher resolution spectrographs and of 8 meter class telescopes. We are starting to submit proposals for these observations. In this paper we briefly describe how candidates are selected and the corresponding observation program.

A Very High Energy Gamma-Ray Spectrum of 1ES 2344+514

OpenAIRE

Schroedter, M.; Badran, H. M.; Buckley, J. H.; Gordo, J. Bussons; Carter-Lewis, D. A.; Duke, C.; Fegan, D. J.; Fegan, S. F.; Finley, J. P.; Gillanders, G. H.; Grube, J.; Horan, D.; Kenny, G. E.; Kertzman, M.; Kosack, K.

2005-01-01

The BL Lacertae (BL Lac) object 1ES 2344+514 (1ES 2344), at a redshift of 0.044, was discovered as a source of very high energy (VHE) gamma rays by the Whipple Collaboration in 1995 \\citep{2344Catanese98}. This detection was recently confirmed by the HEGRA Collaboration \\citep{2344Hegra03}. As is typical for high-frequency peaked blazars, the VHE gamma-ray emission is highly variable. On the night of 20 December, 1995, a gamma-ray flare of 5.3-sigma significance was detected, the brightest ou...

“Orphan” γ-Ray Flares and Stationary Sheaths of Blazar Jets

Science.gov (United States)

MacDonald, Nicholas R.; Jorstad, Svetlana G.; Marscher, Alan P.

2017-11-01

Blazars exhibit flares across the entire electromagnetic spectrum. Many γ-ray flares are highly correlated with flares detected at longer wavelengths; however, a small subset appears to occur in isolation, with little or no correlated variability at longer wavelengths. These “orphan” γ-ray flares challenge current models of blazar variability, most of which are unable to reproduce this type of behavior. MacDonald et al. have developed the Ring of Fire model to explain the origin of orphan γ-ray flares from within blazar jets. In this model, electrons contained within a blob of plasma moving relativistically along the spine of the jet inverse-Compton scatter synchrotron photons emanating off of a ring of shocked sheath plasma that enshrouds the jet spine. As the blob propagates through the ring, the scattering of the ring photons by the blob electrons creates an orphan γ-ray flare. This model was successfully applied to modeling a prominent orphan γ-ray flare observed in the blazar PKS 1510-089. To further support the plausibility of this model, MacDonald et al. presented a stacked radio map of PKS 1510-089 containing the polarimetric signature of a sheath of plasma surrounding the spine of the jet. In this paper, we extend our modeling and stacking techniques to a larger sample of blazars: 3C 273, 4C 71.01, 3C 279, 1055+018, CTA 102, and 3C 345, the majority of which have exhibited orphan γ-ray flares. We find that the model can successfully reproduce these flares, while our stacked maps reveal the existence of jet sheaths within these blazars.

FACT. Flare alerts from blazar monitoring

Energy Technology Data Exchange (ETDEWEB)

Dorner, Daniela [Universitaet Wuerzburg (Germany); Bretz, Thomas [RWTH Aachen (Germany); Collaboration: FACT-Collaboration

2015-07-01

One of the major goals of the First G-APD Cherenkov Telescope is the longterm monitoring of bright TeV blazars. For more than three years, FACT has observed the blazars Mrk 421 and Mrk 501 and a few other sources on a regular basis. To understand these highly variable objects, simultaneous data at different wavelengths are very useful. FACT is not only taking part in multi-wavelength campaigns, but also sending alerts to other instruments in case of enhanced flux, to study flares within the multi-wavelength frame. To send fast alerts, an automatic quick look analysis was set up on site. Once the data are written on disk, they are automatically processed, and the analysis results are published on a website where other observers can monitor the activity of the source in the very high energy band. In addition, alerts are sent in case the flux is higher than a certain predefined value. In 2014, more than five alerts have been sent. Results from three years of monitoring are presented.

Polarization Properties of 24 Fermi-Detected Blazars

Science.gov (United States)

Linford, Justin; Taylor, G. B.; Schinzel, F. K.; Zavala, R. T.

2013-01-01

Gamma-ray emitting blazars have been shown to frequently have significant polarization at radio wavelengths. In early 2012, we obtained Very Long Baseline Array (VLBA) observations of 24 blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. These observations utilized the new 2 gigabit-per-second mode of the VLBA. We observed each source with full polarization at 8.4 GHz, 15 GHz, and 22 GHz with 256 MHz of total bandwidth per polarization. Our sample contains 14 flat-spectrum radio quasars (FSRQs) and 10 BL Lacertae objects (BL Lacs). We analyze the spectral index, rotation measure, and magnetic field structures of these 24 gamma-ray loud blazars.

Flood frequency analysis for nonstationary annual peak records in an urban drainage basin

Science.gov (United States)

Villarini, Gabriele; Smith, James A.; Serinaldi, Francesco; Bales, Jerad; Bates, Paul D.; Krajewski, Witold F.

2009-08-01

Flood frequency analysis in urban watersheds is complicated by nonstationarities of annual peak records associated with land use change and evolving urban stormwater infrastructure. In this study, a framework for flood frequency analysis is developed based on the Generalized Additive Models for Location, Scale and Shape parameters (GAMLSS), a tool for modeling time series under nonstationary conditions. GAMLSS is applied to annual maximum peak discharge records for Little Sugar Creek, a highly urbanized watershed which drains the urban core of Charlotte, North Carolina. It is shown that GAMLSS is able to describe the variability in the mean and variance of the annual maximum peak discharge by modeling the parameters of the selected parametric distribution as a smooth function of time via cubic splines. Flood frequency analyses for Little Sugar Creek (at a drainage area of 110km) show that the maximum flow with a 0.01-annual probability (corresponding to 100-year flood peak under stationary conditions) over the 83-year record has ranged from a minimum unit discharge of 2.1mskm to a maximum of 5.1mskm. An alternative characterization can be made by examining the estimated return interval of the peak discharge that would have an annual exceedance probability of 0.01 under the assumption of stationarity (3.2mskm). Under nonstationary conditions, alternative definitions of return period should be adapted. Under the GAMLSS model, the return interval of an annual peak discharge of 3.2mskm ranges from a maximum value of more than 5000 years in 1957 to a minimum value of almost 8 years for the present time (2007). The GAMLSS framework is also used to examine the links between population trends and flood frequency, as well as trends in annual maximum rainfall. These analyses are used to examine evolving flood frequency over future decades.

Models for High-Energy Radiation from Blazars G. E. Romero1 ...

Indian Academy of Sciences (India)

Abstract. We discuss on the modelling of blazar jets as emitters of multiwavelength radiation with the implementation of a lepto-hadronic treatment. Assuming that injection of non-thermal electrons and protons can take place at the base of the jet, the stationary particle distributions can be found using an inhomogeneous ...

The Evolution of Swift/BAT blazars and the origin of the MeV background

Energy Technology Data Exchange (ETDEWEB)

Ajello, M.; /SLAC /KIPAC, Menlo Park; Costamante, L.; /Stanford U., HEPL /KIPAC, Menlo Park; Sambruna, R.M.; Gehrels, N.; /NASA, Goddard; Chiang, J.; /SLAC /KIPAC, Menlo Park; Rau, A.; /Caltech; Escala, A.; /SLAC /KIPAC, Menlo Park /Cerro Calan Observ.; Greiner, J.; /Garching, Max Planck Inst., MPE; Tueller, J.; /NASA, Goddard; Wall, J.V.; /British Columbia U.; Mushotzky, R.F.; /NASA, Goddard

2009-10-17

We use 3 years of data from the Swift/BAT survey to select a complete sample of X-ray blazars above 15 keV. This sample comprises 26 Flat-Spectrum Radio Quasars (FSRQs) and 12 BL Lac objects detected over a redshift range of 0.03 < z < 4.0. We use this sample to determine, for the first time in the 15-55 keV band, the evolution of blazars. We find that, contrary to the Seyfert-like AGNs detected by BAT, the population of blazars shows strong positive evolution. This evolution is comparable to the evolution of luminous optical QSOs and luminous X-ray selected AGNs. We also find evidence for an epoch-dependence of the evolution as determined previously for radio-quiet AGNs. We interpret both these findings as a strong link between accretion and jet activity. In our sample, the FSRQs evolve strongly, while our best-fit shows that BL Lacs might not evolve at all. The blazar population accounts for 10-20% (depending on the evolution of the BL Lacs) of the Cosmic X-ray background (CXB) in the 15-55 keV band. We find that FSRQs can explain the entire CXB emission for energies above 500 keV solving the mystery of the generation of the MeV background. The evolution of luminous FSRQs shows a peak in redshift (z{sub c} = 4.3 {+-} 0.5) which is larger than the one observed in QSOs and X-ray selected AGNs. We argue that FSRQs can be used as tracers of massive elliptical galaxies in the early Universe.

Research and characterisation of blazar candidates among the Fermi/LAT 3FGL catalogue using multivariate classifications

Science.gov (United States)

Lefaucheur, Julien; Pita, Santiago

2017-06-01

Context. In the recently published 3FGL catalogue, the Fermi/LAT collaboration reports the detection of γ-ray emission from 3034 sources obtained after four years of observations. The nature of 1010 of those sources is unknown, whereas 2023 have well-identified counterparts in other wavelengths. Most of the associated sources are labelled as blazars (1717/2023), but the BL Lac or FSRQ nature of 573 of these blazars is still undetermined. Aims: The aim of this study was two-fold. First, to significantly increase the number of blazar candidates from a search among the large number of Fermi/LAT 3FGL unassociated sources (case A). Second, to determine the BL Lac or FSRQ nature of the blazar candidates, including those determined as such in this work and the blazar candidates of uncertain type (BCU) that are already present in the 3FGL catalogue (case B). Methods: For this purpose, multivariate classifiers - boosted decision trees and multilayer perceptron neural networks - were trained using samples of labelled sources with no caution flag from the 3FGL catalogue and carefully chosen discriminant parameters. The decisions of the classifiers were combined in order to obtain a high level of source identification along with well controlled numbers of expected false associations. Specifically for case A, dedicated classifications were generated for high (| b | >10◦) and low (| b | ≤10◦) galactic latitude sources; in addition, the application of classifiers to samples of sources with caution flag was considered separately, and specific performance metrics were estimated. Results: We obtained a sample of 595 blazar candidates (high and low galactic latitude) among the unassociated sources of the 3FGL catalogue. We also obtained a sample of 509 BL Lacs and 295 FSRQs from the blazar candidates cited above and the BCUs of the 3FGL catalogue. The number of expected false associations is given for different samples of candidates. It is, in particular, notably low ( 9

Roma-BZCAT: a multifrequency catalogue of blazars

Science.gov (United States)

Massaro, E.; Giommi, P.; Leto, C.; Marchegiani, P.; Maselli, A.; Perri, M.; Piranomonte, S.; Sclavi, S.

2009-02-01

We present a new catalogue of blazars based on multifrequency surveys and on an extensive review of the literature. Blazars are classified as BL Lacertae objects, as flat spectrum radio quasars or as blazars of uncertain/transitional type. Each object is identified by a root name, coded as BZB, BZQ and BZU for these three subclasses respectively, and by its coordinates. This catalogue is being built as a tool useful for the identification of the extragalactic sources that will be detected by present and future experiments for X and gamma-ray astronomy, like Swift, AGILE, Fermi-GLAST and Simbol-X. An electronic version is available from the ASI Science Data Center web site at http://www.asdc.asi.it/bzcat.

THE COSMOLOGICAL IMPACT OF LUMINOUS TeV BLAZARS. II. REWRITING THE THERMAL HISTORY OF THE INTERGALACTIC MEDIUM

Energy Technology Data Exchange (ETDEWEB)

Chang, Philip; Broderick, Avery E; Pfrommer, Christoph [Canadian Institute for Theoretical Astrophysics, 60 St. George Street, Toronto, ON M5S 3H8 (Canada)

2012-06-10

The universe is opaque to extragalactic very high energy gamma rays (VHEGRs, E > 100 GeV) because they annihilate and pair produce on the extragalactic background light. The resulting ultrarelativistic pairs are commonly assumed to lose energy primarily through inverse Compton scattering of cosmic microwave background (CMB) photons, reprocessing the original emission from TeV to GeV energies. In Broderick et al., we argued that this is not the case; powerful plasma instabilities driven by the highly anisotropic nature of the ultrarelativistic pair distribution provide a plausible way to dissipate the kinetic energy of the TeV-generated pairs locally, heating the intergalactic medium (IGM). Here, we explore the effect of this heating on the thermal history of the IGM. We collate the observed extragalactic VHEGR sources to determine a local VHEGR heating rate. Given the pointed nature of VHEGR observations, we estimate the correction for the various selection effects using Fermi observations of high- and intermediate-peaked BL Lac objects. As the extragalactic component of the local VHEGR flux is dominated by TeV blazars, we then estimate the evolution of the TeV blazar luminosity density by tying it to the well-observed quasar luminosity density and producing a VHEGR heating rate as a function of redshift. This heating is relatively homogeneous for z {approx}< 4, but there is greater spatial variation at higher redshift (order unity at z {approx} 6) because of the reduced number of blazars that contribute to local heating. We show that this new heating process dominates photoheating in the low-redshift evolution of the IGM and calculate the effect of this heating in a one-zone model. As a consequence, the inclusion of TeV blazar heating qualitatively and quantitatively changes the structure and history of the IGM. Due to the homogeneous nature of the extragalactic background light, TeV blazars produce a uniform volumetric heating rate. This heating is sufficient to

THE COSMOLOGICAL IMPACT OF LUMINOUS TeV BLAZARS. II. REWRITING THE THERMAL HISTORY OF THE INTERGALACTIC MEDIUM

International Nuclear Information System (INIS)

Chang, Philip; Broderick, Avery E.; Pfrommer, Christoph

2012-01-01

The universe is opaque to extragalactic very high energy gamma rays (VHEGRs, E > 100 GeV) because they annihilate and pair produce on the extragalactic background light. The resulting ultrarelativistic pairs are commonly assumed to lose energy primarily through inverse Compton scattering of cosmic microwave background (CMB) photons, reprocessing the original emission from TeV to GeV energies. In Broderick et al., we argued that this is not the case; powerful plasma instabilities driven by the highly anisotropic nature of the ultrarelativistic pair distribution provide a plausible way to dissipate the kinetic energy of the TeV-generated pairs locally, heating the intergalactic medium (IGM). Here, we explore the effect of this heating on the thermal history of the IGM. We collate the observed extragalactic VHEGR sources to determine a local VHEGR heating rate. Given the pointed nature of VHEGR observations, we estimate the correction for the various selection effects using Fermi observations of high- and intermediate-peaked BL Lac objects. As the extragalactic component of the local VHEGR flux is dominated by TeV blazars, we then estimate the evolution of the TeV blazar luminosity density by tying it to the well-observed quasar luminosity density and producing a VHEGR heating rate as a function of redshift. This heating is relatively homogeneous for z ∼< 4, but there is greater spatial variation at higher redshift (order unity at z ∼ 6) because of the reduced number of blazars that contribute to local heating. We show that this new heating process dominates photoheating in the low-redshift evolution of the IGM and calculate the effect of this heating in a one-zone model. As a consequence, the inclusion of TeV blazar heating qualitatively and quantitatively changes the structure and history of the IGM. Due to the homogeneous nature of the extragalactic background light, TeV blazars produce a uniform volumetric heating rate. This heating is sufficient to increase

Modelling the flaring activity of the high-z, hard X-ray-selected blazar IGR J22517+2217: Flaring activity of IGR J22517+2217

International Nuclear Information System (INIS)

Lanzuisi, G.; De Rosa, A.; Ghisellini, G.; Panessa, F.

2012-01-01

We present new Suzaku and Fermi data and re-analysed archival hard X-ray data from the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) and Swift–Burst Alert Telescope (BAT) surveys to investigate the physical properties of the luminous, high-redshift, hard X-ray-selected blazar IGR J22517+2217, through the modelling of its broad-band spectral energy distribution (SED) in two different activity states. Through analysis of new Suzaku data and flux-selected data from archival hard X-ray observations, we build the source SED in two different states, one for the newly discovered flare that occurred in 2005 and one for the following quiescent period. Both SEDs are strongly dominated by the high-energy hump peaked at 10 20 –10 22 Hz, which is at least two orders of magnitude higher than the low-energy (synchrotron) one at 10 11 –10 14 Hz and varies by a factor of 10 between the two states. In both states the high-energy hump is modelled as inverse Compton emission between relativistic electrons and seed photons produced externally to the jet, while the synchrotron self-Compton component is found to be negligible. In our model the observed variability can be accounted for by a variation of the total number of emitting electrons and by a dissipation region radius changing from inside to outside the broad-line region as the luminosity increases. In its flaring activity, IGR J22517+2217 is revealed as one of the most powerful jets among the population of extreme, hard X-ray-selected, high-redshift blazars observed so far.

EVIDENCE FOR SECONDARY EMISSION AS THE ORIGIN OF HARD SPECTRA IN TeV BLAZARS

International Nuclear Information System (INIS)

Zheng, Y. G.; Kang, T.

2013-01-01

We develop a model for the possible origin of hard, very high energy (VHE) spectra from a distant blazar. In the model, both the primary photons produced in the source and secondary photons produced outside it contribute to the observed high-energy γ-ray emission. That is, the primary photons are produced through the synchrotron self-Compton process, and the secondary photons are produced through high-energy proton interactions with background photons along the line of sight. We apply the model to a characteristic case of VHE γ-ray emission in the distant blazar 1ES 1101-232. Assuming suitable electron and proton spectra, we obtain excellent fits to the observed spectra of this blazar. This indicated that the surprisingly low attenuation of the high-energy γ-rays, especially the shape of the VHE γ-ray tail of the observed spectra, can be explained by secondary γ-rays produced in interactions of cosmic-ray protons with background photons in intergalactic space.

Blazar Sheath Illumination of the Outer Molecular Torus: A Resolution of the Seed Photon Problem for the Far-GeV Blazar Flares

Science.gov (United States)

Breiding, Peter; Georganopoulos, Markos; Meyer, Eileen T.

2018-01-01

Recent multiwavelength work led by the Boston University blazar group (e.g., Marscher et al.) strongly suggests that a fraction of the blazar flares seen by the Fermi Large Area Telescope (LAT) take place a few to several pc away from the central engine. However, at such distances from the central engine, there is no adequate external photon field to provide the seed photons required for producing the observed GeV emission under leptonic inverse Compton (IC) models. A possible solution is a spine-sheath geometry for the emitting region (MacDonald et al., but see Nalewajko et al.). Here we use the current view of the molecular torus (e.g., Elitzur; Netzer), in which the torus extends a few pc beyond the dust sublimation radius with dust clouds distributed with a declining density for decreasing polar angle. We show that for a spine-sheath blazar jet embedded in the torus, the wide beaming pattern of the synchrotron radiation of the relatively slow sheath will heat molecular clouds with subsequent IR radiation that will be highly boosted in the spine comoving frame, and that under reasonable conditions this photon field can dominate over the sheath photons directly entering the spine. If the sheath is sufficiently luminous it will sublimate the dust, and if the sheath synchrotron radiation extends to optical-UV energies (as may happen during flares), this will illuminate the sublimated dust clouds to produce emission lines that will vary in unison with the optical-UV continuum, as has been very recently reported for blazar CTA 102 (Jorstad et al.).

PATCHY BLAZAR HEATING: DIVERSIFYING THE THERMAL HISTORY OF THE INTERGALACTIC MEDIUM

International Nuclear Information System (INIS)

Lamberts, Astrid; Chang, Philip; Pfrommer, Christoph; Puchwein, Ewald; Broderick, Avery E.; Shalaby, Mohamad

2015-01-01

TeV-blazars potentially heat the intergalactic medium (IGM) as their gamma rays interact with photons of the extragalactic background light to produce electron–positron pairs, which lose their kinetic energy to the surrounding medium through plasma instabilities. This results in a heating mechanism that is only weakly sensitive to the local density, and therefore approximately spatially uniform, naturally producing an inverted temperature–density relation in underdense regions. In this paper we go beyond the approximation of uniform heating and quantify the heating rate fluctuations due to the clustered distribution of blazars and how this impacts the thermal history of the IGM. We analytically compute a filtering function that relates the heating rate fluctuations to the underlying dark matter density field. We implement it in the cosmological code GADGET-3 and perform large-scale simulations to determine the impact of inhomogeneous heating. We show that because of blazar clustering, blazar heating is inhomogeneous for z ≳ 2. At high redshift, the temperature–density relation shows an important scatter and presents a low temperature envelope of unheated regions, in particular at low densities and within voids. However, the median temperature of the IGM is close to that in the uniform case, albeit slightly lower at low redshift. We find that blazar heating is more complex than initially assumed and that the temperature–density relation is not unique. Our analytic model for the heating rate fluctuations couples well with large-scale simulations and provides a cost-effective alternative to subgrid models

THE CONTRIBUTION OF FERMI -2LAC BLAZARS TO DIFFUSE TEV–PEV NEUTRINO FLUX

Energy Technology Data Exchange (ETDEWEB)

Aartsen, M. G. [Department of Physics, University of Adelaide, Adelaide, 5005 (Australia); Abraham, K. [Physik-department, Technische Universität München, D-85748 Garching (Germany); Ackermann, M. [DESY, D-15735 Zeuthen (Germany); Adams, J. [Dept. of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch (New Zealand); Aguilar, J. A.; Ansseau, I. [Université Libre de Bruxelles, Science Faculty CP230, B-1050 Brussels (Belgium); Ahlers, M. [Dept. of Physics and Wisconsin IceCube Particle Astrophysics Center, University of Wisconsin, Madison, WI 53706 (United States); Ahrens, M. [Oskar Klein Centre and Dept. of Physics, Stockholm University, SE-10691 Stockholm (Sweden); Altmann, D.; Anton, G. [Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, D-91058 Erlangen (Germany); Andeen, K. [Department of Physics, Marquette University, Milwaukee, WI, 53201 (United States); Anderson, T.; Arlen, T. C. [Dept. of Physics, Pennsylvania State University, University Park, PA 16802 (United States); Archinger, M.; Baum, V. [Institute of Physics, University of Mainz, Staudinger Weg 7, D-55099 Mainz (Germany); Arguelles, C.; Axani, S. [Dept. of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Auffenberg, J. [III. Physikalisches Institut, RWTH Aachen University, D-52056 Aachen (Germany); Bai, X. [Physics Department, South Dakota School of Mines and Technology, Rapid City, SD 57701 (United States); Barwick, S. W., E-mail: thorsten.gluesenkamp@fau.de [Dept. of Physics and Astronomy, University of California, Irvine, CA 92697 (United States); Collaboration: IceCube Collaboration; and others

2017-01-20

The recent discovery of a diffuse cosmic neutrino flux extending up to PeV energies raises the question of which astrophysical sources generate this signal. Blazars are one class of extragalactic sources which may produce such high-energy neutrinos. We present a likelihood analysis searching for cumulative neutrino emission from blazars in the 2nd Fermi -LAT AGN catalog (2LAC) using IceCube neutrino data set 2009-12, which was optimized for the detection of individual sources. In contrast to those in previous searches with IceCube, the populations investigated contain up to hundreds of sources, the largest one being the entire blazar sample in the 2LAC catalog. No significant excess is observed, and upper limits for the cumulative flux from these populations are obtained. These constrain the maximum contribution of 2LAC blazars to the observed astrophysical neutrino flux to 27% or less between around 10 TeV and 2 PeV, assuming the equipartition of flavors on Earth and a single power-law spectrum with a spectral index of −2.5. We can still exclude the fact that 2LAC blazars (and their subpopulations) emit more than 50% of the observed neutrinos up to a spectral index as hard as −2.2 in the same energy range. Our result takes into account the fact that the neutrino source count distribution is unknown, and it does not assume strict proportionality of the neutrino flux to the measured 2LAC γ -ray signal for each source. Additionally, we constrain recent models for neutrino emission by blazars.

Flood frequency analysis for nonstationary annual peak records in an urban drainage basin

Science.gov (United States)

Villarini, G.; Smith, J.A.; Serinaldi, F.; Bales, J.; Bates, P.D.; Krajewski, W.F.

2009-01-01

Flood frequency analysis in urban watersheds is complicated by nonstationarities of annual peak records associated with land use change and evolving urban stormwater infrastructure. In this study, a framework for flood frequency analysis is developed based on the Generalized Additive Models for Location, Scale and Shape parameters (GAMLSS), a tool for modeling time series under nonstationary conditions. GAMLSS is applied to annual maximum peak discharge records for Little Sugar Creek, a highly urbanized watershed which drains the urban core of Charlotte, North Carolina. It is shown that GAMLSS is able to describe the variability in the mean and variance of the annual maximum peak discharge by modeling the parameters of the selected parametric distribution as a smooth function of time via cubic splines. Flood frequency analyses for Little Sugar Creek (at a drainage area of 110 km2) show that the maximum flow with a 0.01-annual probability (corresponding to 100-year flood peak under stationary conditions) over the 83-year record has ranged from a minimum unit discharge of 2.1 m3 s- 1 km- 2 to a maximum of 5.1 m3 s- 1 km- 2. An alternative characterization can be made by examining the estimated return interval of the peak discharge that would have an annual exceedance probability of 0.01 under the assumption of stationarity (3.2 m3 s- 1 km- 2). Under nonstationary conditions, alternative definitions of return period should be adapted. Under the GAMLSS model, the return interval of an annual peak discharge of 3.2 m3 s- 1 km- 2 ranges from a maximum value of more than 5000 years in 1957 to a minimum value of almost 8 years for the present time (2007). The GAMLSS framework is also used to examine the links between population trends and flood frequency, as well as trends in annual maximum rainfall. These analyses are used to examine evolving flood frequency over future decades. ?? 2009 Elsevier Ltd.

Models for Very Rapid High-Energy γ-Ray Variability in Blazars G. E. ...

Indian Academy of Sciences (India)

blazar PKS 2155−304 and present synthetic light-curves of the kind that ... radio wavelengths led to a similar situation (see Wagner & Witzel 1995 for a review). Some of the ... If the instabilities grow, the two components will eventually mix.

Relation between Radio Polarization and Spectral Index of Blazars ...

Indian Academy of Sciences (India)

Introduction. Blazars are a very special class of extragalactic objects showing some special proper- ties, including rapid variability, high and variability polarization, high luminosity and superluminal motion, etc. Their optical variability timescales can cover a range of hours to years from radio to γ-rays (Fan et al. 2004; Ulrich ...

Order Tracking Based on Robust Peak Search Instantaneous Frequency Estimation

International Nuclear Information System (INIS)

Gao, Y; Guo, Y; Chi, Y L; Qin, S R

2006-01-01

Order tracking plays an important role in non-stationary vibration analysis of rotating machinery, especially to run-up or coast down. An instantaneous frequency estimation (IFE) based order tracking of rotating machinery is introduced. In which, a peak search algorithms of spectrogram of time-frequency analysis is employed to obtain IFE of vibrations. An improvement to peak search is proposed, which can avoid strong non-order components or noises disturbing to the peak search work. Compared with traditional methods of order tracking, IFE based order tracking is simplified in application and only software depended. Testing testify the validity of the method. This method is an effective supplement to traditional methods, and the application in condition monitoring and diagnosis of rotating machinery is imaginable

Astronomical Plate Archives and Binary Blazars Studies

Czech Academy of Sciences Publication Activity Database

Hudec, René

2011-01-01

Roč. 32, 1-2 (2011), s. 91-95 ISSN 0250-6335. [Conference on Multiwavelength Variability of Blazars. Guangzhou, 22,09,2010-24,09,2010] R&D Projects: GA ČR GA205/08/1207 Grant - others:GA ČR(CZ) GA102/09/0997; MŠMT(CZ) ME09027 Institutional research plan: CEZ:AV0Z10030501 Keywords : astronomical plates * plate archives archives * binary blazars Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 0.400, year: 2011

Over 8 W high peak power UV laser with a high power Q-switched Nd:YVO4 oscillator and the compact extra-cavity sum-frequency mixing

International Nuclear Information System (INIS)

Yan, X P; Liu, Q; Gong, M; Wang, D S; Fu, X

2009-01-01

A 8.2 W UV laser was reported with the compact extra-cavity sum-frequency mixing. The IR fundamental frequency source was a high power and high beam quality Q-switched Nd:YVO 4 oscillator. 38 W fundamental frequency laser at 1064 nm was obtained at the pulse repetition rate of 450 kHz with the beam quality factors of M 2 x = 1.27, M 2 y = 1.21. The type I and type II phase-matched LBO crystals were used as the extra-cavity frequency doubling and mixing crystals respectively. At 38 kHz, 8.2 W UV laser at 355 nm was achieved with the pulse duration of 8 ns corresponding to the pulse peak power as high as 27 kW, and the optical-optical conversion efficiency from IR to UV was 25.6%. The output characteristics of the IR and the harmonic generations varying with the pulse repetition rate were also investigated detailedly

UPPER LIMITS FROM FIVE YEARS OF BLAZAR OBSERVATIONS WITH THE VERITAS CHERENKOV TELESCOPES

Energy Technology Data Exchange (ETDEWEB)

Archambault, S. [Physics Department, McGill University, Montreal, QC H3A 2T8 (Canada); Archer, A.; Buckley, J. H.; Bugaev, V. [Department of Physics, Washington University, St. Louis, MO 63130 (United States); Benbow, W.; Cerruti, M. [Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645 (United States); Bird, R. [School of Physics, University College Dublin, Belfield, Dublin 4 (Ireland); Biteau, J. [Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064 (United States); Buchovecky, M. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Byrum, K. [Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439 (United States); Chen, X. [Institute of Physics and Astronomy, University of Potsdam, D-14476 Potsdam-Golm (Germany); Ciupik, L. [Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605 (United States); Connolly, M. P. [School of Physics, National University of Ireland Galway, University Road, Galway (Ireland); Cui, W.; Feng, Q.; Finley, J. P. [Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907 (United States); Eisch, J. D. [Department of Physics and Astronomy, Iowa State University, Ames, IA 50011 (United States); Errando, M. [Department of Physics and Astronomy, Barnard College, Columbia University, NY 10027 (United States); Falcone, A. [Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802 (United States); Fleischhack, H., E-mail: wystan.benbow@cfa.harvard.edu, E-mail: matteo.cerruti@lpnhe.in2p3.fr, E-mail: caajohns@ucsc.edu [DESY, Platanenallee 6, D-15738 Zeuthen (Germany); Collaboration: VERITAS collaboration; and others

2016-06-01

Between the beginning of its full-scale scientific operations in 2007 and 2012, the VERITAS Cherenkov telescope array observed more than 130 blazars; of these, 26 were detected as very-high-energy (VHE; E > 100 GeV) γ -ray sources. In this work, we present the analysis results of a sample of 114 undetected objects. The observations constitute a total live-time of ∼570 hr. The sample includes several unidentified Fermi -Large Area Telescope (LAT) sources (located at high Galactic latitude) as well as all the sources from the second Fermi -LAT catalog that are contained within the field of view of the VERITAS observations. We have also performed optical spectroscopy measurements in order to estimate the redshift of some of these blazars that do not have spectroscopic distance estimates. We present new optical spectra from the Kast instrument on the Shane telescope at the Lick observatory for 18 blazars included in this work, which allowed for the successful measurement or constraint on the redshift of four of them. For each of the blazars included in our sample, we provide the flux upper limit in the VERITAS energy band. We also study the properties of the significance distributions and we present the result of a stacked analysis of the data set, which shows a 4 σ excess.

UPPER LIMITS FROM FIVE YEARS OF BLAZAR OBSERVATIONS WITH THE VERITAS CHERENKOV TELESCOPES

International Nuclear Information System (INIS)

Archambault, S.; Archer, A.; Buckley, J. H.; Bugaev, V.; Benbow, W.; Cerruti, M.; Bird, R.; Biteau, J.; Buchovecky, M.; Byrum, K.; Chen, X.; Ciupik, L.; Connolly, M. P.; Cui, W.; Feng, Q.; Finley, J. P.; Eisch, J. D.; Errando, M.; Falcone, A.; Fleischhack, H.

2016-01-01

Between the beginning of its full-scale scientific operations in 2007 and 2012, the VERITAS Cherenkov telescope array observed more than 130 blazars; of these, 26 were detected as very-high-energy (VHE; E > 100 GeV) γ -ray sources. In this work, we present the analysis results of a sample of 114 undetected objects. The observations constitute a total live-time of ∼570 hr. The sample includes several unidentified Fermi -Large Area Telescope (LAT) sources (located at high Galactic latitude) as well as all the sources from the second Fermi -LAT catalog that are contained within the field of view of the VERITAS observations. We have also performed optical spectroscopy measurements in order to estimate the redshift of some of these blazars that do not have spectroscopic distance estimates. We present new optical spectra from the Kast instrument on the Shane telescope at the Lick observatory for 18 blazars included in this work, which allowed for the successful measurement or constraint on the redshift of four of them. For each of the blazars included in our sample, we provide the flux upper limit in the VERITAS energy band. We also study the properties of the significance distributions and we present the result of a stacked analysis of the data set, which shows a 4 σ excess.

Data reduction and analysis of the multiband optical images of the blazar Mrk180

Directory of Open Access Journals (Sweden)

M Sabzi Sarvestani

2012-09-01

Full Text Available  Nearly simultaneous multiband monitoring of blazars is very limited and most studies reported in literature are conflicting, too. Although optical variability on intra-night timescales is now a well established phenomenon for blazars, its relationship to long-term variability remains unclear. Possible clues could come from monitoring the optical spectrum for correlation with brightness. The presence or absence of bluer color in blazar color index, when its luminosity is increased on intra-night and inter-night timescales, can provide interesting clues to the origin of blazar variability from hourly to much longer timescales. Luminosity of blazars varies at all wavelengths over a variety of timescales. Various models have been proposed to explain blazar variability. However, the mechanism responsible for variability is not conclusively understood. One factor which can discriminate the various variability models is that of color (spectral index variations of blazars. This factor may help to better understand the mechanism of blazar variability. Therefore, it was initially proposed, by the second author of this paper to the OHP observatory, to carry out quasi-simultaneous multiband monitoring of one of the brightest blazer, Mrk180. Fortunately, it was accepted by the scientific team of the observatory and the 1.20m telescope time was allocated to the project from 23 to 28 April 2009. Because of the weather conditions, we could only monitor this blazar for three nights. Raw data processing and data reduction were performed using the standard system of Europe Southerner Observatory, ESO-MIDAS. We considered two reference stars and measured the magnitudes of the reference stars and the blazar Mrk 180 and then plotted the light curves and the color index diagrams. The light curves showed the optical variations of the blazar. The maximum amplitude value of its variations was 0.185 mag for the V filter. Investigating the blazar color index shows its

Search for neutrino emission from gamma-ray flaring blazars with the ANTARES telescope

OpenAIRE

Adrián-Martínez, S.; Al Samarai, Imen; Albert, A.; André, Michel; Anghinolfi, M.; Anton, G.; Anvar, S.; Ardid, M.; Astraatmadja, T.; Aubert, J.-J.; Baret, B.; Basa, S.; Bertin, V.; Biagi, S.; Bigongiari, C.

2011-01-01

The ANTARES telescope is well-suited to detect neutrinos produced in astrophysical transient sources as it can observe a full hemisphere of the sky at all times with a high duty cycle. Radio-loud active galactic nuclei with jets pointing almost directly towards the observer, the so-called blazars, are particularly attractive potential neutrino point sources. The all-sky monitor LAT on board the Fermi satellite probes the variability of any given gamma-ray bright blazar in the sky on time scal...

Cluster observations of high-frequency waves in the exterior cusp

Directory of Open Access Journals (Sweden)

Y. Khotyaintsev

2004-07-01

Full Text Available We study wave emissions, in the frequency range from above the lower hybrid frequency up to the plasma frequency, observed during one of the Cluster crossings of a high-beta exterior cusp region on 4 March 2003. Waves are localized near narrow current sheets with a thickness a few times the ion inertial length; currents are strong, of the order of 0.1-0.5μA/m² (0.1-0.5mA/m² when mapped to ionosphere. The high frequency part of the waves, frequencies above the electron-cyclotron frequency, is analyzed in more detail. These high frequency waves can be broad-band, can have spectral peaks at the plasma frequency or spectral peaks at frequencies below the plasma frequency. The strongest wave emissions usually have a spectral peak near the plasma frequency. The wave emission intensity and spectral character change on a very short time scale, of the order of 1s. The wave emissions with strong spectral peaks near the plasma frequency are usually seen on the edges of the narrow current sheets. The most probable generation mechanism of high frequency waves are electron beams via bump-on-tail or electron two-stream instability. Buneman and ion-acoustic instability can be excluded as a possible generation mechanism of waves. We suggest that high frequency waves are generated by electron beams propagating along the separatrices of the reconnection region.

CHARACTERIZING THE OPTICAL VARIABILITY OF BRIGHT BLAZARS: VARIABILITY-BASED SELECTION OF FERMI ACTIVE GALACTIC NUCLEI

International Nuclear Information System (INIS)

Ruan, John J.; Anderson, Scott F.; MacLeod, Chelsea L.; Becker, Andrew C.; Davenport, James R. A.; Ivezić, Željko; Burnett, T. H.; Kochanek, Christopher S.; Plotkin, Richard M.; Sesar, Branimir; Stuart, J. Scott

2012-01-01

We investigate the use of optical photometric variability to select and identify blazars in large-scale time-domain surveys, in part to aid in the identification of blazar counterparts to the ∼30% of γ-ray sources in the Fermi 2FGL catalog still lacking reliable associations. Using data from the optical LINEAR asteroid survey, we characterize the optical variability of blazars by fitting a damped random walk model to individual light curves with two main model parameters, the characteristic timescales of variability τ, and driving amplitudes on short timescales σ-circumflex. Imposing cuts on minimum τ and σ-circumflex allows for blazar selection with high efficiency E and completeness C. To test the efficacy of this approach, we apply this method to optically variable LINEAR objects that fall within the several-arcminute error ellipses of γ-ray sources in the Fermi 2FGL catalog. Despite the extreme stellar contamination at the shallow depth of the LINEAR survey, we are able to recover previously associated optical counterparts to Fermi active galactic nuclei with E ≥ 88% and C = 88% in Fermi 95% confidence error ellipses having semimajor axis r < 8'. We find that the suggested radio counterpart to Fermi source 2FGL J1649.6+5238 has optical variability consistent with other γ-ray blazars and is likely to be the γ-ray source. Our results suggest that the variability of the non-thermal jet emission in blazars is stochastic in nature, with unique variability properties due to the effects of relativistic beaming. After correcting for beaming, we estimate that the characteristic timescale of blazar variability is ∼3 years in the rest frame of the jet, in contrast with the ∼320 day disk flux timescale observed in quasars. The variability-based selection method presented will be useful for blazar identification in time-domain optical surveys and is also a probe of jet physics.

The radio-γ-ray connection in Fermi blazars

Science.gov (United States)

Ghirlanda, G.; Ghisellini, G.; Tavecchio, F.; Foschini, L.; Bonnoli, G.

2011-05-01

We study the correlation between the γ-ray flux (Fγ), averaged over the first 11 months of the Fermi survey and integrated above 100 MeV, and the radio flux density (Fr at 20 GHz) of Fermi sources associated with a radio counterpart in the 20-GHz Australia Telescope Compact Array (AT20G) survey. Considering the blazars detected in both bands, the correlation is highly significant and has the form Fγ∝F0.85±0.04r, similar to BL Lacertae objects and flat-spectrum radio quasars. However, only a small fraction (˜1/15) of the AT20G radio sources with flat radio spectra are detected by Fermi. To understand if this correlation is real, we examine the selection effects introduced by the flux limits of both the radio and the γ-ray surveys, and the importance of variability of the γ-ray flux. After accounting for these effects, we find that the radio-γ-ray flux correlation is real, but its slope is steeper than the observed one, that is, Fγ∝Fδr with δ in the range 1.25-1.5. The observed Fγ-Fr correlation and the fraction of radio sources detected by Fermi are reproduced assuming a long-term γ-ray flux variability, following a lognormal probability distribution with standard deviation σ≥ 0.5 (corresponding to Fγ varying by at least a factor of 3). Such a variability is compatible, even if not necessarily equal, with what is observed when comparing, for the sources in common, the EGRET and the Fermi γ-ray fluxes (even if the Fermi fluxes are averaged over ˜1 yr). Another indication of variability is the non-detection of 12 out of 66 EGRET blazars by Fermi, despite its higher sensitivity. We also study the strong linear correlation between the γ-ray and the radio luminosity of the 144 AT20G-Fermi associations with known redshift and show, through partial correlation analysis, that it is statistically robust. Two possible implications of these correlations are discussed: the contribution of blazars to the extragalactic γ-ray background and the prediction

Multi-Band Spectral Properties of Fermi Blazars Benzhong Dai ...

Indian Academy of Sciences (India)

... FSRQs, 41 AGNs of other types and 72 AGNs of unknown type (Abdo et al. 2010a). This large sample enable us to investigate the spectral shapes of blazars from optical to X-ray to γ-ray in more detail than has been done before. For this purpose, we collected data for all Fermi blazars having available spectral information.

Peak effect in surface resistance at microwave frequencies in Dy ...

Indian Academy of Sciences (India)

In the measurements at both frequencies the induced microwave current was always less than the critical current of the films. The reason for observation of this peak effect in these films has been explained in our earlier publication [5]. Comparing figures 1 and 2, it is observed that the peaks in sample S1 are broader and.

Characterizing the Optical Variability of Bright Blazars: Variability-based Selection of Fermi Active Galactic Nuclei

Science.gov (United States)

Ruan, John J.; Anderson, Scott F.; MacLeod, Chelsea L.; Becker, Andrew C.; Burnett, T. H.; Davenport, James R. A.; Ivezić, Željko; Kochanek, Christopher S.; Plotkin, Richard M.; Sesar, Branimir; Stuart, J. Scott

2012-11-01

We investigate the use of optical photometric variability to select and identify blazars in large-scale time-domain surveys, in part to aid in the identification of blazar counterparts to the ~30% of γ-ray sources in the Fermi 2FGL catalog still lacking reliable associations. Using data from the optical LINEAR asteroid survey, we characterize the optical variability of blazars by fitting a damped random walk model to individual light curves with two main model parameters, the characteristic timescales of variability τ, and driving amplitudes on short timescales \\hat{\\sigma }. Imposing cuts on minimum τ and \\hat{\\sigma } allows for blazar selection with high efficiency E and completeness C. To test the efficacy of this approach, we apply this method to optically variable LINEAR objects that fall within the several-arcminute error ellipses of γ-ray sources in the Fermi 2FGL catalog. Despite the extreme stellar contamination at the shallow depth of the LINEAR survey, we are able to recover previously associated optical counterparts to Fermi active galactic nuclei with E >= 88% and C = 88% in Fermi 95% confidence error ellipses having semimajor axis r beaming. After correcting for beaming, we estimate that the characteristic timescale of blazar variability is ~3 years in the rest frame of the jet, in contrast with the ~320 day disk flux timescale observed in quasars. The variability-based selection method presented will be useful for blazar identification in time-domain optical surveys and is also a probe of jet physics.

Stochastic modeling of the Fermi/LAT γ-ray blazar variability

Energy Technology Data Exchange (ETDEWEB)

Sobolewska, M. A.; Siemiginowska, A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kelly, B. C. [Department of Physics, Broida Hall, University of California, Santa Barbara, CA 93107 (United States); Nalewajko, K., E-mail: malgosia@camk.edu.pl [JILA, University of Colorado and National Institute of Standards and Technology, 440 UCB, Boulder, CO 80309 (United States)

2014-05-10

We study the γ-ray variability of 13 blazars observed with the Fermi/Large Area Telescope (LAT). These blazars have the most complete light curves collected during the first four years of the Fermi sky survey. We model them with the Ornstein-Uhlenbeck (OU) process or a mixture of the OU processes. The OU process has power spectral density (PSD) proportional to 1/f {sup α} with α changing at a characteristic timescale, τ{sub 0}, from 0 (τ >> τ{sub 0}) to 2 (τ << τ{sub 0}). The PSD of the mixed OU process has two characteristic timescales and an additional intermediate region with 0 < α < 2. We show that the OU model provides a good description of the Fermi/LAT light curves of three blazars in our sample. For the first time, we constrain a characteristic γ-ray timescale of variability in two BL Lac sources, 3C 66A and PKS 2155-304 (τ{sub 0} ≅ 25 days and τ{sub 0} ≅ 43 days, respectively, in the observer's frame), which are longer than the soft X-ray timescales detected in blazars and Seyfert galaxies. We find that the mixed OU process approximates the light curves of the remaining 10 blazars better than the OU process. We derive limits on their long and short characteristic timescales, and infer that their Fermi/LAT PSD resemble power-law functions. We constrain the PSD slopes for all but one source in the sample. We find hints for sub-hour Fermi/LAT variability in four flat spectrum radio quasars. We discuss the implications of our results for theoretical models of blazar variability.

Multiwaveband Variability of Blazars from Turbulent Plasma Passing through a Standing Shock: The Mother of Multi-zone Models

Science.gov (United States)

Marscher, Alan P.

2011-09-01

Multi-wavelength light curves of bright gamma-ray blazars (e.g., 3C 454.3) are compared with the model proposed by Marscher and Jorstad. In this scenario, much of the optical and high-energy radiation in a blazar is emitted near the 43 GHz core of the jet as seen in VLBA images, parsecs from the central engine. The main physical features are a turbulent ambient jet plasma that passes through a standing recollimation shock in the jet. The model allows for short time-scales of optical and gamma-ray variability by restricting the highest-energy electrons radiating at these frequencies to a small fraction of the turbulent cells, perhaps those with a particular orientation of the magnetic field relative to the shock front. Because of this, the volume filling factor at high frequencies is relatively low, while that of the electrons radiating below about 10 THz is near unity. Such a model is consistent with the (1) red-noise power spectra of flux variations, (2) shorter time-scales of variability at higher frequencies, (3) frequency dependence of polarization and its variability, and (4) breaks in the synchrotron spectrum by more than the radiative loss value of 0.5. Simulated light curves are generated by a numerical code that (as of May 2011) includes synchrotron radiation as well as inverse Compton scattering of seed photons from both a dust torus and a Mach disk at the jet axis. The latter source of seed photons produces more pronounced variability in gamma-ray than in optical light curves, as is often observed. More features are expected to be added to the code by the time of the presentation. This research is supported in part by NASA through Fermi grants NNX08AV65G and NNX10AO59G, and by NSF grant AST-0907893.

UV and X-ray Variability of Blazars Alok C. Gupta

Indian Academy of Sciences (India)

mostly soft X-rays hardness ratio show correlations with blazar luminos- ity and different modes of variability might be operating for different time scales and ... The real cause of blazar variability on diverse time scales is not yet well under- stood. ... stereoscopic system (HESS) at a 45σ significance level (Aharonian et al.

On the intrinsic shape of the gamma-ray spectrum for Fermi blazars

Science.gov (United States)

Kang, Shi-Ju; Wu, Qingwen; Zheng, Yong-Gang; Yin, Yue; Song, Jia-Li; Zou, Hang; Feng, Jian-Chao; Dong, Ai-Jun; Wu, Zhong-Zu; Zhang, Zhi-Bin; Wu, Lin-Hui

2018-05-01

The curvature of the γ-ray spectrumin blazarsmay reflect the intrinsic distribution of emitting electrons, which will further give some information on the possible acceleration and cooling processes in the emitting region. The γ-ray spectra of Fermi blazars are normally fitted either by a single power-law (PL) or a log-normal (call Logarithmic Parabola, LP) form. The possible reason for this difference is not clear. We statistically explore this issue based on the different observational properties of 1419 Fermi blazars in the 3LAC Clean Sample.We find that the γ-ray flux (100MeV–100GeV) and variability index follow bimodal distributions for PL and LP blazars, where the γ-ray flux and variability index show a positive correlation. However, the distributions of γ-ray luminosity and redshift follow a unimodal distribution. Our results suggest that the bimodal distribution of γ-ray fluxes for LP and PL blazars may not be intrinsic and all blazars may have an intrinsically curved γ-ray spectrum, and the PL spectrum is just caused by the fitting effect due to less photons.

High peak power tubes and gate effect Klystrons

International Nuclear Information System (INIS)

Gerbelot, N.; Bres, M.; Faillon, G.; Buzzi, J.M.

1993-01-01

The conventional microwave tubes such as TWTs, Magnetrons, Klystrons... deliver the very high peak powers which are required by radar transmitters but more especially by many particle accelerators. In the range of a few hundred MHz to about 10 GHz, some dozen of MWs per unit are currently obtained and commercially available, according to the frequency and the pulse lengths. But peak power requirements are ever increasing, especially for the expected new linear particle acceleratores, where several hundred MWs per tube would be necessary. Also some special military transmitters begin to request GW pulses, with short pulse lengths - of course - but at nonnegligible repetition rates. Therefore several laboratories and microwave vacuum tube manufacturers have engaged - for several years - studies and development in the field of very high peak microwave power (HPM) toward two main directions: extended operation and extrapolation of the conventional tubes and devices; development of new concepts, among which the most promising are likely the high-current relativistic klystrons - that are also referred to as gate effect klystrons

Detecting The EBL Attenuation Of Blazars With GLAST

Science.gov (United States)

Reyes, Luis C.

2006-09-01

The Large Area Telescope (LAT) on board GLAST (Gamma-ray Large Area Space Telescope) due for launch in Fall 2007 will study the gamma-ray sky in the energy range 20 MeV to >300 GeV. GLAST-LAT's improved sensitivity with respect to previous missions will increase the number of known Blazars from about 100 to thousands, with redshifts up to z 5. Since Gamma rays with energy above 10 GeV interact via pair-production with photons from the Extragalactic Background Light (EBL), the systematic attenuation of GLAST-detected Blazars as a function of redshift would constitute and effective and unique probe to the optical-UV EBL density and its evolution over cosmic history. Based on the GLAST-LAT instrument performance, detailed simulations of expected blazar populations attenuated by EBL have been performed. In this poster we present an analysis of such simulations in order to measure the EBL attenuation, ensuing a clear distinction between competing EBL models.

Multiple testing issues in discriminating compound-related peaks and chromatograms from high frequency noise, spikes and solvent-based nois in LC-MS data sets

NARCIS (Netherlands)

Nyangoma, S.O.; Van Kampen, A.A.; Reijmers, T.H.; Govorukhina, N.I; van der Zee, A.G.; Billingham, I.J; Bischoff, Rainer; Jansen, R.C.

2007-01-01

Multiple testing issues in discriminating compound-related peaks and chromatograms from high frequency noise, spikes and solvent-based noise in LC-MS data sets.Nyangoma SO, van Kampen AA, Reijmers TH, Govorukhina NI, van der Zee AG, Billingham LJ, Bischoff R, Jansen RC. University of Birmingham.

Individual Alpha Peak Frequency Predicts 10 Hz Flicker Effects on Selective Attention.

Science.gov (United States)

Gulbinaite, Rasa; van Viegen, Tara; Wieling, Martijn; Cohen, Michael X; VanRullen, Rufin

2017-10-18

Rhythmic visual stimulation ("flicker") is primarily used to "tag" processing of low-level visual and high-level cognitive phenomena. However, preliminary evidence suggests that flicker may also entrain endogenous brain oscillations, thereby modulating cognitive processes supported by those brain rhythms. Here we tested the interaction between 10 Hz flicker and endogenous alpha-band (∼10 Hz) oscillations during a selective visuospatial attention task. We recorded EEG from human participants (both genders) while they performed a modified Eriksen flanker task in which distractors and targets flickered within (10 Hz) or outside (7.5 or 15 Hz) the alpha band. By using a combination of EEG source separation, time-frequency, and single-trial linear mixed-effects modeling, we demonstrate that 10 Hz flicker interfered with stimulus processing more on incongruent than congruent trials (high vs low selective attention demands). Crucially, the effect of 10 Hz flicker on task performance was predicted by the distance between 10 Hz and individual alpha peak frequency (estimated during the task). Finally, the flicker effect on task performance was more strongly predicted by EEG flicker responses during stimulus processing than during preparation for the upcoming stimulus, suggesting that 10 Hz flicker interfered more with reactive than proactive selective attention. These findings are consistent with our hypothesis that visual flicker entrained endogenous alpha-band networks, which in turn impaired task performance. Our findings also provide novel evidence for frequency-dependent exogenous modulation of cognition that is determined by the correspondence between the exogenous flicker frequency and the endogenous brain rhythms. SIGNIFICANCE STATEMENT Here we provide novel evidence that the interaction between exogenous rhythmic visual stimulation and endogenous brain rhythms can have frequency-specific behavioral effects. We show that alpha-band (10 Hz) flicker impairs stimulus

MAXI INVESTIGATION INTO THE LONG-TERM X-RAY VARIABILITY FROM THE VERY-HIGH-ENERGY γ-RAY BLAZAR Mrk 421

Energy Technology Data Exchange (ETDEWEB)

Isobe, Naoki [Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA) 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan); Sato, Ryosuke; Ueda, Yoshihiro; Hayashida, Masaaki; Shidatsu, Megumi; Kawamuro, Taiki [Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502 (Japan); Ueno, Shiro; Matsuoka, Masaru [ISS Science Project Office, Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), 2-1-1 Sengen, Tsukuba, Ibaraki 305-8505 (Japan); Sugizaki, Mutsumi; Sugimoto, Juri; Mihara, Tatehiro [MAXI team, Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Negoro, Hitoshi, E-mail: n-isobe@ir.isas.jaxa.jp [Department of Physics, Nihon University, 1-8-14 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8308 (Japan)

2015-01-01

The archetypical very-high-energy γ-ray blazar Mrk 421 was monitored for more than three years with the Gas Slit Camera on board Monitor of All Sky X-ray Image (MAXI), and its long-term X-ray variability was investigated. The MAXI light curve in the 3-10 keV range was transformed into the periodogram in the frequency range f = 1 × 10{sup –8}-2 × 10{sup –6} Hz. The artifacts on the periodogram, resulting from data gaps in the observed light curve, were extensively simulated for variations with a power-law-like power spectrum density (PSD). By comparing the observed and simulated periodograms, the PSD index was evaluated as α = 1.60 ± 0.25. This index is smaller than that obtained in the higher-frequency range (f ≳ 1 × 10{sup –5} Hz), namely, α = 2.14 ± 0.06 in the 1998 ASCA observation of the object. The MAXI data impose a lower limit on the PSD break at f {sub b} = 5 × 10{sup –6} Hz, consistent with the break of f {sub b} = 9.5 × 10{sup –6} Hz suggested from the ASCA data. The low-frequency PSD index of Mrk 421 derived with MAXI falls well within the range of typical values among nearby Seyfert galaxies (α = 1-2). The physical implications from these results are briefly discussed.

Controlling nonlinear longitudinal space charge oscillations for high peak current bunch train generation

Directory of Open Access Journals (Sweden)

P. Musumeci

2013-10-01

Full Text Available The evolution of picosecond modulations of the longitudinal profile of an electron beam generated in an rf photoinjector is analyzed and optimized with the goal of obtaining high peak current electron bunch trains at very high frequencies (≥THz. Taking advantage of nonlinear longitudinal space charge forces, it is found that more than 500 A peak current 1 THz bunch trains can be generated using a standard 1.6 cell SLAC/UCLA/BNL rf gun. Postacceleration is used to freeze the longitudinal phase space dynamics after one half plasma oscillation. Applications range from tunable narrow bandwidth THz radiation generation to drivers for high frequency high gradient accelerators.

Equipartition gamma-ray blazars and the location of the gamma-ray emission site in 3C 279

International Nuclear Information System (INIS)

Dermer, Charles D.; Cerruti, Matteo; Lott, Benoit; Boisson, Catherine; Zech, Andreas

2014-01-01

Blazar spectral models generally have numerous unconstrained parameters, leading to ambiguous values for physical properties like Doppler factor δ D or fluid magnetic field B'. To help remedy this problem, a few modifications of the standard leptonic blazar jet scenario are considered. First, a log-parabola function for the electron distribution is used. Second, analytic expressions relating energy loss and kinematics to blazar luminosity and variability, written in terms of equipartition parameters, imply δ D , B', and the peak electron Lorentz factor γ pk ′ . The external radiation field in a blazar is approximated by Lyα radiation from the broad-line region (BLR) and ≈0.1 eV infrared radiation from a dusty torus. When used to model 3C 279 spectral energy distributions from 2008 and 2009 reported by Hayashida et al., we derive δ D ∼ 20-30, B' ∼ few G, and total (IR + BLR) external radiation field energy densities u ∼ 10 –2 -10 –3 erg cm –3 , implying an origin of the γ-ray emission site in 3C 279 at the outer edges of the BLR. This is consistent with the γ-ray emission site being located at a distance R ≲ Γ 2 ct var ∼ 0.1(Γ/30) 2 (t var /10 4 s) pc from the black hole powering 3C 279's jets, where t var is the variability timescale of the radiation in the source frame, and at farther distances for narrow-jet and magnetic-reconnection models. Excess ≳ 5 GeV γ-ray emission observed with Fermi LAT from 3C 279 challenges the model, opening the possibility of a second leptonic component or a hadronic origin of the emission. For low hadronic content, absolute jet powers of ≈10% of the Eddington luminosity are calculated.

Multi-epoch VLBA Imaging of 20 New TeV Blazars: Apparent Jet Speeds

Science.gov (United States)

Piner, B. Glenn; Edwards, Philip G.

2018-01-01

We present 88 multi-epoch Very Long Baseline Array (VLBA) images (most at an observing frequency of 8 GHz) of 20 TeV blazars, all of the high-frequency-peaked BL Lac (HBL) class, that have not been previously studied at multiple epochs on the parsec scale. From these 20 sources, we analyze the apparent speeds of 43 jet components that are all detected at four or more epochs. As has been found for other TeV HBLs, the apparent speeds of these components are relatively slow. About two-thirds of the components have an apparent speed that is consistent (within 2σ) with no motion, and some of these components may be stationary patterns whose apparent speed does not relate to the underlying bulk flow speed. In addition, a superluminal tail to the apparent speed distribution of the TeV HBLs is detected for the first time, with eight components in seven sources having a 2σ lower limit on the apparent speed exceeding 1c. We combine the data from these 20 sources with an additional 18 sources from the literature to analyze the complete apparent speed distribution of all 38 TeV HBLs that have been studied with very long baseline interferometry at multiple epochs. The highest 2σ apparent speed lower limit considering all sources is 3.6c. This suggests that bulk Lorentz factors of up to about 4, but probably not much higher, exist in the parsec-scale radio-emitting regions of these sources, consistent with estimates obtained in the radio by other means such as brightness temperatures. This can be reconciled with the high Lorentz factors estimated from the high-energy data if the jet has velocity structures consisting of different emission regions with different Lorentz factors. In particular, we analyze the current apparent speed data for the TeV HBLs in the context of a model with a fast central spine and a slower outer layer.

The Electrostatic Instability for Realistic Pair Distributions in Blazar/EBL Cascades

Science.gov (United States)

Vafin, S.; Rafighi, I.; Pohl, M.; Niemiec, J.

2018-04-01

This work revisits the electrostatic instability for blazar-induced pair beams propagating through the intergalactic medium (IGM) using linear analysis and PIC simulations. We study the impact of the realistic distribution function of pairs resulting from the interaction of high-energy gamma-rays with the extragalactic background light. We present analytical and numerical calculations of the linear growth rate of the instability for the arbitrary orientation of wave vectors. Our results explicitly demonstrate that the finite angular spread of the beam dramatically affects the growth rate of the waves, leading to the fastest growth for wave vectors quasi-parallel to the beam direction and a growth rate at oblique directions that is only a factor of 2–4 smaller compared to the maximum. To study the nonlinear beam relaxation, we performed PIC simulations that take into account a realistic wide-energy distribution of beam particles. The parameters of the simulated beam-plasma system provide an adequate physical picture that can be extrapolated to realistic blazar-induced pairs. In our simulations, the beam looses only 1% of its energy, and we analytically estimate that the beam would lose its total energy over about 100 simulation times. An analytical scaling is then used to extrapolate the parameters of realistic blazar-induced pair beams. We find that they can dissipate their energy slightly faster by the electrostatic instability than through inverse-Compton scattering. The uncertainties arising from, e.g., details of the primary gamma-ray spectrum are too large to make firm statements for individual blazars, and an analysis based on their specific properties is required.

A Model of Polarisation Rotations in Blazars from Kink Instabilities in Relativistic Jets

Directory of Open Access Journals (Sweden)

Krzysztof Nalewajko

2017-10-01

Full Text Available This paper presents a simple model of polarisation rotation in optically thin relativistic jets of blazars. The model is based on the development of helical (kink mode of current-driven instability. A possible explanation is suggested for the observational connection between polarisation rotations and optical/gamma-ray flares in blazars, if the current-driven modes are triggered by secular increases of the total jet power. The importance of intrinsic depolarisation in limiting the amplitude of coherent polarisation rotations is demonstrated. The polarisation rotation amplitude is thus very sensitive to the viewing angle, which appears to be inconsistent with the observational estimates of viewing angles in blazars showing polarisation rotations. Overall, there are serious obstacles to explaining large-amplitude polarisation rotations in blazars in terms of current-driven kink modes.

Time-frequency peak filtering for random noise attenuation of magnetic resonance sounding signal

Science.gov (United States)

Lin, Tingting; Zhang, Yang; Yi, Xiaofeng; Fan, Tiehu; Wan, Ling

2018-05-01

When measuring in a geomagnetic field, the method of magnetic resonance sounding (MRS) is often limited because of the notably low signal-to-noise ratio (SNR). Most current studies focus on discarding spiky noise and power-line harmonic noise cancellation. However, the effects of random noise should not be underestimated. The common method for random noise attenuation is stacking, but collecting multiple recordings merely to suppress random noise is time-consuming. Moreover, stacking is insufficient to suppress high-level random noise. Here, we propose the use of time-frequency peak filtering for random noise attenuation, which is performed after the traditional de-spiking and power-line harmonic removal method. By encoding the noisy signal with frequency modulation and estimating the instantaneous frequency using the peak of the time-frequency representation of the encoded signal, the desired MRS signal can be acquired from only one stack. The performance of the proposed method is tested on synthetic envelope signals and field data from different surveys. Good estimations of the signal parameters are obtained at different SNRs. Moreover, an attempt to use the proposed method to handle a single recording provides better results compared to 16 stacks. Our results suggest that the number of stacks can be appropriately reduced to shorten the measurement time and improve the measurement efficiency.

Intrinsic brightness temperatures of blazar jets at 15 GHz

Directory of Open Access Journals (Sweden)

Hovatta Talvikki

2013-12-01

Full Text Available We have developed a new Bayesian Markov Chain Monte Carlo method to deconvolve light curves of blazars into individual flares, including proper estimation of the fit errors. We use the method to fit 15GHzlight curves obtained within the OVRO 40-m blazar monitoring program where a large number of AGN have been monitored since 2008 in support of the Fermi Gamma-Ray Space Telescope mission. The time scales obtained from the fitted models are used to calculate the variability brightness temperature of the sources. Additionally, we have calculated brightness temperatures of a sample of these objects using Very Long Baseline Array data from the MOJAVE survey. Combining these two data sets enables us to study the intrinsic brightness temperature distribution in these blazars at 15 GHz. Our preliminary results indicate that the mean intrinsic brightness temperature in a sample of 14 sources is near the equipartition brightness temperature of ~ 1011K.

SUZAKU OBSERVATIONS OF THE EXTREME MeV BLAZAR SWIFT J0746.3+2548

International Nuclear Information System (INIS)

Watanabe, Shin; Sato, Rie; Takahashi, Tadayuki; Edwards, Philip G.; Kataoka, Jun; Madejski, Greg; Romani, Roger; Sikora, Marek; Tavecchio, Fabrizio; Sambruna, Rita; Pursimo, Tapio

2009-01-01

We report the Suzaku observations of the high luminosity blazar SWIFT J0746.3+2548 (J0746) conducted in 2005 November. This object, which, with z = 2.979, is the highest redshift source observed in the Suzaku Guaranteed Time Observer period, is likely to show high gamma-ray flux peaking in the MeV range. As a result of the good photon statistics and high signal-to-noise ratio spectrum, the Suzaku observation clearly confirms that J0746 has an extremely hard spectrum in the energy range of 0.3-24 keV, which is well represented by a single power-law with a photon index of Γ ph ≅ 1.17 and Galactic absorption. The multiwavelength spectral energy distribution of J0746 shows two continuum components, and is well modeled assuming that the high-energy spectral component results from Comptonization of the broad-line region photons. In this paper, we search for the bulk Compton spectral features predicted to be produced in the soft X-ray band by scattering external optical/UV photons by cold electrons in a relativistic jet. We discuss and provide constraints on the pair content resulting from the apparent absence of such features.

Long-term spectral and temporal behavior of the high-frequency peaked BL LAC object 1ES 1959+650

Science.gov (United States)

Backes, M.; Uellenbeck, M.; Hayashida, M.; Satalecka, K.; Tescaro, D.; Terzić, T.; MAGIC Collaboration; Fuhrmann, L.; Nestoras, I.; F-GAMMA project; Lähteenmäki, A.; Tornikoski, M.; Nieppola, E.; Metsähovi; Böttcher, M.; Collmar, W.; Weidinger, M.

2012-12-01

The high-frequency peaked BL Lac object 1ES 1959+650 is well-known for an exceptional outburst, which was observed at very high energy (VHE) γ-rays by the Whipple 10m and HEGRA telescopes in 2002. Remarkably, this outburst lacked associated X-ray emission (a socalled "orphan flare") and by this cannot easily be described by standard Synchrotron Self Compton (SSC) models. Models based on hadronic emission processes have also been proposed to explain the observed behavior. Subsequent multi-wavelength observations during a low flux state at TeV energies in 2006 can, instead, be explained by a standard single-zone SSC model. In this context, 1ES 1959+650 has been regularly monitored by the MAGIC telescope since 2005. During these years, no significant variation in the VHE γ-ray flux has been observed. The low energy part of this is in very good agreement with the high-energy part of the time-integrated energy spectrum as measured by Fermi-LAT. Based on this constant flux level in VHE γ-rays, we assembled the time-integrated spectral energy distribution (SED) of 1ES 1959+650 from radio to VHE γ-rays. Despite the non-variability at very high energies, significant flux and spectral variations have been observed at optical and X-ray frequencies in the meanwhile. Furthermore, the shape of the SED at high energy γ-rays as measured by Fermi-LAT is essentially flat which cannot be explained by either conventional single-zone SSC models, or models invoking external radiation fields (EC).

VizieR Online Data Catalog: Blazars equivalent widths and radio luminosity (Landt+, 2004)

Science.gov (United States)

Landt, H.; Padovani, P.; Perlman, E. S.; Giommi, P.

2004-07-01

Blazars are currently separated into BL Lacertae objects (BL Lacs) and flat spectrum radio quasars based on the strength of their emission lines. This is performed rather arbitrarily by defining a diagonal line in the Ca H&K break value-equivalent width plane, following Marcha et al. (1996MNRAS.281..425M). We readdress this problem and put the classification scheme for blazars on firm physical grounds. We study ~100 blazars and radio galaxies from the Deep X-ray Radio Blazar Survey (DXRBS, Cat. and ) and 2-Jy radio survey and find a significant bimodality for the narrow emission line [OIII]{lambda}5007. This suggests the presence of two physically distinct classes of radio-loud active galactic nuclei (AGN). We show that all radio-loud AGN, blazars and radio galaxies, can be effectively separated into weak- and strong-lined sources using the [OIII]{lambda}5007-[OII]{lambda}3727 equivalent width plane. This plane allows one to disentangle orientation effects from intrinsic variations in radio-loud AGN. Based on DXRBS, the strongly beamed sources of the new class of weak-lined radio-loud AGN are made up of BL Lacs at the ~75 per cent level, whereas those of the strong-lined radio-loud AGN include mostly (~97 per cent) quasars. (4 data files).

Low frequency noise peak near magnon emission energy in magnetic tunnel junctions

Energy Technology Data Exchange (ETDEWEB)

Liu, Liang; Xiang, Li; Guo, Huiqiang; Wei, Jian, E-mail: weijian6791@pku.edu.cn [International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China and Collaborative Innovation Center of Quantum Matter, Beijing (China); Li, D. L.; Yuan, Z. H.; Feng, J. F., E-mail: jiafengfeng@iphy.ac.cn; Han, X. F. [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Coey, J. M. D. [CRANN and School of Physics, Trinity College, Dublin 2 (Ireland)

2014-12-15

We report on the low frequency (LF) noise measurements in magnetic tunnel junctions (MTJs) below 4 K and at low bias, where the transport is strongly affected by scattering with magnons emitted by hot tunnelling electrons, as thermal activation of magnons from the environment is suppressed. For both CoFeB/MgO/CoFeB and CoFeB/AlO{sub x}/CoFeB MTJs, enhanced LF noise is observed at bias voltage around magnon emission energy, forming a peak in the bias dependence of noise power spectra density, independent of magnetic configurations. The noise peak is much higher and broader for unannealed AlO{sub x}-based MTJ, and besides Lorentzian shape noise spectra in the frequency domain, random telegraph noise (RTN) is visible in the time traces. During repeated measurements the noise peak reduces and the RTN becomes difficult to resolve, suggesting defects being annealed. The Lorentzian shape noise spectra can be fitted with bias-dependent activation of RTN, with the attempt frequency in the MHz range, consistent with magnon dynamics. These findings suggest magnon-assisted activation of defects as the origin of the enhanced LF noise.

Low frequency noise peak near magnon emission energy in magnetic tunnel junctions

Directory of Open Access Journals (Sweden)

Liang Liu

2014-12-01

Full Text Available We report on the low frequency (LF noise measurements in magnetic tunnel junctions (MTJs below 4 K and at low bias, where the transport is strongly affected by scattering with magnons emitted by hot tunnelling electrons, as thermal activation of magnons from the environment is suppressed. For both CoFeB/MgO/CoFeB and CoFeB/AlOx/CoFeB MTJs, enhanced LF noise is observed at bias voltage around magnon emission energy, forming a peak in the bias dependence of noise power spectra density, independent of magnetic configurations. The noise peak is much higher and broader for unannealed AlOx-based MTJ, and besides Lorentzian shape noise spectra in the frequency domain, random telegraph noise (RTN is visible in the time traces. During repeated measurements the noise peak reduces and the RTN becomes difficult to resolve, suggesting defects being annealed. The Lorentzian shape noise spectra can be fitted with bias-dependent activation of RTN, with the attempt frequency in the MHz range, consistent with magnon dynamics. These findings suggest magnon-assisted activation of defects as the origin of the enhanced LF noise.

On the origin of gamma rays in Fermi blazars: beyond the broad line region.

Science.gov (United States)

Costamante, L.; Cutini, S.; Tosti, G.; Antolini, E.; Tramacere, A.

2018-05-01

The gamma-ray emission in broad-line blazars is generally explained as inverse Compton (IC) radiation of relativistic electrons in the jet scattering optical-UV photons from the Broad Line Region (BLR), the so-called BLR External Compton scenario. We test this scenario on the Fermi gamma-ray spectra of 106 broad-line blazars detected with the highest significance or largest BLR, by looking for cut-off signatures at high energies compatible with γ-γ interactions with BLR photons. We do not find evidence for the expected BLR absorption. For 2/3 of the sources, we can exclude any significant absorption (τmax 5). We conclude that for 9 out of 10 objects, the jet does not interact with BLR photons. Gamma-rays seem either produced outside the BLR most of the time, or the BLR is ˜100 × larger than given by reverberation mapping. This means that i) External Compton on BLR photons is disfavoured as the main gamma-ray mechanism, vs IC on IR photons from the torus or synchrotron self-Compton; ii) the Fermi gamma-ray spectrum is mostly intrinsic, determined by the interaction of the particle distribution with the seed-photons spectrum; iii) without suppression by the BLR, broad-line blazars can become copious emitters above 100 GeV, as demonstrated by 3C 454.3. We expect the CTA sky to be much richer of broad-line blazars than previously thought.

RELAXATION OF BLAZAR-INDUCED PAIR BEAMS IN COSMIC VOIDS

Energy Technology Data Exchange (ETDEWEB)

Miniati, Francesco [Physics Department, Wolfgang-Pauli-Strasse 27, ETH-Zuerich, CH-8093 Zuerich (Switzerland); Elyiv, Andrii, E-mail: fm@phys.ethz.ch [Institut d' Astrophysique et de Geophysique, Universite de Liege, B-4000 Liege (Belgium)

2013-06-10

The stability properties of a low-density ultrarelativistic pair beam produced in the intergalactic medium (IGM) by multi-TeV gamma-ray photons from blazars are analyzed. The problem is relevant for probes of magnetic field in cosmic voids through gamma-ray observations. In addition, dissipation of such beams could considerably affect the thermal history of the IGM and structure formation. We use a Monte Carlo method to quantify the properties of the blazar-induced electromagnetic shower, in particular the bulk Lorentz factor and the angular spread of the pair beam generated by the shower, as a function of distance from the blazar itself. We then use linear and nonlinear kinetic theory to study the stability of the pair beam against the growth of electrostatic plasma waves, employing the Monte Carlo results for our quantitative estimates. We find that the fastest growing mode, like any perturbation mode with even a very modest component perpendicular to the beam direction, cannot be described in the reactive regime. Due to the effect of nonlinear Landau damping, which suppresses the growth of plasma oscillations, the beam relaxation timescale is found to be significantly longer than the inverse Compton loss time. Finally, density inhomogeneities associated with cosmic structure induce loss of resonance between the beam particles and plasma oscillations, strongly inhibiting their growth. We conclude that relativistic pair beams produced by blazars in the IGM are stable on timescales that are long compared with the electromagnetic cascades. There appears to be little or no effect of pair beams on the IGM.

Multiwavelength Emission from Blazars – Conference Summary ...

Indian Academy of Sciences (India)

emission—radio emission—host galaxies—blazar demographics— .... We still need a comprehensive analysis of the selection effects operating in existing ... to the M-sigma relation, or to investigate the evolution of the fundamental plane for.

What We Talk about When We Talk about Blazars?

Energy Technology Data Exchange (ETDEWEB)

Foschini, Luigi, E-mail: luigi.foschini@brera.inaf.it [INAF – Osservatorio Astronomico di Brera, Lecco (Italy)

2017-07-11

After the discovery of powerful relativistic jets from Narrow-Line Seyfert 1 Galaxies, and the understanding of their similarity with those of blazars, a problem of terminology was born. The word blazar is today associated to BL Lac Objects and Flat-Spectrum Radio Quasars, which are somehow different from Narrow-Line Seyfert 1 Galaxies. Using the same word for all the three classes of AGN could drive either toward some misunderstanding, or to the oversight of some important characteristics. I review the main characteristics of these sources, and finally I propose a new scheme of classification.

VERY HIGH ENERGY γ-RAYS FROM THE UNIVERSE’S MIDDLE AGE: DETECTION OF THE z = 0.940 BLAZAR PKS 1441+25 WITH MAGIC

Energy Technology Data Exchange (ETDEWEB)

Ahnen, M. L.; Biland, A. [ETH Zurich, CH-8093 Zurich (Switzerland); Ansoldi, S.; Biasuzzi, B. [Università di Udine, and INFN Trieste, I-33100 Udine (Italy); Antonelli, L. A.; Bonnoli, G.; Carosi, A. [INAF National Institute for Astrophysics, I-00136 Rome (Italy); Antoranz, P. [Università di Siena, and INFN Pisa, I-53100 Siena (Italy); Babic, A. [Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka, University of Split and University of Zagreb (Croatia); Banerjee, B. [Saha Institute of Nuclear Physics, 1\\AF Bidhannagar, Salt Lake, Sector-1, Kolkata 700064 (India); Bangale, P.; Almeida, U. Barres de; Borracci, F. [Max-Planck-Institut für Physik, D-80805 München (Germany); Barrio, J. A.; Bonnefoy, S. [Universidad Complutense, E-28040 Madrid (Spain); Bednarek, W. [University of Łódź, PL-90236 Lodz (Poland); Bernardini, E. [Deutsches Elektronen-Synchrotron (DESY), D-15738 Zeuthen (Germany); Blanch, O. [IFAE, Campus UAB, E-08193 Bellaterra (Spain); Bretz, T. [Universität Würzburg, D-97074 Würzburg (Germany); Carmona, E., E-mail: fabrizio.tavecchio@brera.inaf.it, E-mail: miguelnievas@ucm.es, E-mail: manganaro@iac.es, E-mail: josefa.becerra@nasa.gov [Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, E-28040 Madrid (Spain); Collaboration: MAGIC Collaboration; Fermi-LAT Collaboration; and others

2015-12-20

The flat-spectrum radio quasar PKS 1441+25 at a redshift of z = 0.940 is detected between 40 and 250 GeV with a significance of 25.5σ using the MAGIC telescopes. Together with the gravitationally lensed blazar QSO B0218+357 (z = 0.944), PKS 1441+25 is the most distant very high energy (VHE) blazar detected to date. The observations were triggered by an outburst in 2015 April seen at GeV energies with the Large Area Telescope on board Fermi. Multi-wavelength observations suggest a subdivision of the high state into two distinct flux states. In the band covered by MAGIC, the variability timescale is estimated to be 6.4 ± 1.9 days. Modeling the broadband spectral energy distribution with an external Compton model, the location of the emitting region is understood as originating in the jet outside the broad-line region (BLR) during the period of high activity, while being partially within the BLR during the period of low (typical) activity. The observed VHE spectrum during the highest activity is used to probe the extragalactic background light at an unprecedented distance scale for ground-based gamma-ray astronomy.

Historical changes in annual peak flows in Maine and implications for flood-frequency analyses

Science.gov (United States)

Hodgkins, Glenn A.

2010-01-01

Flood-frequency analyses use statistical methods to compute peak streamflows for selected recurrence intervals— the average number of years between peak flows that are equal to or greater than a specified peak flow. Analyses are based on annual peak flows at a stream. It has long been assumed that the annual peak streamflows used in these computations were stationary (non-changing) over very long periods of time, except in river basins subject to direct effects of human activities, such as urbanization and regulation. Because of the potential effects of global warming on peak flows, the assumption of peak-flow stationarity has recently been questioned. Maine has many streamgages with 50 to 105 years of recorded annual peak streamflows. In this study, this long-term record has been tested for historical flood-frequency stationarity, to provide some insight into future flood frequency. Changes over time in annual instantaneous peak streamflows at 28 U.S. Geological Survey streamgages with long-term data (50 or more years) and relatively complete records were investigated by examining linear trends for each streamgage’s period of record. None of the 28 streamgages had more than 5 years of missing data. Eight streamgages have substantial streamflow regulation. Because previous studies have suggested that changes over time may have occurred as a step change around 1970, step changes between each streamgage’s older record (start year to 1970) and newer record (1971 to 2006) also were computed. The median change over time for all 28 streamgages is an increase of 15.9 percent based on a linear change and an increase of 12.4 percent based on a step change. The median change for the 20 unregulated streamgages is slightly higher than for all 28 streamgages; it is 18.4 percent based on a linear change and 15.0 percent based on a step change. Peak flows with 100- and 5-year recurrence intervals were computed for the 28 streamgages using the full annual peak-flow record

Equipartition gamma-ray blazars and the location of the gamma-ray emission site in 3C 279

Energy Technology Data Exchange (ETDEWEB)

Dermer, Charles D. [Code 7653, Space Science Division, U.S. Naval Research Laboratory, Washington, DC 20375 (United States); Cerruti, Matteo [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Lott, Benoit [Centre d' Études Nucléaires Bordeaux Gradignan, Université de Bordeaux, CNRS/IN2P3, UMR 5797, F-33175 Gradignan (France); Boisson, Catherine; Zech, Andreas, E-mail: charles.dermer@nrl.navy.mil, E-mail: matteo.cerruti@cfa.harvard.edu [Laboratoire Univers et THeories (LUTH), Observatoire de Paris-Meudon, 5 Place Jules Janssen, F-92195 Meudon Cedex (France)

2014-02-20

Blazar spectral models generally have numerous unconstrained parameters, leading to ambiguous values for physical properties like Doppler factor δ{sub D} or fluid magnetic field B'. To help remedy this problem, a few modifications of the standard leptonic blazar jet scenario are considered. First, a log-parabola function for the electron distribution is used. Second, analytic expressions relating energy loss and kinematics to blazar luminosity and variability, written in terms of equipartition parameters, imply δ{sub D}, B', and the peak electron Lorentz factor γ{sub pk}{sup ′}. The external radiation field in a blazar is approximated by Lyα radiation from the broad-line region (BLR) and ≈0.1 eV infrared radiation from a dusty torus. When used to model 3C 279 spectral energy distributions from 2008 and 2009 reported by Hayashida et al., we derive δ{sub D} ∼ 20-30, B' ∼ few G, and total (IR + BLR) external radiation field energy densities u ∼ 10{sup –2}-10{sup –3} erg cm{sup –3}, implying an origin of the γ-ray emission site in 3C 279 at the outer edges of the BLR. This is consistent with the γ-ray emission site being located at a distance R ≲ Γ{sup 2} ct {sub var} ∼ 0.1(Γ/30){sup 2}(t {sub var}/10{sup 4} s) pc from the black hole powering 3C 279's jets, where t {sub var} is the variability timescale of the radiation in the source frame, and at farther distances for narrow-jet and magnetic-reconnection models. Excess ≳ 5 GeV γ-ray emission observed with Fermi LAT from 3C 279 challenges the model, opening the possibility of a second leptonic component or a hadronic origin of the emission. For low hadronic content, absolute jet powers of ≈10% of the Eddington luminosity are calculated.

Laser generated ultrasound sources using polymer nanocomposites for high frequency metrology

KAUST Repository

Rajagopal, Srinath

2017-11-22

Accurate characterization of ultrasound fields generated by diagnostic and therapeutic transducers is critical for patient safety. This requires hydrophones calibrated to a traceable standard and currently the upper calibration frequency range available to the user community is limited to a frequency of 40 MHz. However, the increasing use of high frequencies for both imaging and therapy necessitates calibrations to frequencies well beyond this range. For this to be possible, a source of high amplitude, broadband, quasi-planar and stable ultrasound fields is required. This is difficult to achieve using conventional piezoelectric sources, but laser generated ultrasound is a promising technique in this regard. In this study, various polymer-carbon nanotube nanocomposites (PNC) were fabricated and tested for their suitability for such an application by varying the polymer type, carbon nanotubes weight content in the polymer, and PNC thickness. A broadband hydrophone was used to measure the peak pressure and bandwidth of the laser generated ultrasound pulse. Peak-positive pressures of up to 8 MPa and −6dB bandwidths of up to 40 MHz were recorded. There is a nonlinear dependence of the peak pressure on the laser fluence and the bandwidth scales inversely proportionally to the peak pressure. The high-pressure plane waves generated from this preliminary investigation has demonstrated that laser generated ultrasound sources are a promising technique for high frequency calibration of hydrophones.

The Imprint of the Extragalactic Background Light in the Gamma-Ray Spectra of Blazars

Science.gov (United States)

Ackermann, M.; Ajello, M.; Allafort, A.; Schady, P.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bellazzini, R; Blandford, R. D.;

Modeling Blazar Spectra by Solving an Electron Transport Equation

Science.gov (United States)

Lewis, Tiffany; Finke, Justin; Becker, Peter A.

2018-01-01

Blazars are luminous active galaxies across the entire electromagnetic spectrum, but the spectral formation mechanisms, especially the particle acceleration, in these sources are not well understood. We develop a new theoretical model for simulating blazar spectra using a self-consistent electron number distribution. Specifically, we solve the particle transport equation considering shock acceleration, adiabatic expansion, stochastic acceleration due to MHD waves, Bohm diffusive particle escape, synchrotron radiation, and Compton radiation, where we implement the full Compton cross-section for seed photons from the accretion disk, the dust torus, and 26 individual broad lines. We used a modified Runge-Kutta method to solve the 2nd order equation, including development of a new mathematical method for normalizing stiff steady-state ordinary differential equations. We show that our self-consistent, transport-based blazar model can qualitatively fit the IR through Fermi g-ray data for 3C 279, with a single-zone, leptonic configuration. We use the solution for the electron distribution to calculate multi-wavelength SED spectra for 3C 279. We calculate the particle and magnetic field energy densities, which suggest that the emitting region is not always in equipartition (a common assumption), but sometimes matter dominated. The stratified broad line region (based on ratios in quasar reverberation mapping, and thus adding no free parameters) improves our estimate of the location of the emitting region, increasing it by ~5x. Our model provides a novel view into the physics at play in blazar jets, especially the relative strength of the shock and stochastic acceleration, where our model is well suited to distinguish between these processes, and we find that the latter tends to dominate.

Infrared polarimetry of the nucleus of Centaurus A: the nearest blazar

Energy Technology Data Exchange (ETDEWEB)

Bailey, J; Sparks, W B; Hough, J H; Axon, D J

1986-07-10

As one of the nearest examples of an active galaxy, NGC5128 (Centaurus A) has been studied in detail over a wide range of wavelengths. The authors have made polarization observations of the infrared nucleus at wavelengths from 1.2 to 3.8 ..mu..m. The nucleus is found to have a large intrinsic polarization of approx.=9% at position angle 147/sup 0/. This position angle is perpendicular to the direction of the X-ray and radio jet. The polarized emission from the nucleus is interpreted as synchrotron radiation from a region whose magnetic field is parallel to the jet direction. The properties of the Cen A nucleus are essentially identical to those of the much more luminous blazars. This suggest that blazar-type activity extends over a very wide range in luminosity, and low-luminosity blazars may be common in elliptical galaxies.

SMARTScience Tools: Interacting With Blazar Data In The Web Browser

Science.gov (United States)

Hasan, Imran; Isler, Jedidah; Urry, C. Megan; MacPherson, Emily; Buxton, Michelle; Bailyn, Charles D.; Coppi, Paolo S.

2014-08-01

The Yale-SMARTS blazar group has accumulated 6 years of optical-IR photometry of more than 70 blazars, mostly bright enough in gamma-rays to be detected with Fermi. Observations were done with the ANDICAM instrument on the SMARTS 1.3 m telescope at the Cerro Tololo Inter-American Observatory. As a result of this long-term, multiwavelength monitoring, we have produced a calibrated, publicly available data set (see www.astro.yale.edu/smarts/glast/home.php), which we have used to find that (i) optical-IR and gamma-ray light curves are well correlated, supporting inverse-Compton models for gamma-ray production (Bonning et al. 2009, 2012), (ii) at their brightest, blazar jets can contribute significantly to the photoionization of the broad-emission-line region, indicating that gamma-rays are produced within 0.1 pc of the black hole in at least some cases (Isler et al. 2014), and (iii) optical-IR and gamma-ray flares are symmetric, implying the time scales are dominated by light-travel-time effects rather than acceleration or cooling (Chatterjee et al. 2012). The volume of data and diversity of projects for which it is used calls out for an efficient means of visualization. To this end, we have developed a suite of visualization tools called SMARTScience Tools, which allow users to interact dynamically with our dataset. The SMARTScience Tools is publicly available via our webpage and can be used to customize multiwavelength light curves and color magnitude diagrams quickly and intuitively. Users can choose specific bands to construct plots, and the plots include features such as band-by-band panning, dynamic zooming, and direct mouse interaction with individual data points. Human and machine readable tables of the plotted data can be directly printed for the user's convenience and for further independent study. The SMARTScience Tools significantly improves the public’s ability to interact with the Yale-SMARTS 6-year data base of blazar photometry, and should make

Polarization and brightness of the blazar S5 0716+714 in 1991-2004

Science.gov (United States)

Doroshenko, V. T.; Kiselev, N. N.

2017-06-01

We investigate the photometric and polarimetric behavior of the blazar S5 0716+714 based on the observations carried out in 1991-2004 at the 125-cm Crimean Astrophysical Observatory telescope (AZT11) with a photopolarimeter that allows simultaneous polarization and brightness measurements to be made in the U BV RI bands. We also provide the U BV photometry for the blazar obtained in 2000-2009 with a 60-cm telescope at the Crimean Station of the Sternberg Astronomical Institute. The pattern of flux variability and the correlation between the brightness, color, and polarization variations have been investigated. In this time interval the blazar showed a significant brightness and polarization variability similar to noise processes.

On the origin of X-ray spectra in luminous blazars

International Nuclear Information System (INIS)

Sikora, Marek; Janiak, Mateusz; Moderski, Rafał; Nalewajko, Krzysztof; Madejski, Greg M.

2013-01-01

Gamma-ray luminosities of some quasar-associated blazars imply jet powers reaching values comparable to the accretion power even if assuming very strong Doppler boosting and very high efficiency of gamma-ray production. With much lower radiative efficiencies of protons than of electrons, and the recent reports of very strong coupling of electrons with shock-heated protons indicated by particle-in-cell simulations, the leptonic models seem to be strongly favored over the hadronic ones. However, the electron-proton coupling combined with the external-radiation-Compton (ERC) models of gamma-ray production in leptonic models predict extremely hard X-ray spectra, with energy indices α x ∼ 0. This is inconsistent with the observed 2-10 keV slopes of blazars, which cluster around α x ∼ 0.6. This problem can be resolved by assuming that electrons can be efficiently cooled down radiatively to non-relativistic energies, or that blazar spectra are entirely dominated by the synchrotron self-Compton (SSC) component up to at least 10 keV. Here, we show that the required cooling can be sufficiently efficient only at distances r < 0.03 pc. SSC spectra, on the other hand, can be produced roughly co-spatially with the observed synchrotron and ERC components, which are most likely located roughly at a parsec scale. We show that the dominant SSC component can also be produced much further than the dominant synchrotron and ERC components, at distances of ≳ 10 pc. Hence, depending on the spatial distribution of the energy dissipation along the jet, one may expect to see γ-ray/optical events with either correlated or uncorrelated X-rays. In all cases the number of e + e – pairs per proton is predicted to be very low. The direct verification of the proposed SSC scenario, and particularly the question of the co-spatiality of the SSC component with other spectral components, requires sensitive observations in the hard X-ray band. This is now possible with the deployment of the Nu

TeV Blazars and Cosmic Infrared Background Radiation

OpenAIRE

Aharonian, F. A.

2001-01-01

The recent developments in studies of TeV radiation from blazars are highlighted and the implications of these results for derivation of cosmologically important information about the cosmic infrared background radiation are discussed.

VizieR Online Data Catalog: Sample of Fermi Blazars (Chen+, 2016)

Science.gov (United States)

Chen, Y.-Y.; Zhang, X.; Xiong, D.-R.; Wang, S.-J.; Yu, X.-L.

2016-04-01

We tried to select a large number of blazars with reliable redshift, radio core and extended radio luminosity at 1.4GHz. Firstly, we considered the following samples of blazars to get the radio core luminosity and extended luminosity at 1.4GHz: Kharb et al. (2010, J/ApJ/710/764), Antonucci & Ulvestad (1985ApJ...294..158A), Cassaro et al. (1999A&AS..139..601C), Murphy et al. (1993MNRAS.264..298M), Landt & Bignall (2008MNRAS.391..967L), Caccianiga & Marcha (2004, Cat. J/MNRAS/348/973), Giroletti et al. (2004). We cross-correlated these samples with the Fermi LAT Third Source Catalog (3FGL), and we acquired the 3FGL spectral index and energy flux at 0.1-100GeV from clean sources in 3FGL (Fermi-LAT Collaboration 2015, J/ApJS/218/23) Using these catalogs, we compiled 201 Fermi blazars. (1 data file).

Journal of Astrophysics and Astronomy | Indian Academy of Sciences

Indian Academy of Sciences (India)

2016-01-27

Jan 27, 2016 ... In this paper, we review the latest research results on the topic of blazar sequence. It seems that the blazar sequence is phenomenally ruled out, while the theoretical blazar sequence still holds. We point out that black hole mass is a dominated parameter accounting for high-power-high-synchrotron-peaked ...

Journal of Astrophysics and Astronomy | Indian Academy of Sciences

Indian Academy of Sciences (India)

Multi-Frequency VLBA Studies of the Parsec-Scale Jets in 3C 66A and 3C 66B ... Multi-Wave Luminosity of High-Synchrotron-Peaked TeV BL Lacs Detected by Fermi LAT ..... This kind of profile has been detected in the polarimetric VLBI observation of many blazar objects, ..... Training in Astronomy for Physics Students.

On one-parametric formula relating the frequencies of twin-peak quasi-periodic oscillations

Science.gov (United States)

Török, Gabriel; Goluchová, Kateřina; Šrámková, Eva; Horák, Jiří; Bakala, Pavel; Urbanec, Martin

2018-01-01

Twin-peak quasi-periodic oscillations (QPOs) are observed in several low-mass X-ray binary systems containing neutron stars. Timing the analysis of X-ray fluxes of more than dozen of such systems reveals remarkable correlations between the frequencies of two characteristic peaks present in the power density spectra. The individual correlations clearly differ, but they roughly follow a common individual pattern. High values of measured QPO frequencies and strong modulation of the X-ray flux both suggest that the observed correlations are connected to orbital motion in the innermost part of an accretion disc. Several attempts to model these correlations with simple geodesic orbital models or phenomenological relations have failed in the past. We find and explore a surprisingly simple analytic relation that reproduces individual correlations for a group of several sources through a single parameter. When an additional free parameter is considered within our relation, it well reproduces the data of a large group of 14 sources. The very existence and form of this simple relation support the hypothesis of the orbital origin of QPOs and provide the key for further development of QPO models. We discuss a possible physical interpretation of our relation's parameters and their links to concrete QPO models.

Parsec-Scale Properties of Gamma-Ray Bright Blazars

Science.gov (United States)

Linford, Justin Dee

The parsec-scale radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been investigated using observations with the Very Long Baseline Array (VLBA). Comparisons between LAT and non-LAT detected samples were made using both archival and contemporaneous data. In total, 244 sources were used in the LAT-detected sample. This very large, radio flux-limited sample of active galactic nuclei (AGN) provides insights into the mechanism that produces strong gamma-ray emission. It has been found that LAT-detected BL Lac objects are very similar to the non-LAT BL Lac objects in most properties, although LAT BL Lac objects may have longer jets. The LAT flat spectrum radio quasars (FSRQs) are significantly different from non-LAT FSRQs and are likely extreme members of the FSRQ population. Archival radio data indicated that there was no significant correlation between radio flux density and gamma-ray flux, especially at lower flux levels. However, contemporaneous observations showed a strong correlation. Most of the differences between the LAT and non-LAT populations are related to the cores of the sources, indicating that the gamma-ray emission may originate near the base of the jets (i.e., within a few pc of the central engine). There is some indication that LAT-detected sources may have larger jet opening angles than the non-LAT sources. Strong core polarization is significantly more common among the LAT sources, suggesting that gamma-ray emission is related to strong, uniform magnetic fields at the base of the jets of the blazars. Observations of sources in two epochs indicate that core fractional polarization was higher when the objects were detected by the LAT. The low-synchrotron peaked (LSP) BL Lac object sample shows indications of contamination by FSRQs which happen to have undetectable emission lines. There is evidence that the LSP BL Lac objects are more strongly beamed than the rest of the BL Lac

Measuring saccade peak velocity using a low-frequency sampling rate of 50 Hz.

Science.gov (United States)

Wierts, Roel; Janssen, Maurice J A; Kingma, Herman

2008-12-01

During the last decades, small head-mounted video eye trackers have been developed in order to record eye movements. Real-time systems-with a low sampling frequency of 50/60 Hz-are used for clinical vestibular practice, but are generally considered not to be suited for measuring fast eye movements. In this paper, it is shown that saccadic eye movements, having an amplitude of at least 5 degrees, can, in good approximation, be considered to be bandwidth limited up to a frequency of 25-30 Hz. Using the Nyquist theorem to reconstruct saccadic eye movement signals at higher temporal resolutions, it is shown that accurate values for saccade peak velocities, recorded at 50 Hz, can be obtained, but saccade peak accelerations and decelerations cannot. In conclusion, video eye trackers sampling at 50/60 Hz are appropriate for detecting the clinical relevant saccade peak velocities in contrast to what has been stated up till now.

High-Average, High-Peak Current Injector Design

CERN Document Server

Biedron, S G; Virgo, M

2005-01-01

There is increasing interest in high-average-power (>100 kW), um-range FELs. These machines require high peak current (~1 kA), modest transverse emittance, and beam energies of ~100 MeV. High average currents (~1 A) place additional constraints on the design of the injector. We present a design for an injector intended to produce the required peak currents at the injector, eliminating the need for magnetic compression within the linac. This reduces the potential for beam quality degradation due to CSR and space charge effects within magnetic chicanes.

The CLASS blazar survey - II. Optical properties

NARCIS (Netherlands)

Caccianiga, A; Marcha, MJ; Anton, S; Mack, KH; Neeser, MJ

2002-01-01

This paper presents the optical properties of the objects selected in the CLASS blazar survey. Because an optical spectrum is now available for 70 per cent of the 325 sources present in the sample, a spectral classification, based on the appearance of the emission/absorption lines, is possible. A

Multi-TeV flaring from blazars: Markarian 421 as a case study

Energy Technology Data Exchange (ETDEWEB)

Sahu, Sarira; Miranda, Luis Salvador [Universidad Nacional Autonoma de Mexico, Instituto de Ciencias Nucleares, Mexico, DF (Mexico); Rajpoot, Subhash [California State University, Department of Physics and Astronomy, Long Beach, CA (United States)

2016-03-15

The TeV blazar Markarian 421 underwent multi-TeV flaring during April 2004 and simultaneously observations in the X-ray and TeV energies were made. It was observed that the TeV outbursts had no counterparts in the lower energy range. One implication of this is that it might be an orphan flare. We show that Fermi-accelerated protons of energy ≤ 168 TeV can interact with the low energy tail of the background synchrotron self-Compton photons in the inner region of the blazar to produce the multi-TeV flare and our results fit very well with the observed spectrum. Based on our study, we predict that the blazars with a deep valley in between the end of the synchrotron spectrum and the beginning of the SSC spectrum are possible candidates for orphan flaring. Future possible candidates for this scenario are the HBLs Mrk 501 and PG 1553 + 113 objects. (orig.)

Comparison of Optical and Multi-Waveband Variations of Selected Gamma-ray Bright Blazars in 2012

Science.gov (United States)

Schultz, Benjamin; Jorstad, S. G.; Marscher, A. P.; Williamson, K. E.; Walker, G. E.

2013-01-01

We present multi-wavelength observations of several gamma-ray bright blazars. We combine optical data obtained with the 17-inch CCD telescope of Maria Mitchell Observatory with space- and ground-based observations carried out with a variety of instruments. These include a number of other optical telescopes, the Fermi Gamma-Ray Space Telescope at photon energies of 0.1-200 GeV, and the Swift satellite at 0.3-10 keV plus optical and UV wavelengths. Three of the observed blazars proved to be particularly active - BL Lac, Mrk501, and CTA-102. BL Lac was of special interest, displaying remarkable activity in multiple wavelengths during this observation period, including the optical, in which it underwent its largest observed flare in a number of years. In addition, CTA-102 has recently undergone an unprecedented multi-wavelength outburst. We cross-correlate the variations in the different wavebands in an effort to guide theoretical interpretations of the optical and high-energy emission from blazars. This project was supported by NSF/REU grant AST-0851892 and the Nantucket Maria Mitchell Association. The research at Boston University was supported in part by NSF grant AST-0907893 and by NASA through Fermi grant NNX11AQ03G.

ROLE OF LINE-OF-SIGHT COSMIC-RAY INTERACTIONS IN FORMING THE SPECTRA OF DISTANT BLAZARS IN TeV GAMMA RAYS AND HIGH-ENERGY NEUTRINOS

International Nuclear Information System (INIS)

Essey, Warren; Kusenko, Alexander; Kalashev, Oleg; Beacom, John F.

2011-01-01

Active galactic nuclei (AGNs) can produce both gamma rays and cosmic rays. The observed high-energy gamma-ray signals from distant blazars may be dominated by secondary gamma rays produced along the line of sight by the interactions of cosmic-ray protons with background photons. This explains the surprisingly low attenuation observed for distant blazars, because the production of secondary gamma rays occurs, on average, much closer to Earth than the distance to the source. Thus, the observed spectrum in the TeV range does not depend on the intrinsic gamma-ray spectrum, while it depends on the output of the source in cosmic rays. We apply this hypothesis to a number of sources and, in every case, we obtain an excellent fit, strengthening the interpretation of the observed spectra as being due to secondary gamma rays. We explore the ramifications of this interpretation for limits on the extragalactic background light and for the production of cosmic rays in AGNs. We also make predictions for the neutrino signals, which can help probe the acceleration of cosmic rays in AGNs.

The WEBT Campaign on the Blazar 3C 279 in 2006

Science.gov (United States)

Böttcher, M.; Basu, S.; Joshi, M.; Villata, M.; Arai, A.; Aryan, N.; Asfandiyarov, I. M.; Bach, U.; Bachev, R.; Berduygin, A.; Blaek, M.; Buemi, C.; Castro-Tirado, A. J.; De Ugarte Postigo, A.; Frasca, A.; Fuhrmann, L.; Hagen-Thorn, V. A.; Henson, G.; Hovatta, T.; Hudec, R.; Ibrahimov, M.; Ishii, Y.; Ivanidze, R.; Jelínek, M.; Kamada, M.; Kapanadze, B.; Katsuura, M.; Kotaka, D.; Kovalev, Y. Y.; Kovalev, Yu. A.; Kubánek, P.; Kurosaki, M.; Kurtanidze, O.; Lähteenmäki, A.; Lanteri, L.; Larionov, V. M.; Larionova, L.; Lee, C.-U.; Leto, P.; Lindfors, E.; Marilli, E.; Marshall, K.; Miller, H. R.; Mingaliev, M. G.; Mirabal, N.; Mizoguchi, S.; Nakamura, K.; Nieppola, E.; Nikolashvili, M.; Nilsson, K.; Nishiyama, S.; Ohlert, J.; Osterman, M. A.; Pak, S.; Pasanen, M.; Peters, C. S.; Pursimo, T.; Raiteri, C. M.; Robertson, J.; Robertson, T.; Ryle, W. T.; Sadakane, K.; Sadun, A.; Sigua, L.; Sohn, B.-W.; Strigachev, A.; Sumitomo, N.; Takalo, L. O.; Tamesue, Y.; Tanaka, K.; Thorstensen, J. R.; Tosti, G.; Trigilio, C.; Umana, G.; Vennes, S.; Vitek, S.; Volvach, A.; Webb, J.; Yamanaka, M.; Yim, H.-S.

2007-12-01

The quasar 3C 279 was the target of an extensive multiwavelength monitoring campaign from 2006 January through April. An optical-IR-radio monitoring campaign by the Whole Earth Blazar Telescope (WEBT) collaboration was organized around target-of-opportunity X-ray and soft γ-ray observations with Chandra and INTEGRAL in 2006 mid-January, with additional X-ray coverage by RXTE and Swift XRT. In this paper we focus on the results of the WEBT campaign. The source exhibited substantial variability of optical flux and spectral shape, with a characteristic timescale of a few days. The variability patterns throughout the optical BVRI bands were very closely correlated with each other, while there was no obvious correlation between the optical and radio variability. After the ToO trigger, the optical flux underwent a remarkably clean quasi-exponential decay by about 1 mag, with a decay timescale of τd~12.8 days. In intriguing contrast to other (in particular, BL Lac type) blazars, we find a lag of shorter wavelength behind longer wavelength variability throughout the RVB wavelength ranges, with a time delay increasing with increasing frequency. Spectral hardening during flares appears delayed with respect to a rising optical flux. This, in combination with the very steep IR-optical continuum spectral index of α0~1.5-2.0, may indicate a highly oblique magnetic field configuration near the base of the jet, leading to inefficient particle acceleration and a very steep electron injection spectrum. An alternative explanation through a slow (timescale of several days) acceleration mechanism would require an unusually low magnetic field of B<~0.2 G, about an order of magnitude lower than inferred from previous analyses of simultaneous SEDs of 3C 279 and other flat-spectrum radio quasars with similar properties. For questions regarding the availability of the data from the WEBT campaign presented in this paper, please contact the WEBT President Massimo Villata at villata@oato.inaf.it.

Climate change is projected to have severe impacts on the frequency and intensity of peak electricity demand across the United States.

Science.gov (United States)

Auffhammer, Maximilian; Baylis, Patrick; Hausman, Catherine H

2017-02-21

It has been suggested that climate change impacts on the electric sector will account for the majority of global economic damages by the end of the current century and beyond [Rose S, et al. (2014) Understanding the Social Cost of Carbon: A Technical Assessment ]. The empirical literature has shown significant increases in climate-driven impacts on overall consumption, yet has not focused on the cost implications of the increased intensity and frequency of extreme events driving peak demand, which is the highest load observed in a period. We use comprehensive, high-frequency data at the level of load balancing authorities to parameterize the relationship between average or peak electricity demand and temperature for a major economy. Using statistical models, we analyze multiyear data from 166 load balancing authorities in the United States. We couple the estimated temperature response functions for total daily consumption and daily peak load with 18 downscaled global climate models (GCMs) to simulate climate change-driven impacts on both outcomes. We show moderate and heterogeneous changes in consumption, with an average increase of 2.8% by end of century. The results of our peak load simulations, however, suggest significant increases in the intensity and frequency of peak events throughout the United States, assuming today's technology and electricity market fundamentals. As the electricity grid is built to endure maximum load, our findings have significant implications for the construction of costly peak generating capacity, suggesting additional peak capacity costs of up to 180 billion dollars by the end of the century under business-as-usual.

Finite-Element Modeling of Viscoelastic Cells During High-Frequency Cyclic Strain

Directory of Open Access Journals (Sweden)

David W. Holdsworth

2012-03-01

Full Text Available Mechanotransduction refers to the mechanisms by which cells sense and respond to local loads and forces. The process of mechanotransduction plays an important role both in maintaining tissue viability and in remodeling to repair damage; moreover, it may be involved in the initiation and progression of diseases such as osteoarthritis and osteoporosis. An understanding of the mechanisms by which cells respond to surrounding tissue matrices or artificial biomaterials is crucial in regenerative medicine and in influencing cellular differentiation. Recent studies have shown that some cells may be most sensitive to low-amplitude, high-frequency (i.e., 1–100 Hz mechanical stimulation. Advances in finite-element modeling have made it possible to simulate high-frequency mechanical loading of cells. We have developed a viscoelastic finite-element model of an osteoblastic cell (including cytoskeletal actin stress fibers, attached to an elastomeric membrane undergoing cyclic isotropic radial strain with a peak value of 1,000 µstrain. The results indicate that cells experience significant stress and strain amplification when undergoing high-frequency strain, with peak values of cytoplasmic strain five times higher at 45 Hz than at 1 Hz, and peak Von Mises stress in the nucleus increased by a factor of two. Focal stress and strain amplification in cells undergoing high-frequency mechanical stimulation may play an important role in mechanotransduction.

Fine Structure of the Core of the Blazar OJ 287-I

Science.gov (United States)

Matveyenko, L. I.; Sivakon', S. S.

2017-12-01

The fine structure of the active region, the bulge, of the blazar OJ 287 has been investigated with a resolution of 20 μas (0.1 pc) at a wavelength of 7 mm, the epochs of 2007-2017. The structure and kinematics correspond to a vortex nature. The surrounding matter, the plasma, is transferred to the center along two arms from opposite directions. The emerging excess angular momentum is carried away along the rotation axis by bipolar outflows, rotating coaxial tubes, in a direction X ≈ -120° in the plane of the sky as it is accumulated. The central high-velocity bipolar outflow has a helical shape. The diameters of the low-velocity flows are ø1 ≈ 0.3 and ø2 ≈ 0.65 mas, or 1.4 and 3 pc, respectively. Ring currents whose tangential directions are observed as parallel chains of components are excited in the flow walls. The peak brightness temperature of the nozzle reaches Tb ≈ 1012-1013 K. A "disk" with a diameter ø ≈ 0.5 mas (≈2.2 pc) is observed by the absorption of synchrotron radiation. The disk is inclined to the plane of the sky at an angle of 60° in the jet direction. The fragments are seen from a distance of ˜0.2 mas outside the absorption zone. The jet sizes exceed considerably the counterjet ones. An enhanced supply of plasma from the northern arm gives rise to an independent vortex 0.2 mas away from the central one in the NW direction. As in the first case, the helical central bipolar outflow is surrounded by a low-velocity component ø ≈ 0.28 mas in diameter with built-in ring currents. The jet is ejected in the direction X = -50° in the plane of the sky. The jet orientation changes, X = -130° at a distance of 1 mas. A high activity of the central and two side nozzles spaced 0.22 mas apart in the direction X = -40° is occasionally observed simultaneously. The active region of the blazar is observed through an ionized medium, a screen, whose influence is significant even at a wavelength of 7 mm. The absorption and refraction of the

Shaping the GeV-spectra of bright blazars

Science.gov (United States)

Hunger, L.; Reimer, A.

2016-05-01

Aims: The non-thermal spectra of jetted active galactic nuclei (AGN) show a variety of shapes and degrees of curvature in their low- and high energy components. From some of the brightest Fermi-LAT blazars, prominent spectral breaks at a few GeV have been regularly detected, which is inconsistent with conventional cooling effects. We study the effects of continuous time-dependent injection of electrons into the jet with differing rates, durations, locations, and power-law spectral indices, and evaluate its impact on the ambient emitting particle spectrum that is observed at a given snapshot time in the framework of a leptonic blazar emission model. With this study, we provide a basis for analyzing ambient electron spectra in terms of injection requirements, with implications for particle acceleration modes. Methods: The emitting electron spectrum is calculated by Compton cooling the continuously injected electrons, where target photons are assumed to be provided by the accretion disk and broad line region (BLR). From this setup, we calculate the non-thermal photon spectra produced by inverse Compton scattering of these external target radiation fields using the full Compton cross-section in the head-on approximation. Results: By means of a comprehensive parameter study we present the resulting ambient electron and photon spectra, and discuss the influence of each injection parameter individually. We found that varying the injection parameters has a notable influence on the spectral shapes, which in turn can be used to set interesting constraints on the particle injection scenarios. By applying our model to the flare state spectral energy distribution (SED) of 3C 454.3, we confirm a previous suggestion that explained the observed spectral changes at a few GeV by a combination of the Compton-scattered disk and BLR radiation. We determine the required injection parameters for this scenario. We also show that this spectral turn-over can also be understood as Compton

NuSTAR DETECTION OF THE BLAZAR B2 1023+25 AT REDSHIFT 5.3

Energy Technology Data Exchange (ETDEWEB)

Sbarrato, T. [Dipartimento di Scienza e Alta Tecnologia, Università dell' Insubria, Via Valleggio 11, I-22100 Como (Italy); Tagliaferri, G.; Ghisellini, G. [INAF-Osservatorio Astronomico di Brera, via E. Bianchi 46, I-23807 Merate (Italy); Perri, M.; Puccetti, S.; Giommi, P. [ASI-Science Data Center, via Galileo Galilei, I-00044 Frascati (Italy); Baloković, M.; Harrison, F. A.; Hovatta, T. [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Nardini, M. [Dipartimento di Fisica G. Occhialini, Università di Milano Bicocca, Piazza della Scienza 3, I-20126 Milano (Italy); Stern, D. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Boggs, S. E. [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States); Brandt, W. N. [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); Christensen, F. E. [DTU Space-National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby (Denmark); Greiner, J.; Rau, A.; Schady, P.; Sudilovsky, V. [Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching (Germany); Hailey, C. J. [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States); Madejski, G. M., E-mail: tullia.sbarrato@brera.inaf.it [Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, Menlo Park, CA 94025 (United States); and others

2013-11-10

B2 1023+25 is an extremely radio-loud quasar at z = 5.3 that was first identified as a likely high-redshift blazar candidate in the SDSS+FIRST quasar catalog. Here, we use the Nuclear Spectroscopic Telescope Array (NuSTAR) to investigate its non-thermal jet emission, whose high-energy component we detected in the hard X-ray energy band. The X-ray flux is ∼ 5.5 x 10{sup -14} erg cm{sup -2} s{sup -1} (5-10 keV) and the photon spectral index is Γ{sub X} ≅ 1.3-1.6. Modeling the full spectral energy distribution, we find that the jet is oriented close to the line of sight, with a viewing angle of ∼3°, and has significant Doppler boosting, with a large bulk Lorentz factor ∼13, which confirms the identification of B2 1023+25 as a blazar. B2 1023+25 is the first object at redshift larger than 5 detected by NuSTAR, demonstrating the ability of NuSTAR to investigate the early X-ray universe and to study extremely active supermassive black holes located at very high redshift.

A Diagnostic Test for Determining the Location of the GeV Emission in Powerful Blazars

Science.gov (United States)

Dotson, Amanda; Georganopoulos, Markos; Kazanas, Demosthenes; Perlman, Eric

2011-01-01

An issue currently under debate in the literature is how far from the black hole is the Fermi-observed GeV emission of powerful blazars emitted. Here we present a clear diagnostic tool for testing whether the Ge V emission site is located within the sub-pc broad emission line (BLR) region or further out in the few pc scale molecular torus (MT) environment. Within the BLR the scatteri takes place at the onset of the Klein-Nishina regime, causing the electron cooling time to become almost energy independent and as a result, the variation of high-energy emission is expected to be achromatic. Contrarily, if the emission site is located outside the BLR, the expected GeY variability is energy-dependent and with amplitude increasing with energy. We demonstrate this using time-dependent numerical simulations of blazar variability.

Comparison Of Optical, UV, X-ray, And Gamma-ray Variations Of Selected Blazars In 2011

Science.gov (United States)

Consiglio, Santina; Marscher, A. P.; Jorstad, S. G.; Walker, G.

2012-01-01

We present multi-wavelength observations of several gamma-ray bright blazars. We combine optical data obtained at Maria Mitchell Observatory on Nantucket Island with space- and ground-based observations carried out with a variety of instruments. These include a number of other optical telescopes, the Fermi Gamma-ray Space Telescope at photon energies of 0.1-200 GeV, the Rossi X-Ray Timing Explorer at 2.4-10 keV, and the Swift satellite at 0.3-10 keV plus optical and UV wavelengths. Three of the observed blazars proved to be particularly active - BL Lac, 3C 279, and PKS 1510-089. BL Lac was of special interest, varying greatly in optical brightness from night to night. In addition, as reported by the VERITAS group, it exhibited a remarkable, short-lived flare at TeV gamma-ray energies on one of the nights. We cross-correlate the variations in the different wavebands in an effort to guide theoretical interpretations of the optical and high-energy emission from blazars. This project was supported by NSF/REU grant AST-0851892 and by the Nantucket Maria Mitchell Association. The research at Boston University was supported in part by NSF grants AST-0907893, and by NASA through Fermi grants NNX08AV65G and NNX11AQ03G.

Discrete ordinates transport methods for problems with highly forward-peaked scattering

International Nuclear Information System (INIS)

Pautz, S.D.

1998-04-01

The author examines the solutions of the discrete ordinates (S N ) method for problems with highly forward-peaked scattering kernels. He derives conditions necessary to obtain reasonable solutions in a certain forward-peaked limit, the Fokker-Planck (FP) limit. He also analyzes the acceleration of the iterative solution of such problems and offer improvements to it. He extends the analytic Fokker-Planck limit analysis to the S N equations. This analysis shows that in this asymptotic limit the S N solution satisfies a pseudospectral discretization of the FP equation, provided that the scattering term is handled in a certain way (which he describes) and that the analytic transport solution satisfies an analytic FP equation. Similar analyses of various spatially discretized S N equations reveal that they too produce solutions that satisfy discrete FP equations, given the same provisions. Numerical results agree with these theoretical predictions. He defines a multidimensional angular multigrid (ANMG) method to accelerate the iterative solution of highly forward-peaked problems. The analyses show that a straightforward application of this scheme is subject to high-frequency instabilities. However, by applying a diffusive filter to the ANMG corrections he is able to stabilize this method. Fourier analyses of model problems show that the resulting method is effective at accelerating the convergence rate when the scattering is forward-peaked. The numerical results demonstrate that these analyses are good predictors of the actual performance of the ANMG method

Sex Comparisons for Relative Peak Torque and Electromyographic Mean Frequency during Fatigue

Science.gov (United States)

Stock, Matt S.; Beck, Travis W.; DeFreitas, Jason M.; Ye, Xin

2013-01-01

Purpose: This study compared the relative peak torque and normalized electromyographic (EMG) mean frequency (MNF) responses during fatiguing isokinetic muscle actions for men versus women. Method: Twenty men M[subscript age] ± SD = 22 ± 2 years) and 20 women M[subscript age] ± SD = 22 ± 1 years) performed 50 maximal concentric isokinetic muscle…

THE SECOND CATALOG OF ACTIVE GALACTIC NUCLEI DETECTED BY THE FERMI LARGE AREA TELESCOPE

International Nuclear Information System (INIS)

Ackermann, M.; Ajello, M.; Allafort, A.; Bechtol, K.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Borgland, A. W.; Bottacini, E.; Antolini, E.; Bonamente, E.; Atwood, W. B.; Bouvier, A.; Axelsson, M.; Baldini, L.; Bellazzini, R.; Bregeon, J.; Ballet, J.; Barbiellini, G.; Bastieri, D.

2011-01-01

The second catalog of active galactic nuclei (AGNs) detected by the Fermi Large Area Telescope (LAT) in two years of scientific operation is presented. The second LAT AGN catalog (2LAC) includes 1017 γ-ray sources located at high Galactic latitudes (|b| > 10°) that are detected with a test statistic (TS) greater than 25 and associated statistically with AGNs. However, some of these are affected by analysis issues and some are associated with multiple AGNs. Consequently, we define a Clean Sample which includes 886 AGNs, comprising 395 BL Lacertae objects (BL Lac objects), 310 flat-spectrum radio quasars (FSRQs), 157 candidate blazars of unknown type (i.e., with broadband blazar characteristics but with no optical spectral measurement yet), 8 misaligned AGNs, 4 narrow-line Seyfert 1 (NLS1s), 10 AGNs of other types, and 2 starburst galaxies. Where possible, the blazars have been further classified based on their spectral energy distributions (SEDs) as archival radio, optical, and X-ray data permit. While almost all FSRQs have a synchrotron-peak frequency 14 Hz, about half of the BL Lac objects have a synchrotron-peak frequency >10 15 Hz. The 2LAC represents a significant improvement relative to the first LAT AGN catalog (1LAC), with 52% more associated sources. The full characterization of the newly detected sources will require more broadband data. Various properties, such as γ-ray fluxes and photon power-law spectral indices, redshifts, γ-ray luminosities, variability, and archival radio luminosities and their correlations are presented and discussed for the different blazar classes. The general trends observed in 1LAC are confirmed.

Peak power ratio generator

Science.gov (United States)

Moyer, R.D.

A peak power ratio generator is described for measuring, in combination with a conventional power meter, the peak power level of extremely narrow pulses in the gigahertz radio frequency bands. The present invention in a preferred embodiment utilizes a tunnel diode and a back diode combination in a detector circuit as the only high speed elements. The high speed tunnel diode provides a bistable signal and serves as a memory device of the input pulses for the remaining, slower components. A hybrid digital and analog loop maintains the peak power level of a reference channel at a known amount. Thus, by measuring the average power levels of the reference signal and the source signal, the peak power level of the source signal can be determined.

Switching transients in high-frequency high-power converters using power MOSFET's

Science.gov (United States)

Sloane, T. H.; Owen, H. A., Jr.; Wilson, T. G.

1979-01-01

The use of MOSFETs in a high-frequency high-power dc-to-dc converter is investigated. Consideration is given to the phenomena associated with the paralleling of MOSFETs and to the effect of stray circuit inductances on the converter circuit performance. Analytical relationships between various time constants during the turning-on and turning-off intervals are derived which provide estimates of plateau and peak levels during these intervals.

Extremes of the jet-accretion power relation of blazars, as explored by NuSTAR

DEFF Research Database (Denmark)

Sbarrato, T.; Ghisellini, G.; Tagliaferri, G.

2016-01-01

.366) and B0222+185 (at z = 2.690) have been observed twice by the Nuclear Spectroscopic Telescope Array (NuSTAR) simultaneously with Swift/X-ray Telescope, showing different variability behaviours. We found that NuSTAR is instrumental to explore the variability of powerful high-redshift blazars, even when...

CONTEMPORANEOUS VLBA 5 GHz OBSERVATIONS OF LARGE AREA TELESCOPE DETECTED BLAZARS

Energy Technology Data Exchange (ETDEWEB)

Linford, J. D.; Taylor, G. B. [Department of Physics and Astronomy, University of New Mexico, MSC07 4220, Albuquerque, NM 87131-0001 (United States); Romani, R. W. [Department of Physics, Stanford University, Stanford, CA 94305 (United States); Helmboldt, J. F. [Naval Research Laboratory, Code 7213, 4555 Overlook Avenue SW, Washington, DC 20375 (United States); Readhead, A. C. S.; Reeves, R.; Richards, J. L. [Astronomy Department, California Institute of Technology, Mail Code 247-17, 1200 East California Boulevard, Pasadena, CA 91125 (United States)

2012-01-10

The radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed contemporaneously by the Very Long Baseline Array (VLBA). In total, 232 sources were observed with the VLBA. Ninety sources that were previously observed as part of the VLBA Imaging and Polarimetry Survey (VIPS) have been included in the sample, as well as 142 sources not found in VIPS. This very large, 5 GHz flux-limited sample of active galactic nuclei (AGNs) provides insights into the mechanism that produces strong {gamma}-ray emission. In particular, we see that {gamma}-ray emission is related to strong, uniform magnetic fields in the cores of the host AGN. Included in this sample are non-blazar AGNs such as 3C84, M82, and NGC 6251. For the blazars, the total VLBA radio flux density at 5 GHz correlates strongly with {gamma}-ray flux. The LAT BL Lac objects tend to be similar to the non-LAT BL Lac objects, but the LAT flat-spectrum radio quasars (FSRQs) are significantly different from the non-LAT FSRQs. Strong core polarization is significantly more common among the LAT sources, and core fractional polarization appears to increase during LAT detection.

CONTEMPORANEOUS VLBA 5 GHz OBSERVATIONS OF LARGE AREA TELESCOPE DETECTED BLAZARS

International Nuclear Information System (INIS)

Linford, J. D.; Taylor, G. B.; Romani, R. W.; Helmboldt, J. F.; Readhead, A. C. S.; Reeves, R.; Richards, J. L.

2012-01-01

The radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed contemporaneously by the Very Long Baseline Array (VLBA). In total, 232 sources were observed with the VLBA. Ninety sources that were previously observed as part of the VLBA Imaging and Polarimetry Survey (VIPS) have been included in the sample, as well as 142 sources not found in VIPS. This very large, 5 GHz flux-limited sample of active galactic nuclei (AGNs) provides insights into the mechanism that produces strong γ-ray emission. In particular, we see that γ-ray emission is related to strong, uniform magnetic fields in the cores of the host AGN. Included in this sample are non-blazar AGNs such as 3C84, M82, and NGC 6251. For the blazars, the total VLBA radio flux density at 5 GHz correlates strongly with γ-ray flux. The LAT BL Lac objects tend to be similar to the non-LAT BL Lac objects, but the LAT flat-spectrum radio quasars (FSRQs) are significantly different from the non-LAT FSRQs. Strong core polarization is significantly more common among the LAT sources, and core fractional polarization appears to increase during LAT detection.

Contemporaneous VLBA 5 GHz Observations of Large Area Telescope Detected Blazars

Science.gov (United States)

Linford, J. D.; Taylor, G. B.; Romani, R. W.; Helmboldt, J. F.; Readhead, A. C. S.; Reeves, R.; Richards, J. L.

2012-01-01

The radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed contemporaneously by the Very Long Baseline Array (VLBA). In total, 232 sources were observed with the VLBA. Ninety sources that were previously observed as part of the VLBA Imaging and Polarimetry Survey (VIPS) have been included in the sample, as well as 142 sources not found in VIPS. This very large, 5 GHz flux-limited sample of active galactic nuclei (AGNs) provides insights into the mechanism that produces strong γ-ray emission. In particular, we see that γ-ray emission is related to strong, uniform magnetic fields in the cores of the host AGN. Included in this sample are non-blazar AGNs such as 3C84, M82, and NGC 6251. For the blazars, the total VLBA radio flux density at 5 GHz correlates strongly with γ-ray flux. The LAT BL Lac objects tend to be similar to the non-LAT BL Lac objects, but the LAT flat-spectrum radio quasars (FSRQs) are significantly different from the non-LAT FSRQs. Strong core polarization is significantly more common among the LAT sources, and core fractional polarization appears to increase during LAT detection.

Power-law to Power-law Mapping of Blazar Spectra from Intergalactic Absorption

International Nuclear Information System (INIS)

Stecker, F W; Scully, S T

2007-01-01

We have derived a useful analytic approximation for determining the effect of intergalactic absorption on the γ-ray spectra of TeV blazars the energy range 0.2 TeV γ γ ) is approximately logarithmic. The effect of this energy dependence is to steepen intrinsic source spectra such that a source with an approximate power-law spectral index Γ s is converted to one with an observed spectral index Γ o ≅ Γ s + ΔΓ(z) where ΔΓ(z) is a linear function of z in the redshift range 0.05-0.4. We apply this approximation to the spectra of 7 TeV blazars

Photoinduced High-Frequency Charge Oscillations in Dimerized Systems

Science.gov (United States)

Yonemitsu, Kenji

2018-04-01

Photoinduced charge dynamics in dimerized systems is studied on the basis of the exact diagonalization method and the time-dependent Schrödinger equation for a one-dimensional spinless-fermion model at half filling and a two-dimensional model for κ-(bis[ethylenedithio]tetrathiafulvalene)2X [κ-(BEDT-TTF)2X] at three-quarter filling. After the application of a one-cycle pulse of a specifically polarized electric field, the charge densities at half of the sites of the system oscillate in the same phase and those at the other half oscillate in the opposite phase. For weak fields, the Fourier transform of the time profile of the charge density at any site after photoexcitation has peaks for finite-sized systems that correspond to those of the steady-state optical conductivity spectrum. For strong fields, these peaks are suppressed and a new peak appears on the high-energy side, that is, the charge densities mainly oscillate with a single frequency, although the oscillation is eventually damped. In the two-dimensional case without intersite repulsion and in the one-dimensional case, this frequency corresponds to charge-transfer processes by which all the bonds connecting the two classes of sites are exploited. Thus, this oscillation behaves as an electronic breathing mode. The relevance of the new peak to a recently found reflectivity peak in κ-(BEDT-TTF)2X after photoexcitation is discussed.

Advance in ERG Analysis: From Peak Time and Amplitude to Frequency, Power, and Energy

Directory of Open Access Journals (Sweden)

Mathieu Gauvin

2014-01-01

Full Text Available Purpose. To compare time domain (TD: peak time and amplitude analysis of the human photopic electroretinogram (ERG with measures obtained in the frequency domain (Fourier analysis: FA and in the time-frequency domain (continuous (CWT and discrete (DWT wavelet transforms. Methods. Normal ERGs n=40 were analyzed using traditional peak time and amplitude measurements of the a- and b-waves in the TD and descriptors extracted from FA, CWT, and DWT. Selected descriptors were also compared in their ability to monitor the long-term consequences of disease process. Results. Each method extracted relevant information but had distinct limitations (i.e., temporal and frequency resolutions. The DWT offered the best compromise by allowing us to extract more relevant descriptors of the ERG signal at the cost of lesser temporal and frequency resolutions. Follow-ups of disease progression were more prolonged with the DWT (max 29 years compared to 13 with TD. Conclusions. Standardized time domain analysis of retinal function should be complemented with advanced DWT descriptors of the ERG. This method should allow more sensitive/specific quantifications of ERG responses, facilitate follow-up of disease progression, and identify diagnostically significant changes of ERG waveforms that are not resolved when the analysis is only limited to time domain measurements.

Detection of the cosmic γ-ray horizon from multiwavelength observations of blazars

Energy Technology Data Exchange (ETDEWEB)

Dominguez, A. [Univ. of California, Riverside, CA (United States); Finke, J. D. [U.S. Naval Research Lab., Washington, DC (United States); Prada, F. [Campus of International Excellence UAM_CSIC, Madrid (Spain); Universidad Autonoma de Madrid (Spain); Instituto de Astrofisica de Andalucia, Granada (Spain); Primack, J. R. [Univ. of California, Santa Cruz, CA (United States); Kitaura, F. S. [Leibniz-Institut fuer Astrophysik, Potsdam (Germany); Siana, B. [Univ. Of California, Riverside, CA (United States); Paneque, D. [Stanford Univ., Stanford, CA (United States). Kavli Inst. sor Particle Astrophysics and Cosmology; Max-Planck-Institut fuer Physik, Munich (Germany)

2013-05-24

The first statistically significant detection of the cosmic γ-ray horizon (CGRH) that is independent of any extragalactic background light (EBL) model is presented. The CGRH is a fundamental quantity in cosmology. It gives an estimate of the opacity of the Universe to very high energy (VHE) γ-ray photons due to photon-photon pair production with the EBL. The only estimations of the CGRH to date are predictions from EBL models and lower limits from γ-ray observations of cosmological blazars and γ-ray bursts. Here, we present homogeneous synchrotron/synchrotron self-Compton (SSC) models of the spectral energy distributions of 15 blazars based on (almost) simultaneous observations from radio up to the highest energy γ-rays taken with the Fermi satellite. These synchrotron/SSC models predict the unattenuated VHE fluxes, which are compared with the observations by imaging atmospheric Cherenkov telescopes. The comparison provides an estimate of the optical depth of the EBL, which allows a derivation of the CGRH through a maximum likelihood analysis that is EBL-model independent. We find that the observed CGRH is compatible with the current knowledge of the EBL.

Search for muon-neutrino emission from GeV and TeV gamma-ray flaring blazars using five years of data of the ANTARES telescope

Energy Technology Data Exchange (ETDEWEB)

Collaboration: ANTARES Collaboration

2015-12-01

The ANTARES telescope is well-suited for detecting astrophysical transient neutrino sources as it can observe a full hemisphere of the sky at all times with a high duty cycle. The background due to atmospheric particles can be drastically reduced, and the point-source sensitivity improved, by selecting a narrow time window around possible neutrino production periods. Blazars, being radio-loud active galactic nuclei with their jets pointing almost directly towards the observer, are particularly attractive potential neutrino point sources, since they are among the most likely sources of the very high-energy cosmic rays. Neutrinos and gamma rays may be produced in hadronic interactions with the surrounding medium. Moreover, blazars generally show high time variability in their light curves at different wavelengths and on various time scales. This paper presents a time-dependent analysis applied to a selection of flaring gamma-ray blazars observed by the FERMI/LAT experiment and by TeV Cherenkov telescopes using five years of ANTARES data taken from 2008 to 2012. The results are compatible with fluctuations of the background. Upper limits on the neutrino fluence have been produced and compared to the measured gamma-ray spectral energy distribution.

Revisiting the incidence of Mg II absorbers along the blazar sightlines

Science.gov (United States)

Mishra, Sapna; Chand, Hum; Gopal-Krishna; Joshi, Ravi

2018-04-01

It is believed that the cool gas clouds traced by Mg II absorption, within a velocity offset of 5000 km/s from the background quasar, are associated with the quasar itself, whereas the absorbers seen at larger velocity offsets towards us are intervening systems and hence their existence is completely independent of the background quasar. Recent evidence by Bergeron et al. 2011 (hereafter BBM), however, seriously questions this canonical view, by showing that the number density of intervening Mg II absorbers along the sightlines towards 45 blazars is, on average, 2 times the expectation based on the Mg II absorption systems seen on the sightlines to normal QSOs. Given the serious implications of this finding, it becomes important to revisit this issue by enlarging the source sample and subjecting it to an independent analysis. Here, we first report our results based on a re-analysis of the spectroscopic data for the BBM sample; this has reproduced their factor 2 excess in dN/dz along blazar sightlines, vis-a-vis the normal QSOs. Next, we assemble a 6 times larger sample of blazar sightlines, albeit with lower SNR. Using this enlarged sample together with the BBM sample, our analysis shows that the dN/dz of Mg II absorbers statistically matches that known for normal QSO sightlines.

The Radio/Gamma-Ray Connection from 120 MHz to 230 GHz

Directory of Open Access Journals (Sweden)

Marcello Giroletti

2016-09-01

Full Text Available Radio loud active galactic nuclei are composed of different spatial features, each one characterized by different spectral properties in the radio band. Among them, blazars are the most common class of sources detected at gamma-rays by Fermi, and their radio emission is dominated by the flat spectrum compact core. In this contribution, we explore the connection between emission at high energy revealed by Fermi and at radio frequencies. Taking as a reference the strong and very highly significant correlation found between gamma rays and cm-λ radio emission, we explore the different behaviours found as we change the energy range in gamma rays and in radio, therefore changing the physical parameters of the zones involved in the emitted radiation. We find that the correlation weakens when we consider (1 gamma rays of energy above 10 GeV (except for high synchrotron peaked blazars or (2 low frequency radio data taken by the Murchison Widefield Array; on the other hand, the correlation strengthens when we consider mm-λ data taken by Atacama Large Millimeter Array (ALMA.

Methods for peak-flow frequency analysis and reporting for streamgages in or near Montana based on data through water year 2015

Science.gov (United States)

Sando, Steven K.; McCarthy, Peter M.

2018-05-10

This report documents the methods for peak-flow frequency (hereinafter “frequency”) analysis and reporting for streamgages in and near Montana following implementation of the Bulletin 17C guidelines. The methods are used to provide estimates of peak-flow quantiles for 50-, 42.9-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities for selected streamgages operated by the U.S. Geological Survey Wyoming-Montana Water Science Center (WY–MT WSC). These annual exceedance probabilities correspond to 2-, 2.33-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year recurrence intervals, respectively.Standard procedures specific to the WY–MT WSC for implementing the Bulletin 17C guidelines include (1) the use of the Expected Moments Algorithm analysis for fitting the log-Pearson Type III distribution, incorporating historical information where applicable; (2) the use of weighted skew coefficients (based on weighting at-site station skew coefficients with generalized skew coefficients from the Bulletin 17B national skew map); and (3) the use of the Multiple Grubbs-Beck Test for identifying potentially influential low flows. For some streamgages, the peak-flow records are not well represented by the standard procedures and require user-specified adjustments informed by hydrologic judgement. The specific characteristics of peak-flow records addressed by the informed-user adjustments include (1) regulated peak-flow records, (2) atypical upper-tail peak-flow records, and (3) atypical lower-tail peak-flow records. In all cases, the informed-user adjustments use the Expected Moments Algorithm fit of the log-Pearson Type III distribution using the at-site station skew coefficient, a manual potentially influential low flow threshold, or both.Appropriate methods can be applied to at-site frequency estimates to provide improved representation of long-term hydroclimatic conditions. The methods for improving at-site frequency estimates by weighting with regional

Beta Peak Frequencies at Rest Correlate with Endogenous GABA+/Cr Concentrations in Sensorimotor Cortex Areas.

Directory of Open Access Journals (Sweden)

Thomas J Baumgarten

Full Text Available Neuronal oscillatory activity in the beta band (15-30 Hz is a prominent signal within the human sensorimotor cortex. Computational modeling and pharmacological modulation studies suggest an influence of GABAergic interneurons on the generation of beta band oscillations. Accordingly, studies in humans have demonstrated a correlation between GABA concentrations and power of beta band oscillations. It remains unclear, however, if GABA concentrations also influence beta peak frequencies and whether this influence is present in the sensorimotor cortex at rest and without pharmacological modulation. In the present study, we investigated the relation between endogenous GABA concentration (measured by magnetic resonance spectroscopy and beta oscillations (measured by magnetoencephalography at rest in humans. GABA concentrations and beta band oscillations were measured for left and right sensorimotor and occipital cortex areas. A significant positive linear correlation between GABA concentration and beta peak frequency was found for the left sensorimotor cortex, whereas no significant correlations were found for the right sensorimotor and the occipital cortex. The results show a novel connection between endogenous GABA concentration and beta peak frequency at rest. This finding supports previous results that demonstrated a connection between oscillatory beta activity and pharmacologically modulated GABA concentration in the sensorimotor cortex. Furthermore, the results demonstrate that for a predominantly right-handed sample, the correlation between beta band oscillations and endogenous GABA concentrations is evident only in the left sensorimotor cortex.

Beta Peak Frequencies at Rest Correlate with Endogenous GABA+/Cr Concentrations in Sensorimotor Cortex Areas

Science.gov (United States)

Baumgarten, Thomas J.; Oeltzschner, Georg; Hoogenboom, Nienke; Wittsack, Hans-Jörg; Schnitzler, Alfons; Lange, Joachim

2016-01-01

Neuronal oscillatory activity in the beta band (15–30 Hz) is a prominent signal within the human sensorimotor cortex. Computational modeling and pharmacological modulation studies suggest an influence of GABAergic interneurons on the generation of beta band oscillations. Accordingly, studies in humans have demonstrated a correlation between GABA concentrations and power of beta band oscillations. It remains unclear, however, if GABA concentrations also influence beta peak frequencies and whether this influence is present in the sensorimotor cortex at rest and without pharmacological modulation. In the present study, we investigated the relation between endogenous GABA concentration (measured by magnetic resonance spectroscopy) and beta oscillations (measured by magnetoencephalography) at rest in humans. GABA concentrations and beta band oscillations were measured for left and right sensorimotor and occipital cortex areas. A significant positive linear correlation between GABA concentration and beta peak frequency was found for the left sensorimotor cortex, whereas no significant correlations were found for the right sensorimotor and the occipital cortex. The results show a novel connection between endogenous GABA concentration and beta peak frequency at rest. This finding supports previous results that demonstrated a connection between oscillatory beta activity and pharmacologically modulated GABA concentration in the sensorimotor cortex. Furthermore, the results demonstrate that for a predominantly right-handed sample, the correlation between beta band oscillations and endogenous GABA concentrations is evident only in the left sensorimotor cortex. PMID:27258089

Polarization Signatures of Kink Instabilities in the Blazar Emission Region from Relativistic Magnetohydrodynamic Simulations

International Nuclear Information System (INIS)

Zhang, Haocheng; Taylor, Greg; Li, Hui; Guo, Fan

2017-01-01

Kink instabilities are likely to occur in the current-carrying magnetized plasma jets. Recent observations of the blazar radiation and polarization signatures suggest that the blazar emission region may be considerably magnetized. While the kink instability has been studied with first-principle magnetohydrodynamic (MHD) simulations, the corresponding time-dependent radiation and polarization signatures have not been investigated. In this paper, we perform comprehensive polarization-dependent radiation modeling of the kink instability in the blazar emission region based on relativistic MHD (RMHD) simulations. We find that the kink instability may give rise to strong flares with polarization angle (PA) swings or weak flares with polarization fluctuations, depending on the initial magnetic topology and magnetization. These findings are consistent with observations. Compared with the shock model, the kink model generates polarization signatures that are in better agreement with the general polarization observations. Therefore, we suggest that kink instabilities may widely exist in the jet environment and provide an efficient way to convert the magnetic energy and produce multiwavelength flares and polarization variations.

Polarization Signatures of Kink Instabilities in the Blazar Emission Region from Relativistic Magnetohydrodynamic Simulations

Energy Technology Data Exchange (ETDEWEB)

Zhang, Haocheng; Taylor, Greg [Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87131 (United States); Li, Hui; Guo, Fan [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

2017-02-01

Kink instabilities are likely to occur in the current-carrying magnetized plasma jets. Recent observations of the blazar radiation and polarization signatures suggest that the blazar emission region may be considerably magnetized. While the kink instability has been studied with first-principle magnetohydrodynamic (MHD) simulations, the corresponding time-dependent radiation and polarization signatures have not been investigated. In this paper, we perform comprehensive polarization-dependent radiation modeling of the kink instability in the blazar emission region based on relativistic MHD (RMHD) simulations. We find that the kink instability may give rise to strong flares with polarization angle (PA) swings or weak flares with polarization fluctuations, depending on the initial magnetic topology and magnetization. These findings are consistent with observations. Compared with the shock model, the kink model generates polarization signatures that are in better agreement with the general polarization observations. Therefore, we suggest that kink instabilities may widely exist in the jet environment and provide an efficient way to convert the magnetic energy and produce multiwavelength flares and polarization variations.

Yet another NIR flare of the Blazar BZBJ1454+5124

Science.gov (United States)

Carrasco, L.; Porras, A.; Recillas, E.; Escobedo, G.; Chavushyan, V.

2018-05-01

We call attention on our recent observation of the Gamma Ray source 3FGLJ1454.5+5124 related with the quasar SBS1452+516 (z=1.0831) On March 28th,2018,(JD24582015.0015), we found this blazar to be in a new outburst.

Parsec-Scale Radio Properties of Gamma-ray Bright Blazars

Science.gov (United States)

Linford, Justin

2012-01-01

The parsec-scale radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been investigated using observations with the Very Long Baseline Array (VLBA). Comparisons between LAT and non-LAT detected samples were made using both archival and contemporaneous data. In total, 244 sources were used in the LAT-detected sample. This very large, radio flux-limited sample of active galactic nuclei (AGN) provides insights into the mechanism that produces strong gamma-ray emission. It has been found that LAT-detected BL Lac objects are very similar to the non-LAT BL Lac objects in most properties, although LAT BL Lac objects may have longer jets. The LAT flat spectrum radio quasars (FSRQs) are significantly different from non-LAT FSRQs and are likely extreme members of the FSRQ population. Archival radio data indicated that there was no significant correlation between radio flux density and gamma-ray flux, especially at lower flux levels. However, contemporaneous observations showed a strong correlation. Most of the differences between the LAT and non-LAT populations are related to the cores of the sources, indicating that the gamma-ray emission may originate near the base of the jets (i.e., within a few pc of the central engine). There is some indication that LAT-detected sources may have larger jet opening angles than the non-LAT sources. Strong core polarization is significantly more common among the LAT sources, suggesting that gamma-ray emission is related to strong, uniform magnetic fields at the base of the jets of the blazars. Observations of sources in two epochs indicate that core fractional polarization was higher when the objects were detected by the LAT. Included in our sample are several non-blazar AGN such as 3C84, M82, and NGC 6251.

HIGH-PRECISION ASTROMETRIC MILLIMETER VERY LONG BASELINE INTERFEROMETRY USING A NEW METHOD FOR MULTI-FREQUENCY CALIBRATION

Energy Technology Data Exchange (ETDEWEB)

Dodson, Richard; Rioja, María J. [International Centre for Radio Astronomy Research, M468, The University of Western Australia, 35 Stirling Hwy, Crawley, Western Australia 6009 (Australia); Molina, Sol N.; Gómez, José L., E-mail: richard.dodson@icrar.org [Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, E-18008 Granada (Spain)

2017-01-10

In this paper we describe a new approach for millimeter Very Long Baseline Interferometry (mm-VLBI) calibration that provides bona-fide astrometric alignment of the millimeter-wavelength images from a single source, for the measurement of frequency-dependent effects, such as “core-shifts” near the black hole of active galactic nucleus jets. We achieve our astrometric alignment by solving first for the ionospheric (dispersive) contributions using wide-band centimeter-wavelength observations. Second, we solve for the tropospheric (non-dispersive) contributions by using fast frequency-switching at the target millimeter-wavelengths. These solutions can be scaled and transferred from low frequency to the high frequency. To complete the calibration chain an additional step is required to remove a residual constant phase offset on each antenna. The result is an astrometric calibration and the measurement of the core-shift between 22 and 43 GHz for the jet in BL Lacertae to be −8 ± 5, 20 ± 6 μ as, in R.A. and decl., respectively. By comparison to conventional phase referencing at centimeter-wavelengths we are able to show that this core shift at millimeter-wavelengths is significantly less than what would be predicted by extrapolating the low-frequency result, which closely followed the predictions of the Blandford and Königl conical jet model. As such it would be the first demonstration for the association of the VLBI core with a recollimation shock, normally hidden at low frequencies due to the optical depth, which could be responsible for the γ -ray production in blazar jets.

HIGH-PRECISION ASTROMETRIC MILLIMETER VERY LONG BASELINE INTERFEROMETRY USING A NEW METHOD FOR MULTI-FREQUENCY CALIBRATION

International Nuclear Information System (INIS)

Dodson, Richard; Rioja, María J.; Molina, Sol N.; Gómez, José L.

2017-01-01

In this paper we describe a new approach for millimeter Very Long Baseline Interferometry (mm-VLBI) calibration that provides bona-fide astrometric alignment of the millimeter-wavelength images from a single source, for the measurement of frequency-dependent effects, such as “core-shifts” near the black hole of active galactic nucleus jets. We achieve our astrometric alignment by solving first for the ionospheric (dispersive) contributions using wide-band centimeter-wavelength observations. Second, we solve for the tropospheric (non-dispersive) contributions by using fast frequency-switching at the target millimeter-wavelengths. These solutions can be scaled and transferred from low frequency to the high frequency. To complete the calibration chain an additional step is required to remove a residual constant phase offset on each antenna. The result is an astrometric calibration and the measurement of the core-shift between 22 and 43 GHz for the jet in BL Lacertae to be −8 ± 5, 20 ± 6 μ as, in R.A. and decl., respectively. By comparison to conventional phase referencing at centimeter-wavelengths we are able to show that this core shift at millimeter-wavelengths is significantly less than what would be predicted by extrapolating the low-frequency result, which closely followed the predictions of the Blandford and Königl conical jet model. As such it would be the first demonstration for the association of the VLBI core with a recollimation shock, normally hidden at low frequencies due to the optical depth, which could be responsible for the γ -ray production in blazar jets.

High-power microwave generation from a frequency-stabilized virtual cathode source

International Nuclear Information System (INIS)

Fazio, M.V.; Hoeberling, R.F.; Kinross-Wright, J.

1988-01-01

The evolution of virtual cathode based high-power microwave-source technology has been directed primarily toward achieving higher peak-power levels. As peak powers in excess of 10 GW have been reported, attention has begun to focus on techniques for producing a more frequency- and phase-stable virtual cathode source. Free-running virtual cathode microwave sources characteristically exhibit bandwidths in a single pulse of tens of percent, which makes them unsuitable for many applications such as power sources for phased array antennas and microwave linear accelerators. Presented here are results of an experimental approach utilizing a high-Q, resonant cavity surrounding the oscillating virtual cathode to achieve frequency stabilization and repeatable narrow-band operation. A cylindrical cavity resonator is used with the microwave power being extracted radially through circumferential slot apertures into L-band waveguide

Visual Method for Spectral Energy Distribution Calculation of ...

Indian Academy of Sciences (India)

Abstract. In this work, we propose to use 'The Geometer's Sketchpad' to the fitting of a spectral energy distribution of blazar based on three effective spectral indices, αRO, αOX, and αRX and the flux density in the radio band. It can make us to see the fitting in detail with both the peak frequency and peak luminosity given ...

GAMMA-RAY EMISSION FROM TWO BLAZARS BEHIND THE GALACTIC PLANE: B2013+370 AND B2023+336

International Nuclear Information System (INIS)

Kara, E.; Errando, M.; Aliu, E.; Mukherjee, R.; Max-Moerbeck, W.; Readhead, A. C. S.; Richards, J. L.; Böttcher, M.; Fortin, P.; Halpern, J. P.

2012-01-01

B2013+370 and B2023+336 are two blazars at low-galactic latitude that were previously proposed to be the counterparts for the EGRET unidentified sources 3EG J2016+3657 and 3EG J2027+3429. Gamma-ray emission associated with the EGRET sources has been detected by the Fermi Gamma-ray Space Telescope, and the two sources, 1FGL J2015.7+3708 and 1FGL J2027.6+3335, have been classified as unidentified in the 1 year catalog. This analysis of the Fermi Large Area Telescope (LAT) data collected during 31 months reveals that the 1FGL sources are spatially compatible with the blazars and are significantly variable, supporting the hypothesis of extragalactic origin for the gamma-ray emission. The gamma-ray light curves are compared with 15 GHz radio light curves from the 40 m telescope at the Owens Valley Radio Observatory. Simultaneous variability is seen in both bands for the two blazar candidates. The study is completed with the X-ray analysis of 1FGL J2015.7+3708 using Swift observations that were triggered in 2010 August by a Fermi-detected flare. The resulting spectral energy distribution shows a two-component structure typical of blazars. We also identify a second source in the field of view of 1FGL J2027.6+3335 with similar characteristics to the known LAT pulsars. This study gives solid evidence favoring blazar counterparts for these two unidentified EGRET and Fermi sources, supporting the hypothesis that a number of unidentified gamma-ray sources at low-galactic latitudes are indeed of extragalactic origin.

BeppoSAX Observations of the TeV Blazar Mkn 421

Energy Technology Data Exchange (ETDEWEB)

Fossati, G.; Chiappetti, L.; Celotti, A.; Ghisellini, G.; Maraschi, L.; Tagliaferri, G.; Tanzi, E.G.; Treves, A.; Bassani, L.; Cappi, M.; Comastri, A.; Frontera, F.; Giarrusso, S.; Grandi, P.; Molendi, S.; Palumbo, G.; Perola, C.; Pian, E.; Salvati, M.; Raiteri, C.; Villata, M.; Urry, C.M

1999-01-01

The blazar Mkn 421 has been observed, as part of the AO1 Core Program, five times from 2 to 7 May 1997. In the LECS+MECS energy band the spectrum shows convex curvature, well represented by a broken power-law. Flux variability (more than a factor 2) has been detected over the entire 0.1-10 keV range, accompanying which the spectrum steepens with the decrease in intensity. Mkn 421 has been also detected with the PDS instrument. Our preliminary analysis indicates that the PDS spectrum lies significantly above the extrapolation from the MECS, suggesting a contribution from a flatter high energy component.

BeppoSAX Observations of the TeV Blazar Mkn 421

International Nuclear Information System (INIS)

Fossati, G.; Chiappetti, L.; Celotti, A.; Ghisellini, G.; Maraschi, L.; Tagliaferri, G.; Tanzi, E.G.; Treves, A.; Bassani, L.; Cappi, M.; Comastri, A.; Frontera, F.; Giarrusso, S.; Grandi, P.; Molendi, S.; Palumbo, G.; Perola, C.; Pian, E.; Salvati, M.; Raiteri, C.; Villata, M.; Urry, C.M.

1999-01-01

The blazar Mkn 421 has been observed, as part of the AO1 Core Program, five times from 2 to 7 May 1997. In the LECS+MECS energy band the spectrum shows convex curvature, well represented by a broken power-law. Flux variability (more than a factor 2) has been detected over the entire 0.1-10 keV range, accompanying which the spectrum steepens with the decrease in intensity. Mkn 421 has been also detected with the PDS instrument. Our preliminary analysis indicates that the PDS spectrum lies significantly above the extrapolation from the MECS, suggesting a contribution from a flatter high energy component

SDSS J14584479+3720215: A BENCHMARK JHK{sub S} BLAZAR LIGHT CURVE FROM THE 2MASS CALIBRATION SCANS

Energy Technology Data Exchange (ETDEWEB)

Davenport, James R. A.; Ruan, John J.; Becker, Andrew C. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Macleod, Chelsea L. [Physics Department, The United States Naval Academy, 572c Holloway Road, Annapolis, MD 21402 (United States); Cutri, Roc M., E-mail: jrad@astro.washington.edu [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States)

2015-04-10

Active galactic nuclei (AGNs) are well-known to exhibit flux variability across a wide range of wavelength regimes, but the precise origin of the variability at different wavelengths remains unclear. To investigate the relatively unexplored near-IR (NIR) variability of the most luminous AGNs, we conduct a search for variability using well sampled JHK{sub s}-band light curves from the Two Micron All Sky Survey (2MASS) calibration fields. Our sample includes 27 known quasars with an average of 924 epochs of observation over three years, as well as one spectroscopically confirmed blazar (SDSS J14584479+3720215) with 1972 epochs of data. This is the best-sampled NIR photometric blazar light curve to date, and it exhibits correlated, stochastic variability that we characterize with continuous auto-regressive moving average (CARMA) models. None of the other 26 known quasars had detectable variability in the 2MASS bands above the photometric uncertainty. A blind search of the 2MASS calibration field light curves for active galactic nucleus (AGN) candidates based on fitting CARMA(1,0) models (damped-random walk) uncovered only seven candidates. All seven were young stellar objects within the ρ Ophiuchus star forming region, five with previous X-ray detections. A significant γ-ray detection (5σ) for the known blazar using 4.5 yr of Fermi photon data is also found. We suggest that strong NIR variability of blazars, such as seen for SDSS J14584479+3720215, can be used as an efficient method of identifying previously unidentified γ-ray blazars, with low contamination from other AGNs.

OPTICAL SPECTROSCOPIC OBSERVATIONS OF GAMMA-RAY BLAZAR CANDIDATES. VI. FURTHER OBSERVATIONS FROM TNG, WHT, OAN, SOAR, AND MAGELLAN TELESCOPES

Energy Technology Data Exchange (ETDEWEB)

Álvarez Crespo, N.; Massaro, F. [Dipartimento di Fisica, Università degli Studi di Torino, via Pietro Giuria 1, I-10125 Torino (Italy); Milisavljevic, D.; Paggi, A.; Smith, Howard A. [Harvard—Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Landoni, M. [INAF-Osservatorio Astronomico di Brera, Via Emilio Bianchi 46, I-23807 Merate (Italy); Chavushyan, V.; Patiño-Álvarez, V. [Instituto Nacional de Astrofísica, Óptica y Electrónica, Apartado Postal 51-216, 72000 Puebla, México (Mexico); Masetti, N. [INAF—Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna, via Gobetti 101, I-40129, Bologna (Italy); Jiménez-Bailón, E. [Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 877, Ensenada, 22800 Baja California, México (Mexico); Strader, J.; Chomiuk, L. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Katagiri, H.; Kagaya, M. [College of Science, Ibaraki University, 2-1-1, Bunkyo, Mito 310-8512 (Japan); Cheung, C. C. [Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States); D’Abrusco, R. [Department of Physical Sciences, University of Napoli Federico II, via Cinthia 9, I-80126 Napoli (Italy); Ricci, F.; La Franca, F. [Dipartimento di Matematica e Fisica, Università Roma Tre, via della Vasca Navale 84, I-00146, Roma (Italy); and others

2016-04-15

Blazars, one of the most extreme classes of active galaxies, constitute so far the largest known population of γ-ray sources, and their number is continuously growing in the Fermi catalogs. However, in the latest release of the Fermi catalog there is still a large fraction of sources that are classified as blazar candidates of uncertain type (BCUs) for which optical spectroscopic observations are necessary to confirm their nature and their associations. In addition, about one-third of the γ-ray point sources listed in the Third Fermi-LAT Source Catalog (3FGL) are still unassociated and lacking an assigned lower-energy counterpart. Since 2012 we have been carrying out an optical spectroscopic campaign to observe blazar candidates to confirm their nature. In this paper, the sixth of the series, we present optical spectroscopic observations for 30 γ-ray blazar candidates from different observing programs we carried out with the Telescopio Nazionale Galileo, William Herschel Telescope, Observatorio Astronómico Nacional, Southern Astrophysical Research Telescope, and Magellan Telescopes. We found that 21 out of 30 sources investigated are BL Lac objects, while the remaining targets are classified as flat-spectrum radio quasars showing the typical broad emission lines of normal quasi-stellar objects. We conclude that our selection of γ-ray blazar candidates based on their multifrequency properties continues to be a successful way to discover potential low-energy counterparts of the Fermi unidentified gamma-ray sources and to confirm the nature of BCUs.

Broad Band Observations of Gravitationally Lensed Blazar during a Gamma-Ray Outburst

Directory of Open Access Journals (Sweden)

Julian Sitarek

2016-09-01

Full Text Available QSO B0218+357 is a gravitationally lensed blazar located at a cosmological redshift of 0.944. In July 2014 a GeV flare was observed by Fermi-LAT, triggering follow-up observations with the MAGIC telescopes at energies above 100 GeV. The MAGIC observations at the expected time of arrival of the trailing component resulted in the first detection of QSO B0218+357 in Very-High-Energy (VHE, >100 GeV gamma rays. We report here the observed multiwavelength emission during the 2014 flare.

High Frequency Oscillatory Ventilation

Directory of Open Access Journals (Sweden)

AC Bryan

1996-01-01

Full Text Available High frequency oscillatory (HFO ventilation using low tidal volume and peak airway pressures is extremely efficient at eliminating carbon dioxide and raising pH in the newborn infant with acute respiratory failure. Improvement in oxygenation requires a strategy of sustained or repetitive inflations to 25 to 30 cm H2O in order to place the lung on the deflation limb of the pressure-volume curve. This strategy has also been shown to decrease the amount of secondary lung injury in animal models. Experience of the use of HFO ventilation as a rescue therapy as well as several published controlled trials have shown improved outcomes and a decrease in the use of extracorporeal membrane oxygenation when it has been used in newborns.

A one-parametric formula relating the frequencies of twin-peak quasi-periodic oscillations

Science.gov (United States)

Török, Gabriel; Goluchová, Kateřina; Šrámková, Eva; Horák, Jiří; Bakala, Pavel; Urbanec, Martin

2017-12-01

Timing analysis of X-ray flux in more than a dozen low-mass X-ray binary systems containing a neutron star reveals remarkable correlations between frequencies of two characteristic peaks present in the power-density spectra. We find a simple analytic relation that well reproduces all these individual correlations. We link this relation to a physical model which involves accretion rate modulation caused by an oscillating torus.

Measurement of the blazar Mrk421 flux above 60 GeV with the CELESTE experiment

International Nuclear Information System (INIS)

Le Gallou, R.

2001-11-01

The CELESTE experiment is based on an ancient solar plant that has been turned into a detector able to detect the particle showers triggered by the interactions of high energy cosmic photons with the earth atmosphere nuclei. The purpose of the CELESTE experiment is to study the emissions of photons by cosmic objects like supernovae remnants, pulsars or active cores of galaxies such as blazars. Blazars are very interesting objects to study because they allow us to investigate matter that is in extreme conditions and to probe a very far past. The aim of this work has been to develop methods for the analysis of the data collected by CELESTE and to validate them. A specific effort has been achieved for the selection of efficient hadronic rejection criteria in order to optimize the sensitivity of the detector. The physics of the detector is detailed from the particle showers to the data analysis. The detector acceptance has been assessed through Monte-Carlo simulations that have been shown that the detection threshold is 30 GeV at the triggering point and 60 GeV after the analysis cuts. The validation tests have been performed on the Crab nebula that is a standard in gamma astronomy for its stability and intensity. CELESTE has been operating since November 1999 in a satisfactory way and has accumulated data on 4 blazars among them Mrk421. Several bursts have been detected on Mrk421 and an average photon flux has been determined. A correlation has been deduced from the activity detected by CELESTE and the activities in the TeV and X ranges which agrees with the simulations

Very fast, high peak-power, planar triode amplifiers for driving optical gates

International Nuclear Information System (INIS)

Howland, M.M.; Davis, S.J.; Gagnon, W.L.

1979-01-01

Recent extensions of the peak power capabilities of planar triodes have made possible the latter's use as very fast pulse amplifiers, to drive optical gates within high-power Nd:glass laser chains. These pulse amplifiers switch voltages in the 20 kV range with rise times of a few nanoseconds, into crystal optical gates that are essentially capacitive loads. This paper describes a simplified procedure for designing these pulse amplifiers. It further outlines the use of bridged-T constant resistance networks to transform load capacitance into pure resistance, independent of frequency

Ketamine increases the frequency of electroencephalographic bicoherence peak on the alpha spindle area induced with propofol.

Science.gov (United States)

Hayashi, K; Tsuda, N; Sawa, T; Hagihira, S

2007-09-01

The reticular and thalamocortical system is known to play a prominent role in spindle wave activity, and the spindle wave is related to the sedative effects of anaesthetics. Recently, bispectral analysis of the EEG has been developed as a better method to indicate nonlinear regulation including the thalamocortical system linking to the cortical area. In the present study, in order to explore the interference of ketamine with the nonlinear regulation of the sub-cortical system, we examined the effect of ketamine on spindle alpha waves through the bispectral analysis. The study included 21 patients. Anaesthesia was induced and maintained using a propofol-TCI system (target-controlled infusion, with target concentration 3.5 microg ml(-1)). An A-2000 BIS monitor was used and the raw EEG signals were collected via an RS232 interface on a personal computer. Bicoherence, the normalized bispectrum, and power spectrum were analysed before and after i.v. administration of 1 mg kg(-1) racemic ketamine. Propofol caused alpha peaks in both power and bicoherence spectra, with average frequencies of 10.6 (SD 0.9) Hz and 10.7 (1.0) Hz, respectively. The addition of ketamine significantly shifted each peak to frequencies of 14.4 (1.4) Hz and 13.6 (1.5) Hz, respectively [P < 0.05, mean (SD)]. Ketamine shifted the alpha peaks of bicoherence induced by propofol to higher frequencies. This suggests that ketamine changes the alpha spindle rhythms through the modulation of the nonlinear sub-cortical reverberating network.

Prediction of high frequency core loss for electrical steel using the data provided by manufacturer

Science.gov (United States)

Roy, Rakesh; Dalal, Ankit; Kumar, Praveen

2016-07-01

This paper describes a technique to determine the core loss data, at high frequencies, using the loss data provided by the lamination manufacturer. Steinmetz equation is used in this proposed method to determine core loss at high frequency. This Steinmetz equation consists of static hysteresis and eddy current loss. The presented technique considers the coefficients of Steinmetz equation as variable with frequency and peak magnetic flux density. The high frequency core loss data, predicted using this model is compared with the catalogue data given by manufacturer and very good accuracy has been obtained for a wide range of frequency.

Peak discharge, flood frequency, and peak stage of floods on Big Cottonwood Creek at U.S. Highway 50 near Coaldale, Colorado, and Fountain Creek below U.S. Highway 24 in Colorado Springs, Colorado, 2016

Science.gov (United States)

Kohn, Michael S.; Stevens, Michael R.; Mommandi, Amanullah; Khan, Aziz R.

2017-12-14

The U.S. Geological Survey (USGS), in cooperation with the Colorado Department of Transportation, determined the peak discharge, annual exceedance probability (flood frequency), and peak stage of two floods that took place on Big Cottonwood Creek at U.S. Highway 50 near Coaldale, Colorado (hereafter referred to as “Big Cottonwood Creek site”), on August 23, 2016, and on Fountain Creek below U.S. Highway 24 in Colorado Springs, Colorado (hereafter referred to as “Fountain Creek site”), on August 29, 2016. A one-dimensional hydraulic model was used to estimate the peak discharge. To define the flood frequency of each flood, peak-streamflow regional-regression equations or statistical analyses of USGS streamgage records were used to estimate annual exceedance probability of the peak discharge. A survey of the high-water mark profile was used to determine the peak stage, and the limitations and accuracy of each component also are presented in this report. Collection and computation of flood data, such as peak discharge, annual exceedance probability, and peak stage at structures critical to Colorado’s infrastructure are an important addition to the flood data collected annually by the USGS.The peak discharge of the August 23, 2016, flood at the Big Cottonwood Creek site was 917 cubic feet per second (ft3/s) with a measurement quality of poor (uncertainty plus or minus 25 percent or greater). The peak discharge of the August 29, 2016, flood at the Fountain Creek site was 5,970 ft3/s with a measurement quality of poor (uncertainty plus or minus 25 percent or greater).The August 23, 2016, flood at the Big Cottonwood Creek site had an annual exceedance probability of less than 0.01 (return period greater than the 100-year flood) and had an annual exceedance probability of greater than 0.005 (return period less than the 200-year flood). The August 23, 2016, flood event was caused by a precipitation event having an annual exceedance probability of 1.0 (return

Variability of Spectral Energy Distribution of Blazar S5 0716+714 B ...

Indian Academy of Sciences (India)

one-zone BPL model is over-simplified in accounting for the radio-optical blazar emission. ... a number of authors (e.g., Vittorini et al. 2009; Raiteri et ... contribution from starlight to the optical bands, which will modify the calculated synchrotron ...

High frequency conductivity of hot electrons in carbon nanotubes

Energy Technology Data Exchange (ETDEWEB)

Amekpewu, M., E-mail: mamek219@gmail.com [Department of Applied Physics, University for Development Studies, Navrongo (Ghana); Mensah, S.Y. [Department of Physics, College of Agriculture and Natural Sciences, U.C.C. (Ghana); Musah, R. [Department of Applied Physics, University for Development Studies, Navrongo (Ghana); Mensah, N.G. [Department of Mathematics, College of Agriculture and Natural Sciences, U.C.C. (Ghana); Abukari, S.S.; Dompreh, K.A. [Department of Physics, College of Agriculture and Natural Sciences, U.C.C. (Ghana)

2016-05-01

High frequency conductivity of hot electrons in undoped single walled achiral Carbon Nanotubes (CNTs) under the influence of ac–dc driven fields was considered. We investigated semi-classically Boltzmann's transport equation with and without the presence of the hot electrons’ source by deriving the current densities in CNTs. Plots of the normalized current density versus frequency of ac-field revealed an increase in both the minimum and maximum peaks of normalized current density at lower frequencies as a result of a strong injection of hot electrons. The applied ac-field plays a twofold role of suppressing the space-charge instability in CNTs and simultaneously pumping an energy for lower frequency generation and amplification of THz radiations. These have enormous promising applications in very different areas of science and technology.

Blazars with arcminute-scale radio halos

International Nuclear Information System (INIS)

Ulvestad, J.S.; Antonucci, R.R.J.; Space Telescope Science Institute, Baltimore, MD)

1986-01-01

About 10-arcsec resolution 20-cm wavelength maps are presented for three nearby BL Lac objects: Mkn 180, whose halo has a linear size of 85 kpc, 2155-304, with a halo about 375 kpc across, and 1727 + 502, whose one-sided diffuse emission extends to a distance of about 145 kpc from its radio core. Little evidence is found for strong radio variability in the cores of the three blazars; these and other results obtained are consistent with the assertion that the three objects should be classified as normal low luminosity double radio galaxies with optically dull nuclei, if seen from other directions. 20 references

Using vehicle-to-grid technology for frequency regulation and peak-load reduction

Science.gov (United States)

White, Corey D.; Zhang, K. Max

This paper explores the potential financial return for using plug-in hybrid electric vehicles as a grid resource. While there is little financial incentive for individuals when the vehicle-to-grid (V2G) service is used exclusively for peak reduction, there is a significant potential for financial return when the V2G service is used for frequency regulation. We propose that these two uses for V2G technology are not mutually exclusive, and that there could exist a "dual-use" program that utilizes V2G for multiple uses simultaneously. In our proposition, V2G could be used for regulation on a daily basis to ensure profits, and be used for peak reduction on days with high electricity demand and poor ambient air quality in order to reap the greatest environmental benefits. The profits for the individual in this type of dual-use program are close to or even higher than the profits experienced in either of the single-use programs. More importantly, we argue that the external benefits of this type of program are much greater as well. At higher V2G participation rates, our analysis shows that the market for regulation capacity could become saturated by V2G-based regulation providers. At the same time, there is plenty of potential for widespread use of V2G technology, especially if the demand for regulation, reserves, and storage grows as more intermittent renewable resources are being incorporated into the power systems.

Understanding the relationship between DOC and nitrate export and dominant rainfall-runoff processes through long-term high frequency measurements

Science.gov (United States)

Schwab, Michael; Klaus, Julian; Pfister, Laurent; Weiler, Markus

2016-04-01

Over the past decades, stream sampling protocols for hydro-geochemical parameters were often limited by logistical and technological constraints. While long-term monitoring protocols were typically based on weekly sampling intervals, high frequency sampling was commonly limited to a few single events. In our study, we combined high frequency and long-term measurements to understand the DOC and nitrate behaviour and dynamics for different runoff events and seasons. Our study area is the forested Weierbach catchment (0.47 km2) in Luxembourg. The fractured schist bedrock is covered by cambisol soils. The runoff response of the catchment is characterized by a double peak behaviour. A first discharge peak occurs during or right after a rainfall event (triggered by fast near surface runoff generation processes), while a second delayed peak lasts several days (generated by subsurface flow/ shallow groundwater flow). Peaks in DOC concentrations are closely linked to the first discharge peak, whereas nitrate concentrations follow the second peak. Our observations were carried out with the field deployable instrument spectro::lyser (scan Messtechnik GmbH). This instrument relies on the principles of UV-Vis spectrometry and measures DOC and nitrate concentrations. The measurements were carried out at a high frequency of 15 minutes in situ in the Weierbach creek for more than two years. In addition, a long-term validation was carried out with data obtained from the analysis of water collected with automatic samplers. The long-term, high-frequency measurements allowed us to calculate a complete and detailed balance of DOC and nitrate export over two years. Transport behaviour of the DOC and nitrate showed different dynamics between the first and second hydrograph peaks. DOC is mainly exported during first peaks, while nitrate is mostly exported during the delayed second peaks. In combination with other measurements in the catchment, the long and detailed observations have

Optical Spectroscopic Observations of γ-Ray Blazar Candidates. III. The 2013/2014 Campaign in the Southern Hemisphere

Science.gov (United States)

Landoni, M.; Massaro, F.; Paggi, A.; D'Abrusco, R.; Milisavljevic, D.; Masetti, N.; Smith, H. A.; Tosti, G.; Chomiuk, L.; Strader, J.; Cheung, C. C.

2015-05-01

We report the results of our exploratory program carried out with the southern Astrophysical Research telescope aimed at associating counterparts and establishing the nature of the Fermi Unidentified γ-ray Sources (UGSs). We selected the optical counterparts of six UGSs from the Fermi catalog on the basis of our recently discovered tight connection between infrared and γ-ray emission found for the γ-ray blazars detected by the Wide-Field Infrared Survey Explorer in its all-sky survey. We perform for the first time a spectroscopic study of the low-energy counterparts of the Fermi UGSs, in the optical band, confirming the blazar-like nature of the whole sample. We also present new spectroscopic observations of six active galaxies of uncertain type associated with Fermi sources which appear to be BL Lac objects. Finally, we report the spectra collected for six known γ-ray blazars belonging to the Roma BZCAT that were obtained to establish their nature or better estimate their redshifts. Two interesting cases of high redshift and extremely luminous BL Lac objects (z ≥ 1.18 and z ≥ 1.02, based on the detection of Mg ii intervening systems) are also discussed. Based on observations obtained at the southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

Analysis of the correlation between γ-ray and radio emissions from γ-ray loud Blazar using the discrete correlation function

International Nuclear Information System (INIS)

Cheng Yong; Zhang Xiong; Wu Lin; Mao Weiming; You Lisha

2006-01-01

The authors collect 119 γ-ray-loud Blazar (97 flat spectrum radio quasars (FSRQs) and 22 BL Lacertae objects (BL Lac)), and investigate respectively the correlation between the γ-ray emission (maximum, minimum, and average data) at 1 GeV and the radio emission at 8.4 GHz by discrete correlation function (DCF) method. Our main results are as follows: there is good correlation between the γ-ray in high state and average state and radio emissions for the whole 119 Blazar and 97 FSRQs. And there are no correlation between γ-ray emission and radio emission in low state. Our result shows that the γ-rays are associated with the radio emission from the jet, and that the γ-ray emission is likely to have come from the synchrotron self-compton model (SSC) process in this case. (authors)

High Tc superconductors at microwave frequencies

International Nuclear Information System (INIS)

Gruener, G.

1991-01-01

The author discusses various experiments conducted in the micro- and millimeter wave spectral range on thin film and single crystal specimens of the high temperature oxide superconductors. For high quality film the surface resistance R s is, except at low temperatures, due to thermally excited carriers, with extrinsic effects playing only a secondary role. Because of the low loss various passive microwave components, such as resonators, delay lines and filters, with performance far superior to those made of normal metals can be fabricated. The conductivity measured at millimeter wave frequencies displays a peak below T c . Whether this is due to coherence factors or due to the change of the relaxation rate when the materials enter the superconducting state remains to be seen

INVESTIGATING BROADBAND VARIABILITY OF THE TeV BLAZAR 1ES 1959+650

International Nuclear Information System (INIS)

Aliu, E.; Archambault, S.; Arlen, T.; Aune, T.; Barnacka, A.; Beilicke, M.; Buckley, J. H.; Bugaev, V.; Benbow, W.; Cerruti, M.; Berger, K.; Bird, R.; Collins-Hughes, E.; Bouvier, A.; Chen, X.; Ciupik, L.; Connolly, M. P.; Cui, W.; Dumm, J.; Eisch, J. D.

2014-01-01

We summarize broadband observations of the TeV-emitting blazar 1ES 1959+650, including optical R-band observations by the robotic telescopes Super-LOTIS and iTelescope, UV observations by Swift Ultraviolet and Optical Telescope, X-ray observations by the Swift X-ray Telescope, high-energy gamma-ray observations with the Fermi Large Area Telescope, and very-high-energy (VHE) gamma-ray observations by VERITAS above 315 GeV, all taken between 2012 April 17 and 2012 June 1 (MJD 56034 and 56079). The contemporaneous variability of the broadband spectral energy distribution is explored in the context of a simple synchrotron self Compton (SSC) model. In the SSC emission scenario, we find that the parameters required to represent the high state are significantly different than those in the low state. Motivated by possible evidence of gas in the vicinity of the blazar, we also investigate a reflected emission model to describe the observed variability pattern. This model assumes that the non-thermal emission from the jet is reflected by a nearby cloud of gas, allowing the reflected emission to re-enter the blob and produce an elevated gamma-ray state with no simultaneous elevated synchrotron flux. The model applied here, although not required to explain the observed variability pattern, represents one possible scenario which can describe the observations. As applied to an elevated VHE state of 66% of the Crab Nebula flux, observed on a single night during the observation period, the reflected emission scenario does not support a purely leptonic non-thermal emission mechanism. The reflected emission model does, however, predict a reflected photon field with sufficient energy to enable elevated gamma-ray emission via pion production with protons of energies between 10 and 100 TeV

Through the Ring of Fire: A Study of the Origin of Orphan Gamma-ray Flares in Blazars

Science.gov (United States)

MacDonald, Nicholas R.; Marscher, Alan P.; Jorstad, Svetlana G.; Joshi, Manasvita

2014-06-01

Blazars exhibit flares across the electromagnetic spectrum. Many gamma-ray flares are highly correlated with flares detected at optical wavelengths; however, a small subset appear to occur in isolation, with no counterpart in the other wave bands. These "orphan" gamma-ray flares challenge current models of blazar variability, most of which are unable to reproduce this type of behavior. We present numerical calculations of the time variable emission of a blazar based on a proposal by Marscher et al. (2010) to explain such events. In this model, a plasmoid ("blob") consisting of a power-law distribution of electrons propagates relativistically along the spine of a blazar jet and passes through a synchrotron emitting ring of electrons representing a shocked portion of the jet sheath. This ring supplies a source of seed photons that are inverse-Compton scattered by the electrons in the moving blob. As the blob approaches the ring, the photon density in the co-moving frame of the plasma increases, resulting in an orphan gamma-ray flare that then dissipates as the blob passes through and then moves away from the ring. The model includes the effects of radiative cooling and a spatially varying magnetic field. Support for the plausibility of this model is provided by observations by Marscher et al.(2010) of an isolated gamma-ray flare that was correlated with the passage of a superluminal knot through the inner jet of quasar PKS 1510-089. Synthetic light-curves produced by this new model are compared to the observed light-curves from this event. In addition, we present polarimetric observations that point to the existence of a jet sheath in the quasar 3C 273. A rough estimate of the bolometric luminosity of the sheath results in a value of ~10^45 erg s^-1 10% of the jet luminosity). This inferred sheath luminosity indicates that the jet sheath in 3C 273 can provide a significant source of seed photons that need to be taken into account when modeling the non

Spectral Index Changes with Brightness for γ-Ray Loud Blazars J. H. ...

Indian Academy of Sciences (India)

spectral index changes depending on γ-ray brightness is obtained. ... the γ-ray band. Key words. Active galactic nuclei (AGN): blazars: γ-ray emission: spectral index. 1. Introduction. Generally, the spectrum of one source changes with its .... Pearl River Scholar Funded Scheme (GDUPS) (2009), Yangcheng Scholar Funded.

Discovery of a GeV Blazar Shining Through the Galactic Plane

Energy Technology Data Exchange (ETDEWEB)

Vandenbroucke, J.; Buehler, R.; Ajello, M.; Bechtol, K.; /Stanford U., HEPL /KIPAC, Menlo Park /SLAC; Bellini, A.; /Padua U., Astron. Dept. /Baltimore, Space Telescope Sci.; Bolte, M.; /UC, Santa Cruz; Cheung, C.C.; /Naval Research Lab, Wash., D.C. /NAS, Washington, D.C.; Civano, F.; /Smithsonian Astrophys. Observ.; Donato, D.; /NASA, Goddard; Fuhrmann, L.; /Bonn, Max Planck Inst., Radioastron.; Funk, S.; Healey, S.E.; /Stanford U., HEPL /KIPAC, Menlo Park /SLAC; Hill, A.B.; /Joseph Fourier U.; Knigge, C.; /Southampton U.; Madejski, G.M.; Romani, R.W.; /Stanford U., HEPL /KIPAC, Menlo Park /SLAC; Santander-Garcia, M.; /IAC, La Laguna /Isaac Newton Group /Laguna U., Tenerife; Shaw, M.S.; /Stanford U., HEPL /KIPAC, Menlo Park /SLAC; Steeghs, D.; /Warwick U.; Torres, M.A.P.; /Smithsonian Astrophys. Observ.; Van Etten, A.; /Stanford U., HEPL /KIPAC, Menlo Park /SLAC /Texas U., Astron. Dept.

2011-08-11

The Fermi Large Area Telescope (LAT) discovered a new gamma-ray source near the Galactic plane, Fermi J0109+6134, when it flared brightly in 2010 February. The low Galactic latitude (b = -1.2{sup o}) indicated that the source could be located within the Galaxy, which motivated rapid multi-wavelength follow-up including radio, optical, and X-ray observations. We report the results of analyzing all 19 months of LAT data for the source, and of X-ray observations with both Swift and the Chandra X-ray Observatory. We determined the source redshift, z = 0.783, using a Keck LRIS observation. Finally, we compiled a broadband spectral energy distribution (SED) from both historical and new observations contemporaneous with the 2010 February flare. The redshift, SED, optical line width, X-ray obsorption, and multi-band variability indicate that this new Gev source is a blazar seen through the Galactic plane. Because several of the optical emission lines have equivalent width > 5 {angstrom}, this blazar belongs in the flat-spectrum radio quasar category.

VizieR Online Data Catalog: Jet kinematics of blazars at 43GHz with the VLBA (Jorstad+, 2017)

Science.gov (United States)

Jorstad, S. G.; Marscher, A. P.; Morozova, D. A.; Troitsky, I. S.; Agudo, I.; Casadio, C.; Foord, A.; Gomez, J. L.; MacDonald, N. R.; Molina, S. N.; Lahteenmaki, A.; Tammi, J.; Tornikoski, M.

2018-04-01

The VLBA-BU-BLAZAR monitoring program consists of approximately monthly observations with the VLBA at 43GHz of a sample of AGNs detected as γ-ray sources. In this paper, we present the results of observations from 2007 June to 2013 January. The sample consists of 21 FSRQs, 12 BLLacs, and 3 radio galaxies (RGs). It includes the blazars and radio galaxies detected at γ-ray energies by EGRET with average flux density at 43GHz exceeding 0.5Jy, declination north of -30°, and optical magnitude in the R band brighter than 18.5. (5 data files).

The WEBT Campaign on the Blazar 3C 279 in 2006

Czech Academy of Sciences Publication Activity Database

Böttcher, M.; Basu, S.; Joshi, M.; Villata, M.; Arai, A.; Aryan, N.; Asfandiyarov, I. M.; Bach, U.; Bachev, R.; Berdyugin, A.; Blažek, Martin; Buemi, C.S.; Castro-Tirado, A.J.; de Ugarte Postigo, A.; Frasca, A.; Fuhrmann, L.; Hagen-Thorn, V.A.; Henson, G.; Hovatta, T.; Hudec, René; Ibrahimov, M.A.; Ishii, Y.; Ivanidze, R.; Jelínek, M.; Kamada, M.; Kapanadze, B.; Katsuura, M.; Kotaka, D.; Kovalev, Y.Y.; Kovalev, Yu.A.; Kubánek, Petr; Kurosaki, M.; Kurtanidze, O.M.; Lähteenmäki, A.; Lanteri, L.; Larionov, V.M.; Larionova, L.; Lee, C.-U.; Leto, P.; Lindfors, E.; Marilli, E.; Marshall, K.; Miller, H.R.; Mingaliev, M.G.; Mirabal, N.; Mizoguchi, S.; Nakamura, K.; Nieppola, E.; Nikolashvili, M.G.; Nilsson, K.; Nishiyama, S.; Ohlert, J.M.; Osterman, M.A.; Pak, S.; Pasanen, M.; Peters, C.S.; Pursimo, T.; Raiteri, C.M.; Robertson, J.; Robertson, T.; Ryle, W.T.; Sadakane, K.; Sadun, A.C.; Sigua, L.A.; Sohn, B.-W.; Strigachev, A.; Sumitomo, N.; Takalo, L.O.; Tamesue, Y.; Tanaka, K.; Thorstensen, J.R.; Tosti, G.; Trigilio, C.; Umana, G.; Vennes, S.; Vítek, S.; Volvach, A.; Webb, J.; Yamanaka, M.; Yim, S.-H.

2007-01-01

Roč. 670, č. 2 (2007), s. 968-977 ISSN 0004-637X Grant - others:EU(XE) ESA-PECS project No. 98023 Institutional research plan: CEZ:AV0Z10030501 Source of funding: V - iné verejné zdroje Keywords : blazars * active galactic nuclei Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 6.405, year: 2007

The extreme blazar AO 0235+164 as seen by extensive ground and space radio observations

Science.gov (United States)

Kutkin, A. M.; Pashchenko, I. N.; Lisakov, M. M.; Voytsik, P. A.; Sokolovsky, K. V.; Kovalev, Y. Y.; Lobanov, A. P.; Ipatov, A. V.; Aller, M. F.; Aller, H. D.; Lahteenmaki, A.; Tornikoski, M.; Gurvits, L. I.

2018-04-01

Clues to the physical conditions in radio cores of blazars come from measurements of brightness temperatures as well as effects produced by intrinsic opacity. We study the properties of the ultra-compact blazar AO 0235+164 with RadioAstron ground-space radio interferometer, multifrequency VLBA, EVN, and single-dish radio observations. We employ visibility modelling and image stacking for deriving structure and kinematics of the source, and use Gaussian process regression to find the relative multiband time delays of the flares. The multifrequency core size and time lags support prevailing synchrotron self-absorption. The intrinsic brightness temperature of the core derived from ground-based very long baseline interferometry (VLBI) is close to the equipartition regime value. In the same time, there is evidence for ultra-compact features of the size of less than 10 μas in the source, which might be responsible for the extreme apparent brightness temperatures of up to 1014 K as measured by RadioAstron. In 2007-2016 the VLBI components in the source at 43 GHz are found predominantly in two directions, suggesting a bend of the outflow from southern to northern direction. The apparent opening angle of the jet seen in the stacked image at 43 GHz is two times wider than that at 15 GHz, indicating a collimation of the flow within the central 1.5 mas. We estimate the Lorentz factor Γ = 14, the Doppler factor δ = 21, and the viewing angle θ = 1.7° of the apparent jet base, derive the gradients of magnetic field strength and electron density in the outflow, and the distance between jet apex and the core at each frequency.

Simultaneous optical and infrared polarization measurements of blazars

International Nuclear Information System (INIS)

Brindle, C.; Hough, J.H.; Bailey, J.A.; Axon, D.J.; Hyland, A.R.

1986-01-01

Measurements are presented of the polarization and flux of a sample of 28 blazars (21 BL Lacs and 7 OVV quasars) at optical and near-infrared wavelengths, with repeated observations for some objects. For 20 objects, these are the first reported polarization measurements in either the optical or infrared, and for most of them the first simultaneous measurements at these wavelengths. Out of a total of 42 observations a spectral dependence of polarization level and position angle is found, although not necessarily occurring together, on 15 occasions. (author)

Advancements of ultra-high peak power laser diode arrays

Science.gov (United States)

Crawford, D.; Thiagarajan, P.; Goings, J.; Caliva, B.; Smith, S.; Walker, R.

2018-02-01

Enhancements of laser diode epitaxy in conjunction with process and packaging improvements have led to the availability of 1cm bars capable of over 500W peak power at near-infrared wavelengths (770nm to 1100nm). Advances in cooler design allow for multi-bar stacks with bar-to-bar pitches as low as 350μm and a scalable package architecture enabled a single diode assembly with total peak powers of over 1MegaWatt of peak power. With the addition of micro-optics, overall array brightness greater than 10kW/cm2 was achieved. Performance metrics of barbased diode lasers specifically engineered for high peak power and high brightness at wavelengths and pulse conditions commonly used to pump a variety of fiber and solid-state materials are presented.

Application of at-site peak-streamflow frequency analyses for very low annual exceedance probabilities

Science.gov (United States)

Asquith, William H.; Kiang, Julie E.; Cohn, Timothy A.

2017-07-17

The U.S. Geological Survey (USGS), in cooperation with the U.S. Nuclear Regulatory Commission, has investigated statistical methods for probabilistic flood hazard assessment to provide guidance on very low annual exceedance probability (AEP) estimation of peak-streamflow frequency and the quantification of corresponding uncertainties using streamgage-specific data. The term “very low AEP” implies exceptionally rare events defined as those having AEPs less than about 0.001 (or 1 × 10–3 in scientific notation or for brevity 10–3). Such low AEPs are of great interest to those involved with peak-streamflow frequency analyses for critical infrastructure, such as nuclear power plants. Flood frequency analyses at streamgages are most commonly based on annual instantaneous peak streamflow data and a probability distribution fit to these data. The fitted distribution provides a means to extrapolate to very low AEPs. Within the United States, the Pearson type III probability distribution, when fit to the base-10 logarithms of streamflow, is widely used, but other distribution choices exist. The USGS-PeakFQ software, implementing the Pearson type III within the Federal agency guidelines of Bulletin 17B (method of moments) and updates to the expected moments algorithm (EMA), was specially adapted for an “Extended Output” user option to provide estimates at selected AEPs from 10–3 to 10–6. Parameter estimation methods, in addition to product moments and EMA, include L-moments, maximum likelihood, and maximum product of spacings (maximum spacing estimation). This study comprehensively investigates multiple distributions and parameter estimation methods for two USGS streamgages (01400500 Raritan River at Manville, New Jersey, and 01638500 Potomac River at Point of Rocks, Maryland). The results of this study specifically involve the four methods for parameter estimation and up to nine probability distributions, including the generalized extreme value, generalized

Time-frequency representation of a highly nonstationary signal via the modified Wigner distribution

Science.gov (United States)

Zoladz, T. F.; Jones, J. H.; Jong, J.

1992-01-01

A new signal analysis technique called the modified Wigner distribution (MWD) is presented. The new signal processing tool has been very successful in determining time frequency representations of highly non-stationary multicomponent signals in both simulations and trials involving actual Space Shuttle Main Engine (SSME) high frequency data. The MWD departs from the classic Wigner distribution (WD) in that it effectively eliminates the cross coupling among positive frequency components in a multiple component signal. This attribute of the MWD, which prevents the generation of 'phantom' spectral peaks, will undoubtedly increase the utility of the WD for real world signal analysis applications which more often than not involve multicomponent signals.

Examining the nature of very-high-energy gamma-ray emission from the AGN PKS 1222+216 and 3C 279

Science.gov (United States)

Price, Sharleen; Brill, Ari; Mukherjee, Reshmi; VERITAS

2018-01-01

Blazars are a type of active galactic nuclei (AGN) that emit jets of ionized matter which move towards the Earth at relativistic speeds. In this research we carried out a study of two objects, 3C 279 and PKS 1222+216, which belong to the subset of blazars known as FSRQs (flat spectrum radio quasars), the most powerful TeV-detected sources at gamma-ray energies with bolometric luminosities exceeding 1048 erg/s. The high-energy emission of quasars peaks in the MeV-GeV band, making these sources very rarely detectable in the TeV energy range. In fact, only six FSRQs have ever been detected in this range by very-high-energy gamma-ray telescopes. We will present results from observing campaigns on 3C 279 in 2014 and 2016, when the object was detected in high flux states by Fermi-LAT. Observations include simultaneous coverage with the Fermi-LAT satellite and the VERITAS ground-based array spanning four decades in energy from 100 MeV to 1 TeV. We will also report VERITAS observations of PKS 1222+216 between 2008 and 2017. The detection/non-detection of TeV emission during flaring episodes at MeV energies will further contribute to our understanding of particle acceleration and gamma-ray emission mechanisms in blazar jets.

Position Angle Changes of Inner-Jets in a Sample of Blazars Ligong ...

Indian Academy of Sciences (India)

Position Angle Changes of Inner-Jets in a Sample of Blazars. Ligong Mi1,3,∗ & Xiang Liu1,2. 1Xinjiang Astronomical Observatory, CAS, 150 Science 1-Street, Urumqi 830011,. People's Republic of China. 2Key Laboratory of Radio Astronomy, CAS, Nanjing 210008, People's Republic of China. 3University of Chinese ...

Active Control of High-Speed Free Jets Using High-Frequency Excitation

Science.gov (United States)

Upadhyay, Puja

work expands on the previous development of low-frequency (2-8 kHz) Resonance Enhanced Micro-actuators (REM) to design actuators that are capable of producing high amplitude pulses at much higher frequencies. Extensive benchtop characterization, using acoustic measurements as well as optical diagnostics using a high resolution micro-schlieren setup, is employed to characterize the flow properties and dynamic response of these actuators. The actuators produced high-amplitude output a range of frequencies, 20.3-27.8 kHz and 54.8-78.2 kHz, respectively. In addition to providing information on the actuator flow physics and performances at various operating conditions, the benchtop study serves to develop relatively easy-to-integrate, high-frequency actuators for active control of high-speed jets for noise reduction. Following actuator characterization studies, the nominally 25 kHz ( StDF ≈ 2.2) actuators are implemented on a Mach 0.9 free jet flow field. Eight actuators are azimuthally distributed at the nozzle exit to excite the initial shear layer at frequencies that are approximately an order of magnitude higher compared to the jet preferred frequency, StP ≈ 0.2-0.3. The influence of control on the mean and turbulent characteristics of the jet, especially the developing shear layer, is examined in great detail using planar and stereoscopic Particle Image Velocimetry (PIV). Examination of cross-stream velocity profiles revealed that actuation leads to strong, spatially coherent streamwise vortex pairs which in turn significantly modify the mean flow field, resulting in a prominently undulated shear layer. These vortices grow as they convect downstream, enhancing local entrainment and significantly thickening the initial shear layer. Azimuthal inhomogeneity introduced in the jet shear layer is also evident in the simultaneous redistribution and reduction of peak turbulent fluctuations in the cross-plane near the nozzle exit. Further downstream, control results in a

The polarization dependence of γγ absorption—implications for γ-ray bursts and blazars

International Nuclear Information System (INIS)

Böttcher, M.

2014-01-01

This paper presents an analysis of the dependence of the opacity for high-energy γ-rays to γγ absorption by low-energy photons on the polarization of the γ-ray and target photons. This process has so far only been considered using the polarization-averaged γγ absorption cross section. It is demonstrated that in the case of polarized γ-ray emission, subject to source-intrinsic γγ absorption by polarized target photons, this may lead to a slight overestimation of the γγ opacity by up to ∼10% in the case of a perfectly ordered magnetic field. Thus, for realistic astrophysical scenarios with partially ordered magnetic fields, the use of the polarization-averaged γγ cross section is justified for practical purposes, such as estimates of minimum Doppler factors inferred for γ-ray bursts and blazars, based on γγ transparency arguments; this paper quantifies the small error incurred by the unpolarized-radiation approximation. Furthermore, it is shown that polarization-dependent γγ absorption of initially polarized γ-rays can lead to a slight increase in the polarization beyond the spectral break caused by γγ absorption. This amount is distinctly different from the change in polarization expected if the same spectral break were produced by a break in the underlying electron distribution. This may serve as a diagnostic of whether γγ absorption is relevant in sources such as γ-ray bursts and blazars where the γ-ray emission may be intrinsically highly polarized.

The role of plasma instabilities in the propagation of gamma-rays from distant Blazars

Energy Technology Data Exchange (ETDEWEB)

Saveliev, A.; Evoli, C.; Sigl, G. [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik

2013-11-15

The observation in the GeV band of distant blazars has been recently used to put constraints on the Extragalactic Background Light (EBL) and Extragalactic Magnetic Fields (EGMF). To support such claims one has to assume that the leptonic component of the electromagnetic cascade initiated by blazar gamma-rays is deflected away by strong enough EGMF, suppressing the signal in the Fermi window. Apart from magnetic fields, the development of such a cascade might be affected by plasma instabilities due to interactions with the ionized component of the Intergalactic Medium (IGM). In this paper we model the electromagnetic cascade through a Monte Carlo simulation in which both effects are taken into account separately, and we derive constraints on these scenarios from the combined Fermi-HESS data set. In the specific case of 1ES 0229+200 observations, we show that both explanations of the GeV flux suppression are compatible with the available data, specifically by assuming a magnetic field of B >or similar 10{sup -16} G or an IGM temperature of T high redshift (z

Frequency up-conversion and spectral breaking of a high power microwave pulse propagation in a self-generated plasma

International Nuclear Information System (INIS)

Kuo, S.P.; Ren, A.

1993-01-01

The main concern of the propagation of high power microwave pulse is the energy loss of the pulse before reaching the destination. The loss is caused by self-generated plasma. There are two processes which are responsible for the energy loss (so called tail erosion). They are collisional damping and cutoff reflection. In very high power region, the cutoff reflection is much more severe than the collisional damping. A frequency up-conversion process may help to avoid the cutoff reflection of powerful electromagnetic pulse propagating in a self-generated plasma. Both chamber experiments and numerical simulation are performed. When the field amplitude only slightly exceeds the breakdown threshold field of the background gas, the result shows that the carrier frequency ω of the pulse shifts upward during the growth of local plasma frequency ωpe 2 . Thus, the self-generated plasma remains underdense to the pulse. However, the spectrum of the pulse starts to break up into two major peaks when the amplitude of the pulse is further increased. The frequency of one of the peaks is lower than the original carrier frequency and that of the other peak is higher than the original carrier frequency. These phenomena are observed both experimentally and numerically. The frequency down shift result is believed to be caused by damping mechanisms. Good agreement between the experimental results and the numerical simulation is obtained

Peak effect in laser ablated DyBa2Cu3O7-δ films at microwave frequencies at subcritical currents

NARCIS (Netherlands)

Bhangale, A.R.; Raychaudhuri, P.; Banerjee, T.; Shirodkar, V.S.

2001-01-01

In this article we report the observation of a peak in the microwave surface resistance (at frequencies ~10 GHz) of laser ablated DyBa2Cu3O7-δ films in magnetic field ranging from 2 to 9 kOe (||c) close to the superconducting transition temperature [Tc(H)]. The exact nature of the peak is sample

THE COSMOLOGICAL IMPACT OF LUMINOUS TeV BLAZARS. I. IMPLICATIONS OF PLASMA INSTABILITIES FOR THE INTERGALACTIC MAGNETIC FIELD AND EXTRAGALACTIC GAMMA-RAY BACKGROUND

Energy Technology Data Exchange (ETDEWEB)

Broderick, Avery E; Chang, Philip; Pfrommer, Christoph [Canadian Institute for Theoretical Astrophysics, 60 St. George Street, Toronto, ON M5S 3H8 (Canada)

2012-06-10

Inverse Compton cascades (ICCs) initiated by energetic gamma rays (E {approx}> 100 GeV) enhance the GeV emission from bright, extragalactic TeV sources. The absence of this emission from bright TeV blazars has been used to constrain the intergalactic magnetic field (IGMF), and the stringent limits placed on the unresolved extragalactic gamma-ray background (EGRB) by Fermi have been used to argue against a large number of such objects at high redshifts. However, these are predicated on the assumption that inverse Compton scattering is the primary energy-loss mechanism for the ultrarelativistic pairs produced by the annihilation of the energetic gamma rays on extragalactic background light photons. Here, we show that for sufficiently bright TeV sources (isotropic-equivalent luminosities {approx}> 10{sup 42} erg s{sup -1}) plasma beam instabilities, specifically the 'oblique' instability, present a plausible mechanism by which the energy of these pairs can be dissipated locally, heating the intergalactic medium. Since these instabilities typically grow on timescales short in comparison to the inverse Compton cooling rate, they necessarily suppress the ICCs. As a consequence, this places a severe constraint on efforts to limit the IGMF from the lack of a discernible GeV bump in TeV sources. Similarly, it considerably weakens the Fermi limits on the evolution of blazar populations. Specifically, we construct a TeV-blazar luminosity function from those objects currently observed and find that it is very well described by the quasar luminosity function at z {approx} 0.1, shifted to lower luminosities and number densities, suggesting that both classes of sources are regulated by similar processes. Extending this relationship to higher redshifts, we show that the magnitude and shape of the EGRB above {approx}10 GeV are naturally reproduced with this particular example of a rapidly evolving TeV-blazar luminosity function.

Implication of the detection of very hard spectra from the TeV blazar Mrk 501

Energy Technology Data Exchange (ETDEWEB)

Shukla, Amit; Hughes, Gareth; Biland, Adrian [ETH Zurich, Institute for Particle Physics (Switzerland); Mannheim, Karl; Dorner, Daniela [Institute for Theoretical Physics and Astrophysics, Universitaet Wuerzburg (Germany); Chitnis, Varsha R. [Department of High Energy Physics, Tata Institute of Fundamental Research, Mumbai (India); Roy, Jayashree; Acharya, Bannanje Sripathi [Center for Excellence in Basic Sciences, UM-DAE Mumbai (India)

2016-07-01

The emission from active galactic nuclei ranges from radio to TeV energies and shows high variability. The origin of the high energy emission is highly debated. The observed emission could be due to a complex superposition of emission from multiple zones. New evidence of the detection of very hard intrinsic gamma-ray spectra obtained from Fermi-LAT observations have challenged the theories about origin of VHE gamma-rays. We have used the 7 years of Fermi-LAT data to search for time intervals with unusually hard spectra from the nearby TeV blazar Mrk 501. In the presentation, we discuss a few possible explanations for the origin of these hard spectra within a leptonic scenario.

Ultrasonic Transducer Peak-to-Peak Optical Measurement

Directory of Open Access Journals (Sweden)

Pavel Skarvada

2012-01-01

Full Text Available Possible optical setups for measurement of the peak-to-peak value of an ultrasonic transducer are described in this work. The Michelson interferometer with the calibrated nanopositioner in reference path and laser Doppler vibrometer were used for the basic measurement of vibration displacement. Langevin type of ultrasonic transducer is used for the purposes of Electro-Ultrasonic Nonlinear Spectroscopy (EUNS. Parameters of produced mechanical vibration have to been well known for EUNS. Moreover, a monitoring of mechanical vibration frequency shift with a mass load and sample-transducer coupling is important for EUNS measurement.

Modelling blazar flaring using a time-dependent fluid jet emission model - an explanation for orphan flares and radio lags

Science.gov (United States)

Potter, William J.

2018-01-01

Blazar jets are renowned for their rapid violent variability and multiwavelength flares, however, the physical processes responsible for these flares are not well understood. In this paper, we develop a time-dependent inhomogeneous fluid jet emission model for blazars. We model optically thick radio flares for the first time and show that they are delayed with respect to the prompt optically thin emission by ∼months to decades, with a lag that increases with the jet power and observed wavelength. This lag is caused by a combination of the travel time of the flaring plasma to the optically thin radio emitting sections of the jet and the slow rise time of the radio flare. We predict two types of flares: symmetric flares - with the same rise and decay time, which occur for flares whose duration is shorter than both the radiative lifetime and the geometric path-length delay time-scale; extended flares - whose luminosity tracks the power of particle acceleration in the flare, which occur for flares with a duration longer than both the radiative lifetime and geometric delay. Our model naturally produces orphan X-ray and γ-ray flares. These are caused by flares that are only observable above the quiescent jet emission in a narrow band of frequencies. Our model is able to successfully fit to the observed multiwavelength flaring spectra and light curves of PKS1502+106 across all wavelengths, using a transient flaring front located within the broad-line region.

High-frequency strontium vapor laser for biomedical applications

Science.gov (United States)

Hvorostovsky, A.; Kolmakov, E.; Kudashev, I.; Redka, D.; Kancer, A.; Kustikova, M.; Bykovskaya, E.; Mayurova, A.; Stupnikov, A.; Ruzankina, J.; Tsvetkov, K.; Lukyanov, N.; Paklinov, N.

2018-02-01

Sr-laser with high pulse repetition rate and high peak radiation power is a unique tool for studying rapidly occurring processes in time (plasma diagnostics, photoablation, etc.). In addition, the study of the frequency characteristics of the active medium of the laser helps to reveal the physics of the formation of an inverse medium in metal vapor lasers. In this paper, an experimental study of an Sr-laser with an active volume of 5.8 cm3 in the pulse repetition frequency range from 25 to 200 kHz is carried out, and a comparison with the frequency characteristics of media with large active volumes is given. We considered the frequency characteristics of the active medium in two modes: at a constant energy in the excitation pulse CU2 / 2 and at a constant average power consumed by the rectifier. In the presented work with a small-volume GRT using the TASITR-5/12 TASITRON switch, a laser was generated for Pairs of strontium at a CSF of 200 kHz. The behavior of the characteristics of the generation lines of 6.456 μm, 1 μm, and 3 μm at increased repetition frequencies is considered. Using the example of large-volume GRT, it is shown that tubes with a large active volume increase their energy characteristics with the growth of the CSF. The possibility of laser operation at pulse repetition rates above 200 kHz is shown.

FACT — LONGTERM MONITORING OF BRIGHT TeV BLAZARS

Directory of Open Access Journals (Sweden)

Katja Meier

2014-06-01

Full Text Available The First G-APD Cherenkov Telescope (FACT, located on the Canary Island of La Palma, has been taking data since October 2011. FACT has been optimized for longterm monitoring of bright TeV blazars, to study their variability time scales and flare probability. G-APD photo-sensors allow for observations even under strong moonlight conditions, and the telescope can be operated remotely. The monitoring strategy of FACT is discussed and preliminary results of the flare of Mrk501 in June 2012 are shown.

Rapid estimation of earthquake magnitude from the arrival time of the peak high‐frequency amplitude

Science.gov (United States)

Noda, Shunta; Yamamoto, Shunroku; Ellsworth, William L.

2016-01-01

We propose a simple approach to measure earthquake magnitude M using the time difference (Top) between the body‐wave onset and the arrival time of the peak high‐frequency amplitude in an accelerogram. Measured in this manner, we find that Mw is proportional to 2logTop for earthquakes 5≤Mw≤7, which is the theoretical proportionality if Top is proportional to source dimension and stress drop is scale invariant. Using high‐frequency (>2  Hz) data, the root mean square (rms) residual between Mw and MTop(M estimated from Top) is approximately 0.5 magnitude units. The rms residuals of the high‐frequency data in passbands between 2 and 16 Hz are uniformly smaller than those obtained from the lower‐frequency data. Top depends weakly on epicentral distance, and this dependence can be ignored for distances earthquake produces a final magnitude estimate of M 9.0 at 120 s after the origin time. We conclude that Top of high‐frequency (>2  Hz) accelerograms has value in the context of earthquake early warning for extremely large events.

Relation between X-Ray and γ-Ray Emissions for Fermi Blazars ...

Indian Academy of Sciences (India)

Abstract. Using γ-ray band data detected by Fermi Large Area Tele- scope (LAT) and X-ray band data for 78 blazars, we find a medium cor- relation between X-ray and γ-ray fluxes in the average state. A medium anticorrelation is also found between X-ray (1 KeV) mean spectral index αx and γ-ray mean spectral index αγ for ...

Prediction of high frequency core loss for electrical steel using the data provided by manufacturer

Energy Technology Data Exchange (ETDEWEB)

Roy, Rakesh [National Institute of Technology Meghalaya, Shillong (India); Dalal, Ankit; Kumar, Praveen [Indian Institute of Technology Guwahati, Assam (India)

2016-07-15

This paper describes a technique to determine the core loss data, at high frequencies, using the loss data provided by the lamination manufacturer. Steinmetz equation is used in this proposed method to determine core loss at high frequency. This Steinmetz equation consists of static hysteresis and eddy current loss. The presented technique considers the coefficients of Steinmetz equation as variable with frequency and peak magnetic flux density. The high frequency core loss data, predicted using this model is compared with the catalogue data given by manufacturer and very good accuracy has been obtained for a wide range of frequency. - Highlights: • A curve fitting algorithm is proposed to predict core loss at high frequency. • The loss data given by the steel manufacturers are used in curve fitting algorithm. • The algorithm is tested on nine different material’s data set given by the manufacturer.

Prediction of high frequency core loss for electrical steel using the data provided by manufacturer

International Nuclear Information System (INIS)

Roy, Rakesh; Dalal, Ankit; Kumar, Praveen

2016-01-01

This paper describes a technique to determine the core loss data, at high frequencies, using the loss data provided by the lamination manufacturer. Steinmetz equation is used in this proposed method to determine core loss at high frequency. This Steinmetz equation consists of static hysteresis and eddy current loss. The presented technique considers the coefficients of Steinmetz equation as variable with frequency and peak magnetic flux density. The high frequency core loss data, predicted using this model is compared with the catalogue data given by manufacturer and very good accuracy has been obtained for a wide range of frequency. - Highlights: • A curve fitting algorithm is proposed to predict core loss at high frequency. • The loss data given by the steel manufacturers are used in curve fitting algorithm. • The algorithm is tested on nine different material’s data set given by the manufacturer.

High frequency ion Bernstein wave heating experiment on JIPP T-IIU tokamak

International Nuclear Information System (INIS)

Seki, T.; Kumazawa, R.; Watari, T.

1992-08-01

An experiment in a new regime of ion Bernstein wave (IBW) heating has been carried out using 130 MHz high power transmitters in the JIPP T-IIU tokamak. The heating regime utilized the IBW branch between the 3rd and 4th harmonics of the hydrogen ion cyclotron frequencies. This harmonic number is the highest among those used in the IBW experiments ever conducted. The net radio-frequency (RF) power injected into the plasma is around 400 kW, limited by the transmitter output power. Core heating of ions and electrons was confirmed in the experiment and density profile peaking was found to feature the IBW heating (IBWH). The peaking of the density profile was also found when IBW was applied to the neutral beam injection heated discharges. An analysis by use of a transport code with these experimental data indicates that the particle confinement should be improved in the plasma core region on the application of IBWH. It is also found that the ion energy distribution function observed during IBWH has less high energy tail than those in conventional ion cyclotron range of frequency heating regimes. The observed IBWH-produced ion energy distribution function is in a reasonable agreement with the calculation based on the quasi-linear RF diffusion / Fokker-Planck model. (author)

High frequency response of open quantum dots

International Nuclear Information System (INIS)

Brunner, R.; Meisels, R.; Kuchar, F.; Ferry, D.; Elhassan, M.; Ishibashi, K.

2002-01-01

Full text: We investigate the response of the transport through open quantum dots to millimeterwave radiation (up to 55 GHz). In the low-field region ( 11 cm -2 and a mobility of 1.2 10 6 cm 2 /Vs. By applying a sufficiently negative voltage to the gates the 2DES is split into two regions connected only by a dot-like region (about 350 nm diameter) between them. The DC data exhibit backscattering peaks at fields of a few tenth of a Tesla. Shubnikovde- Haas (SdH) oscillations appear above 0.5 T. While the SdH oscillations show the usual temperature dependence, the backscattering peaks are temperature independent up to 2.5 K. The backscattering peak shows a reduction of 10 percent due to the millimeterwave irradiation. However, due to the temperature independence of this peak, this reduction cannot simply be attributed to electron heating. This conclusion is supported by the observation of a strong frequency dependence of the reduction of the peak height. (author)

Origin of absorption peaks in reflection loss spectrum in Ku- frequency band of Co-Zr substituted strontium hexaferrites prepared using sucrose precursor

Energy Technology Data Exchange (ETDEWEB)

Narang, Sukhleen Bindra, E-mail: sukhleen2@yahoo.com [Department of Electronics Technology, Guru Nanak Dev University, Amritsar (India); Pubby, Kunal, E-mail: kunalpubby02@gmail.com [Department of Electronics Technology, Guru Nanak Dev University, Amritsar (India); Chawla, S.K., E-mail: sschawla118@gmail.com [Department of Chemistry, Centre for Advanced Studies-I, Guru Nanak Dev University, Amritsar (India); Kaur, Prabhjyot, E-mail: prabhjyot.2525@gmail.com [Department of Chemistry, Centre for Advanced Studies-I, Guru Nanak Dev University, Amritsar (India)

2017-03-15

This study presents the detailed explanation of the factors, contributing towards the absorption peaks in reflection loss spectrum of hexaferrites. Cobalt-Zirconium substituted strontium hexaferrites, synthesized using sucrose precursor sol-gel technique, were analyzed in 12.4–18 GHz frequency range. The concepts of impedance matching through quarter wavelength condition, complex thickness, dielectric phase angle and attenuation constant have been used to determine the location as well as intensity of absorption peaks. This study also demonstrates the potential application of three compositions of this series with doping content (x)==0.0, 0.6 and 0.8 as an effective microwave absorbers in Ku-frequency band. - Highlights: • EM analysis of Sr Hexaferrites in Ku-band. • Factors towards absorption peak intensity & location.

Methods for estimating peak-flow frequencies at ungaged sites in Montana based on data through water year 2011: Chapter F in Montana StreamStats

Science.gov (United States)

Sando, Roy; Sando, Steven K.; McCarthy, Peter M.; Dutton, DeAnn M.

2016-04-05

The U.S. Geological Survey (USGS), in cooperation with the Montana Department of Natural Resources and Conservation, completed a study to update methods for estimating peak-flow frequencies at ungaged sites in Montana based on peak-flow data at streamflow-gaging stations through water year 2011. The methods allow estimation of peak-flow frequencies (that is, peak-flow magnitudes, in cubic feet per second, associated with annual exceedance probabilities of 66.7, 50, 42.9, 20, 10, 4, 2, 1, 0.5, and 0.2 percent) at ungaged sites. The annual exceedance probabilities correspond to 1.5-, 2-, 2.33-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year recurrence intervals, respectively.Regional regression analysis is a primary focus of Chapter F of this Scientific Investigations Report, and regression equations for estimating peak-flow frequencies at ungaged sites in eight hydrologic regions in Montana are presented. The regression equations are based on analysis of peak-flow frequencies and basin characteristics at 537 streamflow-gaging stations in or near Montana and were developed using generalized least squares regression or weighted least squares regression.All of the data used in calculating basin characteristics that were included as explanatory variables in the regression equations were developed for and are available through the USGS StreamStats application (http://water.usgs.gov/osw/streamstats/) for Montana. StreamStats is a Web-based geographic information system application that was created by the USGS to provide users with access to an assortment of analytical tools that are useful for water-resource planning and management. The primary purpose of the Montana StreamStats application is to provide estimates of basin characteristics and streamflow characteristics for user-selected ungaged sites on Montana streams. The regional regression equations presented in this report chapter can be conveniently solved using the Montana StreamStats application.Selected results from

Multi-waveband Behavior of Blazars

Directory of Open Access Journals (Sweden)

Marscher Alan P.

2013-12-01

Full Text Available The author reviews recent progress toward understanding blazars that multi-waveband monitoring observations have advanced. The primary techniques include the compilation of multi-waveband light curves, multi-epoch VLBI images at radio wavelengths, plots of linear polarization vs. time at radio through optical wavelengths, and spectral energy distributions (SEDs. Correlations and the coincidence or lag of events across wavebands and in the images indicate where the events take place relative to the “core” that lies ≳ 0.5 pc from the central engine. Rotations of the polarization electric vector suggest a helical geometry of the magnetic field upstream of the millimeter-wave core, while rapid fluctuations in degree and position angle of polarization imply that the jet plasma is turbulent in and downstream of the core. The author is developing a numerical model that simulates the emission from such turbulence as it interacts with a conical standing shock in the core region.

Low frequency phase signal measurement with high frequency squeezing

OpenAIRE

Zhai, Zehui; Gao, Jiangrui

2011-01-01

We calculate the utility of high-frequency squeezed-state enhanced two-frequency interferometry for low-frequency phase measurement. To use the high-frequency sidebands of the squeezed light, a two-frequency intense laser is used in the interferometry instead of a single-frequency laser as usual. We find that the readout signal can be contaminated by the high-frequency phase vibration, but this is easy to check and avoid. A proof-of-principle experiment is in the reach of modern quantum optic...

Particle acceleration through the resonance of high magnetic field and high frequency electromagnetic wave

International Nuclear Information System (INIS)

Hong, Liu; He, X.T.; Chen, S.G.; Zhang, W.Y.; He, X.T.; Hong, Liu

2004-01-01

We propose a new particle acceleration mechanism. Electrons can be accelerated to relativistic energy within a few electromagnetic wave cycles through the mechanism which is named electromagnetic and magnetic field resonance acceleration (EMRA). We find that the electron acceleration depends not only on the electromagnetic wave intensity, but also on the ratio between electron Larmor frequency and electromagnetic wave frequency. As the ratio approaches to unity, a clear resonance peak is observed, corresponding to the EMRA. Near the resonance regime, the strong magnetic fields still affect the electron acceleration dramatically. We derive an approximate analytical solution of the relativistic electron energy in adiabatic limit, which provides a full understanding of this phenomenon. In typical parameters of pulsar magnetospheres, the mechanism allows particles to increase their energies through the resonance of high magnetic field and high frequency electromagnetic wave in each electromagnetic wave period. The energy spectra of the accelerated particles exhibit the synchrotron radiation behavior. These can help to understand the remaining emission of high energy electron from radio pulsar within supernova remnant. The other potential application of our theory in fast ignition scheme of inertial confinement fusion is also discussed. (authors)

Long-term monitoring of blazars - the DWARF network

Science.gov (United States)

Backes, Michael; Biland, Adrian; Boller, Andrea; Braun, Isabel; Bretz, Thomas; Commichau, Sebastian; Commichau, Volker; Dorner, Daniela; von Gunten, Hanspeter; Gendotti, Adamo; Grimm, Oliver; Hildebrand, Dorothée; Horisberger, Urs; Krähenbühl, Thomas; Kranich, Daniel; Lustermann, Werner; Mannheim, Karl; Neise, Dominik; Pauss, Felicitas; Renker, Dieter; Rhode, Wolfgang; Rissi, Michael; Rollke, Sebastian; Röser, Ulf; Stark, Luisa Sabrina; Stucki, Jean-Pierre; Viertel, Gert; Vogler, Patrick; Weitzel, Quirin

The variability of the very high energy (VHE) emission from blazars seems to be connected with the feeding and propagation of relativistic jets and with their origin in supermassive black hole binaries. The key to understanding their properties is measuring well-sampled gamma-ray lightcurves, revealing the typical source behavior unbiased by prior knowledge from other wavebands. Using ground-based gamma-ray observatories with exposures limited by dark-time, a global network of several telescopes is needed to carry out fulltime measurements. Obviously, such observations are time-consuming and, therefore, cannot be carried out with the present state of the art instruments. The DWARF telescope on the Canary Island of La Palma is dedicated to monitoring observations. It is currently being set up, employing a costefficient and robotic design. Part of this project is the future construction of a distributed network of small telescopes. The physical motivation of VHE long-term monitoring will be outlined in detail and the perspective for a network for 24/7 observations will be presented.

Gamma-Ray Flaring Activity from the Gravitationally Lensed Blazar PKS 1830-211 Observed by Fermi LAT

Energy Technology Data Exchange (ETDEWEB)

Abdo, A. A.; et al.

2015-01-23

The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope routinely detects the MeV-peaked flat-spectrum radio quasar PKS 1830–211 (z = 2.507). Its apparent isotropic γ-ray luminosity (E > 100 MeV), averaged over ~3 years of observations and peaking on 2010 October 14/15 at 2.9 × 10(50) erg s(–)(1), makes it among the brightest high-redshift Fermi blazars. No published model with a single lens can account for all of the observed characteristics of this complex system. Based on radio observations, one expects time-delayed variability to follow about 25 days after a primary flare, with flux about a factor of 1.5 less. Two large γ-ray flares of PKS 1830–211 have been detected by the LAT in the considered period, and no substantial evidence for such a delayed activity was found. This allows us to place a lower limit of about 6 on the γ-ray flux ratio between the two lensed images. Swift XRT observations from a dedicated Target of Opportunity program indicate a hard spectrum with no significant correlation of X-ray flux with the γ-ray variability. The spectral energy distribution can be modeled with inverse Compton scattering of thermal photons from the dusty torus. The implications of the LAT data in terms of variability, the lack of evident delayed flare events, and different radio and γ-ray flux ratios are discussed. Microlensing effects, absorption, size and location of the emitting regions, the complex mass distribution of the system, an energy-dependent inner structure of the source, and flux suppression by the lens galaxy for one image path may be considered as hypotheses for understanding our results.

A Search for Quasi-periodic Oscillations in the Blazar 1ES 1959+650

Energy Technology Data Exchange (ETDEWEB)

Li, Xiao-Pan; Luo, Yu-Hui; Yang, Hai-Yan; Cai, Yan; Yang, Hai-Tao [Department of Physics, Zhaotong University, Zhaotong, 657000 (China); Yang, Cheng, E-mail: lxpzrc@163.com [College of Photoelectron and Communication Engineering, Yunnan Open University, Kunming, 650223 (China)

2017-09-20

We have searched quasi-periodic oscillations (QPOs) in the 15 GHz light curve of the BL Lac object 1ES 1959+650 monitored by the Owens Valley Radio Observatory 40 m telescope during the period from 2008 January to 2016 February, using the Lomb–Scargle Periodogram, power spectral density (PSD), discrete autocorrelation function, and phase dispersion minimization (PDM) techniques. The red noise background has been established via the PSD method, and no QPO can be derived at the 3 σ confidence level accounting for the impact of the red noise variability. We conclude that the light curve of 1ES 1959+650 can be explained by a stochastic red noise process that contributes greatly to the total observed variability amplitude, dominates the power spectrum, causes spurious bumps and wiggles in the autocorrelation function and can result in the variance of the folded light curve decreasing toward lower temporal frequencies when few-cycle, sinusoid-like patterns are present. Moreover, many early supposed periodicity claims for blazar light curves need to be reevaluated assuming red noise.

Evaluation of the Fourier Frequency Spectrum Peaks of Milk Electrical Conductivity Signals as Indexes to Monitor the Dairy Goats’ Health Status by On-Line Sensors

Science.gov (United States)

Zaninelli, Mauro; Agazzi, Alessandro; Costa, Annamaria; Tangorra, Francesco Maria; Rossi, Luciana; Savoini, Giovanni

2015-01-01

The aim of this study is a further characterization of the electrical conductivity (EC) signal of goat milk, acquired on-line by EC sensors, to identify new indexes representative of the EC variations that can be observed during milking, when considering not healthy (NH) glands. Two foremilk gland samples from 42 Saanen goats, were collected for three consecutive weeks and for three different lactation stages (LS: 0–60 Days In Milking (DIM); 61–120 DIM; 121–180 DIM), for a total amount of 1512 samples. Bacteriological analyses and somatic cells counts (SCC) were used to define the health status of the glands. With negative bacteriological analyses and SCC 1,000,000 cells/mL, glands were classified as NH. For each milk EC signal, acquired on-line and for each gland considered, the Fourier frequency spectrum of the signal was calculated and three representative frequency peaks were identified. To evaluate data acquired a MIXED procedure was used considering the HS, LS and LS × HS as explanatory variables in the statistical model.Results showed that the studied frequency peaks had a significant relationship with the gland’s health status. Results also explained how the milk EC signals’ pattern change in case of NH glands. In fact, it is characterized by slower fluctuations (due to the lower frequencies of the peaks) and by an irregular trend (due to the higher amplitudes of all the main frequency peaks). Therefore, these frequency peaks could be used as new indexes to improve the performances of algorithms based on multivariate models which evaluate the health status of dairy goats through the use of gland milk EC sensors. PMID:26307993

3 mm GMVA Observations of Total and Polarized Emission from Blazar and Radio Galaxy Core Regions

Directory of Open Access Journals (Sweden)

Carolina Casadio

2017-10-01

Full Text Available We present total and linearly polarized 3 mm Global mm-VLBI Array (GMVA; mm-VLBI: Very Long Baseline Interferometry observations at millimetre wavelengths images of a sample of blazars and radio galaxies from the VLBA-BU-BLAZAR 7 mm monitoring program designed to probe the innermost regions of active galactic nuclei (AGN jets and locate the sites of gamma-ray emission observed by the Fermi-LAT. The lower opacity at 3 mm and improved angular resolution—on the order of 50 microarcseconds—allow us to distinguish features in the jet not visible in the 7 mm VLBA data. We also compare two different methods used for the calibration of instrumental polarisation and we analyze the resulting images for some of the sources in the sample.

Research on the Vibration Insulation of High-Speed Train Bogies in Mid and High Frequency

Directory of Open Access Journals (Sweden)

Jia Liu

2018-01-01

Full Text Available According to a large amount of the test data, the mid and high frequency vibrations of high-speed bogies are very notable, especially in the 565~616 Hz range, which are just the passing frequencies corresponding to the 22nd to 24th polygonal wear of the wheel. In order to investigate the main cause of wheel higher-order polygon formation, a 3D flexible model of a Chinese high-speed train bogie is developed using the explicit finite element method. The results show that the couple vibration of bogie and wheelset may lead to the high-order wears of wheel. In order to reduce the coupled resonance of the wheelset and the bogie frame, the effects of the stiffness and damping of the primary suspensions, wheelset axle radius, and bogie frame strength on the vibration transmissibility are discussed carefully. The numerical results show that the resonance peaks in high frequency range can be reduced by reducing the stiffness of axle box rotary arm joint, reducing the wheelset axle radius or strengthening the bogie frame location. The related results may provide a reference for structure improvement of the existing bogies and structure design of the new high-speed bogies.

Hydrological model calibration for derived flood frequency analysis using stochastic rainfall and probability distributions of peak flows

Science.gov (United States)

Haberlandt, U.; Radtke, I.

2014-01-01

Derived flood frequency analysis allows the estimation of design floods with hydrological modeling for poorly observed basins considering change and taking into account flood protection measures. There are several possible choices regarding precipitation input, discharge output and consequently the calibration of the model. The objective of this study is to compare different calibration strategies for a hydrological model considering various types of rainfall input and runoff output data sets and to propose the most suitable approach. Event based and continuous, observed hourly rainfall data as well as disaggregated daily rainfall and stochastically generated hourly rainfall data are used as input for the model. As output, short hourly and longer daily continuous flow time series as well as probability distributions of annual maximum peak flow series are employed. The performance of the strategies is evaluated using the obtained different model parameter sets for continuous simulation of discharge in an independent validation period and by comparing the model derived flood frequency distributions with the observed one. The investigations are carried out for three mesoscale catchments in northern Germany with the hydrological model HEC-HMS (Hydrologic Engineering Center's Hydrologic Modeling System). The results show that (I) the same type of precipitation input data should be used for calibration and application of the hydrological model, (II) a model calibrated using a small sample of extreme values works quite well for the simulation of continuous time series with moderate length but not vice versa, and (III) the best performance with small uncertainty is obtained when stochastic precipitation data and the observed probability distribution of peak flows are used for model calibration. This outcome suggests to calibrate a hydrological model directly on probability distributions of observed peak flows using stochastic rainfall as input if its purpose is the

HIGH-RESOLUTION RADIO OBSERVATIONS OF THE REMNANT OF SN 1987A AT HIGH FREQUENCIES

International Nuclear Information System (INIS)

Zanardo, Giovanna; Staveley-Smith, L.; Potter, T. M.; Ng, C.-Y.; Gaensler, B. M.; Manchester, R. N.; Tzioumis, A. K.

2013-01-01

We present new imaging observations of the remnant of Supernova (SN) 1987A at 44 GHz, performed in 2011 with the Australia Telescope Compact Array (ATCA). The 0.''35 × 0.''23 resolution of the diffraction-limited image is the highest achieved to date in high-dynamic range. We also present a new ATCA image at 18 GHz derived from 2011 observations, which is super-resolved to 0.''25. The flux density is 40 ± 2 mJy at 44 GHz and 81 ± 6 mJy at 18 GHz. At both frequencies, the remnant exhibits a ring-like emission with two prominent lobes, and an east-west brightness asymmetry that peaks on the eastern lobe. A central feature of fainter emission appears at 44 GHz. A comparison with previous ATCA observations at 18 and 36 GHz highlights higher expansion velocities of the remnant's eastern side. The 18-44 GHz spectral index is α = –0.80 (S ν ∝ν α ). The spectral index map suggests slightly steeper values at the brightest sites on the eastern lobe, whereas flatter values are associated with the inner regions. The remnant morphology at 44 GHz generally matches the structure seen with contemporaneous X-ray and Hα observations. Unlike the Hα emission, both the radio and X-ray emission peaks on the eastern lobe. The regions of flatter spectral index align and partially overlap with the optically visible ejecta. Simple free-free absorption models suggest that emission from a pulsar wind nebula or a compact source inside the remnant may now be detectable at high frequencies or at low frequencies if there are holes in the ionized component of the ejecta.

Individual Alpha Peak Frequency in Ice Hockey Shooting Performance

Directory of Open Access Journals (Sweden)

Sommer Christie

2017-05-01

Full Text Available There are several important inter- and intra-individual variations in individual alpha peak frequency (IAPF in the cognitive domain. The rationale for the present study was to extend the research on IAPF in the cognitive domain to IAPF in the sport domain. Specifically, the purpose of the present study was twofold: (a to explore whether baseline IAPF is related to performance in an ice hockey shooting task and (b to explore whether a shooting task has an effect on IAPF variability. The present investigation is one of the first studies to examine links between IAPF and sport performance. Study results did not show significant changes in IAPF when comparing baseline IAPF and pre- to post-task IAPF across three performance levels. The findings support previous literature in the cognitive domain suggesting that IAPF is a stable neurophysiological marker. Future research should consider the following methodological suggestions: (a measuring IAPF during sport performance instead of at a resting state, (b changing the pre-performance resting baseline instructions to take into account sport-specific mental preparation, (c exploring an expert-novice paradigm to accentuate performance ability differences between groups (d comparing tasks with different levels of complexity, and (e analyzing the possible correlation between IAPF and performance on different days.

[High-frequency components of occlusal sound in sliding movement].

Science.gov (United States)

Nagai, K

1990-03-01

We postulated that high-frequency components of the occlusal sound occurring due to the characteristic vibration of teeth can be useful data for confirmation of the stability in occlusion, and studied the high-frequency components in the cases both of an experimental sliding movement and a normal occlusion. The results obtained were as follows. 1. A study on high-frequency components of the occlusal sound in an experimental sliding movement. 1) A study on wave type of the occlusal sound revealed one damped oscillation in an impact form and two in a slide form. 2) Spectrum analysis of the damped oscillation showed a similar spectrum pattern with a peak existing between 16KHz or more and 17KHz or less in both impact and slide cases. 2. A study on high-frequency components of the occlusal sound in a normal occlusion case. 1) The wave type in occlusal sound we have observed in a normal occlusion group and in a prosthetic or operative group was as follows: One damped oscillation shown in an impact form and two damped oscillation in a slide form which were the same as those shown in the case where an interference device was attached. 2) Duration of the sliding movement was short in a normal occlusion group, but was prolonged in a prosthetic or operative group. 3) The incidence of the wave type in occlusal sound was 56.7% in a prosthetic or operative group as compared to 87.8% in a normal occlusion group in an impact form. In contrast, the incidence was 43.3% in a prosthetic or operative group as compared to 12.2% in a normal occlusion group in a slide form. Such difference in the incidence between the wave types suggested that high-frequency components of occlusal sound can be an index for judgement of the stability in occlusion.

γ-Ray Emission from the Extreme Blazar 1ES 0229+200 J. Li, T ...

Indian Academy of Sciences (India)

Abstract. Based on the traditional Synchrotron Self-Compton (SSC) model, we consider a secondary γ-ray emission component to an extreme blazar 1ES 0229 + 200 for the multiwavelength radiation. By assuming a suitable electron spectra and Inter-Galactic Magnetic Field (IGMF), we obtained excellent fits to observed ...

High-frequency, high-intensity photoionization

Science.gov (United States)

Reiss, H. R.

1996-02-01

Two analytical methods for computing ionization by high-frequency fields are compared. Predicted ionization rates compare well, but energy predictions for the onset of ionization differ radically. The difference is shown to arise from the use of a transformation in one of the methods that alters the zero from which energy is measured. This alteration leads to an apparent energy threshold for ionization that can, especially in the stabilization regime, differ strongly from the laboratory measurement. It is concluded that channel closings in intense-field ionization can occur at high as well as low frequencies. It is also found that the stabilization phenomenon at high frequencies, very prominent for hydrogen, is absent in a short-range potential.

Low-frequency oscillations at high density in JFT-2

International Nuclear Information System (INIS)

Maeno, Masaki; Katagiri, Masaki; Suzuki, Norio; Fujisawa, Noboru

1977-12-01

Low-frequency oscillations in a plasma were measured with magnetic probes and Si surface-barrier detectors, and behaviour of the high density plasmas was studied. The plasma current profile in the phase of decreasing density after the interruption of gas input is more peaked than during gas input. The introduction of hydrogen during a discharge results in a reduction of the impurities flux. The increase of density by fast gas input is limited with a negative voltage spike. Immediately before a negative voltage spike, oscillations of m=1,2 grow, leading to the spike. (auth.)

Evaluation of the Fourier Frequency Spectrum Peaks of Milk Electrical Conductivity Signals as Indexes to Monitor the Dairy Goats’ Health Status by On-Line Sensors

Directory of Open Access Journals (Sweden)

Mauro Zaninelli

2015-08-01

Full Text Available The aim of this study is a further characterization of the electrical conductivity (EC signal of goat milk, acquired on-line by EC sensors, to identify new indexes representative of the EC variations that can be observed during milking, when considering not healthy (NH glands. Two foremilk gland samples from 42 Saanen goats, were collected for three consecutive weeks and for three different lactation stages (LS: 0–60 Days In Milking (DIM; 61–120 DIM; 121–180 DIM, for a total amount of 1512 samples. Bacteriological analyses and somatic cells counts (SCC were used to define the health status of the glands. With negative bacteriological analyses and SCC < 1,000,000 cells/mL, glands were classified as healthy. When bacteriological analyses were positive or showed a SCC > 1,000,000 cells/mL, glands were classified as NH. For each milk EC signal, acquired on-line and for each gland considered, the Fourier frequency spectrum of the signal was calculated and three representative frequency peaks were identified. To evaluate data acquired a MIXED procedure was used considering the HS, LS and LS × HS as explanatory variables in the statistical model.Results showed that the studied frequency peaks had a significant relationship with the gland’s health status. Results also explained how the milk EC signals’ pattern change in case of NH glands. In fact, it is characterized by slower fluctuations (due to the lower frequencies of the peaks and by an irregular trend (due to the higher amplitudes of all the main frequency peaks. Therefore, these frequency peaks could be used as new indexes to improve the performances of algorithms based on multivariate models which evaluate the health status of dairy goats through the use of gland milk EC sensors.

High frequency source localization in a shallow ocean sound channel using frequency difference matched field processing.

Science.gov (United States)

Worthmann, Brian M; Song, H C; Dowling, David R

2015-12-01

Matched field processing (MFP) is an established technique for source localization in known multipath acoustic environments. Unfortunately, in many situations, particularly those involving high frequency signals, imperfect knowledge of the actual propagation environment prevents accurate propagation modeling and source localization via MFP fails. For beamforming applications, this actual-to-model mismatch problem was mitigated through a frequency downshift, made possible by a nonlinear array-signal-processing technique called frequency difference beamforming [Abadi, Song, and Dowling (2012). J. Acoust. Soc. Am. 132, 3018-3029]. Here, this technique is extended to conventional (Bartlett) MFP using simulations and measurements from the 2011 Kauai Acoustic Communications MURI experiment (KAM11) to produce ambiguity surfaces at frequencies well below the signal bandwidth where the detrimental effects of mismatch are reduced. Both the simulation and experimental results suggest that frequency difference MFP can be more robust against environmental mismatch than conventional MFP. In particular, signals of frequency 11.2 kHz-32.8 kHz were broadcast 3 km through a 106-m-deep shallow ocean sound channel to a sparse 16-element vertical receiving array. Frequency difference MFP unambiguously localized the source in several experimental data sets with average peak-to-side-lobe ratio of 0.9 dB, average absolute-value range error of 170 m, and average absolute-value depth error of 10 m.

Peak radiated power measurement of the DOE Mark II container tag with integrated ST-676 sensor radio frequency identification device.

Energy Technology Data Exchange (ETDEWEB)

Jursich, Mark

2010-04-01

The total peak radiated power of the Department of Energy Mark II container tag was measured in the electromagnetic reverberation chamber facility at Sandia National Laboratories. The tag's radio frequency content was also evaluated for possible emissions outside the intentional transmit frequency band. No spurious emissions of any significance were found, and the radiated power conformed to the manufacturer's specifications.

Peak capacity, peak-capacity production rate, and boiling point resolution for temperature-programmed GC with very high programming rates

Science.gov (United States)

Grall; Leonard; Sacks

2000-02-01

Recent advances in column heating technology have made possible very fast linear temperature programming for high-speed gas chromatography. A fused-silica capillary column is contained in a tubular metal jacket, which is resistively heated by a precision power supply. With very rapid column heating, the rate of peak-capacity production is significantly enhanced, but the total peak capacity and the boiling-point resolution (minimum boiling-point difference required for the separation of two nonpolar compounds on a nonpolar column) are reduced relative to more conventional heating rates used with convection-oven instruments. As temperature-programming rates increase, elution temperatures also increase with the result that retention may become insignificant prior to elution. This results in inefficient utilization of the down-stream end of the column and causes a loss in the rate of peak-capacity production. The rate of peak-capacity production is increased by the use of shorter columns and higher carrier gas velocities. With high programming rates (100-600 degrees C/min), column lengths of 6-12 m and average linear carrier gas velocities in the 100-150 cm/s range are satisfactory. In this study, the rate of peak-capacity production, the total peak capacity, and the boiling point resolution are determined for C10-C28 n-alkanes using 6-18 m long columns, 50-200 cm/s average carrier gas velocities, and 60-600 degrees C/min programming rates. It was found that with a 6-meter-long, 0.25-mm i.d. column programmed at a rate of 600 degrees C/min, a maximum peak-capacity production rate of 6.1 peaks/s was obtained. A total peak capacity of about 75 peaks was produced in a 37-s long separation spanning a boiling-point range from n-C10 (174 degrees C) to n-C28 (432 degrees C).

Active inductor shunt peaking in high-speed VCSEL driver design

CERN Document Server

Liang, Futian; Hou, Suen; Liu, Chonghan; Liu, Tiankuan; Su, Da-Shung; Teng, Ping-Kun; Xiang, Annie; Ye, Jingbo; Jin, Ge

2013-01-01

An all transistor active inductor shunt peaking structure has been used in a prototype of 8-Gbps high-speed VCSEL driver which is designed for the optical link in ATLAS liquid Argon calorimeter upgrade. The VCSEL driver is fabricated in a commercial 0.25-um Silicon-on-Sapphire (SoS) CMOS process for radiation tolerant purpose. The all transistor active inductor shunt peaking is used to overcome the bandwidth limitation from the CMOS process. The peaking structure has the same peaking effect as the passive one, but takes a small area, does not need linear resistors and can overcome the process variation by adjust the peaking strength via an external control. The design has been tapped out, and the prototype has been proofed by the preliminary electrical test results and bit error ratio test results. The driver achieves 8-Gbps data rate as simulated with the peaking. We present the all transistor active inductor shunt peaking structure, simulation and test results in this paper.

High-frequency DOC and nitrate measurements provide new insights into their export and their relationships to rainfall-runoff processes

Science.gov (United States)

Schwab, Michael; Klaus, Julian; Pfister, Laurent; Weiler, Markus

2015-04-01

Over the past decades, stream sampling protocols for environmental tracers were often limited by logistical and technological constraints. Long-term sampling programs would typically rely on weekly sampling campaigns, while high-frequency sampling would remain restricted to a few days or hours at best. We stipulate that the currently predominant sampling protocols are too coarse to capture and understand the full amplitude of rainfall-runoff processes and its relation to water quality fluctuations. Weekly sampling protocols are not suited to get insights into the hydrological system during high flow conditions. Likewise, high frequency measurements of a few isolated events do not allow grasping inter-event variability in contributions and processes. Our working hypothesis is based on the potential of a new generation of field-deployable instruments for measuring environmental tracers at high temporal frequencies over an extended period. With this new generation of instruments we expect to gain new insights into rainfall-runoff dynamics, both at intra- and inter-event scales. Here, we present the results of one year of DOC and nitrate measurements with the field deployable UV-Vis spectrometer spectro::lyser (scan Messtechnik GmbH). The instrument measures the absorption spectrum from 220 to 720 nm in situ and at high frequencies and derives DOC and nitrate concentrations. The measurements were carried out at 15 minutes intervals in the Weierbach catchment (0.47 km2) in Luxemburg. This fully forested catchment is characterized by cambisol soils and fractured schist as underlying bedrock. The time series of DOC and nitrate give insights into the high frequency dynamics of stream water. Peaks in DOC concentrations are closely linked to discharge peaks that occur during or right after a rainfall event. Those first discharge peaks can be linked to fast near surface runoff processes and are responsible for a remarkable amount of DOC export. A special characterisation of

Peak-flow frequency analyses and results based on data through water year 2011 for selected streamflow-gaging stations in or near Montana: Chapter C in Montana StreamStats

Science.gov (United States)

Sando, Steven K.; McCarthy, Peter M.; Dutton, DeAnn M.

2016-04-05

Chapter C of this Scientific Investigations Report documents results from a study by the U.S. Geological Survey, in cooperation with the Montana Department of Transportation and the Montana Department of Natural Resources, to provide an update of statewide peak-flow frequency analyses and results for Montana. The purpose of this report chapter is to present peak-flow frequency analyses and results for 725 streamflow-gaging stations in or near Montana based on data through water year 2011. The 725 streamflow-gaging stations included in this study represent nearly all streamflowgaging stations in Montana (plus some from adjacent states or Canadian Provinces) that have at least 10 years of peak-flow records through water year 2011. For 29 of the 725 streamflow-gaging stations, peak-flow frequency analyses and results are reported for both unregulated and regulated conditions. Thus, peak-flow frequency analyses and results are reported for a total of 754 analyses. Estimates of peak-flow magnitudes for 66.7-, 50-, 42.9-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities are reported. These annual exceedance probabilities correspond to 1.5-, 2-, 2.33-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year recurrence intervals.

Process stabilization by peak current regulation in reactive high-power impulse magnetron sputtering of hafnium nitride

International Nuclear Information System (INIS)

Shimizu, T; Villamayor, M; Helmersson, U; Lundin, D

2016-01-01

A simple and cost effective approach to stabilize the sputtering process in the transition zone during reactive high-power impulse magnetron sputtering (HiPIMS) is proposed. The method is based on real-time monitoring and control of the discharge current waveforms. To stabilize the process conditions at a given set point, a feedback control system was implemented that automatically regulates the pulse frequency, and thereby the average sputtering power, to maintain a constant maximum discharge current. In the present study, the variation of the pulse current waveforms over a wide range of reactive gas flows and pulse frequencies during a reactive HiPIMS process of Hf-N in an Ar–N 2 atmosphere illustrates that the discharge current waveform is a an excellent indicator of the process conditions. Activating the reactive HiPIMS peak current regulation, stable process conditions were maintained when varying the N 2 flow from 2.1 to 3.5 sccm by an automatic adjustment of the pulse frequency from 600 Hz to 1150 Hz and consequently an increase of the average power from 110 to 270 W. Hf–N films deposited using peak current regulation exhibited a stable stoichiometry, a nearly constant power-normalized deposition rate, and a polycrystalline cubic phase Hf-N with (1 1 1)-preferred orientation over the entire reactive gas flow range investigated. The physical reasons for the change in the current pulse waveform for different process conditions are discussed in some detail. (paper)

Variations of the Blazar AO 0235+164 in 2006-2015

Science.gov (United States)

Hagen-Thorn, V. A.; Larionov, V. M.; Morozova, D. A.; Arkharov, A. A.; Hagen-Thorn, E. I.; Shablovinskaya, E. S.; Prokop'eva, M. S.; Yakovleva, V. A.

2018-02-01

The results of optical, radio, and gamma-ray observations of the blazar AO 0235+16 are presented, including photometric ( BV RIJHK) and polarimetric ( R)monitoring carried out at St. Petersburg State University and the Central (Pulkovo) Astronomical Observatory in 2007-2015, 43 GHz Very Long Baseline Interferometry radio observations processed at Boston University, and a gamma-ray light curve based on observationswith the Fermi space observatory are presented. Two strong outbursts were detected. The relative spectral energy distributions of the variable components responsible for the outbursts are determined; these follow power laws, but with different spectral indices. The degree of polarization was high in both outbursts; only an average relationship between the brightness and polarization can be found. There was no time lag between the variations in the optical and gamma-ray, suggesting that the sources of the radiation in the optical and gamma-ray are located in the same region of the jet.

NUSTAR, SWIFT, and GROND Observations of the Flaring MEV Blazar PMN J0641-0320

DEFF Research Database (Denmark)

Ajello, M.; Ghisellini, G.; Paliya, V. S.

2016-01-01

Area Telescope and subsequent follow-up observations with NuSTAR, Swift, and GROND of a new member of the MeV blazar family: PMN J0641-0320. Our optical spectroscopy provides confirmation that this is a flat-spectrum radio quasar located at a redshift of z = 1.196. Its very hard NuSTAR spectrum (power...

Quality properties of pre- and post-rigor beef muscle after interventions with high frequency ultrasound.

Science.gov (United States)

Sikes, Anita L; Mawson, Raymond; Stark, Janet; Warner, Robyn

2014-11-01

The delivery of a consistent quality product to the consumer is vitally important for the food industry. The aim of this study was to investigate the potential for using high frequency ultrasound applied to pre- and post-rigor beef muscle on the metabolism and subsequent quality. High frequency ultrasound (600kHz at 48kPa and 65kPa acoustic pressure) applied to post-rigor beef striploin steaks resulted in no significant effect on the texture (peak force value) of cooked steaks as measured by a Tenderometer. There was no added benefit of ultrasound treatment above that of the normal ageing process after ageing of the steaks for 7days at 4°C. Ultrasound treatment of post-rigor beef steaks resulted in a darkening of fresh steaks but after ageing for 7days at 4°C, the ultrasound-treated steaks were similar in colour to that of the aged, untreated steaks. High frequency ultrasound (2MHz at 48kPa acoustic pressure) applied to pre-rigor beef neck muscle had no effect on the pH, but the calculated exhaustion factor suggested that there was some effect on metabolism and actin-myosin interaction. However, the resultant texture of cooked, ultrasound-treated muscle was lower in tenderness compared to the control sample. After ageing for 3weeks at 0°C, the ultrasound-treated samples had the same peak force value as the control. High frequency ultrasound had no significant effect on the colour parameters of pre-rigor beef neck muscle. This proof-of-concept study showed no effect of ultrasound on quality but did indicate that the application of high frequency ultrasound to pre-rigor beef muscle shows potential for modifying ATP turnover and further investigation is warranted. Crown Copyright © 2014. Published by Elsevier B.V. All rights reserved.

Methods for estimating magnitude and frequency of floods in Arizona, developed with unregulated and rural peak-flow data through water year 2010

Science.gov (United States)

Paretti, Nicholas V.; Kennedy, Jeffrey R.; Turney, Lovina A.; Veilleux, Andrea G.

2014-01-01

Flooding is among the worst natural disasters responsible for loss of life and property in Arizona, underscoring the importance of accurate estimation of flood magnitude for proper structural design and floodplain mapping. Twenty-four years of additional peak-flow data have been recorded since the last comprehensive regional flood frequency analysis conducted in Arizona. Periodically, flood frequency estimates and regional regression equations must be revised to maintain the accurate estimation of flood frequency and magnitude.

High-Speed Microscale Optical Tracking Using Digital Frequency-Domain Multiplexing.

Science.gov (United States)

Maclachlan, Robert A; Riviere, Cameron N

2009-06-01

Position-sensitive detectors (PSDs), or lateral-effect photodiodes, are commonly used for high-speed, high-resolution optical position measurement. This paper describes the instrument design for multidimensional position and orientation measurement based on the simultaneous position measurement of multiple modulated sources using frequency-domain-multiplexed (FDM) PSDs. The important advantages of this optical configuration in comparison with laser/mirror combinations are that it has a large angular measurement range and allows the use of a probe that is small in comparison with the measurement volume. We review PSD characteristics and quantitative resolution limits, consider the lock-in amplifier measurement system as a communication link, discuss the application of FDM to PSDs, and make comparisons with time-domain techniques. We consider the phase-sensitive detector as a multirate DSP problem, explore parallels with Fourier spectral estimation and filter banks, discuss how to choose the modulation frequencies and sample rates that maximize channel isolation under design constraints, and describe efficient digital implementation. We also discuss hardware design considerations, sensor calibration, probe construction and calibration, and 3-D measurement by triangulation using two sensors. As an example, we characterize the resolution, speed, and accuracy of an instrument that measures the position and orientation of a 10 mm × 5 mm probe in 5 degrees of freedom (DOF) over a 30-mm cube with 4-μm peak-to-peak resolution at 1-kHz sampling.

Ferromagnetic resonance frequency increase and resonance line broadening of a ferromagnetic Fe–Co–Hf–N film with in-plane uniaxial anisotropy by high-frequency field perturbation

International Nuclear Information System (INIS)

Seemann, K.; Leiste, H.; Krüger, K.

2013-01-01

Soft ferromagnetic Fe-Co-Hf-N films, produced by reactive r.f. magnetron sputtering, are useful to study the ferromagnetic resonance (FMR) by means of frequency domain permeability measurements up to the GHz range. Films with the composition Fe 33 Co 43 Hf 10 N 14 exhibit a saturation polarisation J s of around 1.35 T. They are consequently considered as being uniformly magnetised due to an in-plane uniaxial anisotropy of approximately μ 0 H u ≈4.5 m T after annealing them, e.g., at 400 °C in a static magnetic field for 1 h. Being exposed to a high-frequency field, the precession of magnetic moments leads to a marked frequency-dependent permeability with a sharp Lorentzian shaped imaginary part at around 2.33 GHz (natural resonance peak), which is in a very good agreement with the modified Landau–Lifschitz–Gilbert (LLG) differential equation. A slightly increased FMR frequency and a clear increase in the resonance line broadening due to an increase of the exciting high-frequency power (1–25.1 mW), considered as an additional perturbation of the precessing system of magnetic moments, could be discovered. By solving the homogenous LLG differential equation with respect to the in-plane uniaxial anisotropy, it was revealed that the high-frequency field perturbation impacts the resonance peak position f FMR and resonance line broadening Δf FMR characterised by a completed damping parameter α=α eff +Δα. Adapted from this result, the increase in f FMR and decrease in lifetime of the excited level of magnetic moments associated with Δf FMR , similar to a spin-½ particle in a static magnetic field, was theoretically elaborated as well as compared with experimental data. - Highlights: • Impact on the resonance frequency and resonance line by the high-frequency power. • Theoretic approach by solving the LLG differential equation. • Experimental verification and magnon processes. • Theoretical and experimental determination of the resonance state

Gnevyshev peaks in solar radio emissions at different frequencies

Directory of Open Access Journals (Sweden)

R. P. Kane

2009-04-01

Full Text Available Sunspots have a major 11-year cycle, but the years near the sunspot maximum show two or more peaks called GP (Gnevyshev Peaks. In this communication, it was examined whether these peaks in sunspots are reflected in other parameters such as Lyman-α (the chromospheric emission 121.6 nm, radio emissions 242–15 400 MHz emanating from altitude levels 2000–12 000 km, the low latitude (+45° to −45° solar open magnetic flux and the coronal green line emission (Fe XIV, 530.3 nm. In the different solar cycles 20–23, the similarity extended at least upto the level of 609 MHz, but in cycle 22, the highest level was of 242 MHz. The extension to the higher level in cycle 22 does not seem to be related to the cycle strength Rz(max, or to the cycle length.

The VLBA-BU-BLAZAR Multi-Wavelength Monitoring Program

Directory of Open Access Journals (Sweden)

Svetlana Jorstad

2016-10-01

Full Text Available We describe a multiwavelength program of monitoring of a sample of bright γ-ray blazars, which the Boston University (BU group has being carrying out since June 2007. The program includes monthly monitoring with the Very Long Baseline Array at 43 GHz, optical photometric and polarimetric observations, construction and analysis of UV and X-ray light curves obtained with the Rossi X-ray Timing Explorer (RXTE and Swift satellites, and construction and analysis of γ-ray light curves based on data provided by the Large Area Telescope of the Fermi Gamma-ray Space Telescope. We present general results about the kinematics of parsec-scale radio jets, as well as the connection between γ-ray outbursts and jet events.

Neuroscience imaging enabled by new highly tunable and high peak power femtosecond lasers

Science.gov (United States)

Hakulinen, T.; Klein, J.

2017-02-01

Neuroscience applications benefit from recent developments in industrial femtosecond laser technology. New laser sources provide several megawatts of peak power at wavelength of 1040 nm, which enables simultaneous optogenetics photoactivation of tens or even hundreds of neurons using red shifted opsins. Another recent imaging trend is to move towards longer wavelengths, which would enable access to deeper layers of tissue due to lower scattering and lower absorption in the tissue. Femtosecond lasers pumping a non-collinear optical parametric amplifier (NOPA) enable the access to longer wavelengths with high peak powers. High peak powers of >10 MW at 1300 nm and 1700 nm allow effective 3-photon excitation of green and red shifted calcium indicators respectively and access to deeper, sub-cortex layers of the brain. Early results include in vivo detection of spontaneous activity in hippocampus within an intact mouse brain, where neurons express GCaMP6 activated in a 3-photon process at 1320 nm.

High-intensity Interval Training Frequency: Cardiometabolic Effects and Quality of Life.

Science.gov (United States)

Stavrinou, Pinelopi S; Bogdanis, Gregory C; Giannaki, Christoforos D; Terzis, Gerasimos; Hadjicharalambous, Marios

2018-02-01

The effects of high intensity interval training (HIIT) frequency on cardiometabolic health and quality of life were examined in 35 healthy inactive adults (age: 31.7±2.6 yrs, VO 2 peak: 32.7±7.4 ml·: kg -1 ·: min -1 ). Participants were randomly assigned to a control (CON) and two training groups, which performed 10×60-s cycling at ~83% of peak power, two (HIIT-2) or three times per week (HIIT-3) for eight weeks. Compared with CON, both training regimes resulted in similar improvements in VO 2 peak (HIIT-2: 10.8%, p=0.048, HIIT-3: 13.6%, p=0.017), waist circumference (HIIT-2: -1.4 cm, p=0.048, HIIT-3: -2.4 cm, p=0.028), thigh cross-sectional area (HIIT-2: 11.4 cm 2 , p=0.001, HIIT-3: 9.3 cm 2 , p=0.001) and the physical health component of quality of life (HIIT-2: 8.4, p=0.001, HIIT-3: 12.2, p=0.001). However, HIIT-3 conferred additional health-related benefits by reducing total body and trunk fat percentage (pHIIT only twice per week is effective in promoting cardiometabolic health-related adaptations and quality of life in inactive adults. However, higher HIIT frequency is required for an effect on fat deposits, cholesterol and mental component of well-being. © Georg Thieme Verlag KG Stuttgart · New York.

High-speed Light Peak optical link for high energy applications

Energy Technology Data Exchange (ETDEWEB)

Chang, F.X. [Academia Sinica, Taipei, Taiwan (China); Chiang, F. [FOCI Fiber Optic Comm., Inc., Hsinchu, Taiwan (China); Deng, B. [Hubei Polytechnic University, Huangshi, Hubei (China); Southern Methodist University, Dallas, TX (United States); Hou, J. [FOCI Fiber Optic Comm., Inc., Hsinchu, Taiwan (China); Hou, S., E-mail: suen@gate.sinica.edu.tw [Academia Sinica, Taipei, Taiwan (China); Liu, C.; Liu, T. [Southern Methodist University, Dallas, TX (United States); Teng, P.K. [Academia Sinica, Taipei, Taiwan (China); Wang, C.H. [National United University, Miaoli, Taiwan (China); Xu, T. [Shandong University, Ji' nan (China); Southern Methodist University, Dallas, TX (United States); Ye, J. [Southern Methodist University, Dallas, TX (United States)

2014-11-21

Optical links provide high speed data transmission with low mass fibers favorable for applications in high energy experiments. We report investigation of a compact Light Peak optical engine designed for data transmission at 4.8 Gbps. The module is assembled with bare die VCSEL, PIN diodes and a control IC aligned within a prism receptacle for light coupling to fiber ferrule. Radiation damage in the receptacle was examined with {sup 60}Co gamma ray. Radiation induced single event effects in the optical engine were studied with protons, neutrons and X-ray tests.

Science with the ASTRI mini-array for the Cherenkov Telescope Array: blazars and fundamental physics

Science.gov (United States)

Bonnoli, Giacomo; Tavecchio, Fabrizio; Giuliani, Andrea; Bigongiari, Ciro; Di Pierro, Federico; Stamerra, Antonio; Pareschi, Giovanni; Vercellone, Stefano; ASTRI Collaboration; CTA Consortium

2016-05-01

ASTRI (“Astronomia a Specchi con Tecnologia Replicante Italiana”) is a flagship project of the Italian Ministry of Research (MIUR), devoted to the realization, operation and scientific validation of an end-to-end prototype for the Small Size Telescope (SST) envisaged to become part of the Cherenkov Telescope Array (CTA). The ASTRI SST-2M telescope prototype is characterized by a dual mirror, Schwarzschild-Couder optical design and a compact camera based on silicon photo-multipliers. It will be sensitive to multi-TeV very high energy (VHE) gamma rays up to 100 TeV, with a PSF ~ 6’ and a wide (9.6°) unaberrated optical field of view. Right after validation of the design in single-dish observations at the Serra La Nave site (Sicily, Italy) during 2015, the ASTRI collaboration will be able to start deployment, at the final CTA southern site, of the ASTRI mini-array, proposed to constitute the very first CTA precursor. Counting 9 ASTRI SST-2M telescopes, the ASTRI mini-array will overtake current IACT systems in differential sensitivity above 5 TeV, thus allowing unprecedented observations of known and predicted bright TeV emitters in this band, including some extragalactic sources such as extreme high-peaked BL Lacs with hard spectra. We exploited the ASTRI scientific simulator ASTRIsim in order to understand the feasibility of observations tackling blazar and cosmic ray physics, including discrimination of hadronic and leptonic scenarios for the VHE emission from BL Lac relativistic jets and indirect measurements of the intergalactic magnetic field and of the extragalactic background light. We selected favorable targets, outlining observation modes, exposure times, multi-wavelength coverage needed and the results expected. Moreover, the perspectives for observation of effects due to the existence of axion-like particles or to Lorentz invariance violations have been investigated.

An Automated Measurement of Ciliary Beating Frequency using a Combined Optical Flow and Peak Detection.

Science.gov (United States)

Kim, Woojae; Han, Tae Hwa; Kim, Hyun Jun; Park, Man Young; Kim, Ku Sang; Park, Rae Woong

2011-06-01

The mucociliary transport system is a major defense mechanism of the respiratory tract. The performance of mucous transportation in the nasal cavity can be represented by a ciliary beating frequency (CBF). This study proposes a novel method to measure CBF by using optical flow. To obtain objective estimates of CBF from video images, an automated computer-based image processing technique is developed. This study proposes a new method based on optical flow for image processing and peak detection for signal processing. We compare the measuring accuracy of the method in various combinations of image processing (optical flow versus difference image) and signal processing (fast Fourier transform [FFT] vs. peak detection [PD]). The digital high-speed video method with a manual count of CBF in slow motion video play, is the gold-standard in CBF measurement. We obtained a total of fifty recorded ciliated sinonasal epithelium images to measure CBF from the Department of Otolaryngology. The ciliated sinonasal epithelium images were recorded at 50-100 frames per second using a charge coupled device camera with an inverted microscope at a magnification of ×1,000. The mean square errors and variance for each method were 1.24, 0.84 Hz; 11.8, 2.63 Hz; 3.22, 1.46 Hz; and 3.82, 1.53 Hz for optical flow (OF) + PD, OF + FFT, difference image [DI] + PD, and DI + FFT, respectively. Of the four methods, PD using optical flow showed the best performance for measuring the CBF of nasal mucosa. The proposed method was able to measure CBF more objectively and efficiently than what is currently possible.

Pulsed-High Field/High-Frequency EPR Spectroscopy

Science.gov (United States)

Fuhs, Michael; Moebius, Klaus

Pulsed high-field/high-frequency electron paramagnetic resonance (EPR) spectroscopy is used to disentangle many kinds of different effects often obscured in continuous wave (cw) EPR spectra at lower magnetic fields/microwave frequencies. While the high magnetic field increases the resolution of G tensors and of nuclear Larmor frequencies, the high frequencies allow for higher time resolution for molecular dynamics as well as for transient paramagnetic intermediates studied with time-resolved EPR. Pulsed EPR methods are used for example for relaxation-time studies, and pulsed Electron Nuclear DOuble Resonance (ENDOR) is used to resolve unresolved hyperfine structure hidden in inhomogeneous linewidths. In the present article we introduce the basic concepts and selected applications to structure and mobility studies on electron transfer systems, reaction centers of photosynthesis as well as biomimetic models. The article concludes with an introduction to stochastic EPR which makes use of an other concept for investigating resonance systems in order to increase the excitation bandwidth of pulsed EPR. The limited excitation bandwidth of pulses at high frequency is one of the main limitations which, so far, made Fourier transform methods hardly feasible.

Numerical calculation of high frequency fast wave current drive in a reactor grade tokamak

International Nuclear Information System (INIS)

Ushigusa, Kenkichi; Hamamatsu, Kiyotaka

1988-02-01

A fast wave current drive with a high frequency is estimated for a reactor grade tokamak by the ray tracing and the quasi-linear Fokker-Planck calculations with an assumption of single path absorption. The fast wave can drive RF current with the drive efficiency of η CD = n-bar e (10 19 m -3 )I RC (A)R(m)/P RF (W) ∼ 3.0 when the wave frequency is selected to be f/f ci > 7. A sharp wave spectrum and a ph|| >/υ Te ∼ 3.0 are required to obtain a good efficiency. A center peaked RF current profile can be formed with an appropriate wave spectrum even in the high temperature plasma. (author)

Very Rapid High-amplitude Gamma-Ray Variability in Luminous Blazar PKS 1510-089 Studied with Fermi-LAT

Energy Technology Data Exchange (ETDEWEB)

Saito, S.; Stawarz, L.; Tanaka, Y.T.; Takahashi, T.; Madejski, G.; D' Ammando, F.

2013-03-20

Here we report on the detailed analysis of the γ-ray light curve of a luminous blazar PKS 1510-089 observed in the GeV range with the Large Area Telescope (LAT) onboard the Fermi satellite during the period 2011 September - December. By investigating the properties of the detected three major flares with the shortest possible time binning allowed by the photon statistics, we find a variety of temporal characteristics and variability patterns. This includes a clearly asymmetric profile (with a faster flux rise and a slower decay) of the flare resolved on sub-daily timescales, a superposition of many short uncorrelated flaring events forming the apparently coherent longer-duration outburst, and a huge single isolated outburst unresolved down to the timescale of three-hours. In the latter case we estimate the corresponding γ-ray flux doubling timescale to be below one hour, which is extreme and never previously reported for any active galaxy

BL Lacertae Objects Beyond Redshift 1.3 - UV-to-NIR Photometry and Photometric Redshift for Fermi/LAT Blazars

Science.gov (United States)

Rau, A.; Schady, P.; Greiner, J.; Salvato, M.; Ajello, M.; Bottacini, E.; Gehrels, N.; Afonso, P. M. J.; Elliott, J.; Filgas, R.;

75 FR 81284 - Nationwide Use of High Frequency and Ultra High Frequency Active SONAR Technology; Draft...

Science.gov (United States)

2010-12-27

... Frequency and Ultra High Frequency Active SONAR Technology; Draft Programmatic Environmental Assessment and... Programmatic Environmental Assessment (PEA) for the Nationwide Use of High Frequency (HF) and Ultra High... potential impacts of each alternative on the human and natural environments. DATES: Comments and related...

Proposal for a race-track microtron with high peak current

NARCIS (Netherlands)

Ernst, G.J.; Haselhoff, E.H.; Witteman, W.J.; Botman, J.I.M.; van Genderen, W.; Hagedoorn, H.L.; van der Heide, J.A.; Kleeven, W.J.G.M.

1989-01-01

In order to obtain high gain in a free electron laser a high-quality electron beam with high peak current is required. It is well-known that a microtron is able to produce a high-quality beam having low emittance and small energy spread (1%). Because a circular microtron has a limited high-current

Results of the first simultaneous X-ray, optical, and radio campaign on the blazar PKS 1622-297

NARCIS (Netherlands)

Meyer, Angela Osterman; Miller, H. Richard; Marshall, Kevin; Ryle, Wesley T.; Aller, Hugh; Aller, Margo; McFarland, John P.; Pollock, Joseph T.; Reichart, Daniel E.; Crain, J. Adam; Ivarsen, Kevin M.; LaCluyze, Aaron P.; Nysewander, Melissa C.

Coordinated X-ray, optical, and radio observations of the blazar PKS 1622-297 were obtained during a three-week campaign in 2006 using the Rossi X-Ray Timing Explorer (RXTE), the University of Michigan Radio Astronomy Observatory, and optical telescopes at Cerro Tololo Inter-American Observatory.

Climate Change Impacts on Peak Electricity Consumption: US vs. Europe.

Science.gov (United States)

Auffhammer, M.

2016-12-01

It has been suggested that climate change impacts on the electric sector will account for the majority of global economic damages by the end of the current century and beyond. This finding is at odds with the relatively modest increase in climate driven impacts on consumption. Comprehensive high frequency load balancing authority level data have not been used previously to parameterize the relationship between electric demand and temperature for any major economy. Using statistical models we analyze multi-year data from load balancing authorities in the United States of America and the European Union, which are responsible for more than 90% of the electricity delivered to residential, industrial, commercial and agricultural customers. We couple the estimated response functions between total daily consumption and daily peak load with an ensemble of downscaled GCMs from the CMIP5 archive to simulate climate change driven impacts on both outcomes. We show moderate and highly spatially heterogeneous changes in consumption. The results of our peak load simulations, however, suggest significant changes in the intensity and frequency of peak events throughout the United States and Europe. As the electricity grid is built to endure maximum load, which usually occurs on the hottest day of the year, our findings have significant implications for the construction of costly peak generating and transmission capacity.

Evidence of resonant mode coupling and the relationship between low and high frequencies in a rapidly rotating a star

International Nuclear Information System (INIS)

Breger, M.; Montgomery, M. H.

2014-01-01

In the theory of resonant mode coupling, the parent and child modes are directly related in frequency and phase. The oscillations present in the fast rotating δ Sct star KIC 8054146 allow us to test the most general and generic aspects of such a theory. The only direct way to separate the parent and coupled (child) modes is to examine the correlations in amplitude variability between the different frequencies. For the dominant family of related frequencies, only a single mode and a triplet are the origins of nine dominant frequency peaks ranging from 2.93 to 66.30 cycles day –1 (as well as dozens of small-amplitude combination modes and a predicted and detected third high-frequency triplet). The mode-coupling model correctly predicts the large amplitude variations of the coupled modes as a product of the amplitudes of the parent modes, while the phase changes are also correctly modeled. This differs from the behavior of 'normal' combination frequencies in that the amplitudes are three orders of magnitude larger and may exceed even the amplitudes of the parent modes. We show that two dominant low frequencies at 5.86 and 2.93 cycles day –1 in the gravity-mode region are not harmonics of each other, and their properties follow those of the almost equidistant high-frequency triplet. We note that the previously puzzling situation of finding two strong peaks in the low-frequency region related by nearly a factor of two in frequency has been seen in other δ Sct stars as well.

Evidence of resonant mode coupling and the relationship between low and high frequencies in a rapidly rotating a star

Energy Technology Data Exchange (ETDEWEB)

Breger, M.; Montgomery, M. H. [Department of Astronomy, University of Texas, Austin, TX 78712 (United States)

2014-03-10

In the theory of resonant mode coupling, the parent and child modes are directly related in frequency and phase. The oscillations present in the fast rotating δ Sct star KIC 8054146 allow us to test the most general and generic aspects of such a theory. The only direct way to separate the parent and coupled (child) modes is to examine the correlations in amplitude variability between the different frequencies. For the dominant family of related frequencies, only a single mode and a triplet are the origins of nine dominant frequency peaks ranging from 2.93 to 66.30 cycles day{sup –1} (as well as dozens of small-amplitude combination modes and a predicted and detected third high-frequency triplet). The mode-coupling model correctly predicts the large amplitude variations of the coupled modes as a product of the amplitudes of the parent modes, while the phase changes are also correctly modeled. This differs from the behavior of 'normal' combination frequencies in that the amplitudes are three orders of magnitude larger and may exceed even the amplitudes of the parent modes. We show that two dominant low frequencies at 5.86 and 2.93 cycles day{sup –1} in the gravity-mode region are not harmonics of each other, and their properties follow those of the almost equidistant high-frequency triplet. We note that the previously puzzling situation of finding two strong peaks in the low-frequency region related by nearly a factor of two in frequency has been seen in other δ Sct stars as well.

High frequency energy measurements

International Nuclear Information System (INIS)

Stotlar, S.C.

1981-01-01

High-frequency (> 100 MHz) energy measurements present special problems to the experimenter. Environment or available electronics often limit the applicability of a given detector type. The physical properties of many detectors are frequency dependent and in some cases, the physical effect employed can be frequency dependent. State-of-the-art measurements generally involve a detection scheme in association with high-speed electronics and a method of data recording. Events can be single or repetitive shot requiring real time, sampling, or digitizing data recording. Potential modification of the pulse by the detector and the associated electronics should not be overlooked. This presentation will review typical applications, methods of choosing a detector, and high-speed detectors. Special considerations and limitations of some applications and devices will be described

Peak-to-average power ratio reduction in orthogonal frequency division multiplexing-based visible light communication systems using a modified partial transmit sequence technique

Science.gov (United States)

Liu, Yan; Deng, Honggui; Ren, Shuang; Tang, Chengying; Qian, Xuewen

2018-01-01

We propose an efficient partial transmit sequence technique based on genetic algorithm and peak-value optimization algorithm (GAPOA) to reduce high peak-to-average power ratio (PAPR) in visible light communication systems based on orthogonal frequency division multiplexing (VLC-OFDM). By analysis of hill-climbing algorithm's pros and cons, we propose the POA with excellent local search ability to further process the signals whose PAPR is still over the threshold after processed by genetic algorithm (GA). To verify the effectiveness of the proposed technique and algorithm, we evaluate the PAPR performance and the bit error rate (BER) performance and compare them with partial transmit sequence (PTS) technique based on GA (GA-PTS), PTS technique based on genetic and hill-climbing algorithm (GH-PTS), and PTS based on shuffled frog leaping algorithm and hill-climbing algorithm (SFLAHC-PTS). The results show that our technique and algorithm have not only better PAPR performance but also lower computational complexity and BER than GA-PTS, GH-PTS, and SFLAHC-PTS technique.

Effect of high-frequency excitation on natural frequencies of spinning discs

DEFF Research Database (Denmark)

Hansen, Morten Hartvig

2000-01-01

The effect of high-frequency, non-resonant parametric excitation on the low-frequency response of spinning discs is considered. The parametric excitation is obtained through a non-constant rotation speed, where the frequency of the pulsating overlay is much higher than the lowest natural frequenc......The effect of high-frequency, non-resonant parametric excitation on the low-frequency response of spinning discs is considered. The parametric excitation is obtained through a non-constant rotation speed, where the frequency of the pulsating overlay is much higher than the lowest natural...

High-temperature peaks of thermostimulated luminescence in the ammonium halogens

International Nuclear Information System (INIS)

Kim, L.M.; Musenova, Eh.K.; Mukhamedrakhimov, K.U.

2003-01-01

The ammonium halogen crystals (AHC) are the close analogs of the alkali halogen crystals by the type of chemical bonds and crystal lattice structure. The ammonium halogen after irradiation by X-rays within 80-300 K range have two peaks of thermo-stimulation luminescence. Its maximums in dependence of anions type are in the 110-120 K and 170-180 K ranges. The first range is related with activation of auto-localized holes migration, and the second one - with the NH 3 + defects decay. Experimentally is established, that the pure ammonium halogens have memory about the previous irradiation at heating up to 300 K. After repeat irradiation the recombination luminescence high-temperature peak's shoulder is appearing. The second luminescence peak's shoulder revealing does not depend on the impurity center nature. It is known, that in the AHC there is the next thermo-stimulation luminescence peak within 340-360 K. The thermal annealing of this peak leads to the memory effect disappearance. So, the observing phenomenon is related with own defect of the matrix in the cation sublattice. Experimentally is established, that at a room temperature the AHC memorizing about previous irradiation during 20 h

High fat diet promotes achievement of peak bone mass in young rats

Energy Technology Data Exchange (ETDEWEB)

Malvi, Parmanand; Piprode, Vikrant; Chaube, Balkrishna; Pote, Satish T. [National Centre for Cell Science, Savitribai Phule Pune University Campus, Ganeshkhind, Pune 411 007 (India); Mittal, Monika; Chattopadhyay, Naibedya [Division of Endocrinology and Center for Research in Anabolic Skeletal Targets in Health and Illness (ASTHI), CSIR-Central Drug Research Institute, Jankipuram Extension, Sitapur Road, Lucknow 226 031 (India); Wani, Mohan R. [National Centre for Cell Science, Savitribai Phule Pune University Campus, Ganeshkhind, Pune 411 007 (India); Bhat, Manoj Kumar, E-mail: manojkbhat@nccs.res.in [National Centre for Cell Science, Savitribai Phule Pune University Campus, Ganeshkhind, Pune 411 007 (India)

2014-12-05

Highlights: • High fat diet helps in achieving peak bone mass at younger age. • Shifting from high fat to normal diet normalizes obese parameters. • Bone parameters are sustained even after withdrawal of high fat diet. - Abstract: The relationship between obesity and bone is complex. Epidemiological studies demonstrate positive as well as negative correlation between obesity and bone health. In the present study, we investigated the impact of high fat diet-induced obesity on peak bone mass. After 9 months of feeding young rats with high fat diet, we observed obesity phenotype in rats with increased body weight, fat mass, serum triglycerides and cholesterol. There were significant increases in serum total alkaline phosphatase, bone mineral density and bone mineral content. By micro-computed tomography (μ-CT), we observed a trend of better trabecular bones with respect to their microarchitecture and geometry. This indicated that high fat diet helps in achieving peak bone mass and microstructure at younger age. We subsequently shifted rats from high fat diet to normal diet for 6 months and evaluated bone/obesity parameters. It was observed that after shifting rats from high fat diet to normal diet, fat mass, serum triglycerides and cholesterol were significantly decreased. Interestingly, the gain in bone mineral density, bone mineral content and trabecular bone parameters by HFD was retained even after body weight and obesity were normalized. These results suggest that fat rich diet during growth could accelerate achievement of peak bone mass that is sustainable even after withdrawal of high fat diet.

High fat diet promotes achievement of peak bone mass in young rats

International Nuclear Information System (INIS)

Malvi, Parmanand; Piprode, Vikrant; Chaube, Balkrishna; Pote, Satish T.; Mittal, Monika; Chattopadhyay, Naibedya; Wani, Mohan R.; Bhat, Manoj Kumar

2014-01-01

Highlights: • High fat diet helps in achieving peak bone mass at younger age. • Shifting from high fat to normal diet normalizes obese parameters. • Bone parameters are sustained even after withdrawal of high fat diet. - Abstract: The relationship between obesity and bone is complex. Epidemiological studies demonstrate positive as well as negative correlation between obesity and bone health. In the present study, we investigated the impact of high fat diet-induced obesity on peak bone mass. After 9 months of feeding young rats with high fat diet, we observed obesity phenotype in rats with increased body weight, fat mass, serum triglycerides and cholesterol. There were significant increases in serum total alkaline phosphatase, bone mineral density and bone mineral content. By micro-computed tomography (μ-CT), we observed a trend of better trabecular bones with respect to their microarchitecture and geometry. This indicated that high fat diet helps in achieving peak bone mass and microstructure at younger age. We subsequently shifted rats from high fat diet to normal diet for 6 months and evaluated bone/obesity parameters. It was observed that after shifting rats from high fat diet to normal diet, fat mass, serum triglycerides and cholesterol were significantly decreased. Interestingly, the gain in bone mineral density, bone mineral content and trabecular bone parameters by HFD was retained even after body weight and obesity were normalized. These results suggest that fat rich diet during growth could accelerate achievement of peak bone mass that is sustainable even after withdrawal of high fat diet

Frequency conversion of high-intensity, femtosecond laser pulses

Energy Technology Data Exchange (ETDEWEB)

Banks, P S

1997-06-01

Almost since the invention of the laser, frequency conversion of optical pulses via non- linear processes has been an area of active interest. However, third harmonic generation using ~(~1 (THG) in solids is an area that has not received much attention because of ma- terial damage limits. Recently, the short, high-intensity pulses possible with chirped-pulse amplification (CPA) laser systems allow the use of intensities on the order of 1 TW/cm2 in thin solids without damage. As a light source to examine single-crystal THG in solids and other high field inter- actions, the design and construction of a Ti:sapphire-based CPA laser system capable of ultimately producing peak powers of 100 TW is presented. Of special interest is a novel, all-reflective pulse stretcher design which can stretch a pulse temporally by a factor of 20,000. The stretcher design can also compensate for the added material dispersion due to propagation through the amplifier chain and produce transform-limited 45 fs pulses upon compression. A series of laser-pumped amplifiers brings the peak power up to the terawatt level at 10 Hz, and the design calls for additional amplifiers to bring the power level to the 100 TW level for single shot operation. The theory for frequency conversion of these short pulses is presented, focusing on conversion to the third harmonic in single crystals of BBO, KD*P, and d-LAP (deuterated I-arginine phosphate). Conversion efficiencies of up to 6% are obtained with 500 fs pulses at 1053 nm in a 3 mm thick BBO crystal at 200 GW/cm 2. Contributions to this process by unphasematched, cascaded second harmonic generation and sum frequency generation are shown to be very significant. The angular relationship between the two orders is used to measure the tensor elements of C = xt3)/4 with Crs = -1.8 x 1O-23 m2/V2 and .15Cri + .54Crs = 4.0 x 1O-23 m2/V2. Conversion efficiency in d-LAP is about 20% that in BBO and conversion efficiency in KD*P is 1% that of BBO. It is calculated

Geographies of High Frequency Trading

DEFF Research Database (Denmark)

Grindsted, Thomas Skou

2016-01-01

This paper investigates the geographies of high frequency trading. Today shares shift hands within micro seconds, giving rise to a form of financial geographies termed algorithmic capitalism. This notion refers to the different spatio-temporalities produced by high frequency trading, under...... the valuation of time. As high frequency trading accelerates financial markets, the paper examines the spatio-temporalities of automated trading by the ways in which the speed of knowledge exploitation in financial markets is not only of interest, but also the expansion between different temporalities....... The paper demonstrates how the intensification of time-space compression produces radical new dynamics in the financial market and develops information rent in HFT as convertible to a time rent and a spatio-temporal rent. The final section discusses whether high frequency trading only responds to crises...

Different Mode of Afferents Determines the Frequency Range of High Frequency Activities in the Human Brain: Direct Electrocorticographic Comparison between Peripheral Nerve and Direct Cortical Stimulation.

Directory of Open Access Journals (Sweden)

Katsuya Kobayashi

Full Text Available Physiological high frequency activities (HFA are related to various brain functions. Factors, however, regulating its frequency have not been well elucidated in humans. To validate the hypothesis that different propagation modes (thalamo-cortical vs. cortico-coritcal projections, or different terminal layers (layer IV vs. layer II/III affect its frequency, we, in the primary somatosensory cortex (SI, compared HFAs induced by median nerve stimulation with those induced by electrical stimulation of the cortex connecting to SI. We employed 6 patients who underwent chronic subdural electrode implantation for presurgical evaluation. We evaluated the HFA power values in reference to the baseline overriding N20 (earliest cortical response and N80 (late response of somatosensory evoked potentials (HFA(SEP(N20 and HFA(SEP(N80 and compared those overriding N1 and N2 (first and second responses of cortico-cortical evoked potentials (HFA(CCEP(N1 and HFA(CCEP(N2. HFA(SEP(N20 showed the power peak in the frequency above 200 Hz, while HFA(CCEP(N1 had its power peak in the frequency below 200 Hz. Different propagation modes and/or different terminal layers seemed to determine HFA frequency. Since HFA(CCEP(N1 and HFA induced during various brain functions share a similar broadband profile of the power spectrum, cortico-coritcal horizontal propagation seems to represent common mode of neural transmission for processing these functions.

VizieR Online Data Catalog: The CLASS blazar survey. I. (Marcha+, 2001)

Science.gov (United States)

Marcha, M. J.; Caccianiga, A.; Browne, I. W. A.; Jackson, N.

2002-04-01

This paper presents a new complete and well-defined sample of flat-spectrum radio sources (FSRS) selected from the Cosmic Lens All-Sky Survey (CLASS), with the further constraint of a bright (mag<=17.5) optical counterpart. The sample has been designed to produce a large number of low-luminosity blazars in order to test the current unifying models in the low-luminosity regime. In this first paper the new sample is presented and the radio properties of the 325 sources contained therein are discussed. (1 data file).

Search for muon-neutrino emission from GeV and TeV gamma-ray flaring blazars using five years of data of the ANTARES telescope

OpenAIRE

Adrián-Martínez, S.; Albert, A.; André, M.; Anton, G.; Ardid, M.; Aubert, J. -J.; Baret, B.; Barrios-Martí, J.; Basa, S.; Bertin, V.; Biagi, S.; Bogazzi, C.; Bormuth, R.; Bou-Cabo, M.; Bouwhuis, M. C.

2015-01-01

The ANTARES telescope is well-suited for detecting astrophysical transient neutrino sources as it can observe a full hemisphere of the sky at all times with a high duty cycle. The background due to atmospheric particles can be drastically reduced, and the point-source sensitivity improved, by selecting a narrow time window around possible neutrino production periods. Blazars, being radio-loud active galactic nuclei with their jets pointing almost directly towards the observer, ...

Free-space optical communications with peak and average constraints: High SNR capacity approximation

KAUST Repository

Chaaban, Anas

2015-09-07

The capacity of the intensity-modulation direct-detection (IM-DD) free-space optical channel with both average and peak intensity constraints is studied. A new capacity lower bound is derived by using a truncated-Gaussian input distribution. Numerical evaluation shows that this capacity lower bound is nearly tight at high signal-to-noise ratio (SNR), while it is shown analytically that the gap to capacity upper bounds is a small constant at high SNR. In particular, the gap to the high-SNR asymptotic capacity of the channel under either a peak or an average constraint is small. This leads to a simple approximation of the high SNR capacity. Additionally, a new capacity upper bound is derived using sphere-packing arguments. This bound is tight at high SNR for a channel with a dominant peak constraint.

Noninvasive Diagnosis of Coronary Artery Disease Using 12-Lead High-Frequency Electrocardiograms

Science.gov (United States)

Schlegel, Todd T.; Arenare, Brian

2006-01-01

method is the presence versus the absence of reduced-amplitude zones (RAZs). In terms that must be simplified for the sake of brevity, an RAZ comprises several cycles of a high-frequency QRS signal during which the amplitude of the high-frequency oscillation in a portion of the signal is abnormally low (see figure). A given signal sample exhibiting an interval of reduced amplitude may or may not be classified as an RAZ, depending on quantitative criteria regarding peaks and troughs within the reduced-amplitude portion of the high-frequency QRS signal. This analysis is performed in all 12 leads in real time.

Hydration-coupled protein boson peak measured by incoherent neutron scattering

International Nuclear Information System (INIS)

Nakagawa, Hiroshi; Kataoka, Mikio; Joti, Yasumasa; Kitao, Akio; Shibata, Kaoru; Tokuhisa, Atsushi; Tsukushi, Itaru; Go, Nobuhiro

2006-01-01

The boson peak of a protein was examined in relation to hydration using staphylococcal nuclease. Although the boson peak is commonly observed in synthetic polymers, glassy materials and amorphous materials, the origin of the boson peak is not fully understood. The motions that contribute to the peak are harmonic vibrations. Upon hydration the peak frequency shifts to a higher frequency and the effective force constant of the vibration increases at low temperatures, suggesting that the protein energy surface is modified. Hydration of the protein leads to a more rugged surface and the vibrational motions are trapped within the local minimum at cryogenic temperatures. The origin of the protein boson peak may be related to this rugged energy surface

The Connection between the Radio Jet and the γ-ray Emission in the Radio Galaxy 3C 120 and the Blazar CTA 102

Directory of Open Access Journals (Sweden)

Carolina Casadio

2016-09-01

Full Text Available We present multi-wavelength studies of the radio galaxy 3C 120 and the blazar CTA 102 during unprecedented γ-ray flares for both sources. In both studies the analysis of γ-ray data has been compared with a series of 43 GHz VLBA images from the VLBA-BU-BLAZAR program, providing the necessary spatial resolution to probe the parsec scale jet evolution during the high energy events. To extend the radio dataset for 3C 120 we also used 15 GHz VLBA data from the MOJAVE sample. These two objects which represent very different classes of AGN, have similar properties during the γ-ray events. The γ-ray flares are associated with the passage of a new superluminal component through the mm VLBI core, but not all ejections of new components lead to γ-ray events. In both sources γ-ray events occurred only when the new components are moving in a direction closer to our line of sight. We locate the γ-ray dissipation zone a short distance from the radio core but outside of the broad line region, suggesting synchrotron self-Compton scattering as the probable mechanism for the γ-ray production.

Influence of multiple sclerosis, age and degree of disability, in the position of the contrast sensitivity curve peak

Directory of Open Access Journals (Sweden)

A F Nunes

2014-01-01

Full Text Available Context: Contrast sensitivity (CS function is one of the most important tests available for evaluating visual impairment. Multiple sclerosis (MS can produce highly selective losses in visual function and psychophysical studies have demonstrated CS deficits for some spatial frequencies. Aims: This work studies the differences in CS between a group of controls and a group of MS patients, focusing on the location of the maximum sensitivity peak, shape of the curve, and determination of the most affected spatial frequencies. Materials and Methods: Using a sinusoidal stimulus the authors assessed CS function in 28 subjects with definitive relapsing remitting MS, and in 50 controls with acuities of 20/25 or better. The peaks of the CS curves were studied by fitting third degree polynomials to individual sets of data. Results: Compared with the control group, the CS function curve for MS subjects showed more deficits in extreme points (low- and high-spatial frequencies. Our results display significant CS losses, at the high-frequencies band level, in the beginning of the disease. When the disease progresses and the disabilities appear, there are greater losses at the low-frequencies band level. In average, the CS curve peaks for the MS group were shifted in relation to the control group. Conclusions: CS losses in the MS group suggest an association with ageing and disability level in the expanded disability status scale. The position of the CS function peak is influenced by MS, age, and degree of disability.

Bayesian Peptide Peak Detection for High Resolution TOF Mass Spectrometry.

Science.gov (United States)

Zhang, Jianqiu; Zhou, Xiaobo; Wang, Honghui; Suffredini, Anthony; Zhang, Lin; Huang, Yufei; Wong, Stephen

2010-11-01

In this paper, we address the issue of peptide ion peak detection for high resolution time-of-flight (TOF) mass spectrometry (MS) data. A novel Bayesian peptide ion peak detection method is proposed for TOF data with resolution of 10 000-15 000 full width at half-maximum (FWHW). MS spectra exhibit distinct characteristics at this resolution, which are captured in a novel parametric model. Based on the proposed parametric model, a Bayesian peak detection algorithm based on Markov chain Monte Carlo (MCMC) sampling is developed. The proposed algorithm is tested on both simulated and real datasets. The results show a significant improvement in detection performance over a commonly employed method. The results also agree with expert's visual inspection. Moreover, better detection consistency is achieved across MS datasets from patients with identical pathological condition.

Main flood peaks in the medieval Carpathian Basin (1000-1500): Annual and decadal overview

Science.gov (United States)

Kiss, Andrea

2013-04-01

The analysis of over 140 reported floods is mainly based on contemporary legal evidence (charters), partly on other types of contemporary documentary evidence. Majority of sources contains data on individual flood events (i.e. occurrence, seasonality, magnitude). Concerning main flood peaks, evidence on annual and multi-annual (decadal, multi-decadal) level is also available. Despite data increase in the 13th century, only in the 14th-15th centuries documentation is representative enough to draw further conclusions. Apart from secondary flood peaks (probably in the mid-13th century and the turn of the 13th-14th centuries), three main periods with high flood frequencies are detected: 1330s-1350s, 1390s-1430s, and the late 1480s-1490s (continuing in the early 16th century). The first major flood peak was primarily reported in the eastern Carpathian Basin (the Tisa catchment), and can be characterised by a number of high-intensity flood events (with 1342-1343 in centre). During the second major, prolonged flood peak of 1390s-1430s, and that of the third, late 15th century one the importance of floods occurred on the Danube and in the Danube catchment area has to be as well highlighted. Moreover, in the first half of the 15th century long-term hydrological problems (prolonged high water-level and high flood frequency problems) can be identified. In some cases high flood-frequency periods were accompanied by documented hydromorphological impacts and some impacts on society can be also detected. Results show good agreement with the decadal precipitation reconstruction based on speleothem investigations carried out in North-Hungary.

Statistical analysis of the low-temperature dislocation peak of internal friction (Bordoni peak) in nanostructured copper

International Nuclear Information System (INIS)

Vatazhuk, E.N.; Natsik, V.D.

2011-01-01

The temperature-frequency dependence of internal friction in the nanostructured samples of Cu and fibred composite C-32 vol.%Nb with the sizes of structure fragments approx 200 nm is analyzed. Experiments are used as initial information for such analysis. The characteristic for the heavily deformed copper Bordoni peak, located nearby a temperature 90 K, was recorded on temperature dependence of vibration decrement (frequencies 73-350 kHz) in previous experiments. The peak is due to the resonance interaction of sound with the system of thermal activated relaxators, and its width considerably greater in comparison with the width of standard internal friction peak with the single relaxation time. Statistical analysis of the peak is made in terms of assumption that the reason of broadening is random activation energy dispersion of relaxators as a result of intense distortion of copper crystal structure. Good agreement of experimental data and Seeger theory considers thermal activated paired kinks at linear segments of dislocation lines, placed in potential Peierls relief valley, as relaxators of Bordoni peak, was established. It is shown that the registered peak height in experiment correspond to presence at the average one dislocation segment in the interior of crystalline grain with size of 200 nm. Empirical estimates for the critical Peierls stress σp ∼ 2x10 7 Pa and integrated density of the interior grain dislocations ρ d ∼ 10 13 m -2 are made. Nb fibers in the composite Cu-Nb facilitate to formation of nanostructured copper, but do not influence evidently on the Bordoni peak.

Binaural beats at high frequencies.

Science.gov (United States)

McFadden, D; Pasanen, E G

1975-10-24

Binaural beats have long been believed to be audible only at low frequencies, but an interaction reminiscent of a binaural beat can sometimes be heard when different two-tone complexes of high frequency are presented to the two ears. The primary requirement is that the frequency separation in the complex at one ear be slightly different from that in the other--that is, that there be a small interaural difference in the envelope periodicities. This finding is in accord with other recent demonstrations that the auditory system is not deaf to interaural time differences at high frequencies.

ALMA High Frequency Techniques

Science.gov (United States)

Meyer, J. D.; Mason, B.; Impellizzeri, V.; Kameno, S.; Fomalont, E.; Chibueze, J.; Takahashi, S.; Remijan, A.; Wilson, C.; ALMA Science Team

2015-12-01

The purpose of the ALMA High Frequency Campaign is to improve the quality and efficiency of science observing in Bands 8, 9, and 10 (385-950 GHz), the highest frequencies available to the ALMA project. To this end, we outline observing modes which we have demonstrated to improve high frequency calibration for the 12m array and the ACA, and we present the calibration of the total power antennas at these frequencies. Band-to-band (B2B) transfer and bandwidth switching (BWSW), techniques which improve the speed and accuracy of calibration at the highest frequencies, are most necessary in Bands 8, 9, and 10 due to the rarity of strong calibrators. These techniques successfully enable increased signal-to-noise on the calibrator sources (and better calibration solutions) by measuring the calibrators at lower frequencies (B2B) or in wider bandwidths (BWSW) compared to the science target. We have also demonstrated the stability of the bandpass shape to better than 2.4% for 1 hour, hidden behind random noise, in Band 9. Finally, total power observing using the dual sideband receivers in Bands 9 and 10 requires the separation of the two sidebands; this procedure has been demonstrated in Band 9 and is undergoing further testing in Band 10.

Fermi-LAT View of Bright Flaring Gamma-Ray Blazars

Science.gov (United States)

Bastieri, D.; Ciprini, S.; Gasparrini, D.

2011-06-01

The Fermi LAT provides a continuous and uniform monitoring of the Universe in the gamma-ray band. During the first year many gamma-ray blazar flares, some unidentified transients and emission by the Sun while in a quiet state were promptly detected. This is mainly due to the design of the mission, featuring a detector, the LAT with a wide field of view, and to the operation of the spacecraft itself, that can cover every region of the sky every 3 hours. Nevertheless, the scientific exploitation of this monitoring is more fruitful when early information about transients reaches a broader community. In this respect, the indefatigable activity of flare advocates, who worked on weekly shifts to validate the results and quickly broadcast information about flares and new detections, was the key to most scientific results.

Magnetic and frequency properties for nanocrystalline Fe-Ni alloys prepared by high-energy milling method

International Nuclear Information System (INIS)

Liu Yongsheng; Zhang Jincang; Yu, Liming; Jia Guangqiang; Jing Chao; Cao Shixun

2005-01-01

Fe-based nano-crystalline soft magnetic alloy with Ni-doping was fabricated successfully by high-energy milling. It was proved that a Fe-Ni solid solution is formed and the evaluated average grain size is about 20 nm. The effect of doping Ni on the frequency properties was systematically investigated. From the magnetic measurement results, it can be concluded that, the nickel doped decreases the resonance frequency of Fe-Ni alloy, but Ni doping enhances the frequency stability. The corresponding value of initial permeability as a function of Ni doping concentration was given at 10 kHz and the result indicates that the peak value of initial permeability shifts to the region of low Ni concentration for the samples milled for 72 h

A design technique of low cost but high quality peak stretcher

Energy Technology Data Exchange (ETDEWEB)

Lo, H Y; Su, C S; Hsu, J Y; Wang, L

1981-03-01

This paper presents the design of low cost but high quality pulse peak stretcher incorporated with a LSI of 12 bit ADC and SKD-85 microcomputer. The conflict between the capacitor high charging speed and longer holding time for realizing a high quality stretcher is discussed and solved. For a lager number of channels available in a dual ramp Wilkinson-type ADC, two-stage stretchers connected in series are designed. The first stage is a fast-discharge to keep the output stretched pulse follow-up the input quickly and the second-stage (main stretcher) is a slow-discharge to keep the transient of the circuit minimum. Both of these two peak stretchers are described and the experiment results are photographically recorded.

Gamma-ray astronomy from the ground and the space: first analyses of the HESS-II hybrid array and search for blazar candidates among the unidentified Fermi-LAT sources

International Nuclear Information System (INIS)

Lefaucheur, Julien

2015-01-01

This manuscript is about high energy gamma-ray astronomy (between 30 GeV and 300 GeV) with the Fermi-LAT satellite and very high energy gamma-ray astronomy (above ∼100 GeV) via the H.E.S.S. experiment. The second phase of the H.E.S.S. experiment began in July 2012 with the inauguration of a fifth 28 m-diameter telescope added to the initial array composed of four 12 m-diameter imaging atmospheric Cherenkov telescopes. In the first part of this thesis, we present the development of an analysis in hybrid mode based on a multivariate method dedicated to detect and study sources with different spectral shapes and the first analysis results on real data. The second part is dedicated to the research of blazar candidates among the Fermi-LAT unidentified sources of the 2FGL catalog. A first development is based on a multivariate approach using discriminant parameters built with the 2FGL catalog parameters. A second development is done with the use of the WISE satellite catalog and a non-parametric technic in order to find the blazar-like infrared counterparts of the unidentified sources of the 2FGL catalog. (author)

One-point fluctuation analysis of the high-energy neutrino sky

Energy Technology Data Exchange (ETDEWEB)

Feyereisen, Michael R.; Ando, Shin' ichiro [GRAPPA Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands); Tamborra, Irene, E-mail: m.r.feyereisen@uva.nl, E-mail: tamborra@nbi.ku.dk, E-mail: s.ando@uva.nl [Niels Bohr International Academy, Niels Bohr Institute, Blegdamsvej 17, 2100 Copenhagen (Denmark)

2017-03-01

We perform the first one-point fluctuation analysis of the high-energy neutrino sky. This method reveals itself to be especially suited to contemporary neutrino data, as it allows to study the properties of the astrophysical components of the high-energy flux detected by the IceCube telescope, even with low statistics and in the absence of point source detection. Besides the veto-passing atmospheric foregrounds, we adopt a simple model of the high-energy neutrino background by assuming two main extra-galactic components: star-forming galaxies and blazars. By leveraging multi-wavelength data from Herschel and Fermi , we predict the spectral and anisotropic probability distributions for their expected neutrino counts in IceCube. We find that star-forming galaxies are likely to remain a diffuse background due to the poor angular resolution of IceCube, and we determine an upper limit on the number of shower events that can reasonably be associated to blazars. We also find that upper limits on the contribution of blazars to the measured flux are unfavourably affected by the skewness of the blazar flux distribution. One-point event clustering and likelihood analyses of the IceCube HESE data suggest that this method has the potential to dramatically improve over more conventional model-based analyses, especially for the next generation of neutrino telescopes.

High-precision analogue peak detector for X-ray imaging applications

OpenAIRE

Dlugosz, Rafal Tomasz; Iniewski, Kris

2007-01-01

A new analogue high-precision peak detector is presented. Owing to its very low power consumption the circuit is particularly well suited for photon energy detection in multichannel receiver integrated circuits used in nuclear medicine.

High-frequency Trader Subjectivity

DEFF Research Database (Denmark)

Borch, Christian; Lange, Ann-Christina

2017-01-01

In this article, we examine the recent shift in financial markets toward high-frequency trading (HFT). This turn is being legitimized with reference to how algorithms are allegedly more rational and efficient than human traders, and less prone to emotionally motivated decisions. We argue......-techniques of the ideal high-frequency trader. We demonstrate that these traders face the challenge of avoiding emotional interference in their algorithms and that they deploy a set of disciplinary self-techniques to curb the importance of emotional attachment....

Testing the Equivalence Principle and Lorentz Invariance with PeV Neutrinos from Blazar Flares.

Science.gov (United States)

Wang, Zi-Yi; Liu, Ruo-Yu; Wang, Xiang-Yu

2016-04-15

It was recently proposed that a giant flare of the blazar PKS B1424-418 at redshift z=1.522 is in association with a PeV-energy neutrino event detected by IceCube. Based on this association we here suggest that the flight time difference between the PeV neutrino and gamma-ray photons from blazar flares can be used to constrain the violations of equivalence principle and the Lorentz invariance for neutrinos. From the calculated Shapiro delay due to clusters or superclusters in the nearby universe, we find that violation of the equivalence principle for neutrinos and photons is constrained to an accuracy of at least 10^{-5}, which is 2 orders of magnitude tighter than the constraint placed by MeV neutrinos from supernova 1987A. Lorentz invariance violation (LIV) arises in various quantum-gravity theories, which predicts an energy-dependent velocity of propagation in vacuum for particles. We find that the association of the PeV neutrino with the gamma-ray outburst set limits on the energy scale of possible LIV to >0.01E_{pl} for linear LIV models and >6×10^{-8}E_{pl} for quadratic order LIV models, where E_{pl} is the Planck energy scale. These are the most stringent constraints on neutrino LIV for subluminal neutrinos.

Evaluation of the shape of the specular peak for high glossy surfaces

Science.gov (United States)

Obein, Gaël.; Ouarets, Shiraz; Ged, Guillaume

2014-02-01

Gloss is the second most relevant visual attribute of a surface beside its colour. While the colour originates from the wavelength repartition of the reflected light, gloss originates from its angular distribution. When an observer is asked to evaluate the gloss of a surface, he always first orientate his eyes along the specular direction before lightly tilting the examined sample. This means that gloss is located in and around the specular direction, in a peak that is called the specular peak. On the one hand, this peak is flat and broad on matte surfaces on the other hand, it is narrow and sharp on high gloss surfaces. For the late ones, the FWHM of the specular peak is less than 2° which can be quite difficult to measure. We developed a dedicated facility capable of measuring specular peak with a FWHM up to 0,1 °. We measured the evolution of the peak according to the angle of illumination and the specular gloss of the sample in the restricted field of very glossy surface. The facility and peaks measured are presented in the paper. The next step will be to identify the correlations between the peak and the roughness of the sample.

Towards high frequency heterojunction transistors: Electrical characterization of N-doped amorphous silicon-graphene diodes

Science.gov (United States)

Strobel, C.; Chavarin, C. A.; Kitzmann, J.; Lupina, G.; Wenger, Ch.; Albert, M.; Bartha, J. W.

2017-06-01

N-type doped amorphous hydrogenated silicon (a-Si:H) is deposited on top of graphene (Gr) by means of very high frequency (VHF) and radio frequency plasma-enhanced chemical vapor deposition (PECVD). In order to preserve the structural integrity of the monolayer graphene, a plasma excitation frequency of 140 MHz was successfully applied during the a-Si:H VHF-deposition. Raman spectroscopy results indicate the absence of a defect peak in the graphene spectrum after the VHF-PECVD of (n)-a-Si:H. The diode junction between (n)-a-Si:H and graphene was characterized using temperature dependent current-voltage (IV) and capacitance-voltage measurements, respectively. We demonstrate that the current at the (n)-a-Si:H-graphene interface is dominated by thermionic emission and recombination in the space charge region. The Schottky barrier height (qΦB), derived by temperature dependent IV-characteristics, is about 0.49 eV. The junction properties strongly depend on the applied deposition method of (n)-a-Si:H with a clear advantage of the VHF(140 MHz)-technology. We have demonstrated that (n)-a-Si:H-graphene junctions are a promising technology approach for high frequency heterojunction transistors.

High-frequency energy in singing and speech

Science.gov (United States)

Monson, Brian Bruce

While human speech and the human voice generate acoustical energy up to (and beyond) 20 kHz, the energy above approximately 5 kHz has been largely neglected. Evidence is accruing that this high-frequency energy contains perceptual information relevant to speech and voice, including percepts of quality, localization, and intelligibility. The present research was an initial step in the long-range goal of characterizing high-frequency energy in singing voice and speech, with particular regard for its perceptual role and its potential for modification during voice and speech production. In this study, a database of high-fidelity recordings of talkers was created and used for a broad acoustical analysis and general characterization of high-frequency energy, as well as specific characterization of phoneme category, voice and speech intensity level, and mode of production (speech versus singing) by high-frequency energy content. Directionality of radiation of high-frequency energy from the mouth was also examined. The recordings were used for perceptual experiments wherein listeners were asked to discriminate between speech and voice samples that differed only in high-frequency energy content. Listeners were also subjected to gender discrimination tasks, mode-of-production discrimination tasks, and transcription tasks with samples of speech and singing that contained only high-frequency content. The combination of these experiments has revealed that (1) human listeners are able to detect very subtle level changes in high-frequency energy, and (2) human listeners are able to extract significant perceptual information from high-frequency energy.

Retinal ganglion cells: mechanisms underlying depolarization block and differential responses to high frequency electrical stimulation of ON and OFF cells

Science.gov (United States)

Kameneva, T.; Maturana, M. I.; Hadjinicolaou, A. E.; Cloherty, S. L.; Ibbotson, M. R.; Grayden, D. B.; Burkitt, A. N.; Meffin, H.

2016-02-01

Objective. ON and OFF retinal ganglion cells (RGCs) are known to have non-monotonic responses to increasing amplitudes of high frequency (2 kHz) biphasic electrical stimulation. That is, an increase in stimulation amplitude causes an increase in the cell’s spike rate up to a peak value above which further increases in stimulation amplitude cause the cell to decrease its activity. The peak response for ON and OFF cells occurs at different stimulation amplitudes, which allows differential stimulation of these functional cell types. In this study, we investigate the mechanisms underlying the non-monotonic responses of ON and OFF brisk-transient RGCs and the mechanisms underlying their differential responses. Approach. Using in vitro patch-clamp recordings from rat RGCs, together with simulations of single and multiple compartment Hodgkin-Huxley models, we show that the non-monotonic response to increasing amplitudes of stimulation is due to depolarization block, a change in the membrane potential that prevents the cell from generating action potentials. Main results. We show that the onset for depolarization block depends on the amplitude and frequency of stimulation and reveal the biophysical mechanisms that lead to depolarization block during high frequency stimulation. Our results indicate that differences in transmembrane potassium conductance lead to shifts of the stimulus currents that generate peak spike rates, suggesting that the differential responses of ON and OFF cells may be due to differences in the expression of this current type. We also show that the length of the axon’s high sodium channel band (SOCB) affects non-monotonic responses and the stimulation amplitude that leads to the peak spike rate, suggesting that the length of the SOCB is shorter in ON cells. Significance. This may have important implications for stimulation strategies in visual prostheses.

Module Integrated GaN Power Stage for High Switching Frequency Operation

DEFF Research Database (Denmark)

Nour, Yasser; Knott, Arnold

2017-01-01

is integrated on a high glass transition temperature 0.4 mmthick FR4 substrate configured as a 70 pin ball grid arraypackage. The power stage is tested up to switching frequency of12 MHz. The power stage achieved 88.5 % peak efficiency whenconfigured as a soft switching buck converter operating at 7MHz......An increased attention has been detected todevelop smaller and lighter high voltage power converters in therange of 50 V to 400 V domains. The applications for theseconverters are mainly focused for Power over Ethernet (PoE),LED lighting and ac adapters. Design for high power density isone...... of the targets for next generation power converters. Thispaper presents an 80 V input capable multi-chip moduleintegration of enhancement mode gallium nitride (GaN) fieldeffect transistors (FETs) based power stage. The module design ispresented and validated through experimental results. The powerstage...

Differential effects of high-frequency versus low-frequency exercise training in rehabilitation of patients with coronary artery disease

NARCIS (Netherlands)

Nieuwland, W.; Berkhuysen, M.A.; van Veldhuisen, D.J.; Brugemann, J.; Landsman, M.L.J.; van Sonderen, E.; Lie, K.I.; Crijns, H.J.G.M.; Rispens, P.

2000-01-01

OBJECTIVES We sought to study the influence of frequency of exercise training during cardiac rehabilitation on functional capacity (i.e., peak oxygen consumption [VO2] and ventilatory anaerobic threshold [VAT]) and quality of life (QoL). BACKGROUND Although the value of cardiac rehabilitation is now

High-power, continuous-wave, solid-state, single-frequency, tunable source for the ultraviolet.

Science.gov (United States)

Aadhi, A; Apurv Chaitanya, N; Singh, R P; Samanta, G K

2014-06-15

We report the development of a compact, high-power, continuous-wave, single-frequency, ultraviolet (UV) source with extended wavelength tunability. The device is based on single-pass, intracavity, second-harmonic-generation (SHG) of the signal radiation of a singly resonant optical parametric oscillator (SRO) working in the visible and near-IR wavelength range. The SRO is pumped in the green with a 25-mm-long, multigrating, MgO doped periodically poled stoichiometric lithium tantalate (MgO:sPPLT) as nonlinear crystal. Using three grating periods, 8.5, 9.0, and 9.5 μm of the MgO:sPPLT crystal and a single set of cavity mirrors, the SRO can be tuned continuously across 710.7-836.3 nm in the signal and corresponding idler across 2115.8-1462.1 nm with maximum idler power of 1.9 W and maximum out-coupled signal power of 254 mW. By frequency-doubling the intracavity signal with a 5-mm-long bismuth borate (BIBO) crystal, we can further tune the SRO continuously over 62.8 nm across 355.4-418.2 nm in the UV with maximum single-frequency UV power, as much as 770 mW at 398.28 nm in a Gaussian beam profile. The UV radiation has an instantaneous line-width of ∼14.5  MHz and peak-peak frequency stability of 151 MHz over 100 s. More than 95% of the tuning range provides UV power >260  mW. Access to lower UV wavelengths can in principle be realized by operating the SRO in the visible using shorter grating periods.

Econometrics of financial high-frequency data

CERN Document Server

Hautsch, Nikolaus

2011-01-01

This book covers major approaches in high-frequency econometrics. It discusses implementation details, provides insights into properties of high-frequency data as well as institutional settings and presents applications.

Heterogeneous shear elasticity of glasses: The origin of the boson peak

KAUST Repository

Marruzzo, Alessia

2013-03-08

The local elasticity of glasses is known to be inhomogeneous on a microscopic scale compared to that of crystalline materials. Their vibrational spectrum strongly deviates from that expected from Debye\\'s elasticity theory: The density of states deviates from Debye\\'s law, the sound velocity shows a negative dispersion in the boson-peak frequency regime and there is a strong increase of the sound attenuation near the boson-peak frequency. By comparing a mean-field theory of shear-elastic heterogeneity with a large-scale simulation of a soft-sphere glass we demonstrate that the observed anomalies in glasses are caused by elastic heterogeneity. By observing that the macroscopic bulk modulus is frequency independent we show that the boson-peak-related vibrational anomalies are predominantly due to the spatially fluctuating microscopic shear stresses. It is demonstrated that the boson-peak arises from the steep increase of the sound attenuation at a frequency which marks the transition from wave-like excitations to disorder-dominated ones.

Heterogeneous shear elasticity of glasses: The origin of the boson peak

KAUST Repository

Marruzzo, Alessia; Schirmacher, Walter; Fratalocchi, Andrea; Ruocco, Giancarlo

2013-01-01

The local elasticity of glasses is known to be inhomogeneous on a microscopic scale compared to that of crystalline materials. Their vibrational spectrum strongly deviates from that expected from Debye's elasticity theory: The density of states deviates from Debye's law, the sound velocity shows a negative dispersion in the boson-peak frequency regime and there is a strong increase of the sound attenuation near the boson-peak frequency. By comparing a mean-field theory of shear-elastic heterogeneity with a large-scale simulation of a soft-sphere glass we demonstrate that the observed anomalies in glasses are caused by elastic heterogeneity. By observing that the macroscopic bulk modulus is frequency independent we show that the boson-peak-related vibrational anomalies are predominantly due to the spatially fluctuating microscopic shear stresses. It is demonstrated that the boson-peak arises from the steep increase of the sound attenuation at a frequency which marks the transition from wave-like excitations to disorder-dominated ones.

Efficient high-peak-power and high-repetition-rate eye-safe laser using an intracavity KTP OPO

International Nuclear Information System (INIS)

Guo, J; Jiao, Z X; Wang, B; He, G Y

2015-01-01

An efficient high-peak-power and high-repetition-rate intracavity KTP optical parametric oscillator pumped by a Q-switched Nd:YVO 4 laser is demonstrated. We achieved 1.5 W output power of 1.5 μm at 10 kHz repetition rate with the pulse duration of 6 ns. The maximum peak power of 25 kW and the maximum pulse energy of 150 μJ have been obtained. The maximum conversion efficiency of 9.5% is achieved with respect to a laser diode power of 10.5 W. (paper)

Optical flare observed in the flaring gamma-ray blazar CGRaBS J0809+5341 (87GB 080551.6+535010)

Science.gov (United States)

Pursimo, Tapio; Galindo-Guil, F. J.; Serrano, Pere Blay; Ojha, Roopesh

2017-11-01

We report optical photometry of the blazar CGRaBS J0809+5341 (87GB 080551.6+535010), obtained with the 2.56m Nordic Optical Telescope in La Palma, to look for any enhanced optical activity associated with a recent flare in the daily averaged gamma-ray flux (ATel#10905).

Frequency Domain Electroretinography in Retinitis Pigmentosa versus Normal Eyes

Directory of Open Access Journals (Sweden)

Homa Hassan-Karimi

2012-01-01

Full Text Available Purpose: To compare electroretinogram (ERG characteristics in patients with retinitis pigmentosa (RP and normal subjects using frequency domain analysis. Methods: Five basic ERG recordings were performed in normal subjects and patients with a clinical diagnosis of RP according to the ISCEV (International Society of Clinical Electrophysiology of Vision protocol. Frequency domain analysis was performed by MATLAB software. Different frequency domain parameters were compared between the study groups. Results: Peak frequency (Fmod of flicker and oscillatory responses in RP patients showed significant (P<0.0001 high pass response as compared to normal controls. Peak frequency (Fmod of the other responses was not significantly different between the two groups. Conclusion: In addition to conventional ERG using time domain methods, frequency domain analysis may be useful for diagnosis of RP. Oscillatory and flicker responses may be analyzed in frequency domain. Fast Fourier transform may reveal two distinct high pass responses (shift to higher frequencies in Fmod. Time and frequency domain analyses may be performed simultaneously with many modern ERG machines and may therefore be recommended in RP patients.

Searches for high frequency variations in the 8-B neutrino flux at the Sudbury neutrino observatory

Energy Technology Data Exchange (ETDEWEB)

Rielage, Keith [Los Alamos National Laboratory; Seibert, Stanley R [Los Alamos National Laboratory; Hime, Andrew [Los Alamos National Laboratory; Elliott, Steven R [Los Alamos National Laboratory; Stonehill, L C [Los Alamos National Laboratory; Wouters, J M [Los Alamos National Laboratory; Aharmim, B [LAURENTIAN UNIV; Ahmed, S N [QUEEN' S UNIV; Anthony, A E [UNIV OF TEXAS; Barros, N [PORTUGAL; Beier, E W [UNIV OF PA; Bellerive, A [CARLETON UNIV; Belttran, B [UNIV OF ALBERTA; Bergevin, M [LBNL; Biller, S D [UNIV OF OXFORD; Boudjemline, K [CARLETON UNIV; Burritt, T H [UNIV OF WASHINGTON; Cai, B [QUEEN' S UNIV; Chan, Y D [LBNL; Chauhan, D [LAURENTIAN UNIV; Chen, M [QUEEN' S UNIV; Cleveland, B T [UNIV OF OXFORD; Cox - Mobrand, G A [UNIV OF WASHINGTON; Dai, X [QUEEN' S UNIV; Deng, H [UNIV OF PA; Detwiler, J [LBNL; Dimarco, M [QUEEN' S UNIV; Doe, P J [UNIV OF WASHINGTON; Drouin, P - L [CARLTON UNIV; Duba, C A [UNIV OF WASHINGTON; Duncan, F A [SNOLAB, SUDBURY; Dunford, M [UNIV OF PA; Earle, E D [QUEEN' S UNIV; Evans, H C [QUEEN' S UNIV; Ewan, G T [QUEEN' S UNIV; Farine, J [LAURENTTIAN UNIV; Fergani, H [UNIV OF OXFORD; Fleurot, F [LAURENTIAN UNIV; Ford, R J [SNOLAB, SUDBURY; Formaggilo, J A [MASSACHUSETTS INST. OF TECH.; Gagnon, N [UNIV OF WASHINGTON; Goon, J Tm [LOUISIANA STATE UNIV; Guillian, E [QUEEN' S UNIV; Habib, S [UNIV OF ALBERTA; Hahn, R L [BNL; Hallin, A L [UNIV OF ALBERTA; Hallman, E D [LAURENTIAN UNIV; Harvey, P J [QUEEN' S UNIV; Hazama, R [UNIV OF WASHINGTON; Heintzelman, W J [UNIV OF PA; Heise, J [SNOLAB, SUDBURY; Helmer, R L [TRIUMF; Howard, C [UNIV OF ALBERTA; Howe, M A [UNIV OF WASHINGTON; Huang, M [UNIV OF TEXAS; Jamieson, B [UNIV OF BRITISH COLUMBIA; Jelley, N A [UNIV OF OXFORD; Keeter, K J [SNOLAB, SUDBURY; Klein, J R [UNIV OF TEXAS; Kos, M [QUEEN' S UNIV; Kraus, C [QUEEN' S UNIV; Krauss, C B [UNIV OF ALBERTA; Kutter, T [LOUISIANA STATE UNIV; Kyba, C C M [UNIV OF PA; Law, J [UNIV OF GUELPH; Lawson, I T [SNOLAB, SUDBURY; Lesko, K T [LBNL; Leslie, J R [QUEEN' S UNIV; Loach, J C [UNIV OF OXFORD; Maclellan, R [QUEEN' S UNIV; Majerus, S [UNIV OF OXFORD; Mak, H B [QUEEN' S UNIV; Maneira, J [PORTUGAL; Martin, R [QUEEN' S UNIV; Mccauley, N [UNIV OF PA; Mc Donald, A B [QUEEN' S UNIV; Mcgee, S [UNIV OF WASHINGTON; Miffin, C [CARLETON UNIV; Miller, M L [MASSACHUSETTS INST. OF TECH.; Monreal, B [MASSACHUSETTS INST. OF TECH.; Monroe, J [MASSACHUSETTS INST. OF TECH; Morissette, B [SNOLAB, SUDBURY; Nickel, B G [UNIV OF GUELPH; Noble, A J [QUEEN' S UNIV; O' Keeffe, H M [UNIV OF OXFORD; Oblath, N S [UNIV OF WASHINGTON; Orebi Gann, G D [UNIV OF OXFORD; Oser, S M [UNIV OF BRITISH COLUMBIA; Ott, R A [MASSACHUSETTS INST. OF TECH.; Peeters, S J M [UNIV OF OXFORD; Poon, A W P [LBNL; Prior, G [LBNL; Reitzner, S D [UNIV OF GUELPH; Robertson, B C [QUEEN' S UNIV; Robertson, R G H [UNIV OF WASHINGTON; Rollin, E [CARLETON UNIV; Schwendener, M H [LAURENTIAN UNIV; Secrest, J A [UNIV OF PA; Seibert, S R [UNIV OF TEXAS; Simard, O [CARLETON UNIV; Sinclair, D [CARLETON UNIV; Sinclair, L [CARLETON UNIV; Skensved, P [QUEEN' S UNIV; Sonley, T J [MASSACHUSETTS INST. OF TECH.; Tesic, G [CARLETON UNIV; Tolich, N [UNIV OF WASHINGTON; Tsui, T [UNIV OF BRITISH COLUMBIA; Tunnell, C D [UNIV OF TEXAS; Van Berg, R [UNIV OF PA; Van Devender, B A [UNIV OF WASHINGTON; Virtue, C J [LAURENTIAN UNIV; Wall, B L [UNIV OF WASHINGTON; Waller, D [CARLETON UNIV; Wan Chan Tseung, H [UNIV OF OXFORD; West, N [UNIV OF OXFORD; Wilkerson, J F [UNIV OF WASHINGTON; Wilson, J R [UNIV OF OXFORD; Wright, A [QUEEN' S UNIV; Yeh, M [BNL; Zhang, F [CARLETON UNIV; Zuber, K [UNIV OF OXFORD

2009-01-01

We have peformed three searches for high-frequency signals in the solar neutrino flux measured by the Sudbury Neutrino Observatory (SNO), motivated by the possibility that solar g-mode oscillations could affect the production or propagation of solar {sup 8}B neutrinos. The first search looked for any significant peak in the frequency range l/day to 144/day, with a sensitivity to sinusoidal signals with amplitudes of 12% or greater. The second search focused on regions in which g-mode signals have been claimed by experiments aboard the SoHO satellite, and was sensitive to signals with amplitudes of 10% or greater. The third search looked for extra power across the entire frequency band. No statistically significant signal was detected in any of the three searches.

Peak activation of lower limb musculature during high flexion kneeling and transitional movements.

Science.gov (United States)

Kingston, David C; Tennant, Liana M; Chong, Helen C; Acker, Stacey M

2016-09-01

Few studies have measured lower limb muscle activation during high knee flexion or investigated the effects of occupational safety footwear. Therefore, our understanding of injury and disease mechanisms, such as knee osteoarthritis, is limited for these high-risk postures. Peak activation was assessed in eight bilateral lower limb muscles for twelve male participants, while shod or barefoot. Transitions between standing and kneeling had peak quadriceps and tibialis anterior (TA) activations above 50% MVC. Static kneeling and simulated tasks performed when kneeling had peak TA activity above 15% MVC but below 10% MVC for remaining muscles. In three cases, peak muscle activity was significantly higher (mean 8.9% MVC) when shod. However, net compressive knee joint forces may not be significantly increased when shod. EMG should be used as a modelling input when estimating joint contact forces for these postures, considering the activation levels in the hamstrings and quadriceps muscles during transitions. Practitioner Summary: Kneeling transitional movements are used in activities of daily living and work but are linked to increased knee osteoarthritis risk. We found peak EMG activity of some lower limb muscles to be over 70% MVC during transitions and minimal influence of wearing safety footwear.

OPTICAL AND INFRARED PHOTOMETRY OF THE BLAZAR PKS 0537-441: LONG AND SHORT TIMESCALE VARIABILITY

International Nuclear Information System (INIS)

Impiombato, D.; Treves, A.; Covino, S.; Foschini, L.; Fugazza, D.; Pian, E.; Tosti, G.; Ciprini, S.; Nicastro, L.

2011-01-01

We present a large collection of photometric data on the blazar PKS 0537-441 in the VRIJHK bands taken in 2004-2009. At least three flare-like episodes with months duration and >3 mag amplitude are apparent. The spectral energy distribution is consistent with a power law, and no indication of a thermal component is found. We searched for short timescale variability, and an interesting event was identified in the J band, with a duration of ∼25 minutes.

Energy peaks: A high energy physics outlook

Science.gov (United States)

Franceschini, Roberto

2017-12-01

Energy distributions of decay products carry information on the kinematics of the decay in ways that are at the same time straightforward and quite hidden. I will review these properties and discuss their early historical applications, as well as more recent ones in the context of (i) methods for the measurement of masses of new physics particle with semi-invisible decays, (ii) the characterization of Dark Matter particles produced at colliders, (iii) precision mass measurements of Standard Model particles, in particular of the top quark. Finally, I will give an outlook of further developments and applications of energy peak method for high energy physics at colliders and beyond.

High-frequency homogenization of zero frequency stop band photonic and phononic crystals

CERN Document Server

Antonakakis, Tryfon; Guenneau, Sebastien

2013-01-01

We present an accurate methodology for representing the physics of waves, for periodic structures, through effective properties for a replacement bulk medium: This is valid even for media with zero frequency stop-bands and where high frequency phenomena dominate. Since the work of Lord Rayleigh in 1892, low frequency (or quasi-static) behaviour has been neatly encapsulated in effective anisotropic media. However such classical homogenization theories break down in the high-frequency or stop band regime. Higher frequency phenomena are of significant importance in photonics (transverse magnetic waves propagating in infinite conducting parallel fibers), phononics (anti-plane shear waves propagating in isotropic elastic materials with inclusions), and platonics (flexural waves propagating in thin-elastic plates with holes). Fortunately, the recently proposed high-frequency homogenization (HFH) theory is only constrained by the knowledge of standing waves in order to asymptotically reconstruct dispersion curves an...

High precision 16K, 16 channel peak sensing CAMAC ADC

International Nuclear Information System (INIS)

Jain, Mamta; Subramaniam, E.T

2013-01-01

A high density, peak sensing, analog to digital converter (ADC) double width module with CAMAC back plane has been developed for nuclear physics experiments with a large number of detectors. This module has sixteen independent channels in plug-in daughter card mother board mode

An evaluation of peak inspiratory pressure, tidal volume, and ventilatory frequency during ventilation with a neonatal self-inflating bag resuscitator.

Science.gov (United States)

Bassani, Mariana Almada; Filho, Francisco Mezzacappa; de Carvalho Coppo, Maria Regina; Martins Marba, Sérgio Tadeu

2012-04-01

Although the self-inflating bag is widely used in the hospital setting, variability of delivered ventilatory parameters is usually high, which might result in both hypoventilation and lung injury. The aims of this study were to assess possible sources of the high variability and to evaluate the adequacy of obtained values in relation to the recommended values for neonatal resuscitation. This was an experimental study in which 172 health professionals (physicians, resident physicians, physiotherapists, nurses, and nursing technicians) who work with neonatal intensive care manually ventilated a test lung (adjusted to simulate the lungs of an intubated term newborn) with a self-inflating bag in 5 different handling techniques, using 10, 5, 4, 3, and 2 fingers. Delivered values of peak inspiratory pressure (PIP), tidal volume (V(T)), and ventilatory frequency (f) were compared, taking into account the different handling modalities and professions by analysis of variance for repeated measures. Chi-square, the Friedman test and the Fisher exact tests were performed to compare the delivered and standard values. PIP and V(T) were significantly affected by the handling technique, with higher values for a greater number of fingers used for ventilation. Profession also influenced V(T) and f significantly: physiotherapists tended to deliver higher volumes and lower rates. Nevertheless, we observed high variability of all studied ventilatory parameters and overall inadequacy of obtained values. Most volunteers delivered excessive pressures and volumes at insufficient ventilatory frequency. Delivered values seem to depend on operators' individual and professional differences, as well as on the number of fingers used to compress the bag. However, from the clinical point of view, it is important to point out the high occurrence of inadequate delivered values, regardless of handling technique and profession.

A beam-synchronous gated peak-detector for the LHC beam observation system

CERN Document Server

Levens, T E; Wehrle, U

2013-01-01

Measurements of the bunch peak amplitude using the longitudinal wideband wall-current monitor are a vital tool used in the Large Hadron Collider (LHC) beam observation system. These peak-detected measurements can be used to diagnose bunch shape oscillations, for example coherent quadrupole oscillations, that occur at injection and during beam manipulations. Peak-detected Schottky diagnostics can also be used to obtain the synchrotron frequency distribution and other parameters from a bunched beam under stable conditions. For the LHC a beam-synchronous gated peak detector has been developed to allow individual bunches to be monitored without the influence of other bunches circulating in the machine. The requirement for the observation of both low intensity pilot bunches and high intensity bunches for physics requires a detector front-end with a high bandwidth and a large dynamic range while the usage for Schottky measurements requires low noise electronics. This paper will present the design of this detector s...

On the Importance of High Frequency Gravity Waves for Ice Nucleation in the Tropical Tropopause Layer

Science.gov (United States)

Jensen, Eric J.

2016-01-01

Recent investigations of the influence of atmospheric waves on ice nucleation in cirrus have identified a number of key processes and sensitivities: (1) ice concentrations produced by homogeneous freezing are strongly dependent on cooling rates, with gravity waves dominating upper tropospheric cooling rates; (2) rapid cooling driven by high-frequency waves are likely responsible for the rare occurrences of very high ice concentrations in cirrus; (3) sedimentation and entrainment tend to decrease ice concentrations as cirrus age; and (4) in some situations, changes in temperature tendency driven by high-frequency waves can quench ice nucleation events and limit ice concentrations. Here we use parcel-model simulations of ice nucleation driven by long-duration, constant-pressure balloon temperature time series, along with an extensive dataset of cold cirrus microphysical properties from the recent ATTREX high-altitude aircraft campaign, to statistically examine the importance of high-frequency waves as well as the consistency between our theoretical understanding of ice nucleation and observed ice concentrations. The parcel-model simulations indicate common occurrence of peak ice concentrations exceeding several hundred per liter. Sedimentation and entrainment would reduce ice concentrations as clouds age, but 1-D simulations using a wave parameterization (which underestimates rapid cooling events) still produce ice concentrations higher than indicated by observations. We find that quenching of nucleation events by high-frequency waves occurs infrequently and does not prevent occurrences of large ice concentrations in parcel simulations of homogeneous freezing. In fact, the high-frequency variability in the balloon temperature data is entirely responsible for production of these high ice concentrations in the simulations.

Effect of ischemia and cooling on the response to high frequency stimulation in rat tail nerves

DEFF Research Database (Denmark)

Andersen, H.; Nielsen, J.F.; Sørensen, B.

2000-01-01

In normal rat tail nerves the effect of temperature and ischemia on the response to long-term high frequency stimulation (HFS) (143 Hz) was studied. The effect of temperature was studied in two consecutive tests at 14 degrees C and 35 degrees C. Prior to the HFS the peak-to-peak amplitude (PP......-amp) of the compound nerve action potential was 139 +/- 20 microV (mean +/- SD) and 127 +/- 37 microV at 35 degrees C and 14 degrees C, respectively (NS). After 15 min of HFS the PP-amp was reduced to 45.3 +/- 20.5% of baseline level at 14 degrees C as compared with 80.8 +/- 10.2% at 35 degrees C (p

A low-frequency asymptotic model of seismic reflection from a high-permeability layer

Energy Technology Data Exchange (ETDEWEB)

Silin, Dmitriy; Goloshubin, Gennady

2009-03-01

Analysis of compression wave propagation through a high-permeability layer in a homogeneous poroelastic medium predicts a peak of reflection in the low-frequency end of the spectrum. An explicit formula expresses the resonant frequency through the elastic moduli of the solid skeleton, the permeability of the reservoir rock, the fluid viscosity and compressibility, and the reservoir thickness. This result is obtained through a low-frequency asymptotic analysis of the Biot's model of poroelasticity. A new physical interpretation of some coefficients of the classical poroelasticity is a result of the derivation of the main equations from the Hooke's law, momentum and mass balance equations, and the Darcy's law. The velocity of wave propagation, the attenuation factor, and the wave number, are expressed in the form of power series with respect to a small dimensionless parameter. The latter is equal to the product of the kinematic reservoir fluid mobility, an imaginary unit, and the frequency of the signal. Retaining only the leading terms of the series leads to explicit and relatively simple expressions for the reflection and transmission coefficients for a planar wave crossing an interface between two permeable media, as well as wave reflection from a thin highly-permeable layer (a lens). The practical implications of the theory developed here are seismic modeling, inversion, and attribute analysis.

High-frequency EPR on high-spin transition-metal sites

NARCIS (Netherlands)

Mathies, Guinevere

2012-01-01

The electronic structure of transition-metal sites can be probed by electron-paramagnetic-resonance (EPR) spectroscopy. The study of high-spin transition-metal sites benefits from EPR spectroscopy at frequencies higher than the standard 9.5 GHz. However, high-frequency EPR is a developing field. In

Sharp or broad pulse peak for high resolution instruments? Choice of moderator performance

International Nuclear Information System (INIS)

Arai, M.; Watanabe, N.; Teshigawara, M.

2001-01-01

We demonstrate a concept how we should choose moderator performance to realize required performance for instruments. Neutron burst pulse can be characterized with peak intensity, peak width and tail. Those can be controllable by designing moderator, i.e. material, temperature, shape, decoupling, poisoning and having premoderator. Hence there are large number of variable parameters to be determined. Here we discuss the required moderator performance for some typical examples, i.e. high resolution powder instrument, chopper instrument, high resolution back scattering machine. (author)

Time resolved measurements of cathode fall in high frequency fluorescent lamps

International Nuclear Information System (INIS)

Hadrath, S; Garner, R C; Lieder, G H; Ehlbeck, J

2007-01-01

Measurements are presented of the time resolved cathode and anode falls of high frequency fluorescent lamps for a range of discharge currents typically encountered in dimming mode. Measurements were performed with the movable anode technique. Supporting spectroscopic emission measurements were made of key transitions (argon 420.1 nm and mercury 435.8 nm), whose onset coincide with cathode fall equalling the value associated with the energy, relative to the ground state, of the upper level of the respective transition. The measurements are in general agreement with the well-known understanding of dimmed lamp operation: peak cathode fall decreases with increasing lamp current and with increasing auxiliary coil heating. However, the time dependence of the measurements offers additional insight

Determination of trapping parameters of the high temperature thermoluminescence peak in equilibrated ordinary chondrites

International Nuclear Information System (INIS)

Akridge, Jannette M.C.; Benoit, Paul H.; Sears, Derek W.G.

2001-01-01

Most meteorites exhibit thermoluminescence (TL) that can be used to constrain their recent thermal and irradiation history, but quantitative conclusions require a knowledge of the detailed TL peak structure of the TL glow curve. We have determined TL peak parameters for the high temperature portion of the glow curve for six ordinary chondrites: Chicora (LL6); Innisfree (L5); Lost City (H5); Paragould (LL6); Pribram (H5); and Tilden (L6). The saturation dose for all these meteorites is approximately 3600 Gy. Published procedures were used to determine the number and temperatures of peaks in the high temperature (>570 K) portion of the glow curve and peak fitting was used to estimate TL trap parameters for each peak. These data were then tested and adjusted, if necessary, by comparing calculated decay results with TL glow curves for samples heated at ∼420 K for various times. We find evidence for four TL peaks in the high temperature portion of the glow curve, where trapping parameters vary slightly from meteorite to meteorite. For the Lost City meteorite, the TL peak temperatures (K), activation energies (E, eV), and Arrhenius factors (s, x 10 -9 s -1 ) are: 325, 1.26, 4.8; 360, 1.33, 3.88; 401, 1.44, 5.8; and 455, 1.5, 2.25, respectively. These data could be used to estimate dose rates for meteorites; however, the albedo values required for the calculation are not yet sufficiently known. However, terrestrial ages, or surface exposure ages, for meteorite finds from hot deserts like those in Australia or North Africa, can be estimated from these data

Determination of trapping parameters of the high temperature thermoluminescence peak in equilibrated ordinary chondrites

Energy Technology Data Exchange (ETDEWEB)

Akridge, Jannette M.C.; Benoit, Paul H. E-mail: pbenoit@comp.uark.edu; Sears, Derek W.G

2001-02-01

Most meteorites exhibit thermoluminescence (TL) that can be used to constrain their recent thermal and irradiation history, but quantitative conclusions require a knowledge of the detailed TL peak structure of the TL glow curve. We have determined TL peak parameters for the high temperature portion of the glow curve for six ordinary chondrites: Chicora (LL6); Innisfree (L5); Lost City (H5); Paragould (LL6); Pribram (H5); and Tilden (L6). The saturation dose for all these meteorites is approximately 3600 Gy. Published procedures were used to determine the number and temperatures of peaks in the high temperature (>570 K) portion of the glow curve and peak fitting was used to estimate TL trap parameters for each peak. These data were then tested and adjusted, if necessary, by comparing calculated decay results with TL glow curves for samples heated at {approx}420 K for various times. We find evidence for four TL peaks in the high temperature portion of the glow curve, where trapping parameters vary slightly from meteorite to meteorite. For the Lost City meteorite, the TL peak temperatures (K), activation energies (E, eV), and Arrhenius factors (s, x 10{sup -9} s{sup -1}) are: 325, 1.26, 4.8; 360, 1.33, 3.88; 401, 1.44, 5.8; and 455, 1.5, 2.25, respectively. These data could be used to estimate dose rates for meteorites; however, the albedo values required for the calculation are not yet sufficiently known. However, terrestrial ages, or surface exposure ages, for meteorite finds from hot deserts like those in Australia or North Africa, can be estimated from these data.

Feature selection and classifier parameters estimation for EEG signals peak detection using particle swarm optimization.

Science.gov (United States)

Adam, Asrul; Shapiai, Mohd Ibrahim; Tumari, Mohd Zaidi Mohd; Mohamad, Mohd Saberi; Mubin, Marizan

2014-01-01

Electroencephalogram (EEG) signal peak detection is widely used in clinical applications. The peak point can be detected using several approaches, including time, frequency, time-frequency, and nonlinear domains depending on various peak features from several models. However, there is no study that provides the importance of every peak feature in contributing to a good and generalized model. In this study, feature selection and classifier parameters estimation based on particle swarm optimization (PSO) are proposed as a framework for peak detection on EEG signals in time domain analysis. Two versions of PSO are used in the study: (1) standard PSO and (2) random asynchronous particle swarm optimization (RA-PSO). The proposed framework tries to find the best combination of all the available features that offers good peak detection and a high classification rate from the results in the conducted experiments. The evaluation results indicate that the accuracy of the peak detection can be improved up to 99.90% and 98.59% for training and testing, respectively, as compared to the framework without feature selection adaptation. Additionally, the proposed framework based on RA-PSO offers a better and reliable classification rate as compared to standard PSO as it produces low variance model.

Reduction of chemical formulas from the isotopic peak distributions of high-resolution mass spectra.

Science.gov (United States)

Roussis, Stilianos G; Proulx, Richard

2003-03-15

A method has been developed for the reduction of the chemical formulas of compounds in complex mixtures from the isotopic peak distributions of high-resolution mass spectra. The method is based on the principle that the observed isotopic peak distribution of a mixture of compounds is a linear combination of the isotopic peak distributions of the individual compounds in the mixture. All possible chemical formulas that meet specific criteria (e.g., type and number of atoms in structure, limits of unsaturation, etc.) are enumerated, and theoretical isotopic peak distributions are generated for each formula. The relative amount of each formula is obtained from the accurately measured isotopic peak distribution and the calculated isotopic peak distributions of all candidate formulas. The formulas of compounds in simple spectra, where peak components are fully resolved, are rapidly determined by direct comparison of the calculated and experimental isotopic peak distributions. The singular value decomposition linear algebra method is used to determine the contributions of compounds in complex spectra containing unresolved peak components. The principles of the approach and typical application examples are presented. The method is most useful for the characterization of complex spectra containing partially resolved peaks and structures with multiisotopic elements.

Improvement of the XANAM System and Acquisition of a Peak Signal with a High S/N ratio

International Nuclear Information System (INIS)

Suzuki, S; Nakamura, M; Kinoshita, K; Koike, Y; Fujikawa, K; Matsudaira, N; Chun, W-J; Nomura, M; Asakura, K

2007-01-01

We have made remarkable progress in detecting X-ray-induced frequency shift signals, which will promote development of a chemically sensitive NC-AFM. A highperformance controller provides a tenfold higher signal to noise ratio than that previously reported. We confirmed that the frequency shift or complementary Z-feedback signal dependence on X-ray energy has a peak. An important feature of the signal is that it does not follow the absorption spectrum of a surface element. These new findings are important to elucidate this novel X-ray-induced phenomenon

Environmental impacts of public transport. Why peak-period travellers cause a greater environmental burden than off-peak travellers

International Nuclear Information System (INIS)

Rietveld, P.

2002-01-01

Given the difference between peak and off-peak occupancy rates in public transport, emissions per traveller kilometre are lower in the peak than in the off-peak period, whereas the opposite pattern is observed for cars. It is argued that it is much more fruitful to analyse environmental effects in marginal terms. This calls for a careful analysis of capacity management policies of public transport suppliers that are facing increased demand during both peak and off-peak periods. A detailed analysis of capacity management by the Netherlands Railways (NS) revealed that off-peak capacity supply is mainly dictated by the demand levels during the peak period. The analysis included the effects of increased frequency and increased vehicle size on environmental impacts, while environmental economies of vehicle size were also taken into account. The main conclusion is that the marginal environmental burden during the peak hours is much higher than is usually thought, whereas it is almost zero during the off-peak period. This implies a pattern that is the precise opposite of the average environmental burden. Thus, an analysis of environmental effects of public transport based on average performance would yield misleading conclusions [nl

High Frequency Components Recovery in Music Signals

Directory of Open Access Journals (Sweden)

V. Sebesta

1999-04-01

Full Text Available A new technique is presented which improves the subjective quality of band-limited music by recovery of high frequency components. Sequences of harmonics are found in the band-limited signal and these sequences are expanded to the high frequency band to estimate the lost part of spectrum. High frequency signal is generated to match this estimation and is added to the band-limited signal.

High Frequency Near-Field Ground Motion Excited by Strike-Slip Step Overs

Science.gov (United States)

Hu, Feng; Wen, Jian; Chen, Xiaofei

2018-03-01

We performed dynamic rupture simulations on step overs with 1-2 km step widths and present their corresponding horizontal peak ground velocity distributions in the near field within different frequency ranges. The rupture speeds on fault segments are determinant in controlling the near-field ground motion. A Mach wave impact area at the free surface, which can be inferred from the distribution of the ratio of the maximum fault-strike particle velocity to the maximum fault-normal particle velocity, is generated in the near field with sustained supershear ruptures on fault segments, and the Mach wave impact area cannot be detected with unsustained supershear ruptures alone. Sub-Rayleigh ruptures produce stronger ground motions beyond the end of fault segments. The existence of a low-velocity layer close to the free surface generates large amounts of high-frequency seismic radiation at step over discontinuities. For near-vertical step overs, normal stress perturbations on the primary fault caused by dipping structures affect the rupture speed transition, which further determines the distribution of the near-field ground motion. The presence of an extensional linking fault enhances the near-field ground motion in the extensional regime. This work helps us understand the characteristics of high-frequency seismic radiation in the vicinities of step overs and provides useful insights for interpreting the rupture speed distributions derived from the characteristics of near-field ground motion.

High-Frequency Seafloor Acoustics

CERN Document Server

Jackson, Darrell R

2007-01-01

High-Frequency Seafloor Acoustics is the first book in a new series sponsored by the Office of Naval Research on the latest research in underwater acoustics. This exciting new title provides ready access to experimental data, theory, and models relevant to high-frequency seafloor acoustics and will be of interest to sonar engineers and researchers working in underwater acoustics. The physical characteristics of the seafloor affecting acoustic propagation and scattering are covered, including physical and geoacoustic properties and surface roughness. Current theories for acoustic propagation in sediments are presented along with corresponding models for reflection, scattering, and seafloor penetration. The main text is backed up by an extensive bibliography and technical appendices.

Comparative study of boson peak in normal and secondary alcohols with terahertz time-domain spectroscopy

International Nuclear Information System (INIS)

Yomogida, Yoshiki; Sato, Yuki; Nozaki, Ryusuke; Mishina, Tomobumi; Nakahara, Jun'ichiro

2010-01-01

Using terahertz (THz) time-domain spectroscopy, we measured the complex permittivity of some normal (1-propanol, 1-butanol, and 1-pentanol) and secondary alcohols (2-propanol, 2-butanol, and 2-pentanol) in the frequency ranges from 0.2 to 2.5 THz at temperatures from 253 to 323 K. For all the samples, the complex permittivity in the THz region includes the following three components: (i) a high frequency side of dielectric relaxation processes, (ii) a broad mode around 1 THz, and (iii) a low frequency side of an intermolecular vibration mode located above 2.5 THz. The mode around 1 THz is recognized as a boson peak which is related to the local structure of disordered materials. The intensity of the boson peak in secondary alcohols is higher than that in normal alcohols. On the other hand, the number of carbon atoms slightly affects the appearance of the boson peak. These observations indicate that the position of an OH group in a molecule has a profound effect on the local structures in monohydric alcohols.

High frequency monitoring of pesticides in runoff water to improve understanding of their transport and environmental impacts.

Science.gov (United States)

Lefrancq, Marie; Jadas-Hécart, Alain; La Jeunesse, Isabelle; Landry, David; Payraudeau, Sylvain

2017-06-01

Rainfall-induced peaks in pesticide concentrations can occur rapidly. Low frequency sampling may therefore largely underestimate maximum pesticide concentrations and fluxes. Detailed storm-based sampling of pesticide concentrations in runoff water to better predict pesticide sources, transport pathways and toxicity within the headwater catchments is lacking. High frequency monitoring (2min) of seven pesticides (Dimetomorph, Fluopicolide, Glyphosate, Iprovalicarb, Tebuconazole, Tetraconazole and Triadimenol) and one degradation product (AMPA) were assessed for 20 runoff events from 2009 to 2012 at the outlet of a vineyard catchment in the Layon catchment in France. The maximum pesticide concentrations were 387μgL -1 . Samples from all of the runoff events exceeded the legal limit of 0.1μgL -1 for at least one pesticide (European directive 2013/39/EC). High resolution sampling used to detect the peak pesticide levels revealed that Toxic Units (TU) for algae, invertebrates and fish often exceeded the European Uniform principles (25%). The point and average (time or discharge-weighted) concentrations indicated up to a 30- or 4-fold underestimation of the TU obtained when measuring the maximum concentrations, respectively. This highlights the important role of sampling methods for assessing peak exposure. High resolution sampling combined with concentration-discharge hysteresis analyses revealed that clockwise responses were predominant (52%), indicating that Hortonian runoff is the prevailing surface runoff trigger mechanism in the study catchment. The hysteresis patterns for suspended solids and pesticides were highly dynamic and storm- and chemical-dependent. Intense rainfall events induced stronger C-Q hysteresis (magnitude). This study provides new insights into the complexity of pesticide dynamics in runoff water and highlights the ability of hysteresis analysis to improve understanding of pesticide supply and transport. Copyright © 2017 Elsevier B.V. All

Multiwavelength Picture of the Blazar S5 0716+714 during Its Brightest Outburst

Directory of Open Access Journals (Sweden)

Marina Manganaro

2016-11-01

Full Text Available S5 0716+714 is a well known BL Lac object, and one of the brightest and most active blazars. The discovery in the Very High Energy band (VHE, E > 100 GeV by MAGIC happened in 2008. In January 2015, the source went through the brightest optical state ever observed, triggering MAGIC follow-up and a VHE detection with ∼ 13 σ significance (ATel ♯ 6999 . Rich multiwavelength coverage of the flare allowed us to construct the broad-band spectral energy distribution of S5 0716+714 during its brightest outburst. In this work, we will present the preliminary analysis of MAGIC and Fermi-LAT data of the flaring activity in January and February 2015 for the HE (0.1 < HE < 300 GeV and VHE band, together with radio (Metsähovi, OVRO, VLBA, Effelsberg, sub-millimeter (SMA, optical (Tuorla, Perkins, Steward, AZT-8+ST7, LX-200, Kanata, X-ray and UV (Swift-XRT and UVOT, in the same time-window and discuss the time variability of the multiwavelength light curves during this impressive outburst.

Compact, Energy-Efficient High-Frequency Switched Capacitor Neural Stimulator With Active Charge Balancing.

Science.gov (United States)

Hsu, Wen-Yang; Schmid, Alexandre

2017-08-01

Safety and energy efficiency are two major concerns for implantable neural stimulators. This paper presents a novel high-frequency, switched capacitor (HFSC) stimulation and active charge balancing scheme, which achieves high energy efficiency and well-controlled stimulation charge in the presence of large electrode impedance variations. Furthermore, the HFSC can be implemented in a compact size without any external component to simultaneously enable multichannel stimulation by deploying multiple stimulators. The theoretical analysis shows significant benefits over the constant-current and voltage-mode stimulation methods. The proposed solution was fabricated using a 0.18 μm high-voltage technology, and occupies only 0.035 mm 2 for a single stimulator. The measurement result shows 50% peak energy efficiency and confirms the effectiveness of active charge balancing to prevent the electrode dissolution.

LES-based generation of high-frequency fluctuation in wind turbulence obtained by meteorological model

Science.gov (United States)

Tamura, Tetsuro; Kawaguchi, Masaharu; Kawai, Hidenori; Tao, Tao

2017-11-01

The connection between a meso-scale model and a micro-scale large eddy simulation (LES) is significant to simulate the micro-scale meteorological problem such as strong convective events due to the typhoon or the tornado using LES. In these problems the mean velocity profiles and the mean wind directions change with time according to the movement of the typhoons or tornadoes. Although, a fine grid micro-scale LES could not be connected to a coarse grid meso-scale WRF directly. In LES when the grid is suddenly refined at the interface of nested grids which is normal to the mean advection the resolved shear stresses decrease due to the interpolation errors and the delay of the generation of smaller scale turbulence that can be resolved on the finer mesh. For the estimation of wind gust disaster the peak wind acting on buildings and structures has to be correctly predicted. In the case of meteorological model the velocity fluctuations have a tendency of diffusive variation without the high frequency component due to the numerically filtering effects. In order to predict the peak value of wind velocity with good accuracy, this paper proposes a LES-based method for generating the higher frequency components of velocity and temperature fields obtained by meteorological model.

Behavioral in-effectiveness of high frequency electromagnetic field in mice.

Science.gov (United States)

Salunke, Balwant P; Umathe, Sudhir N; Chavan, Jagatpalsingh G

2015-03-01

The present investigation was carried out with an objective to study the influence of high frequency electromagnetic field (HF-EMF) on anxiety, obsessive compulsive disorder (OCD) and depression-like behavior. For exposure to HF-EMF, non-magnetic material was used to fabricate the housing. Mice were exposed to HF-EMF (2.45GHz), 60min/day for 7 or 30 or 60 or 90 or 120days. The exposure was carried out by switching-on inbuilt class-I BLUETOOTH device that operates on 2.45GHz frequency in file transfer mode at a peak density of 100mW. Mice were subjected to the assessment of anxiety, OCD and depression-like behavior for 7 or 30 or 60 or 90 or 120days of exposure. The anxiety-like behavior was assessed by elevated plus maze, open field test and social interaction test. OCD-like behavior was assessed by marble burying behavior, whereas depression-like behavior was assessed by forced swim test and tail suspension test. The present experiment demonstrates that up to 120days of exposure to HF-EMF does not produce anxiety, OCD and depression-like behavior in mice. Copyright © 2014 Elsevier Inc. All rights reserved.

High-Performance Control in Radio Frequency Power Amplification Systems

DEFF Research Database (Denmark)

Høyerby, Mikkel Christian Kofod

. It is clearly shown that single-phase switch-mode control systems based on oscillation (controlled unstable operation) of the whole power train provide the highest possible control bandwidth. A study of the limitations of cartesian feedback is also included. It is shown that bandwidths in excess of 4MHz can...... frequency power amplifiers (RFPAs) in conjunction with cartesian feedback (CFB) used to linearize the overall transmitter system. On a system level, it is demonstrated how envelope tracking is particularly useful for RF carriers with high peak-to-average power ratios, such as TEDS with 10dB. It is also...... demonstrated how the envelope tracking technique introduces a number of potential pitfalls to the system, namely in the form of power supply ripple intermodulation (PSIM), reduced RFPA linearity and a higherimpedance supply rail for the RFPA. Design and analysis techniques for these three issues are introduced...

Pulsed high-peak-power and single-frequency fibre laser design for LIDAR aircraft safety application

Science.gov (United States)

Liégeois, Flavien; Vercambre, Clément; Hernandez, Yves; Salhi, Mohamed; Giannone, Domenico

2006-09-01

Laser wind velocimeters work by monitoring the Doppler shift induced on the backscattered light by aerosols that are present in the air. Recently there has been a growing interest in the scientific community for developing systems operating at wavelengths near 1.5 μm and based on all-fibre lasers configuration. In this paper, we propose a new all-fibre laser source that is suitable for Doppler velocimetry in aircraft safety applications. The all-fibre laser has been specifically conceived for aircraft safety application. Our prototype has a conveniently narrow linewidth (9 kHz) and is modulated and amplified through an all fibre Master Oscillator Power Amplifier (MOPA) configuration. According to the measurements, we performed the final characteristics of the laser consist in a maximum peak power of 2.7 kW and an energy of 27 μJ energy per pulses of 10 ns at 30 kHz repetition rate. The only limiting factor of these performances is the Stimulated Brillouin Scattering.

Real-time bilinear rotation decoupling in absorptive mode J-spectroscopy: Detecting low-intensity metabolite peak close to high-intensity metabolite peak with convenience

Science.gov (United States)

Verma, Ajay; Baishya, Bikash

2016-05-01

;Pure shift; NMR spectra display singlet peak per chemical site. Thus, high resolution is offered at the cost of valuable J-coupling information. In the present work, real-time BIRD (BIlinear Rotation Decoupling) is applied to the absorptive-mode 2D J-spectroscopy to provide pure shift spectrum in the direct dimension and J-coupling information in the indirect dimension. Quite often in metabolomics, proton NMR spectra from complex bio-fluids display tremendous signal overlap. Although conventional J-spectroscopy in principle overcomes this problem by separating the multiplet information from chemical shift information, however, only magnitude mode of the experiment is practical, sacrificing much of the potential high resolution that could be achieved. Few J-spectroscopy methods have been reported so far that produce high-resolution pure shift spectrum along with J-coupling information for crowded spectral regions. In the present work, high-quality J-resolved spectrum from important metabolomic mixture such as tissue extract from rat cortex is demonstrated. Many low-intensity metabolite peaks which are obscured by the broad dispersive tails from high-intensity metabolite peaks in regular magnitude mode J-spectrum can be clearly identified in real-time BIRD J-resolved spectrum. The general practice of removing such spectral overlap is tedious and time-consuming as it involves repeated sample preparation to change the pH of the tissue extract sample and subsequent spectra recording.

Multiband Diagnostics of Unidentified 1FGL Sources with Suzaku and Swift X-Ray Observations

Science.gov (United States)

Takeuchi, Y.; Kataoka, J.; Maeda, K.; Takahashi, Y.; Nakamori, T.; Tahara, M.

2013-10-01

We have analyzed all the archival X-ray data of 134 unidentified (unID) gamma-ray sources listed in the first Fermi/LAT (1FGL) catalog and subsequently followed up by the Swift/XRT. We constructed the spectral energy distributions (SEDs) from radio to gamma-rays for each X-ray source detected, and tried to pick up unique objects that display anomalous spectral signatures. In these analyses, we target all the 1FGL unID sources, using updated data from the second Fermi/LAT (2FGL) catalog on the Large Area Telescope (LAT) position and spectra. We found several potentially interesting objects, particularly three sources, 1FGL J0022.2-1850, 1FGL J0038.0+1236, and 1FGL J0157.0-5259, which were then more deeply observed with Suzaku as a part of an AO-7 program in 2012. We successfully detected an X-ray counterpart for each source whose X-ray spectra were well fitted by a single power-law function. The positional coincidence with a bright radio counterpart (currently identified as an active galactic nucleus, AGN) in the 2FGL error circles suggests these sources are definitely the X-ray emission from the same AGN, but their SEDs show a wide variety of behavior. In particular, the SED of 1FGL J0038.0+1236 is not easily explained by conventional emission models of blazars. The source 1FGL J0022.2-1850 may be in a transition state between a low-frequency peaked and a high-frequency peaked BL Lac object, and 1FGL J0157.0-5259 could be a rare kind of extreme blazar. We discuss the possible nature of these three sources observed with Suzaku, together with the X-ray identification results and SEDs of all 134 sources observed with the Swift/XRT.

LOW-FREQUENCY OSCILLATIONS IN XTE J1550-564

International Nuclear Information System (INIS)

Rao Fengyun; Belloni, Tomaso; Stella, Luigi; Zhang Shuangnan; Li Tipei

2010-01-01

We present the results of a timing analysis of the low-frequency quasi-periodic oscillation (QPO) in the Rossi X-Ray Timing Explorer data of the black hole binary XTE J1550-564 during its 1998 outburst. The QPO frequency is observed to vary on timescales between ∼100 s and days, correlated with the count rate contribution from the optically thick accretion disk: we studied this correlation and discuss its influence on the QPO width. In all observations, the quality factors (ν 0 /FWHM) of the fundamental and second harmonic peaks were observed to be consistent, suggesting that the quasi-periodic nature of the oscillation is due to frequency modulation. In addition to the QPO and its harmonic peaks, a new 1.5ν component was detected in the power spectra. This component is broad, with a quality factor of ∼0.6. From this, we argue that the peak observed at half the QPO frequency, usually referred to as 'sub-harmonic', could be the fundamental frequency, leading to the sequence 1:2:3:4. We also studied the energy dependence of the timing features and conclude that the two continuum components observed in the power spectrum, although both more intense at high energies, show a different dependence on energy. At low energies, the lowest-frequency component dominates, while at high energies the higher-frequency one has a higher fractional rms. An interplay between these two components was also observed as a function of their characteristic frequency. In this source, the transition between the low/hard state and the hard-intermediate state appears to be a smooth process.

Gender Identification Using High-Frequency Speech Energy: Effects of Increasing the Low-Frequency Limit.

Science.gov (United States)

Donai, Jeremy J; Halbritter, Rachel M

The purpose of this study was to investigate the ability of normal-hearing listeners to use high-frequency energy for gender identification from naturally produced speech signals. Two experiments were conducted using a repeated-measures design. Experiment 1 investigated the effects of increasing high-pass filter cutoff (i.e., increasing the low-frequency spectral limit) on gender identification from naturally produced vowel segments. Experiment 2 studied the effects of increasing high-pass filter cutoff on gender identification from naturally produced sentences. Confidence ratings for the gender identification task were also obtained for both experiments. Listeners in experiment 1 were capable of extracting talker gender information at levels significantly above chance from vowel segments high-pass filtered up to 8.5 kHz. Listeners in experiment 2 also performed above chance on the gender identification task from sentences high-pass filtered up to 12 kHz. Cumulatively, the results of both experiments provide evidence that normal-hearing listeners can utilize information from the very high-frequency region (above 4 to 5 kHz) of the speech signal for talker gender identification. These findings are at variance with current assumptions regarding the perceptual information regarding talker gender within this frequency region. The current results also corroborate and extend previous studies of the use of high-frequency speech energy for perceptual tasks. These findings have potential implications for the study of information contained within the high-frequency region of the speech spectrum and the role this region may play in navigating the auditory scene, particularly when the low-frequency portion of the spectrum is masked by environmental noise sources or for listeners with substantial hearing loss in the low-frequency region and better hearing sensitivity in the high-frequency region (i.e., reverse slope hearing loss).

High peak power picosecond hybrid fiber and solid-state amplifier system

International Nuclear Information System (INIS)

Wushouer, X; Yan, P; Yu, H; Liu, Q; Fu, X; Yan, X; Gong, M

2010-01-01

We report the high peak power picosecond hybrid fiber and solid-state laser amplifier system. The passively mode-locked solid-state seed source produced an average power of 1.8 W with pulse width of 14 ps and repetition rate of 86 MHz. It was directly coupled into the first Yb-doped polarized photonic crystal fiber amplifier stage. To avoid the nonlinear effects in fiber, the output power from the first stage was merely amplified to 24 W with the narrow spectra broadening of 0.21 nm. For the improvement of the peak power, the dual-end pumped composite Nd:YVO 4 amplifier system has been chosen at the second stage. To reduce the serious thermal effect, the thermally bonded composite YVO 4 – Nd:YVO 4 – YVO 4 rod crystal was used as the gain medium. The 53 W TEM 00 mode with the peak power of 40 kW, beam quality of M 2 < 1.15, corresponding to the optical-optical efficiency of 42.4% was obtained at the hybrid amplifier laser system. The system allows using a low power seed source and demonstrates an increase in the peak power beyond a fiber master oscillator power amplifier's (MOPA's) limit

High frequency conductivity in carbon nanotubes

Directory of Open Access Journals (Sweden)

S. S. Abukari

2012-12-01

Full Text Available We report on theoretical analysis of high frequency conductivity in carbon nanotubes. Using the kinetic equation with constant relaxation time, an analytical expression for the complex conductivity is obtained. The real part of the complex conductivity is initially negative at zero frequency and become more negative with increasing frequency, until it reaches a resonance minimum at ω ∼ ωB for metallic zigzag CNs and ω < ωB for armchair CNs. This resonance enhancement is indicative for terahertz gain without the formation of current instabilities induced by negative dc conductivity. We noted that due to the high density of states of conduction electrons in metallic zigzag carbon nanotubes and the specific dispersion law inherent in hexagonal crystalline structure result in a uniquely high frequency conductivity than the corresponding values for metallic armchair carbon nanotubes. We suggest that this phenomenon can be used to suppress current instabilities that are normally associated with a negative dc differential conductivity.

Diurnal and Seasonal Responses of High Frequency Chlorophyll Fluorescence and PRI Measurements to Abiotic Stress in Almonds

Science.gov (United States)

Bambach-Ortiz, N. E.; Paw U, K. T.

2016-12-01

Plants have evolved to efficiently utilize light to synthesize energy-rich carbon compounds, and at the same time, dissipate absorbed but excessive photon that would otherwise transfer excitation energy to potentially toxic reactive oxygen species (ROS). Nevertheless, even the most rapidly growing plants with the highest rates of photosynthesis only utilize about half of the light their leaves absorb during the hours of peak irradiance in sun-exposed habitats. Usually, that daily peak of irradiance coincides with high temperature and a high vapor pressure deficit, which are conditions related to plant stomata closure. Consequently, specially in water stressed environments, plants need to have mechanisms to dissipate most of absorbed photons. Plants avoid photo-oxidative damage of the photosynthetic apparatus due to the formation of ROS under excess light using different mechanisms in order to either lower the amount of ROS formation or detoxify already formed ROS. Photoinhibition is defined as a reduction in photosynthetic activity due largely to a sustained reduction in the photochemical efficiency of Photosystem II (PSII), which can be assessed by monitoring Chlorophyll a fluorescence (ChlF). Alternatively, monitoring abiotic stress effects upon photosynthetic activity and photoinhibition may be possible using high frequency spectral reflectance sensors. We aim to find the potential relationships between high frequency PRI and ChlF as indicators of photoinhibition and permanent photodamage at a seasonal scale. Preliminary results show that PRI responses are sensitive to photoinhibition, but provide a poor representation of permanent photodamage observed at a seasonal scale.

Planck 2015 results. XXV. Diffuse low-frequency Galactic foregrounds

CERN Document Server

Ade, P.A.R.; Alves, M.I.R.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A.J.; Barreiro, R.B.; Bartlett, J.G.; Bartolo, N.; Battaner, E.; Benabed, K.; Benoit, A.; Benoit-Levy, A.; Bernard, J.P.; Bersanelli, M.; Bielewicz, P.; Bock, J.J.; Bonaldi, A.; Bonavera, L.; Bond, J.R.; Borrill, J.; Bouchet, F.R.; Boulanger, F.; Bucher, M.; Burigana, C.; Butler, R.C.; Calabrese, E.; Cardoso, J.F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chary, R.R.; Chiang, H.C.; Christensen, P.R.; Colombi, S.; Colombo, L.P.L.; Combet, C.; Couchot, F.; Coulais, A.; Crill, B.P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R.D.; Davis, R.J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J.M.; Desert, F.X.; Dickinson, C.; Diego, J.M.; Dole, H.; Donzelli, S.; Dore, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Ensslin, T.A.; Eriksen, H.K.; Falgarone, E.; Fergusson, J.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A.A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Ghosh, T.; Giard, M.; Giraud-Heraud, Y.; Gjerlow, E.; Gonzalez-Nuevo, J.; Gorski, K.M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J.E.; Hansen, F.K.; Hanson, D.; Harrison, D.L.; Helou, G.; Henrot-Versille, S.; Hernandez-Monteagudo, C.; Herranz, D.; Hildebrandt, S.R.; Hivon, E.; Hobson, M.; Holmes, W.A.; Hornstrup, A.; Hovest, W.; Huffenberger, K.M.; Hurier, G.; Jaffe, A.H.; Jaffe, T.R.; Jones, W.C.; Juvela, M.; Keihanen, E.; Keskitalo, R.; Kisner, T.S.; Kneissl, R.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lahteenmaki, A.; Lamarre, J.M.; Lasenby, A.; Lattanzi, M.; Lawrence, C.R.; Leahy, J.P.; Leonardi, R.; Lesgourgues, J.; Levrier, F.; Liguori, M.; Lilje, P.B.; Linden-Vornle, M.; Lopez-Caniego, M.; Lubin, P.M.; Macias-Perez, J.F.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Maris, M.; Marshall, D.J.; Martin, P.G.; Martinez-Gonzalez, E.; Masi, S.; Matarrese, S.; McGehee, P.; Meinhold, P.R.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschenes, M.A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J.A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C.B.; Norgaard-Nielsen, H.U.; Noviello, F.; Novikov, D.; Novikov, I.; Orlando, E.; Oxborrow, C.A.; Paci, F.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Pearson, T.J.; Peel, M.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Pratt, G.W.; Prezeau, G.; Prunet, S.; Puget, J.L.; Rachen, J.P.; Reach, W.T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rossetti, M.; Roudier, G.; Rubino-Martin, J.A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Seiffert, M.D.; Shellard, E.P.S.; Spencer, L.D.; Stolyarov, V.; Stompor, R.; Strong, A.W.; Sudiwala, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.S.; Sygnet, J.F.; Tauber, J.A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vidal, M.; Vielva, P.; Villa, F.; Wade, L.A.; Wandelt, B.D.; Watson, R.; Wehus, I.K.; Wilkinson, A.; Yvon, D.; Zacchei, A.; Zonca, A.

2016-01-01

(abridged) We discuss the Galactic foreground emission between 20 and 100GHz based on observations by Planck/WMAP. The Commander component-separation tool has been used to separate the various astrophysical processes in total intensity. Comparison with RRL templates verifies the recovery of the free-free emission along the Galactic plane. Comparison of the high-latitude Halpha emission with our free-free map shows residuals that correlate with dust optical depth, consistent with a fraction (~30%) of Halpha having been scattered by high-latitude dust. We highlight a number of diffuse spinning dust morphological features at high latitude. There is substantial spatial variation in the spinning dust spectrum, with the emission peak ranging from below 20GHz to more than 50GHz. There is a strong tendency for the spinning dust component near many prominent HII regions to have a higher peak frequency, suggesting that this increase in peak frequency is associated with dust in the photodissociation regions around the n...

INTEGRAL observations of the GeV blazar PKS 1502+106 and the hard X-ray bright Seyfert galaxy Mkn 841

Czech Academy of Sciences Publication Activity Database

Pian, E.; Ubertini, P.; Bazzano, A.; Beckmann, V.; Eckert, D.; Ghisellini, G.; Pursimo, T.; Tagliaferri, G.; Tavecchio, F.; Türler, M.; Bianchi, S.; Bianchin, V.; Hudec, René; Maraschi, L.; Raiteri, C.M.; Soldi, S.; Treves, A.; Villata, M.

2011-01-01

Roč. 526, February (2011), A125/1-A125/7 ISSN 0004-6361 Grant - others:ESA(XE) ESA PECS project No.98023; GA ČR(CZ) ga102/09/0997 Institutional research plan: CEZ:AV0Z10030501 Keywords : active galaxies * blazar PKS 1502+106 Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.587, year: 2011

High-frequency conductivity of photoionized plasma

Energy Technology Data Exchange (ETDEWEB)

Anakhov, M. V.; Uryupin, S. A., E-mail: uryupin@sci.lebedev.ru [National Research Nuclear University “MEPhI,” (Russian Federation)

2016-08-15

The tensor of the high-frequency conductivity of a plasma created via tunnel ionization of atoms in the field of linearly or circularly polarized radiation is derived. It is shown that the real part of the conductivity tensor is highly anisotropic. In the case of a toroidal velocity distribution of photoelectrons, the possibility of amplification of a weak high-frequency field polarized at a sufficiently large angle to the anisotropy axis of the initial nonequilibrium distribution is revealed.

78 FR 70567 - Nationwide Use of High Frequency and Ultra High Frequency Active SONAR Technology; Final...

Science.gov (United States)

2013-11-26

... Frequency and Ultra High Frequency Active SONAR Technology; Final Programmatic Environmental Assessment and... each alternative on the human and natural environments. FOR FURTHER INFORMATION CONTACT: If you have... Programmatic Environmental Assessment The scope of the PEA focuses on potential impacts associated with the...

Sheath impedance effects in very high frequency plasma experiments

International Nuclear Information System (INIS)

Schwarzenbach, W.; Howling, A.A.; Fivaz, M.; Brunner, S.; Hollenstein, C.

1995-05-01

The frequency dependence (13.56 MHz to 70 MHz) of the ion energy distribution at the ground electrode was measured by mass spectrometry in a symmetrical capacitive argon discharge. Reduced sheath impedance at Very High Frequency allows high levels of plasma power and substrate ion flux whilst maintaining low levels of ion energy and electrode voltage. The lower limit of ion bombardment energy is fixed by the sheath floating potential at high frequency, in contrast to low frequencies where only the rf voltage amplitude is determinant. The capacitive sheaths are thinner at high frequencies which accentuates the high frequency reduction in sheath impedance. It is argued that the frequency dependence of sheath impedance is responsible for the principal characteristics of Very High Frequency plasmas. The measurements are summarised by simple physical descriptions and compared with a Particle-In-Cell simulation. (author) figs., tabs., refs

Photon and neutrino emission from active galactic nuclei

Energy Technology Data Exchange (ETDEWEB)

Biermann, Peter L. [MPI for Radioastronomy, Bonn (Germany); Becker, Julia K. [Inst. for Phys., Univ. Bochum, Bochum (Germany); Caramete, Laurentiu I. [MPI for Radioastronomy, Bonn (Germany); Fraschetti, Federico [Inst. for Phys., Univ. Bochum, Bochum (Germany); Kneiske, Tanja [Inst. fuer Exp.Physik, Univ. Hamburg, Hamburg (Germany); Meli, Athina [Erlangen Center for Astroparticle Physics, University Erlangen-Nuremberg (Germany); Stanev, Todor [Bartol Research Inst., Univ. of Delaware, Newark, DE (United States)

2011-08-15

Supermassive black holes in the centers of galaxies are very common. They are known to rotate, accrete, spin down and eject highly relativistic jets; those jets pointed at us all seem to show a spectrum with two strong bumps, one in the TeV photon range, and one in X-rays - ordered by the emission frequency of the first bump this constitutes the blazar sequence. Here we wish to explain this sequence as primary synchrotron emission of energetic electrons and protons, and secondary emission from interactions at the first strong shockwave pattern in the relativistic jet. With two key assumptions on particle scattering, this concept predicts that the two basic maximum peak frequencies {nu}{sub syn,e,p} scale with the mass of the central black hole as {nu}{sub e,p{approx}}M{sub BH}{sup -1/2}, of {nu}{sub syn,p}/{nu}{sub syn,e}=(m{sub p}/m{sub e}){sup 3}, and the luminosities with the mass itself L{sub e,p{approx}}M{sub BH}. Due to strong losses of the leptons, the peak luminosities are generally the same, but with large variations around equality. This model predicts large fluxes in ultra high energy cosmic rays, and also large neutrino luminosities.

Altered osmotic swelling behavior of proteoglycan-depleted bovine articular cartilage using high frequency ultrasound

International Nuclear Information System (INIS)

Wang, Q; Zheng, Y P; Leung, G; Mak, A F T; Lam, W L; Guo, X; Lu, H B; Qin, L

2008-01-01

Swelling behavior is an electrochemical mechanical property of articular cartilage. It plays an important role in weight bearing and joint lubrication. In this study, the altered transient and inhomogeneous swelling behavior of the degenerated articular cartilage was observed and quantified in situ using ultrasound. Three groups of bovine patellar articular cartilage samples (n = 10 x 3) were obtained and digested by trypsin for 10, 20 and 30 min respectively to mimic different levels of degeneration. The osmotic-free shrinkage and swelling behavior induced by changing the concentration of the bathing saline solution from 0.15 M to 2 M and then back to 0.15 M were characterized using high-frequency ultrasound (central frequency = 35 MHz) before and after digestion. It was found that the degenerated cartilage specimens showed a weaker shrinkage-swelling behavior compared with the normal cartilage samples. However, no significant differences in the peak shrinkage or swelling strains were observed between different groups. The absolute values of the peak shrinkage strain significantly (p < 0.05) decreased by 45.4%, 42.1% and 50.6% respectively after the trypsin digestion for 10, 20 and 30 min, but such significance was not demonstrated for the peak swelling strains. Due to the potential alterations in the collagen-PG matrix during trypsin digestion, the correlation between the swelling strain and the shrinkage strain of the degenerated samples changed slightly in comparison with the normal samples. The proposed ultrasound method has been successfully used to measure the transient and inhomogeneous swelling behavior of the degenerated articular cartilage and has the potential for the characterization of osteoarthritis

Cooking Appliances Using High-Frequency Heating

OpenAIRE

木村, 秀行; Hideyuki, KIMURA; (株)日立製作所機械研究所

2007-01-01

We have produced a guide suitable for people with no technical knowledge of cooking appliances that use high-frequency heating. In general, cooking appliances that use an electric heat source are popular since, they are simple to use because the offer easy heat control, are safe because they do not have naked flames, and do not make kitchens dirty because there is no exhaust. In recent years, high-efficiency cooking appliances using high-frequency heating technology have surged in popularity....

Carbon nanotube transistor based high-frequency electronics

Science.gov (United States)

Schroter, Michael

At the nanoscale carbon nanotubes (CNTs) have higher carrier mobility and carrier velocity than most incumbent semiconductors. Thus CNT based field-effect transistors (FETs) are being considered as strong candidates for replacing existing MOSFETs in digital applications. In addition, the predicted high intrinsic transit frequency and the more recent finding of ways to achieve highly linear transfer characteristics have inspired investigations on analog high-frequency (HF) applications. High linearity is extremely valuable for an energy efficient usage of the frequency spectrum, particularly in mobile communications. Compared to digital applications, the much more relaxed constraints for CNT placement and lithography combined with already achieved operating frequencies of at least 10 GHz for fabricated devices make an early entry in the low GHz HF market more feasible than in large-scale digital circuits. Such a market entry would be extremely beneficial for funding the development of production CNTFET based process technology. This talk will provide an overview on the present status and feasibility of HF CNTFET technology will be given from an engineering point of view, including device modeling, experimental results, and existing roadblocks. Carbon nanotube transistor based high-frequency electronics.

Molecular Rayleigh Scattering Diagnostic for Measurement of High Frequency Temperature Fluctuations

Science.gov (United States)

Mielke, Amy F.; Elam, Kristie A.

2005-01-01

A novel technique for measurement of high frequency temperature fluctuations in unseeded gas flows using molecular Rayleigh scattering is investigated. The spectrum of laser light scattered from molecules in a gas flow is resolved using a Fabry-Perot interferometer. The width of the spectral peak is broadened by thermal motion of the molecules and hence is related to gas temperature. The interference fringe pattern containing spectral information is divided into four concentric regions using a series of mirrors angled with respect to one another. Light from each of these regions is directed towards photomultiplier tubes and sampled at 10 kHz using photon counting electronics. Monitoring the relative change in intensity within each region allows measurement of gas temperature. Independently monitoring the total scattered intensity provides a measure of gas density. This technique also has the potential to simultaneously measure a single component of flow velocity by monitoring the spectral peak location. Measurements of gas temperature and density are demonstrated using a low speed heated air jet surrounded by an unheated air co-flow. Mean values of temperature and density are shown for radial scans across the jet flow at a fixed axial distance from the jet exit plane. Power spectra of temperature and density fluctuations at several locations in the jet are also shown. The instantaneous measurements have fairly high uncertainty; however, long data records provide highly accurate statistically quantities, which include power spectra. Mean temperatures are compared with thermocouple measurements as well as the temperatures derived from independent density measurements. The accuracy for mean temperature measurements was +/- 7 K.

High frequency oscillations in brain hemodynamic response

Science.gov (United States)

Akin, Ata; Bolay, Hayrunnisa

2007-07-01

Tight autoregulation of vessel tone guarantees proper delivery of nutrients to the tissues. This regulation is maintained at a more delicate level in the brain since any decrease in the supply of glucose and oxygen to neuronal tissues might lead to unrecoverable injury. Functional near infrared spectroscopy has been proposed as a new tool to monitor the cerebrovascular response during cognitive activity. We have observed that during a Stroop task three distinct oscillatory patterns govern the control of the cerebrovascular reactivity: very low frequency (0.02-0.05 Hz), low frequency (0.08-0.12 Hz) and high frequency (0.12-0.18 Hz). High frequency oscillations have been shown to be related to stress level of the subjects. Our findings indicate that as the stress level is increased so does the energy of the high frequency component indicating a higher stimulation from the autonomic nervous system.

High-frequency applications of high-temperature superconductor thin films

Science.gov (United States)

Klein, N.

2002-10-01

High-temperature superconducting thin films offer unique properties which can be utilized for a variety of high-frequency device applications in many areas related to the strongly progressing market of information technology. One important property is an exceptionally low level of microwave absorption at temperatures attainable with low power cryocoolers. This unique property has initiated the development of various novel type of microwave devices and commercialized subsystems with special emphasis on application in advanced microwave communication systems. The second important achievement related to efforts in oxide thin and multilayer technology was the reproducible fabrication of low-noise Josephson junctions in high-temperature superconducting thin films. As a consequence of this achievement, several novel nonlinear high-frequency devices, most of them exploiting the unique features of the ac Josephson effect, have been developed and found to exhibit challenging properties to be utilized in basic metrology and Terahertz technology. On the longer timescale, the achievements in integrated high-temperature superconductor circuit technology may offer a strong potential for the development of digital devices with possible clock frequencies in the range of 100 GHz.

High-frequency applications of high-temperature superconductor thin films

International Nuclear Information System (INIS)

Klein, N.

2002-01-01

High-temperature superconducting thin films offer unique properties which can be utilized for a variety of high-frequency device applications in many areas related to the strongly progressing market of information technology. One important property is an exceptionally low level of microwave absorption at temperatures attainable with low power cryocoolers. This unique property has initiated the development of various novel type of microwave devices and commercialized subsystems with special emphasis on application in advanced microwave communication systems. The second important achievement related to efforts in oxide thin and multilayer technology was the reproducible fabrication of low-noise Josephson junctions in high-temperature superconducting thin films. As a consequence of this achievement, several novel nonlinear high-frequency devices, most of them exploiting the unique features of the ac Josephson effect, have been developed and found to exhibit challenging properties to be utilized in basic metrology and Terahertz technology. On the longer timescale, the achievements in integrated high-temperature superconductor circuit technology may offer a strong potential for the development of digital devices with possible clock frequencies in the range of 100 GHz. (author)

Extremely high frequency RF effects on electronics.

Energy Technology Data Exchange (ETDEWEB)

Loubriel, Guillermo Manuel; Vigliano, David; Coleman, Phillip Dale; Williams, Jeffery Thomas; Wouters, Gregg A.; Bacon, Larry Donald; Mar, Alan

2012-01-01

The objective of this work was to understand the fundamental physics of extremely high frequency RF effects on electronics. To accomplish this objective, we produced models, conducted simulations, and performed measurements to identify the mechanisms of effects as frequency increases into the millimeter-wave regime. Our purpose was to answer the questions, 'What are the tradeoffs between coupling, transmission losses, and device responses as frequency increases?', and, 'How high in frequency do effects on electronic systems continue to occur?' Using full wave electromagnetics codes and a transmission-line/circuit code, we investigated how extremely high-frequency RF propagates on wires and printed circuit board traces. We investigated both field-to-wire coupling and direct illumination of printed circuit boards to determine the significant mechanisms for inducing currents at device terminals. We measured coupling to wires and attenuation along wires for comparison to the simulations, looking at plane-wave coupling as it launches modes onto single and multiconductor structures. We simulated the response of discrete and integrated circuit semiconductor devices to those high-frequency currents and voltages, using SGFramework, the open-source General-purpose Semiconductor Simulator (gss), and Sandia's Charon semiconductor device physics codes. This report documents our findings.

Calculation of Leakage Inductance for High Frequency Transformers

DEFF Research Database (Denmark)

Ouyang, Ziwei; Jun, Zhang; Hurley, William Gerard

2015-01-01

Frequency dependent leakage inductance is often observed. High frequency eddy current effects cause a reduction in leakage inductance. The proximity effect between adjacent layers is responsible for the reduction of leakage inductance. This paper gives a detailed analysis of high frequency leakag...

High-frequency Rayleigh-wave method

Science.gov (United States)

Xia, J.; Miller, R.D.; Xu, Y.; Luo, Y.; Chen, C.; Liu, J.; Ivanov, J.; Zeng, C.

2009-01-01

High-frequency (???2 Hz) Rayleigh-wave data acquired with a multichannel recording system have been utilized to determine shear (S)-wave velocities in near-surface geophysics since the early 1980s. This overview article discusses the main research results of high-frequency surface-wave techniques achieved by research groups at the Kansas Geological Survey and China University of Geosciences in the last 15 years. The multichannel analysis of surface wave (MASW) method is a non-invasive acoustic approach to estimate near-surface S-wave velocity. The differences between MASW results and direct borehole measurements are approximately 15% or less and random. Studies show that simultaneous inversion with higher modes and the fundamental mode can increase model resolution and an investigation depth. The other important seismic property, quality factor (Q), can also be estimated with the MASW method by inverting attenuation coefficients of Rayleigh waves. An inverted model (S-wave velocity or Q) obtained using a damped least-squares method can be assessed by an optimal damping vector in a vicinity of the inverted model determined by an objective function, which is the trace of a weighted sum of model-resolution and model-covariance matrices. Current developments include modeling high-frequency Rayleigh-waves in near-surface media, which builds a foundation for shallow seismic or Rayleigh-wave inversion in the time-offset domain; imaging dispersive energy with high resolution in the frequency-velocity domain and possibly with data in an arbitrary acquisition geometry, which opens a door for 3D surface-wave techniques; and successfully separating surface-wave modes, which provides a valuable tool to perform S-wave velocity profiling with high-horizontal resolution. ?? China University of Geosciences (Wuhan) and Springer-Verlag GmbH 2009.

High-efficiency water-loaded microwave antenna in ultra-high-frequency band

Science.gov (United States)

Gong, Zilun; Bartone, Chris; Yang, Fuyi; Yao, Jie

2018-03-01

High-index dielectrics are widely used in microwave antennas to control the radiation characteristics. Liquid water, with a high dielectric index at microwave frequency, is an interesting material to achieving tunable functionalities. Here, we demonstrate a water-loaded microwave antenna system that has high loss-tolerance and wideband tunability enabled by fluidity. Our simulation and experimental results show that the resonance frequency can be effectively tuned by the size of loading water. Furthermore, the antenna systems with water loading can achieve high radiation efficiency (>90%) in the ultra-high-frequency (0.3-3 GHz) band. This work brings about opportunities in realistic tunable microwave antenna designs enabled by liquid.

Temporal Characteristics of High-Frequency Lower-Limb Oscillation during Freezing of Gait in Parkinson’s Disease

Directory of Open Access Journals (Sweden)

Don A. Yungher

2014-01-01

Full Text Available A cardinal feature of freezing of gait (FOG is high frequency (3–8 Hz oscillation of the legs, and this study aimed to quantify the temporal pattern of lower-body motion prior to and during FOG. Acceleration data was obtained from sensors attached to the back, thighs, shanks, and feet in 14 Parkinson’s disease patients performing timed-up-and-go tasks, and clinical assessment of FOG was performed by two experienced raters from video. A total of 23 isolated FOG events, defined as occurring at least 5 s after gait initiation and with no preceding FOG, were identified from the clinical ratings. The corresponding accelerometer records were analyzed within a 4 s window centered at the clinical onset of freezing. FOG-related high-frequency oscillation (an increase in power in the 3–8 Hz band >3 SD from baseline followed a distal to proximal onset pattern, appearing at the feet, shanks, thighs, and then back over a period of 250 ms. Peak power tended to decrease as the focus of oscillation moved from feet to back. There was a consistent delay (mean 872 ms between the onset of high frequency oscillation at the feet and clinical onset of FOG. We infer that FOG is characterized by high frequency oscillation at the feet, which progresses proximally and is mechanically damped at the torso.

High-Frequency Percussive Ventilation Revisited

Science.gov (United States)

2010-01-01

be implemented. ‡ Follow the reverse of the ventilation sequence if respiratory alkalosis develops—however, start at ventilation goal sequence 1 not at...High-frequency percussive ventilation (HFPV) has demonstrated a potential role as a rescue option for refractory acute respiratory distress syndrome...frequency percussive ventilation (HFPV) has demon- strated a potential role as a salvage option for refrac- tory acute respiratory distress syndrome

High frequency system project implementation plan

International Nuclear Information System (INIS)

Moon, L.L.

1976-01-01

The High Frequency System is a new mobile, digital diagnostic recording system for use at the Nevada Test Site. Many different kinds of event data will be digitized in real-time by this system, and these data will be recorded and stored for later read-out and transmission to NADCEN. The hardware and software requirements of the High Frequency System are examined, and the parameters of the system are proposed

Forecasting Value-at-Risk Using High-Frequency Information

Directory of Open Access Journals (Sweden)

Huiyu Huang

2013-06-01

Full Text Available in the prediction of quantiles of daily Standard&Poor’s 500 (S&P 500 returns we consider how to use high-frequency 5-minute data. We examine methods that incorporate the high frequency information either indirectly, through combining forecasts (using forecasts generated from returns sampled at different intraday interval, or directly, through combining high frequency information into one model. We consider subsample averaging, bootstrap averaging, forecast averaging methods for the indirect case, and factor models with principal component approach, for both direct and indirect cases. We show that in forecasting the daily S&P 500 index return quantile (Value-at-Risk or VaR is simply the negative of it, using high-frequency information is beneficial, often substantially and particularly so, in forecasting downside risk. Our empirical results show that the averaging methods (subsample averaging, bootstrap averaging, forecast averaging, which serve as different ways of forming the ensemble average from using high-frequency intraday information, provide an excellent forecasting performance compared to using just low-frequency daily information.

High intensity aerobic interval training improves peak oxygen consumption in patients with metabolic syndrome: CAT

Directory of Open Access Journals (Sweden)

Alexis Espinoza Salinas

2014-06-01

Full Text Available Introduction A number of cardiovascular risk factors characterizes the metabolic syndrome: insulin resistance (IR, low HDL cholesterol and high triglycerides. The aforementioned risk factors lead to elevated levels of abdominal adipose tissue, resulting in oxygen consumption deficiency. Purpose To verify the validity and applicability of using high intensity interval training (HIIT in subjects with metabolic syndrome and to answer the following question: Can HIIT improve peak oxygen consumption? Method The systematic review "Effects of aerobic interval training on exercise capacity and metabolic risk factors in individuals with cardiometabolic disorders" was analyzed. Results Data suggests high intensity aerobic interval training increases peak oxygen consumption by a standardized mean difference of 3.60 mL/kg-1/min-1 (95% confidence interval, 0.28-4.91. Conclusion In spite of the methodological shortcomings of the primary studies included in the systematic review, we reasonably conclude that implementation of high intensity aerobic interval training in subjects with metabolic syndrome, leads to increases in peak oxygen consumption.

High-frequency modulation of ion-acoustic waves.

Science.gov (United States)

Albright, N. W.

1972-01-01

A large amplitude, high-frequency electromagnetic oscillation is impressed on a nonrelativistic, collisionless plasma from an external source. The frequency is chosen to be far from the plasma frequency (in fact, lower). The resulting electron velocity distribution function strongly modifies the propagation of ion-acoustic waves parallel to the oscillating electric field. The complex frequency is calculated numerically.

Time dependent approach of TeV blazars based on a model of inhomogeneous stratified jet

International Nuclear Information System (INIS)

Boutelier, T.

2009-05-01

The study of the emission and variability mechanisms of TeV blazars has been the subject of intensive research for years. The homogeneous one-zone model commonly used is puzzling since it yields very high Lorentz factor, in contradiction with other observational evidences. In this work, I describe a new time dependent multi-zone approach, in the framework of the two-flow model. I compute the emission of a full jet, where relativistic electron-positron pairs distributed in pileup propagate. The evolution and the emission of the plasma is computed taking into account a turbulent heating term, some radiative cooling, and a pair production term due to photo-annihilation process. Applied to PKS 2155-304, the model allows the reproduction of the full spectra, as well as the simultaneous multi wavelength variability, with a relatively small Lorentz factor. The variability is explained by the instability of the pair creation process. Nonetheless, the value is still high to agree with other observational evidences in radio. Hence, I show in the last part of this work how to conciliate high Lorentz factor with the absence of apparent superluminal movement in radio, by taking into account the effect of the opening angle on the appearance of relativistic jets. (author)

Periodic permanent magnet focusing system with high peak field

International Nuclear Information System (INIS)

Zhang Hong; Liu Weiwei; Bai Shuxin; Chen Ke

2008-01-01

In this study, hybrid periodic permanent magnet (PPM) system is studied, which has high axial magnetic field and low magnetic leakage. By simulation computation, some laws of magnetic field distribution vs. structure dimensions were obtained. A hybrid PPM is designed and constructed whose peak field reaches 0.6 T. The factors inducing discrepancies between computational results and practical measurements are analyzed. The magnetic field distribution is very sensitive to the variations of constructional parameters. Construction accuracy greatly influences the magnetic field distribution. Research results obtained here are potentially valuable for future work

The Influence of High-Frequency Envelope Information on Low-Frequency Vowel Identification in Noise.

Directory of Open Access Journals (Sweden)

Wiebke Schubotz

Full Text Available Vowel identification in noise using consonant-vowel-consonant (CVC logatomes was used to investigate a possible interplay of speech information from different frequency regions. It was hypothesized that the periodicity conveyed by the temporal envelope of a high frequency stimulus can enhance the use of the information carried by auditory channels in the low-frequency region that share the same periodicity. It was further hypothesized that this acts as a strobe-like mechanism and would increase the signal-to-noise ratio for the voiced parts of the CVCs. In a first experiment, different high-frequency cues were provided to test this hypothesis, whereas a second experiment examined more closely the role of amplitude modulations and intact phase information within the high-frequency region (4-8 kHz. CVCs were either natural or vocoded speech (both limited to a low-pass cutoff-frequency of 2.5 kHz and were presented in stationary 3-kHz low-pass filtered masking noise. The experimental results did not support the hypothesized use of periodicity information for aiding low-frequency perception.

The Influence of High-Frequency Envelope Information on Low-Frequency Vowel Identification in Noise.

Science.gov (United States)

Schubotz, Wiebke; Brand, Thomas; Kollmeier, Birger; Ewert, Stephan D

2016-01-01

Vowel identification in noise using consonant-vowel-consonant (CVC) logatomes was used to investigate a possible interplay of speech information from different frequency regions. It was hypothesized that the periodicity conveyed by the temporal envelope of a high frequency stimulus can enhance the use of the information carried by auditory channels in the low-frequency region that share the same periodicity. It was further hypothesized that this acts as a strobe-like mechanism and would increase the signal-to-noise ratio for the voiced parts of the CVCs. In a first experiment, different high-frequency cues were provided to test this hypothesis, whereas a second experiment examined more closely the role of amplitude modulations and intact phase information within the high-frequency region (4-8 kHz). CVCs were either natural or vocoded speech (both limited to a low-pass cutoff-frequency of 2.5 kHz) and were presented in stationary 3-kHz low-pass filtered masking noise. The experimental results did not support the hypothesized use of periodicity information for aiding low-frequency perception.

Frequency-dependent effects of background noise on subcortical response timing.

Science.gov (United States)

Tierney, A; Parbery-Clark, A; Skoe, E; Kraus, N

2011-12-01

The addition of background noise to an auditory signal delays brainstem response timing. This effect has been extensively documented using manual peak selection. Peak picking, however, is impractical for large-scale studies of spectrotemporally complex stimuli, and leaves open the question of whether noise-induced delays are frequency-dependent or occur across the frequency spectrum. Here we use an automated, objective method to examine phase shifts between auditory brainstem responses to a speech sound (/da/) presented with and without background noise. We predicted that shifts in neural response timing would also be reflected in frequency-specific phase shifts. Our results indicate that the addition of background noise causes phase shifts across the subcortical response spectrum (70-1000 Hz). However, this noise-induced delay is not uniform such that some frequency bands show greater shifts than others: low-frequency phase shifts (300-500 Hz) are largest during the response to the consonant-vowel formant transition (/d/), while high-frequency shifts (720-1000 Hz) predominate during the response to the steady-state vowel (/a/). Most importantly, phase shifts occurring in specific frequency bands correlate strongly with shifts in the latencies of the predominant peaks in the auditory brainstem response, while phase shifts in other frequency bands do not. This finding confirms the validity of phase shift detection as an objective measure of timing differences and reveals that this method detects noise-induced shifts in timing that may not be captured by traditional peak latency measurements. Copyright © 2011 Elsevier B.V. All rights reserved.

High Frequency Acoustic Propagation using Level Set Methods

Science.gov (United States)

2007-01-01

solution of the high frequency approximation to the wave equation. Traditional solutions to the Eikonal equation in high frequency acoustics are...the Eikonal equation derived from the high frequency approximation to the wave equation, ucuH ∇±=∇ )(),( xx , with the nonnegative function c(x...For simplicity, we only consider the case ucuH ∇+=∇ )(),( xx . Two difficulties must be addressed when solving the Eikonal equation in a fixed

High frequency measurements of shot noise suppression in atomic-scale metal contacts

Science.gov (United States)

Wheeler, Patrick J.; Evans, Kenneth; Russom, Jeffrey; King, Nicholas; Natelson, Douglas

2009-03-01

Shot noise provides a means of assessing the number and transmission coefficients of transmitting channels in atomic- and molecular-scale junctions. Previous experiments at low temperatures in metal and semiconductor point contacts have demonstrated the expected suppression of shot noise when junction conductance is near an integer multiple of the conductance quantum, G0≡2e^2/h. Using high frequency techniques, we demonstrate the high speed acquisition of such data at room temperature in mechanical break junctions. In clean Au contacts conductance histograms with clear peaks at G0, 2G0, and 3G0 are acquired within hours, and histograms of simultaneous measurements of the shot noise show clear suppression at those conductance values. We describe the dependence of the noise on bias voltage and analyze the noise vs. conductance histograms in terms of a model that averages over transmission coefficients.

Investigating the Innermost Jet Structures of Blazar S5 0716+714 Using Uniquely Dense Intra-day Photo-polarimetric Observations

Directory of Open Access Journals (Sweden)

Gopal Bhatta

2016-10-01

Full Text Available The sub-hour timescale variability commonly observed in blazars—widely known as intra-day or microvariability—has been extensively studied in optical photo-polarimetric bands over the past 25–30 years. In addition, there have been comprehensive theoretical discussions on the topic, with various models and scenarios proposed; however, the phenomenon still remains relatively poorly understood. Here we present the summary of our optical microvariability studies over the past few years based on multi-frequency photo-polarimetric Whole Earth Blazar Telescope (WEBT observation campaigns. The primary objective of the study was to explore the characteristics of the source microvariability on timescales of a few minutes to a few days using exceptionally dense photo-polarimetric observations. The results show that the source often displays fast variability with an amplitude as large as 0.3 mag within a few hours, as well as color variability on similar time scales often characterized by “bluer-when-brighter” trend. Similarly, the correlation between variability in flux and polarization appears to depend upon the configuration of the optical polarization angle relative to the positional angle of the innermost radio core of the jet. Other fascinating observations include a sudden and temporary disappearance in the observed variability lasting for ∼6 h. In addition, the modeling of individual microflares strongly suggests that the phenomenon of microvariability can be best explained by convolved emission from compact emission sites distributed stochastically in the turbulent jet. Besides, analysis of some of the well resolved micro-flares exhibiting high degrees of polarization points towards a complex magnetic geometry pervading the jet with the possible presence of small-scale regions of highly ordered and enhanced magnetic field similar to so-called “magnetic islands”.

High frequency dynamics in centrifugal compressors

NARCIS (Netherlands)

Twerda, A.; Meulendijks, D.; Smeulers, J.P.M.; Handel, R. van den; Lier, L.J. van

2008-01-01

Problems with centrifugal compressors relating to high frequency, i.e. Blade passing frequency (BPF) are increasing. Pulsations and vibrations generated in centrifugal compressors can lead to nuisance, due to strong tonal noise, and even breakdown. In several cases the root cause of a failure or a

Capabilities, performance, and future possibilities of high frequency polyphase resonant converters

International Nuclear Information System (INIS)

Reass, W.A.; Baca, D.M.; Bradley, J.T. III; Hardek, T.W.; Kwon, S.I.; Lynch, M.T.; Rees, D.E.

2004-01-01

High Frequency Polyphase Resonant Power Conditioning (PRPC) techniques developed at Los Alamos National Laboratory (LANL) are now being utilized for the Oak Ridge National Laboratory (ORNL) Spallation Neutron Source (SNS) accelerator klystron RF amplifier power systems. Three different styles of polyphase resonant converter modulators were developed for the SNS application. The various systems operate up to 140 kV, or 11 MW pulses, or up to 1.1 MW average power, all from a DC input of +/- 1.2 kV. Component improvements realized with the SNS effort coupled with new applied engineering techniques have resulted in dramatic changes in RF power conditioning topology. As an example, the high-voltage transformers are over 100 times smaller and lighter than equivalent 60 Hz versions. With resonant conversion techniques, load protective networks are not required. A shorted load de-tunes the resonance and little power transfer can occur. This provides for power conditioning systems that are inherently self-protective, with automatic fault 'ride-through' capabilities. By altering the Los Alamos design, higher power and CW power conditioning systems can be realized without further demands of the individual component voltage or current capabilities. This has led to designs that can accommodate 30 MW long pulse applications and megawatt class CW systems with high efficiencies. The same PRPC techniques can also be utilized for lower average power systems (∼250 kW). This permits the use of significantly higher frequency conversion techniques that result in extremely compact systems with short pulse (10 to 100 us) capabilities. These lower power PRPC systems may be suitable for medical Linacs and mobile RF systems. This paper will briefly review the performance achieved for the SNS accelerator and examine designs for high efficiency megawatt class CW systems and 30 MW peak power applications. The devices and designs for compact higher frequency converters utilized for short pulse

High and low spatial frequencies in website evaluations.

Science.gov (United States)

Thielsch, Meinald T; Hirschfeld, Gerrit

2010-08-01

Which features of websites are important for users' perceptions regarding aesthetics or usability? This study investigates how evaluations of aesthetic appeal and usability depend on high vs. low spatial frequencies. High spatial frequencies convey information on fine details, whereas low spatial frequencies convey information about the global layout. Participants rated aesthetic appeal and usability of 50 website screenshots from different domains. Screenshots were presented unfiltered, low-pass filtered with blurred targets or high-pass filtered with high-pass filtered targets. The main result is that low spatial frequencies can be seen to have a unique contribution in perceived website aesthetics, thus confirming a central prediction from processing fluency theory. There was no connection between low spatial frequencies and usability evaluations, whereas strong correlations were found between ratings of high-pass filtered websites and those of unfiltered websites in aesthetics and usability. This study thus offers a new perspective on the biological basis of users' website perceptions. This research links ergonomics to neurocognitive models of visual processing. This paper investigates how high and low spatial frequencies, which are neurologically processed in different visual pathways, independently contribute to users' perceptions of websites. This is very relevant for theories of website perceptions and for practitioners of web design.

StreamStats in Oklahoma - Drainage-Basin Characteristics and Peak-Flow Frequency Statistics for Ungaged Streams

Science.gov (United States)

Smith, S. Jerrod; Esralew, Rachel A.

2010-01-01

drainage-basin outlet for the period 1961-1990, 10-85 channel slope (slope between points located at 10 percent and 85 percent of the longest flow-path length upstream from the outlet), and percent impervious area. The Oklahoma StreamStats application interacts with the National Streamflow Statistics database, which contains the peak-flow regression equations in a previously published report. Fourteen peak-flow (flood) frequency statistics are available for computation in the Oklahoma StreamStats application. These statistics include the peak flow at 2-, 5-, 10-, 25-, 50-, 100-, and 500-year recurrence intervals for rural, unregulated streams; and the peak flow at 2-, 5-, 10-, 25-, 50-, 100-, and 500-year recurrence intervals for rural streams that are regulated by Natural Resources Conservation Service floodwater retarding structures. Basin characteristics and streamflow statistics cannot be computed for locations in playa basins (mostly in the Oklahoma Panhandle) and along main stems of the largest river systems in the state, namely the Arkansas, Canadian, Cimarron, Neosho, Red, and Verdigris Rivers, because parts of the drainage areas extend outside of the processed hydrologic units.

Bulk Comptonization: new hints from the luminous blazar 4C+25.05

Science.gov (United States)

Kammoun, E. S.; Nardini, E.; Risaliti, G.; Ghisellini, G.; Behar, E.; Celotti, A.

2018-01-01

Blazars are often characterized by a spectral break at soft X-rays, whose origin is still debated. While most sources show a flattening, some exhibit a blackbody-like soft excess with temperatures of the order of ∼0.1 keV, similar to low-luminosity, non-jetted Seyferts. Here, we present the analysis of the simultaneous XMM-Newton and NuSTAR observations of the luminous flat-spectrum radio quasar 4C+25.05 (z = 2.368). The observed 0.3-30 keV spectrum is best described by the sum of a hard X-ray power law (Γ = 1.38_{-0.03}^{+0.05}) and a soft component, approximated by a blackbody with kT_BB = 0.66_{-0.04}^{+0.05} keV (rest frame). If the spectrum of 4C+25.05 is interpreted in the context of bulk Comptonization by cold electrons of broad-line region photons emitted in the direction of the jet, such an unusual temperature implies a bulk Lorentz factor of the jet of Γbulk ∼ 11.7. Bulk Comptonization is expected to be ubiquitous on physical grounds, yet no clear signature of it has been found so far, possibly due to its transient nature and the lack of high-quality, broad-band X-ray spectra.

Sources for high frequency heating. Performance and limitations

International Nuclear Information System (INIS)

Le Gardeur, R.

1976-01-01

The various problems encountered in high frequency heating of plasmas can be decomposed into three spheres of action: theoretical development, antenna designing, and utilization of power sources. By classifying heating into three spectral domains, present and future needs are enumerated. Several specific antenna designs are treated. High frequency power sources are reviewed. The actual development of the gyratron is discussed in view of future needs in very high frequency heating of plasmas [fr

An inkjet vision measurement technique for high-frequency jetting

Energy Technology Data Exchange (ETDEWEB)

Kwon, Kye-Si, E-mail: kskwon@sch.ac.kr; Jang, Min-Hyuck; Park, Ha Yeong [Department of Mechanical Engineering, Soonchunhyang University 22, Soonchunhyang-Ro, Shinchang, Asan Chungnam 336-745 (Korea, Republic of); Ko, Hyun-Seok [Department of Electrical and Robot Engineering, Soonchunhyang University, 22, Soonchunhyang-Ro, Shinchang, Asan Chungnam 336-745 (Korea, Republic of)

2014-06-15

Inkjet technology has been used as manufacturing a tool for printed electronics. To increase the productivity, the jetting frequency needs to be increased. When using high-frequency jetting, the printed pattern quality could be non-uniform since the jetting performance characteristics including the jetting speed and droplet volume could vary significantly with increases in jet frequency. Therefore, high-frequency jetting behavior must be evaluated properly for improvement. However, it is difficult to measure high-frequency jetting behavior using previous vision analysis methods, because subsequent droplets are close or even merged. In this paper, we present vision measurement techniques to evaluate the drop formation of high-frequency jetting. The proposed method is based on tracking target droplets such that subsequent droplets can be excluded in the image analysis by focusing on the target droplet. Finally, a frequency sweeping method for jetting speed and droplet volume is presented to understand the overall jetting frequency effects on jetting performance.

An inkjet vision measurement technique for high-frequency jetting

International Nuclear Information System (INIS)

Kwon, Kye-Si; Jang, Min-Hyuck; Park, Ha Yeong; Ko, Hyun-Seok

2014-01-01

Inkjet technology has been used as manufacturing a tool for printed electronics. To increase the productivity, the jetting frequency needs to be increased. When using high-frequency jetting, the printed pattern quality could be non-uniform since the jetting performance characteristics including the jetting speed and droplet volume could vary significantly with increases in jet frequency. Therefore, high-frequency jetting behavior must be evaluated properly for improvement. However, it is difficult to measure high-frequency jetting behavior using previous vision analysis methods, because subsequent droplets are close or even merged. In this paper, we present vision measurement techniques to evaluate the drop formation of high-frequency jetting. The proposed method is based on tracking target droplets such that subsequent droplets can be excluded in the image analysis by focusing on the target droplet. Finally, a frequency sweeping method for jetting speed and droplet volume is presented to understand the overall jetting frequency effects on jetting performance

A wideband, frequency up-converting bounded vibration energy harvester for a low-frequency environment

International Nuclear Information System (INIS)

Ashraf, K; Md Khir, M H; Baharudin, Z; Dennis, J O

2013-01-01

This paper presents a bounded vibration energy harvester to effectively harvest energy from a wide band of low-frequency environmental vibrations ranging from 10 to 18 Hz. Rigid mechanical stoppers are used to confine the seismic mass movement within the elastic limits of the spring. Experimental results show the effectiveness of the proposed technique in increasing the efficiency of the energy harvester. When excited at a frequency of 10 Hz with a peak acceleration of 1 g, the harvester responds at a higher frequency of 20 Hz and gives a peak power of 2.68 mW and a peak to peak voltage of 2.62 V across a load of 220 Ω. The average power density of 65.74 μW cm −3 obtained at 10 Hz 1 g excitation monotonically increases with frequency up to 341.86 μW cm −3 at 18 Hz. An analytical model describing the nonlinear dynamics of the proposed harvester is also presented. A simple technique to estimate the energy losses during impact and thereof a method to incorporate these losses in the model are suggested. The presented model not only predicts the experimental voltage waveform and frequency response of the device with good similarity but also predicts the RMS voltage from the harvester for the whole range of operating frequencies with an RMS error of 5.2%. (paper)

Relative thermoluminescent efficiencies proton/gamma and helium/gamma of peaks of high temperature in TLD-100 dosemeters

International Nuclear Information System (INIS)

Flores M, E.

2007-01-01

The increase of the applications of ion beams in radiotherapy treatments has generated interest in the study of the thermoluminescent materials (TL) that allow to determine the applied doses. A way to quantify the TL response from these materials to ions is by means of the relative thermoluminescent efficiency. In the group of Thermoluminescent dosimetry of the Institute of Physics of the UNAM (IFUNAM) the thermoluminescent response of the TLD-100 dosemeters has been studied, which present a glow curve characteristic with several peaks that correspond to traps and luminescent centers in the material. The stable peaks know each other as 4, 5, 6a, 6b, 7, 8, 9 and 10. The efficiencies should be measured using the response so much to the radiation of interest (in this case protons and helium ions) as the response to gamma radiation. In previous works with ions of low energy taken place in the Pelletron accelerator of the IFUNAM was only measured the TL efficiency for the peak 5 and the total signal. It had not been possible to measure the efficiency of the peaks of high temperature (6a-10) because, for the gamma radiation, the peaks of high temperature show very small signals; however, recently Massillon carries out measures of efficiency TL of peaks of high temperature for ions of intermediate energy using a protocol special of reading and of deconvolution that allows to measure the signals coming from the peaks of high temperature. In this work is implemented this same protocol to complete the study of TL efficiencies at low energy of protons and helium and to determine if the values of efficiency depend on the used reading protocol. For it is reported it measures of the relative efficiency of the peaks of high temperature from the TLD-100 exposed to protons of 1.5 MeV and nuclei of helium of 3 and 7.5 MeV. (Author)

High frequency electromagnetic dosimetry

CERN Document Server

Sánchez-Hernández, David A

2009-01-01

Along with the growth of RF and microwave technology applications, there is a mounting concern about the possible adverse effects over human health from electromagnetic radiation. Addressing this issue and putting it into perspective, this groundbreaking resource provides critical details on the latest advances in high frequency electromagnetic dosimetry.

High frequency noise studies at the Hartousov mofette area (CZE)

Science.gov (United States)

Schmidt, Andreas; Flores-Estrella, Hortencia; Pommerencke, Julia; Umlauft, Josefine

2014-05-01

Ambient noise analysis has been used as a reliable tool to investigate sub-surface structures at seismological quiet regions with none or less specific seismic events. Here, we consider the acoustic signals from a single mofette at the Hartoušov area (CZE) as a noise-like high frequency source caused by multiple near surface degassing processes in a restricted location. From this assumption we have used different array geometries for recording at least one hour of continuous noise. We installed triangular arrays with 3 component geophones: the first deployment consisted on two co-centric triangles with side length of 30 and 50 m with the mofette in the center; the second deployment consisted on two triangular arrays, both with side length of 30 m, co-directional to the mofette. Furthermore, we also installed profiles with 24 channels and vertical geophones locating them in different positions with respect to the mofette. In this work, we present preliminary results from the data analysis dependent on the geometry, to show the characteristics of the noise wave-field referring to frequency content and propagation features, such as directionality and surface wave velocity. The spectral analysis shows that the energy is concentrated in a frequency band among 10 and 40 Hz. However, in this interval there is no evidence of any exclusive fundamental frequencies. From this, man-induced influences can be identified as intermittent signal peaks in narrow frequency bands and can be separated to receive the revised mofette wave-field record. The inversion of dispersive surface waves, that were detected by interferometric methods, provides a velocity model down to 12 m with an S-wave velocity between 160 and 180 m/s on the uppermost layer. Furthermore, the interferometric signal properties indicate that it is not possible to characterize the mofette as a punctual source, but rather as a conglomerate of multiple sources with time and location variations.

PEAK SHIFTS PRODUCED BY CORRELATED RESPONSE TO SELECTION.