WorldWideScience

Sample records for rapidly fading afterglow

  1. Adaptive Channel-Tracking Method and Equalization for MC-CDMA Systems over Rapidly Fading Channel under Colored Noise

    Directory of Open Access Journals (Sweden)

    Chen Bor-Sen

    2010-01-01

    Full Text Available A recursive maximum-likelihood (RML algorithm for channel estimation under rapidly fading channel and colored noise in a multicarrier code-division multiple-access (MC-CDMA system is proposed in this paper. A moving-average model with exogenous input (MAX is given to describe the transmission channel and colored noise. Based on the pseudoregression method, the proposed RML algorithm can simultaneously estimate the parameters of channel and colored noise. Following the estimation results, these parameters can be used to enhance the minimum mean-square error (MMSE equalizer. Considering high-speed mobile stations, a one-step linear trend predictor is added to improve symbol detection. Simulation results indicate that the proposed RML estimator can track the channel more precisely than the conventional estimator. Meanwhile, the performance of the proposed enhanced MMSE equalizer is robust to the rapidly Rayleigh fading channel under colored noise in the MC-CDMA systems.

  2. Adaptive Channel-Tracking Method and Equalization for MC-CDMA Systems over Rapidly Fading Channel under Colored Noise

    Science.gov (United States)

    Yang, Chang-Yi; Chen, Bor-Sen

    2010-12-01

    A recursive maximum-likelihood (RML) algorithm for channel estimation under rapidly fading channel and colored noise in a multicarrier code-division multiple-access (MC-CDMA) system is proposed in this paper. A moving-average model with exogenous input (MAX) is given to describe the transmission channel and colored noise. Based on the pseudoregression method, the proposed RML algorithm can simultaneously estimate the parameters of channel and colored noise. Following the estimation results, these parameters can be used to enhance the minimum mean-square error (MMSE) equalizer. Considering high-speed mobile stations, a one-step linear trend predictor is added to improve symbol detection. Simulation results indicate that the proposed RML estimator can track the channel more precisely than the conventional estimator. Meanwhile, the performance of the proposed enhanced MMSE equalizer is robust to the rapidly Rayleigh fading channel under colored noise in the MC-CDMA systems.

  3. Time-dependent thermal effects in GRB afterglows

    Energy Technology Data Exchange (ETDEWEB)

    Postnov, K.A.; Blinnikov, S.I.; Kosenko, D.I.; Sorokina, E.I

    2004-06-01

    Time-dependent thermal effects should accompany standard non-thermal afterglows of GRB when {gamma}-rays pass through inhomogeneous surroundings of the GRB site. Thermal relaxation of an optically thin plasma is calculated using time-dependent collisional ionization of the plasma ion species. X-ray emission lines are similar to those found in the fading X-ray afterglow of GRB 011211. Thermal relaxation of clouds or shells around the GRB site could also contribute to the varying late optical GRB afterglows, such as in GRB 021004 and GRB 030329.

  4. Discovery and Redshift of an Optical Afterglow in 71 deg2: iPTF13bxl and GRB 130702A

    Science.gov (United States)

    Singer, Leo P.; Cenko, S. Bradley; Kasliwal, Mansi M.; Perley, Daniel A.; Ofek, Eran O.; Brown, Duncan A.; Nugent, Peter E.; Kulkarni, S. R.; Corsi, Alessandra; Frail, Dale A.; Bellm, Eric; Mulchaey, John; Arcavi, Iair; Barlow, Tom; Bloom, Joshua S.; Cao, Yi; Gehrels, Neil; Horesh, Assaf; Masci, Frank J.; McEnery, Julie; Rau, Arne; Surace, Jason A.; Yaron, Ofer

    2013-10-01

    We report the discovery of the optical afterglow of the γ-ray burst (GRB) 130702A, identified upon searching 71 deg2 surrounding the Fermi Gamma-ray Burst Monitor (GBM) localization. Discovered and characterized by the intermediate Palomar Transient Factory, iPTF13bxl is the first afterglow discovered solely based on a GBM localization. Real-time image subtraction, machine learning, human vetting, and rapid response multi-wavelength follow-up enabled us to quickly narrow a list of 27,004 optical transient candidates to a single afterglow-like source. Detection of a new, fading X-ray source by Swift and a radio counterpart by CARMA and the Very Large Array confirmed the association between iPTF13bxl and GRB 130702A. Spectroscopy with the Magellan and Palomar 200 inch telescopes showed the afterglow to be at a redshift of z = 0.145, placing GRB 130702A among the lowest redshift GRBs detected to date. The prompt γ-ray energy release and afterglow luminosity are intermediate between typical cosmological GRBs and nearby sub-luminous events such as GRB 980425 and GRB 060218. The bright afterglow and emerging supernova offer an opportunity for extensive panchromatic follow-up. Our discovery of iPTF13bxl demonstrates the first observational proof-of-principle for ~10 Fermi-iPTF localizations annually. Furthermore, it represents an important step toward overcoming the challenges inherent in uncovering faint optical counterparts to comparably localized gravitational wave events in the Advanced LIGO and Virgo era.

  5. Fading Skies

    Science.gov (United States)

    Sio, Betsy Menson

    2009-01-01

    A sky fading from blue to white to red at the horizon, and water darkening from light to midnight blue. Strong diagonals slashing through the image, drawing a viewer's eyes deeper into the picture, and delicate trees poised to convey a sense of beauty. These are the fascinating strengths of the ukiyo-e woodblock prints of Japanese artist Ando…

  6. DISCOVERY AND REDSHIFT OF AN OPTICAL AFTERGLOW IN 71 deg{sup 2}: iPTF13bxl AND GRB 130702A

    Energy Technology Data Exchange (ETDEWEB)

    Singer, Leo P.; Brown, Duncan A. [LIGO Laboratory, California Institute of Technology, Pasadena, CA 91125 (United States); Bradley Cenko, S.; Gehrels, Neil; McEnery, Julie [Astrophysics Science Division, NASA Goddard Space Flight Center, Mail Code 661, Greenbelt, MD 20771 (United States); Kasliwal, Mansi M.; Mulchaey, John [Observatories of the Carnegie Institution for Science, 813 Santa Barbara St, Pasadena, CA 91101 (United States); Perley, Daniel A.; Kulkarni, S. R.; Bellm, Eric; Barlow, Tom; Cao, Yi; Horesh, Assaf [Cahill Center for Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Ofek, Eran O.; Arcavi, Iair [Benoziyo Center for Astrophysics, The Weizmann Institute of Science, Rehovot 76100 (Israel); Nugent, Peter E.; Bloom, Joshua S. [Department of Astronomy, University of California Berkeley, B-20 Hearst Field Annex 3411, Berkeley, CA 94720-3411 (United States); Corsi, Alessandra [George Washington University, Corcoran Hall, Washington, DC 20052 (United States); Frail, Dale A. [National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (United States); Masci, Frank J., E-mail: lsinger@caltech.edu [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States); and others

    2013-10-20

    We report the discovery of the optical afterglow of the γ-ray burst (GRB) 130702A, identified upon searching 71 deg{sup 2} surrounding the Fermi Gamma-ray Burst Monitor (GBM) localization. Discovered and characterized by the intermediate Palomar Transient Factory, iPTF13bxl is the first afterglow discovered solely based on a GBM localization. Real-time image subtraction, machine learning, human vetting, and rapid response multi-wavelength follow-up enabled us to quickly narrow a list of 27,004 optical transient candidates to a single afterglow-like source. Detection of a new, fading X-ray source by Swift and a radio counterpart by CARMA and the Very Large Array confirmed the association between iPTF13bxl and GRB 130702A. Spectroscopy with the Magellan and Palomar 200 inch telescopes showed the afterglow to be at a redshift of z = 0.145, placing GRB 130702A among the lowest redshift GRBs detected to date. The prompt γ-ray energy release and afterglow luminosity are intermediate between typical cosmological GRBs and nearby sub-luminous events such as GRB 980425 and GRB 060218. The bright afterglow and emerging supernova offer an opportunity for extensive panchromatic follow-up. Our discovery of iPTF13bxl demonstrates the first observational proof-of-principle for ∼10 Fermi-iPTF localizations annually. Furthermore, it represents an important step toward overcoming the challenges inherent in uncovering faint optical counterparts to comparably localized gravitational wave events in the Advanced LIGO and Virgo era.

  7. iPTF14yb: The First Discovery of a Gamma-Ray Burst Afterglow Independent of a High-Energy Trigger

    Science.gov (United States)

    Cenko, S. Bradley; Urban, Alex L.; Perley, Daniel A.; Horesh, Assaf; Corsi, Alessandra; Fox, Derek B.; Cao, Yi; Kasliwal, Mansi M.; Lien, Amy; Arcavi, Iair; hide

    2015-01-01

    We report here the discovery by the Intermediate Palomar Transient Factory (iPTF) of iPTF14yb, a luminous (Mr >> -27.8 mag), cosmological (redshift 1.9733), rapidly fading optical transient. We demonstrate, based on probabilistic arguments and a comparison with the broader population, that iPTF14yb is the optical afterglow of the long-duration gamma-ray burst GRB 140226A. This marks the first unambiguous discovery of a GRB afterglow prior to (and thus entirely independent of) an associated high-energy trigger. We estimate the rate of iPTF14yb-like sources (i.e., cosmologically distant relativistic explosions) based on iPTF observations, inferring an all-sky value of Rrel = 610/yr (68% confidence interval of 110-2000/yr). Our derived rate is consistent (within the large uncertainty) with the all-sky rate of on-axis GRBs derived by the Swift satellite. Finally, we briefly discuss the implications of the nondetection to date of bona fide "orphan" afterglows (i.e., those lacking detectable high-energy emission) on GRB beaming and the degree of baryon loading in these relativistic jets.

  8. Chameleon Induced Atomic Afterglow

    CERN Document Server

    Brax, Philippe

    2010-01-01

    The chameleon is a scalar field whose mass depends on the density of its environment. Chameleons are necessarily coupled to matter particles and will excite transitions between atomic energy levels in an analogous manner to photons. When created inside an optical cavity by passing a laser beam through a constant magnetic field, chameleons are trapped between the cavity walls and form a standing wave. This effect will lead to an afterglow phenomenon even when the laser beam and the magnetic field have been turned off, and could be used to probe the interactions of the chameleon field with matter.

  9. On the anomalous afterglow seen in a chameleon afterglow search

    Energy Technology Data Exchange (ETDEWEB)

    Steffen, Jason H.; Baumbaugh, Alan; Chou, Aaron S.; Tomlin, Ray; /Fermilab; Upadhye, Amol; /Argonne, PHY

    2012-05-01

    We present data from our investigation of the anomalous orange-colored afterglow that was seen in the GammeV Chameleon Afterglow Search (CHASE). These data include information about the broadband color of the observed glow, the relationship between the glow and the temperature of the apparatus, and other data taken prior to, and during the science operations of CHASE. While differing in several details, the generic properties of the afterglow from CHASE are similar to luminescence seen in some vacuum compounds. Contamination from this, or similar, luminescent signatures will likely impact the design of implementation of future experiments involving single photon detectors and high intensity light sources in a cryogenic environment.

  10. ON THE AFTERGLOW AND PROGENITOR OF FRB 150418

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Bing, E-mail: zhang@physics.unlv.edu [Department of Physics and Astronomy, University of Nevada Las Vegas, Las Vegas, NV 89154 (United States)

    2016-05-01

    Keane et al. recently detected a fading radio source following FRB 150418, leading to the identification of a putative host galaxy at z = 0.492 ± 0.008. Assuming that the fading source is the afterglow of FRB 150418, I model the afterglow and constrain the isotropic energy of the explosion to be a few 10{sup 50} erg, comparable to that of a short-duration gamma-ray burst (GRB). The outflow may have a jet opening angle of ∼0.22 rad, so that the beaming-corrected energy is below 10{sup 49} erg. The results rule out most fast radio burst (FRB) progenitor models for this FRB, but may be consistent with either of the following two scenarios. The first scenario invokes a merger of an NS–NS binary, which produced an undetected short GRB and a supra-massive neutron star, which subsequently collapsed into a black hole, probably hundreds of seconds after the short GRB. The second scenario invokes a merger of a compact star binary (BH–BH, NS–NS, or BH–NS) system whose pre-merger dynamical magnetospheric activities made the FRB, which is followed by an undetected short GRB-like transient. The gravitational-wave (GW) event GW 150914 would be a sister of FRB 150418 in this second scenario. In both cases, one expects an exciting prospect of GW/FRB/GRB associations.

  11. Fading and interference mitigation in wireless communications

    CERN Document Server

    Panic, Stefan; Anastasov, Jelena; Spalevic, Petar

    2013-01-01

    The rapid advancement of various wireless communication system services has created the need to analyze the possibility of their performance improvement. Introducing the basic principles of digital communications performance analysis and its mathematical formalization, Fading and Interference Mitigation in Wireless Communications will help you stay up to date with recent developments in the performance analysis of space diversity reception over fading channels in the presence of cochannel interference.The book presents a unified method for computing the performance of digital communication sys

  12. The afterglow and complex environment of the optically dim burst GRB 980613

    DEFF Research Database (Denmark)

    Hjorth, J.; Thomsen, Bente; Nielsen, S.R.

    2002-01-01

    not exhibit an unusually rapid decay (power-law decay slope alpha X-ray spectral index (beta(RX) approximate to 0.6), indicating a maximal reddening of the afterglow of approximate to0.45 mag in R. Hence, the dimness......We report the identification of the optical afterglow of GRB 980613 in R- and I-band images obtained between 16 and 48 hr after the gamma-ray burst. Early near-infrared (NIR) H and K' observations are also reported. The afterglow was optically faint (R approximate to 23) at discovery but did...

  13. What we learn from the afterglow of GRB 021211

    CERN Document Server

    Dado, S; De Rújula, Alvaro; Dado, Shlomo; Dar, Arnon; Rujula, Alvaro De

    2003-01-01

    The behaviour of the afterglow (AG) of gamma-ray bursts (GRBs) directly provides, in the cannonball (CB) model, information about the environment of their progenitor stars. The well observed early temporal decline of the AG of GRB 021211 is precisely the one predicted in the presence of a progenitor's ``wind'' which resulted in a density profile $\\propto 1/r^2$ around the star. The subsequent fast fading --which makes this GRB ``quasi-dark''-- is the one anticipated if, further away, the interstellar density is roughly constant and relatively high. The CB-model fit to the AG clearly shows the presence of an associated supernova akin to SN1998bw, and allows even for the determination of the broad-band spectrum of the host galaxy. GRB 990123 and GRB 021004, whose AGs were also measured very early, are also discussed.

  14. Fading characteristics of martian analogue materials and the applicability of a correction procedure

    DEFF Research Database (Denmark)

    Morthekai, P.; Jain, Mayank; Murray, A.S.

    2008-01-01

    The anomalous fading of trapped charge in martian analogue materials such as basalt and andesite rock samples is measured. Optically stimulated luminescence (OSL) signals show rapid fading (of between 4% and 27% per decade). Fading rates obtained using high temperature thermoluminescence signals ...... of the growth curve. (C) 2008 Elsevier Ltd. All rights reserved....

  15. GLAST Prospects for Swift-Era Afterglows

    Energy Technology Data Exchange (ETDEWEB)

    Gou, L.J.; /Penn State U., Astron. Astrophys.; Meszaros, P.; /Penn State U.

    2011-11-23

    We calculate the GeV spectra of gamma-ray burst afterglows produced by inverse Compton scattering of these objects sub-MeV emission. We improve on earlier treatments by using refined afterglow parameters and new model developments motivated by recent Swift observations. We present time-dependent GeV spectra for standard, constant-parameter models, as well as for models with energy injection and with time-varying parameters, for a range of burst parameters. We evaluate the limiting redshift to which such afterglows can be detected by the GLAST Large Area Telescope, as well as by AGILE.

  16. Circular polarization in the optical afterglow of GRB 121024A

    DEFF Research Database (Denmark)

    Wiersema, K.; Covino, S.; Toma, K.

    2014-01-01

    Gamma-ray bursts (GRBs) are most probably powered by collimated relativistic outflows (jets) from accreting black holes at cosmological distances. Bright afterglows are produced when the outflow collides with the ambient medium. Afterglow polarization directly probes the magnetic properties...

  17. Short GRB afterglows observed with GROND

    DEFF Research Database (Denmark)

    Nicuesa Guelbenzu, A.; Klose, S.; Rossi, A.

    2013-01-01

    cases: GRBs 090305, 090426, 090510, 090927, and 100117A. Three of the aforementioned six bursts with optical light curves show a break: GRBs 090426 and 090510 as well as GRB 090305. For GRB 090927, no break is seen in the optical/X-ray light curve until about 150 ks/600 ks after the burst. A decay slope...... of short bursts. In three cases, GROND was on target within less than 10 min after the trigger, leading to the discovery of the afterglow of GRB 081226A and its faint underlying host galaxy. In addition, GROND was able to image the optical afterglow and follow the light curve evolution in five further...

  18. Afterglow of chlorophyll in vivo and photosynthesis

    NARCIS (Netherlands)

    Goedheer, J.C.

    1962-01-01

    Two pigment systems are involved in the afterglow of chlorophyll a-containing cells. Absorption in only one of these systems (promoting or “p” system) is effective in producing luminescence. If light is absorbed simultaneously by the other (quenching or “q” system), a decrease in luminescence

  19. Radio Afterglows of Gamma Ray Bursts

    Indian Academy of Sciences (India)

    Even though radio band is the least explored of the afterglow spectrum, it has played an important role in the progress of GRB physics, specifically in confirming the hypothesized relativistic effects. Currently radio astronomy is in the beginning of a revolution. The high sensitive Square Kilometer Array (SKA) is being planned ...

  20. Perceptual Fading without Retinal Adaptation

    Science.gov (United States)

    Hsieh, Po-Jang; Colas, Jaron T.

    2012-01-01

    A retinally stabilized object readily undergoes perceptual fading and disappears from consciousness. This startling phenomenon is commonly believed to arise from local bottom-up sensory adaptation to edge information that occurs early in the visual pathway, such as in the lateral geniculate nucleus of the thalamus or retinal ganglion cells. Here…

  1. Multiwavelength detectability of Pop III GRBs from afterglow simulations

    Science.gov (United States)

    Macpherson, D.; Coward, D.

    2017-05-01

    Afterglows of gamma-ray bursts (GRBs) from Population III (Pop III) stars could reveal the formation history and properties of these first generation stars. Through detailed simulation, we predict the prospects of detecting these afterglows with a range of established, existing and upcoming telescopes across the spectrum from radio waves to X-rays. The simulations show that the afterglow light curves of Pop III GRBs at high redshift (≳8) are very similar to those of Pop I/II GRBs at lower redshift (˜2), with the distinction that Lyα absorption at Pop III redshifts removes any optical [and some near-infrared (NIR)] component. We calculate that within a single field of view (FOV) of the Australian Square Kilometre Array Pathfinder (ASKAP) telescope there will be on average four detectable Pop III GRB afterglows. This is the product of ASKAP's large FOV and excellent sensitivity at wavelengths where the afterglows are very long-lasting. We show that the exceptional sensitivity of the James Webb Space Telescope (JWST) Near-InfraRed Camera will make this the optimal instrument for afterglow follow-up and redshift measurement, while JWST Near-InfraRed Spectrograph will be able to detect the absorption features of Pop III-enriched environments in 70 per cent of directed Pop III GRB afterglows. We also find that the Atacama Large Millimetre Array is very poorly suited to observe these afterglows, and that the Spectrum-Roentgen-Gamma 4 yr all-sky X-ray survey has a 12 per cent chance of detecting an orphan Pop III GRB afterglow. The optimal strategy for detecting, identifying and studying Pop III GRB afterglows is to have JWST attempt NIR photometry of afterglows with a detected radio component but no detected optical component.

  2. Jet simulations and gamma-ray burst afterglow jet breaks

    NARCIS (Netherlands)

    van Eerten, H. J.; Meliani, Z.; Wijers, Ramj; Keppens, R.

    2011-01-01

    The conventional derivation of the gamma-ray burst afterglow jet break time uses only the blast wave fluid Lorentz factor and therefore leads to an achromatic break. We show that in general gamma-ray burst afterglow jet breaks are chromatic across the self-absorption break. Depending on

  3. Jet simulations and gamma-ray burst afterglow jet breaks

    NARCIS (Netherlands)

    van Eerten, H. J.; Meliani, Z.; Wijers, R.A.M.J.; Keppens, R.

    2010-01-01

    The conventional derivation of the gamma-ray burst afterglow jet break time uses only the blast wave fluid Lorentz factor and therefore leads to an achromatic break. We show that in general gamma-ray burst afterglow jet breaks are chromatic across the self-absorption break. Depending on

  4. Physics of the GRB 030328 afterglow and its environment

    NARCIS (Netherlands)

    Maiorano, E.; Masetti, N.; Palazzi, E.; Savaglio, S.; Rol, E.; Vreeswijk, P.M.; Pian, E.; Price, P.A.; Peterson, B.A.; Jelínek, M.; Amati, L.; Andersen, M.I.; Castro-Tirado, A.J.; Castro Cerón, J.M.; de Ugarte Postigo, A.; Frontera, F.; Fruchter, A.S.; Fynbo, J.P.U.; Gorosabel, J.; Henden, A.A.; Hjorth, J.; Jensen, B.L.; Klose, S.; Kouveliotou, C.; Masi, G.; Møller, P.; Nicastro, L.; Ofek, E.O.; Pandey, S.B.; Rhoads, J.E.; Tanvir, N.R.; Wijers, R.A.M.J.; van den Heuvel, E.P.J.

    2006-01-01

    Aims.To investigate the physical nature of the afterglow emission. We report on the photometric, spectroscopic and polarimetric observations of the optical afterglow of Gamma-Ray Burst (GRB) 030328 detected by HETE-2. Methods.Photometric, spectroscopic and polarimetric monitoring of the optical

  5. Influence on the long afterglow properties by the environmental temperature

    Energy Technology Data Exchange (ETDEWEB)

    Wu Haoyi [School of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou 510006 (China); Hu Yihua, E-mail: huyh@gdut.edu.c [School of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou 510006 (China); Wang Yinhai; Mou Zhongfei [School of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou 510006 (China)

    2010-01-15

    Sr{sub 2}MgSi{sub 2}O{sub 7}:Eu{sup 2+}, Dy{sup 3+} (SMED) and Ba{sub 2}MgSi{sub 2}O{sub 7}:Eu{sup 2+}, Dy{sup 3+} (BMED) were synthesized with the solid-state reaction. The SMED shows long afterglow while the afterglow of BMED is not visible at room temperature. When the environmental temperature is 150 deg. C, the afterglow of SMED is not obvious while the BMED shows the long afterglow. The decay curves measured at different temperatures conform to this phenomenon. It ascribes to the different trap depths of different samples. The thermoluminescence (TL) curves of SMED peaks at 80 deg. C. BMED has two TL peaks peaking at about 80 and 175 deg. C respectively. The low temperature peak is weak and its density is small. The high-temperature peak reveals that one trap of BMED is deeper than the one of SMED. The afterglows of the phosphors strongly depend on the environmental temperature since the lifetime of the trapping carriers is temperature-dependence. BMED is a potential optimum long afterglow phosphor for the purpose of high-temperature application.

  6. Fading and shadowing in wireless systems

    CERN Document Server

    Shankar, P Mohana

    2017-01-01

    This book offers a comprehensive overview of fading and shadowing in wireless channels. A number of statistical models including simple, hybrid, compound and cascaded ones are presented along with a detailed discussion of diversity techniques employed to mitigate the effects of fading and shadowing. The effects of co-channel interference before and after the implementation of diversity are also analyzed. To facilitate easy understanding of the models and the analysis, the background on probability and random variables is presented with relevant derivations of densities of the sums, products, ratios as well as order statistics of random variables. The book also provides material on digital modems of interest in wireless systems. The updated edition expands the background materials on probability by offering sections on Laplace and Mellin transforms, parameter estimation, statistical testing and receiver operating characteristics. Newer models for fading, shadowing and shadowed fading are included along with th...

  7. Fading AGN Candidates: AGN Histories and Outflow Signatures

    Energy Technology Data Exchange (ETDEWEB)

    Keel, William C.; Maksym, W. Peter [Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL 35487 (United States); Lintott, Chris J. [Astrophysics, Oxford University and Adler Planetarium, 1300 S. Lakeshore Drive, Chicago, IL 60605 (United States); Bennert, Vardha N.; Scott, Bryan; Showley, Charles; Flatland, Kelsi [Physics Department, California Polytechnic State University, San Luis Obispo, CA 93407 (United States); Chojnowski, S. Drew [Department of Astronomy, New Mexico State University, P.O. Box 30001, MSC 4500, Las Cruces, NM 88003-8001 (United States); Moiseev, Alexei; Smirnova, Aleksandrina [Special Astrophysical Observatory, Russian Academy of Sciences, Nizhny Arkhyz, 369167 (Russian Federation); Schawinski, Kevin; Sartori, Lia F. [Institute for Astronomy, ETH Zürich, Wolfgang-Pauli-Straße 27, CH-8093 Zurich (Switzerland); Urry, C. Megan [Department of Physics, Yale University, P.O. Box 208120, New Haven, CT 06520-8120 (United States); Pancoast, Anna [Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Schirmer, Mischa, E-mail: wkeel@ua.edu [Gemini Observatory, La Serena (Chile)

    2017-02-01

    We consider the energy budgets and radiative history of eight fading active galactic nuclei (AGNs), identified from an energy shortfall between the requirements to ionize very extended (radius > 10 kpc) ionized clouds and the luminosity of the nucleus as we view it directly. All show evidence of significant fading on timescales of ≈50,000 yr. We explore the use of minimum ionizing luminosity Q {sub ion} derived from photoionization balance in the brightest pixels in H α at each projected radius. Tests using presumably constant Palomar–Green QSOs, and one of our targets with detailed photoionization modeling, suggest that we can derive useful histories of individual AGNs, with the caveat that the minimum ionizing luminosity is always an underestimate and subject to uncertainties about fine structure in the ionized material. These consistency tests suggest that the degree of underestimation from the upper envelope of reconstructed Q {sub ion} values is roughly constant for a given object and therefore does not prevent such derivation. The AGNs in our sample show a range of behaviors, with rapid drops and standstills; the common feature is a rapid drop in the last ≈2×10{sup 4} yr before the direct view of the nucleus. The e -folding timescales for ionizing luminosity are mostly in the thousands of years, with a few episodes as short as 400 yr. In the limit of largely obscured AGNs, we find additional evidence for fading from the shortfall between even the lower limits from recombination balance and the maximum luminosities derived from far-infrared fluxes. We compare these long-term light curves, and the occurrence of these fading objects among all optically identified AGNs, to simulations of AGN accretion; the strongest variations over these timespans are seen in models with strong and local (parsec-scale) feedback. We present Gemini integral-field optical spectroscopy, which shows a very limited role for outflows in these ionized structures. While rings and

  8. Fading Characteristics of Wireless Channel on High-Speed Railway in Hilly Terrain Scenario

    Directory of Open Access Journals (Sweden)

    Fengyu Luan

    2013-01-01

    Full Text Available This paper focuses on the fading characteristics of wireless channel on High-Speed Railway (HSR in hilly terrain scenario. Due to the rapid speed, the fading characteristics of HSR channel are highly correlated with time or Transmit-Receive distance and have their own special property. To investigate the fading characteristics, the measurement is conducted on the Guangzhou-Shenzhen passenger-dedicated line in China with the speed of 295 km/h in the data-collection area at 2.4 GHz. From the measured data, the amplitude of each path is estimated by using the Subspace-Alternating Generalized Expectation-Maximization (SAGE algorithm along with other parameters of channel impulse responses. Then the fading parameters, including path loss, shadow fading, and K-factor, are analysed. With the numerical results in the measurement and analysis, the fading characteristics have been revealed and modelled. It is supposed that this work has a promotion for HSR communication system design and improvement.

  9. Gamma-ray Bursts and their Afterglows in the Whole Electromagnetic Domain

    Science.gov (United States)

    Castro-Tirado, Alberto J.

    2007-08-01

    Since their discovery in 1967, GRBs have been puzzling to astrophysicists. With the advent of a new generation of X--ray satellites in the late 90's, it was possible to carry out deep multi-wavelength observations of the counterparts associated with the long GRBs class just within a few hours of occurrence, thanks to the observation of the fading X-ray emission that follows the more energetic gamma-ray photons once the GRB event has ended. The fact that this emission (the afterglow) extends at longer wavelengths, led to the discovery optical/IR/radio counterparts in the last decade, greatly improving our understanding of these sources. The launch of the Swift satellite in 2004 allows to detect about 100 events/yr, with a mean redshift of 2.7 for the long duration GRB class. The central engines that power these extraordinary events are thought to be the collapse of massive stars whereas the merging of compact objects seems to support the few detections of short GRBs detected so far. Searches for emission at VHE and UHE have been unsuccessful till now.

  10. Prompt and Afterglow Emission from Short GRB Cocoons

    Science.gov (United States)

    Morsony, Brian; Lazzati, Davide; López-Cámara, Diego; Workman, Jared; Moskal, Jeremiah; Cantiello, Matteo; Perna, Rosalba

    2018-01-01

    We present simulations of short GRB jets that create a wide cocoon of mildly relativistic material surrounding the narrow, highly relativistic jet. We model the prompt and afterglow emission from the jet and cocoon at a range of observer angles relative to the jet axis. Even far off axis, prompt X-ray and gamma-ray emission from the cocoon may be detectable by FERMI GBM out to several 10’s of Mpc. Afterglow emission off-axis is dominated by cocoon material at early times (hours - days). The afterglow should be detectable at a wide range of frequencies (radio, optical, X-ray) for a large fraction of off-axis short GRBs within 200 Mpc, the detection range of aLIGO at design sensitivity. Given recent events, cocoon emission may be very important in the future for localizing LIGO-detected neutron star mergers.

  11. GRB 081029: A Gamma-Ray Burst with a Multi-Component Afterglow

    Science.gov (United States)

    Holland, Stephen T.; De Pasquale, Massimiliano; Mao, Jirong; Sakamoto, Takanori; Schady, Patricia; Covino, Stefano; Fan, Yi-Zhong; Jin, Zhi-Ping; D'Avanzo, Paolo; Antonelli, Angelo; hide

    2012-01-01

    We present an analysis of the unusual optical light curve of the gamma-ray burst GRB 081029, a long-soft burst with a redshift of z = 3.8479. We combine X-ray and optical observations from the Swift X-Ray Telescope and the Swift Ultra Violet/Optical Telescope with ground-based optical and infrared data obtained using the REM, ROTSE, and CTIO 1.3-m telescopes to construct a detailed data set extending from 86 s to approx.100,000 s after the BAT trigger. Our data covers a wide energy range, from 10 keV to 0.77 eV (1.24 A to 16000 A). The X-ray afterglow shows a shallow initial decay followed by a rapid decay starting at about 18,000 s. The optical and infrared afterglow, however, shows an uncharacteristic rise at about 3000 s that does not correspond to any feature in the X-ray light curve. Our data are not consistent with synchrotron radiation from a jet interacting with an external medium, a two-component jet, or continuous energy injection from the central engine. We find that the optical light curves can be broadly explained by a collision between two ejecta shells within a two-component jet. A growing number of gamma-ray burst afterglows are consistent with complex jets, which suggests that some (or all) gamma-ray burst jets are complex and will require detailed modelling to fully understand them.injection

  12. Visualisation of Honeypot Data Using Graphviz and Afterglow

    Directory of Open Access Journals (Sweden)

    Craig Valli

    2009-06-01

    Full Text Available This research in progress paper explores the use of Graphviz and Afterglow for the analysis of data emanating from a honeypot system. Honeypot systems gather a wide range of data that is often difficult to readily search for patterns and trends using conventional log file analysis techniques. The data from the honeypots has been statically extracted and processed through Afterglow scripts to produce inputs suitable for use by the DOT graph based tools contained within Graphviz.  This paper explores some of the benefits and drawbacks of currently using this type of approach.

  13. The bright optical afterglow of the long GRB 001007

    DEFF Research Database (Denmark)

    Ceron, J.M.C.; Castro-Tirado, A.J.; Gorosabel, J.

    2002-01-01

    We present optical follow up observations of the long GRB 001007 between 6.14 hours and similar to468 days after the event. An unusually bright optical afterglow (OA) was seen to decline following a steep power law decay with index alpha = -2.03 +/- 0.11, possibly indicating a break in the light ...

  14. The optical afterglow and host galaxy of GRB 000926

    DEFF Research Database (Denmark)

    Fynbo, J.U.; Gorosabel, J.; Dall, T.H.

    2002-01-01

    In this paper we illustrate with the case of GRB 000926 how Gamma Ray Bursts (GRBs) can be used as cosmological lighthouses to identify and study star forming galaxies at high redshifts. The optical afterglow of the burst was located with optical imaging at the Nordic Optical Telescope 20.7 hours...

  15. GRB 030227: The first multiwavelength afterglow of an INTEGRAL GRB

    DEFF Research Database (Denmark)

    Castro-Tirado, A.J.; Gorosabel, J.; Guziy, S.

    2003-01-01

    We present multiwavelength observations of a gamma-ray burst detected by INTEGRAL (GRB 030227) between 5.3 hours and similar to1.7 days after the event. Here we report the discovery of a dim optical afterglow (OA) that would not have been detected by many previous searches due to its faintess (R...

  16. Circular polarization in the optical afterglow of GRB 121024A.

    Science.gov (United States)

    Wiersema, K; Covino, S; Toma, K; van der Horst, A J; Varela, K; Min, M; Greiner, J; Starling, R L C; Tanvir, N R; Wijers, R A M J; Campana, S; Curran, P A; Fan, Y; Fynbo, J P U; Gorosabel, J; Gomboc, A; Götz, D; Hjorth, J; Jin, Z P; Kobayashi, S; Kouveliotou, C; Mundell, C; O'Brien, P T; Pian, E; Rowlinson, A; Russell, D M; Salvaterra, R; di Serego Alighieri, S; Tagliaferri, G; Vergani, S D; Elliott, J; Fariña, C; Hartoog, O E; Karjalainen, R; Klose, S; Knust, F; Levan, A J; Schady, P; Sudilovsky, V; Willingale, R

    2014-05-08

    Gamma-ray bursts (GRBs) are most probably powered by collimated relativistic outflows (jets) from accreting black holes at cosmological distances. Bright afterglows are produced when the outflow collides with the ambient medium. Afterglow polarization directly probes the magnetic properties of the jet when measured minutes after the burst, and it probes the geometric properties of the jet and the ambient medium when measured hours to days after the burst. High values of optical polarization detected minutes after the burst of GRB 120308A indicate the presence of large-scale ordered magnetic fields originating from the central engine (the power source of the GRB). Theoretical models predict low degrees of linear polarization and no circular polarization at late times, when the energy in the original ejecta is quickly transferred to the ambient medium and propagates farther into the medium as a blast wave. Here we report the detection of circularly polarized light in the afterglow of GRB 121024A, measured 0.15 days after the burst. We show that the circular polarization is intrinsic to the afterglow and unlikely to be produced by dust scattering or plasma propagation effects. A possible explanation is to invoke anisotropic (rather than the commonly assumed isotropic) electron pitch-angle distributions, and we suggest that new models are required to produce the complex microphysics of realistic shocks in relativistic jets.

  17. Detecting radio afterglows of gamma-ray bursts with FAST

    National Research Council Canada - National Science Library

    Zhi-Bin Zhang Si-Wei Kong Yong-Feng Huang Di Li Long-Biao Li

    2015-01-01

    Using the generic hydrodynamic model of gamma-ray burst (GRB) after- glows, we calculate the radio afterglow light curves of low luminosity, high luminosity, failed and standard GRBs in different observational bands of FAST's energy window...

  18. Colour variations in the GRB 120327A afterglow

    Czech Academy of Sciences Publication Activity Database

    Melandri, A.; Covino, S.; Zaninoni, E.; Campana, S.; Bolmer, J.; Cobb, B. E.; Gorosabel, J.; Kim, J.W.; Kuindersma, S.; Kuroda, D.; Malesani, D.; Mundell, C. G.; Nappo, F.; Sbarufatti, B.; Smith, R. J.; Steele, I.A.; Topinka, M.; Trotter, G.; Virgili, F. J.; Bernardini, M. G.; D'Avanzo, P.; D'Elia, V.; Fugazza, D.; Ghirlanda, G.; Gomboc, A.; Greiner, J.; Guidorzi, C.; Haislip, J.B.; Hanayama, H.; Hanlon, L.; Im, M.; Ivarsen, K.M.; Japelj, J.; Jelínek, Martin; Kawai, N.; Kobayashi, S.; Kopac, D.; LaCluyze, A.; Martin-Carrillo, A.; Murphy, D.; Reichart, D. E.; Salvaterra, R.; Salafia, O. S.; Tagliaferri, G.; Vergani, S. D.

    2017-01-01

    Roč. 607, October (2017), A29/1-A29/5 E-ISSN 1432-0746 Institutional support: RVO:67985815 Keywords : gamma-ray burst * time-dependent photoionization * early optical afterglow Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.014, year: 2016

  19. The Supercritical Pile GRB Model: The Prompt to Afterglow Evolution

    Science.gov (United States)

    Mastichiadis, A.; Kazanas, D.

    2009-01-01

    The "Supercritical Pile" is a very economical GRB model that provides for the efficient conversion of the energy stored in the protons of a Relativistic Blast Wave (RBW) into radiation and at the same time produces - in the prompt GRB phase, even in the absence of any particle acceleration - a spectral peak at energy approx. 1 MeV. We extend this model to include the evolution of the RBW Lorentz factor Gamma and thus follow its spectral and temporal features into the early GRB afterglow stage. One of the novel features of the present treatment is the inclusion of the feedback of the GRB produced radiation on the evolution of Gamma with radius. This feedback and the presence of kinematic and dynamic thresholds in the model can be the sources of rich time evolution which we have began to explore. In particular. one can this may obtain afterglow light curves with steep decays followed by the more conventional flatter afterglow slopes, while at the same time preserving the desirable features of the model, i.e. the well defined relativistic electron source and radiative processes that produce the proper peak in the (nu)F(sub nu), spectra. In this note we present the results of a specific set of parameters of this model with emphasis on the multiwavelength prompt emission and transition to the early afterglow.

  20. Gamma-ray burst afterglows from transrelativistic blast wave simulations

    NARCIS (Netherlands)

    van Eerten, H. J.; Leventis, K.; Meliani, Z.; Wijers, R.A.M.J.; Keppens, R.

    2010-01-01

    We present a study of the intermediate regime between ultrarelativistic and non-relativistic flow for gamma-ray burst afterglows. The hydrodynamics of spherically symmetric blast waves is numerically calculated using the AMRVAC adaptive mesh refinement code. Spectra and light curves are calculated

  1. Gamma-ray burst afterglows from transrelativistic blast wave simulations

    NARCIS (Netherlands)

    van Eerten, H. J.; Leventis, K.; Meliani, Z.; Wijers, Ramj; Keppens, R.

    2010-01-01

    We present a study of the intermediate regime between ultrarelativistic and non-relativistic flow for gamma-ray burst afterglows. The hydrodynamics of spherically symmetric blast waves is numerically calculated using the amrvac adaptive mesh refinement code. Spectra and light curves are calculated

  2. VLT identification of the optical afterglow of the gamma-ray burst GRB 000131 at z=4.50

    DEFF Research Database (Denmark)

    Andersen, M.I.; Hjorth, J.; Pedersen, H.

    2000-01-01

    Angstrom. This places GRB 000131 at a redshift of 4.500 +/- 0.015. The inferred isotropic energy release in gamma rays alone was similar to 10(54) erg (depending on the assumed cosmology). The rapid power-law decay of the afterglow (index alpha = 2.25, similar to bursts with a prior break in the lightcurve......We report the discovery of the gamma-ray burst GRB 000131 and its optical afterglow. The optical identification was made with the VLT 84 hours after the burst following a BATSE detection and an Inter Planetary Network localization. GRB 000131 was a bright, long-duration GRB, with an apparent...... precursor signal 62 s prior to trigger. The afterglow was detected in ESO VLT, NTT, and DK1.54m follow-up observations. Broad-band and spectroscopic observations of the spectral energy distribution reveals a sharp break at optical wavelengths which is interpreted as a Ly alpha absorption edge at 6700...

  3. Three-body recombination and dynamics of electrons and excited states in the low-pressure argon afterglow

    Science.gov (United States)

    Tsankov, Tsanko Vaskov; Johnsen, Rainer; Czarnetzki, Uwe

    2016-09-01

    The afterglow phase occurs naturally during the power-off period in pulsed low-pressure plasmas and in atmospheric pressure ns discharges. During that period the electron energy rapidly declines and the charged particles are lost due to diffusion and recombination. In low-pressure discharges the dominant process is three-body recombination (TBR) of Ar+ ions with electrons. It leads to complex dynamics of the excited states, dominated by collisional-radiative cascades that eventually repopulate the metastable states. In this contribution the afterglow dynamics of an argon discharge is analyzed in detail to elucidate the roles played by the various processes. An analytical model for the fast drop of the electron energy by evaporative cooling and electron-ion collisions is combined with a time-dependent collisional radiative model for the atomic excited states that numerically solves the electron energy and density balance equations. By including further gas heating and cooling, the model leads to excellent agreement with experiments utilizing different diagnostic techniques, and hence gives insight into the interplay of the various processes in the afterglow. Work Supported by the DFG (Grant No. TS 307/1-1).

  4. Modeling cellular networks in fading environments with dominant specular components

    KAUST Repository

    AlAmmouri, Ahmad

    2016-07-26

    Stochastic geometry (SG) has been widely accepted as a fundamental tool for modeling and analyzing cellular networks. However, the fading models used with SG analysis are mainly confined to the simplistic Rayleigh fading, which is extended to the Nakagami-m fading in some special cases. However, neither the Rayleigh nor the Nakagami-m accounts for dominant specular components (DSCs) which may appear in realistic fading channels. In this paper, we present a tractable model for cellular networks with generalized two-ray (GTR) fading channel. The GTR fading explicitly accounts for two DSCs in addition to the diffuse components and offers high flexibility to capture diverse fading channels that appear in realistic outdoor/indoor wireless communication scenarios. It also encompasses the famous Rayleigh and Rician fading as special cases. To this end, the prominent effect of DSCs is highlighted in terms of average spectral efficiency. © 2016 IEEE.

  5. Gamma-ray Burst Formation Environment: Comparison of Redshift Distributions of GRB Afterglows

    Directory of Open Access Journals (Sweden)

    Sung-Eun Kim

    2005-12-01

    Full Text Available Since gamma-ray bursts(GRBs have been first known to science societites in 1973, many scientists are involved in their studies. Observations of GRB afterglows provide us with much information on the environment in which the observed GRBs are born. Study of GRB afterglows deals with longer timescale emissions in lower energy bands (e.g., months or even up to years than prompt emissions in gamma-rays. Not all the bursts accompany afterglows in whole ranges of wavelengths. It has been suggested as a reason for that, for instance, that radio and/or X-ray afterglows are not recorded mainly due to lower sensitivity of detectors, and optical afterglows due to extinctions in intergalactic media or self-extinctions within a host galaxy itself. Based on the idea that these facts may also provide information on the GRB environment, we analyze statistical properties of GRB afterglows. We first select samples of the redshift-known GRBs according to the wavelength of afterglow they accompanied. We then compare their distributions as a function of redshift, using statistical methods. As a results, we find that the distribution of the GRBs with X-ray afterglows is consistent with that of the GRBs with optical afterglows. We, therefore, conclude that the lower detection rate of optical afterglows is not due to extinctions in intergalactic media.

  6. Resource-efficient fusion over fading and non-fading reporting channels for cooperative spectrum sensing.

    Science.gov (United States)

    Guimarães, Dayan Adionel; Aquino, Guilherme Pedro

    2015-01-16

    Recently, a novel resource-efficient technique for the reporting channel transmissions in cooperative spectrum sensing was proposed. In this technique, secondary users are allowed to simultaneously send their local decisions to the fusion center, saving time and frequency resources. Expressions for the probabilities of detection and false alarm for the unitary-gain AWGN reporting channels were derived, while simulation results were given for both the AWGN and Rayleigh fading channels. Here, we provide an expression that is applicable to AWGN channels with different real-valued gains and to time-varying real-valued gains. A simple suboptimum receiver is proposed for the general complex-valued fading and non-fading channels, with an improved performance in the low signal-to-noise ratio condition. Numerical results are shown for both the AWGN and Rayleigh fading reporting channels, demonstrating the accuracy of the derived expressions and the attractive performance of the proposed receiver.

  7. Coulomb fission of a charged dust cloud in an afterglow plasma

    Science.gov (United States)

    Merlino, Robert; Meyer, John

    2015-11-01

    A dust cloud of 1 micron diameter silica microspheres was confined in a DC glow discharge dusty plasma in argon at a pressure of 100 mTorr (13 Pa). Laser sheet illumination and a fast video camera (2000 frames/s) was used to record the dynamics of this cloud following the switch-off of the plasma and confining forces. Due to the rapid decay of the plasma, and the substantial residual charge on the particles in the plasma afterglow, the cloud evolved under the mutual Coulomb repulsion forces. A variety of dynamic evolutions were observed with different clouds and under different conditions including, Coulomb explosion and expansion. In one case, the cloud underwent a Coulomb fission process, fragmenting into two clouds. Observations and analysis of this Coulomb fission event will be presented. Work supported by DOE.

  8. Transient Survey Rates for Orphan Afterglows from Compact Merger Jets

    OpenAIRE

    Lamb, Gavin P; Tanaka, Masaomi; Kobayashi, Shiho

    2017-01-01

    Orphan afterglows from short $\\gamma$-ray bursts (GRB) are potential candidates for electromagnetic (EM) counterpart searches to gravitational wave (GW) detected neutron star or neutron star black hole mergers. Various jet dynamical and structure models have been proposed that can be tested by the detection of a large sample of GW-EM counterparts. We make predictions for the expected rate of optical transients from these jet models for future survey telescopes, without a GW or GRB trigger. A ...

  9. Very High Energy Neutrinos from nearby long GRB Afterglows

    Science.gov (United States)

    Thomas, Jessymol K.; Moharana, Reetanjali; Razzaque, Soebur

    2017-09-01

    Long duration Gamma Ray Bursts (GRBs) are well-motivated sources of Ultra High Energy Cosmic Rays (UHECRs) and neutrinos. During the afterglow phase these particles can be produced as a result of acceleration and interaction there in. We have modeled afterglow spectra and light curves from synchrotron cooling of accelerated electrons. We have fitted data of 17 long GRBs detected within redshift 0.5 in case of the GRB blastwave evolving in a wind and constant density interstellar medium. The afterglow photons can interact with the shock accelerated protons to produce very high energy neutrinos. We have calculated the neutrino flux for photo-pion interactions for all these GRBs. As IceCube have been detecting very high energy neutrinos for the last four years and a larger future extension called Gen 2 is planned, this calculation will help in understanding more about GRB neutrino production. Calculation of flux and estimation of events for Northern Hemisphere GRBs are done for the upcoming neutrino observatory KM3NeT.

  10. The Arcminute Microkelvin Imager catalogue of gamma-ray burst afterglows at 15.7 GHz

    Science.gov (United States)

    Anderson, G. E.; Staley, T. D.; van der Horst, A. J.; Fender, R. P.; Rowlinson, A.; Mooley, K. P.; Broderick, J. W.; Wijers, R. A. M. J.; Rumsey, C.; Titterington, D. J.

    2018-01-01

    We present the Arcminute Microkelvin Imager (AMI) Large Array catalogue of 139 gamma-ray bursts (GRBs). AMI observes at a central frequency of 15.7 GHz and is equipped with a fully automated rapid-response mode, which enables the telescope to respond to high-energy transients detected by Swift. On receiving a transient alert, AMI can be on-target within 2 min, scheduling later start times if the source is below the horizon. Further AMI observations are manually scheduled for several days following the trigger. The AMI GRB programme probes the early-time (GRBs, and has obtained some of the earliest radio detections (GRB 130427A at 0.36 and GRB 130907A at 0.51 d post-burst). As all Swift GRBs visible to AMI are observed, this catalogue provides the first representative sample of GRB radio properties, unbiased by multiwavelength selection criteria. We report the detection of six GRB radio afterglows that were not previously detected by other radio telescopes, increasing the rate of radio detections by 50 per cent over an 18-month period. The AMI catalogue implies a Swift GRB radio detection rate of ≳ 15 per cent, down to ∼0.2 mJy beam-1. However, scaling this by the fraction of GRBs AMI would have detected in the Chandra & Frail sample (all radio-observed GRBs between 1997 and 2011), it is possible ∼ 44-56 per cent of Swift GRBs are radio bright, down to ∼0.1-0.15 mJy beam-1. This increase from the Chandra & Frail rate (∼30 per cent) is likely due to the AMI rapid-response mode, which allows observations to begin while the reverse-shock is contributing to the radio afterglow.

  11. Capacity Fade Analysis of Sulfur Cathodes in Lithium–Sulfur Batteries

    Science.gov (United States)

    Yan, Jianhua; Liu, Xingbo

    2016-01-01

    Rechargeable lithium–sulfur (Li–S) batteries are receiving ever‐increasing attention due to their high theoretical energy density and inexpensive raw sulfur materials. However, their rapid capacity fade has been one of the key barriers for their further improvement. It is well accepted that the major degradation mechanisms of S‐cathodes include low electrical conductivity of S and sulfides, precipitation of nonconductive Li2S2 and Li2S, and poly‐shuttle effects. To determine these degradation factors, a comprehensive study of sulfur cathodes with different amounts of electrolytes is presented here. A survey of the fundamentals of Li–S chemistry with respect to capacity fade is first conducted; then, the parameters obtained through electrochemical performance and characterization are used to determine the key causes of capacity fade in Li–S batteries. It is confirmed that the formation and accumulation of nonconductive Li2S2/Li2S films on sulfur cathode surfaces are the major parameters contributing to the rapid capacity fade of Li–S batteries. PMID:27981001

  12. Capacity Fade Analysis of Sulfur Cathodes in Lithium-Sulfur Batteries.

    Science.gov (United States)

    Yan, Jianhua; Liu, Xingbo; Li, Bingyun

    2016-12-01

    Rechargeable lithium-sulfur (Li-S) batteries are receiving ever-increasing attention due to their high theoretical energy density and inexpensive raw sulfur materials. However, their rapid capacity fade has been one of the key barriers for their further improvement. It is well accepted that the major degradation mechanisms of S-cathodes include low electrical conductivity of S and sulfides, precipitation of nonconductive Li2S2 and Li2S, and poly-shuttle effects. To determine these degradation factors, a comprehensive study of sulfur cathodes with different amounts of electrolytes is presented here. A survey of the fundamentals of Li-S chemistry with respect to capacity fade is first conducted; then, the parameters obtained through electrochemical performance and characterization are used to determine the key causes of capacity fade in Li-S batteries. It is confirmed that the formation and accumulation of nonconductive Li2S2/Li2S films on sulfur cathode surfaces are the major parameters contributing to the rapid capacity fade of Li-S batteries.

  13. Fading and Shadowing in Wireless Systems

    CERN Document Server

    Shankar, P Mohana

    2012-01-01

    In recent decades, growth in the field of wireless communications has led to an exponential rise in the number of journals catering to the research community. Still unmet, however, is the need to fully and comprehensively understand the effects of channel degradation brought on by the statistical fluctuations in the channel. These fluctuations mainly manifest as variations in signal power observed in the channel generally modeled using a variety of probability distributions, both in straight forms as well as in compound forms. While the former might explain some of the effects, it is the latter, namely, the compound models, which incorporate both short term and long term power fluctuations in the channel, explain the much more complex nature of the signals in these channels. Fading and Shadowing in Wireless Systems offers a pedagogical approach to the topic, with insight into the modeling and analysis of fading and shadowing. Beginning with statistical background and digital communications, the book is formul...

  14. Observations of GRB X-ray afterglows with SODART/SRG

    DEFF Research Database (Denmark)

    Brandt, Søren Kristian; Lund, Niels; Pedersen, Henrik

    1998-01-01

    Despite recent progress with the detection of afterglows of Gamma Ray Bursts (GRBs), the nature of these events is unknown. However, important clues to understanding what the GRBs are, may very well be found by studying the X-ray afterglows. The combination on SRG of the MOXE all-sky monitor for ...

  15. Spectrophotometric analysis of gamma-ray burst afterglow extinction curves with X-Shooter

    NARCIS (Netherlands)

    Japelj, J.; Covino, S.; Gomboc, A.; Vergani, S.D.; Goldoni, P.; Selsing, J.; Cano, Z.; D’Elia, V.; Flores, H.; Fynbo, J.P.U.; Hammer, F.; Hjorth, J.; Jakobsson, P.; Kaper, L.; Kopač, D.; Krühler, T.; Melandri, A.; Piranomonte, S.; Sánchez-Ramírez, R.; Tagliaferri, G.; Tanvir, N.R.; de Ugarte Postigo, A.; Watson, D.; Wijers, R.A.M.J.

    2015-01-01

    We use gamma-ray burst (GRB) afterglow spectra observed with the VLT/X-Shooter spectrograph to measure rest-frame extinction in GRB lines-of-sight by modelling the broadband near-infrared (NIR) to X-ray afterglow spectral energy distributions (SEDs). Our sample consists of nine Swift GRBs, of which

  16. Viewing angle and environment effects in gamma-ray bursts: sources of afterglow diversity

    NARCIS (Netherlands)

    Meszaros, P.; Rees, M.J.; Wijers, R.A.M.J.

    1998-01-01

    We discuss the afterglows from the evolution of both spherical and anisotropic fireballs decelerating in an inhomogeneous external medium. We consider both the radiative and adiabatic evolution regimes and analyze the physical conditions under which these regimes can be used. Afterglows may be

  17. Capacity Fade Analysis of Sulfur Cathodes in Lithium?Sulfur Batteries

    OpenAIRE

    Yan, Jianhua; Liu, Xingbo; Li, Bingyun

    2016-01-01

    Rechargeable lithium?sulfur (Li?S) batteries are receiving ever?increasing attention due to their high theoretical energy density and inexpensive raw sulfur materials. However, their rapid capacity fade has been one of the key barriers for their further improvement. It is well accepted that the major degradation mechanisms of S?cathodes include low electrical conductivity of S and sulfides, precipitation of nonconductive Li2S2 and Li2S, and poly?shuttle effects. To determine these degradation...

  18. A New Era of Submillimeter GRB Afterglow Follow-Ups with the Greenland Telescope

    Directory of Open Access Journals (Sweden)

    Yuji Urata

    2015-01-01

    Full Text Available Planned rapid submillimeter (submm gamma-ray-bursts (GRBs follow-up observations conducted using the Greenland Telescope (GLT are presented. The GLT is a 12-m submm telescope to be located at the top of the Greenland ice sheet, where the high altitude and dry weather porvide excellent conditions for observations at submm wavelengths. With its combination of wavelength window and rapid responding system, the GLT will explore new insights on GRBs. Summarizing the current achievements of submm GRB follow-ups, we identify the following three scientific goals regarding GRBs: (1 systematic detection of bright submm emissions originating from reverse shock (RS in the early afterglow phase, (2 characterization of forward shock and RS emissions by capturing their peak flux and frequencies and performing continuous monitoring, and (3 detections of GRBs at a high redshift as a result of the explosion of first generation stars through systematic rapid follow-ups. The light curves and spectra calculated by available theoretical models clearly show that the GLT could play a crucial role in these studies.

  19. Why does consciousness fade in early sleep?

    Science.gov (United States)

    Tononi, Giulio; Massimini, Marcello

    2008-01-01

    Consciousness fades during deep nonrapid eye movement (NREM) sleep early in the night, yet cortical neurons remain active, keep receiving sensory inputs, and can display patterns of synchronous activity. Why then does consciousness fade? According to the integrated information theory of consciousness, what is critical for consciousness is not firing rates, sensory input, or synchronization per se, but rather the ability of a system to integrate information. If consciousness is the capacity to integrate information, then the brain should be able to generate consciousness to the extent that it has a large repertoire of available states (information), yet it cannot be decomposed into a collection of causally independent subsystems (integration). A key prediction stemming from this hypothesis is that such ability should be greatly reduced in deep NREM sleep; the dreamless brain either breaks down into causally independent modules, shrinks its repertoire of possible responses, or both. In this article, we report the results of a series of experiments in which we employed a combination of transcranial magnetic stimulation and high-density electroencephalography (TMS/hd-EEG) to directly test this prediction in humans. Altogether, TMS/hdEEG measurements suggest that the sleeping brain, despite being active and reactive, loses its ability of entering states that are both integrated and differentiated; it either breaks down in causally independent modules, responding to TMS with a short and local activation, or it bursts into an explosive and aspecific response, producing a full-fledged slow wave.

  20. T1 VSAT Fade Compensation Statistical Results

    Science.gov (United States)

    Johnson, Sandra K.; Acosta, Roberto; Ugweje, Oke

    2000-01-01

    New satellite communication systems are steadily seeking to use higher frequency bands to accommodate the requirements for additional capacity. At these higher frequencies, propagation impairments that did not significantly affect the signal at lower frequencies begin to have considerable impact. In Ka-band. the next logical commercial frequency band to be used for satellite communication, attenuation of the signal due to rain is a primary concern. An experimental satellite built by NASA, the Advanced Communication Technology Satellite (ACTS). launched in September 1993, is the first U.S. communication satellite operating in the Ka-band. In addition to higher carrier frequencies, a number of other new technologies, including on-board baseband processing. multiple beam antennas, and rain fade detection and compensation techniques, were designed into the ACTS. Verification experiments have been conducted since the launch to characterize the new technologies. The focus of this paper is to characterize the method used by the ACTS TI Very Small Aperture Terminal (TI VSAT) ground stations in detecting the presence of fade in the communication signal and to adaptively compensate for it by the addition of burst rate reduction and forward error correction. Measured data obtained from the ACTS program was used to validate the compensation technique. A software process was developed and demonstrated to statistically characterize the increased availability achieved by the compensation techniques in terms of the bit error rate time enhancement factor. Several improvements to the ACTS technique are discussed and possible implementations for future Ka band system are offered.

  1. Colour variations in the GRB 120327A afterglow

    Science.gov (United States)

    Melandri, A.; Covino, S.; Zaninoni, E.; Campana, S.; Bolmer, J.; Cobb, B. E.; Gorosabel, J.; Kim, J.-W.; Kuin, P.; Kuroda, D.; Malesani, D.; Mundell, C. G.; Nappo, F.; Sbarufatti, B.; Smith, R. J.; Steele, I. A.; Topinka, M.; Trotter, A. S.; Virgili, F. J.; Bernardini, M. G.; D'Avanzo, P.; D'Elia, V.; Fugazza, D.; Ghirlanda, G.; Gomboc, A.; Greiner, J.; Guidorzi, C.; Haislip, J. B.; Hanayama, H.; Hanlon, L.; Im, M.; Ivarsen, K. M.; Japelj, J.; Jelínek, M.; Kawai, N.; Kobayashi, S.; Kopac, D.; LaCluyzé, A. P.; Martin-Carrillo, A.; Murphy, D.; Reichart, D. E.; Salvaterra, R.; Salafia, O. S.; Tagliaferri, G.; Vergani, S. D.

    2017-10-01

    Aims: We present a comprehensive temporal and spectral analysis of the long Swift GRB 120327A afterglow data to investigate possible causes of the observed early-time colour variations. Methods: We collected data from various instruments and telescopes in X-ray, ultraviolet, optical, and near-infrared bands, and determined the shapes of the afterglow early-time light curves. We studied the overall temporal behaviour and the spectral energy distributions from early to late times. Results: The ultraviolet, optical, and near-infrared light curves can be modelled with a single power-law component between 200 and 2 × 104 s after the burst event. The X-ray light curve shows a canonical steep-shallow-steep behaviour that is typical of long gamma-ray bursts. At early times a colour variation is observed in the ultraviolet/optical bands, while at very late times a hint of a re-brightening is visible. The observed early-time colour change can be explained as a variation in the intrinsic optical spectral index, rather than an evolution of the optical extinction. Table 2 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/607/A29

  2. Fermi and Swift Gamma-Ray Burst Afterglow Population Studies

    Science.gov (United States)

    Racusin, Judith L.; Oates, S. R.; Schady, P.; Burrows, D. N.; dePasquale, M.; Donato, D.; Gehrels, N.; Koch, S.; McEnery, J.; Piran, T.; hide

    2011-01-01

    The new and extreme population of GRBs detected by Fermi -LAT shows several new features in high energy gamma-rays that are providing interesting and unexpected clues into GRB prompt and afterglow emission mechanisms. Over the last 6 years, it has been Swift that has provided the robust dataset of UV/optical and X-ray afterglow observations that opened many windows into components of GRB emission structure. The relationship between the LAT detected GRBs and the well studied, fainter, less energetic GRBs detected by Swift -BAT is only beginning to be explored by multi-wavelength studies. We explore the large sample of GRBs detected by BAT only, BAT and Fermi -GBM, and GBM and LAT, focusing on these samples separately in order to search for statistically significant differences between the populations, using only those GRBs with measured redshifts in order to physically characterize these objects. We disentangle which differences are instrumental selection effects versus intrinsic properties, in order to better understand the nature of the special characteristics of the LAT bursts.

  3. Flash-induced fading: Dependence on colour and shape similarity

    NARCIS (Netherlands)

    Vergeer, M.; Lier, R.J. van

    2005-01-01

    We investigated the effects of perceptual grouping by colour and shape similarity on flash-induced perceptual fading. This flash-induced fading effect (Kanai et al, 2003 Journal of Cognitive Neuroscience 15 664 - 672) is considered as a time-locked variant of the Troxler effect. In the original

  4. Grouping effects in flash-induced perceptual fading

    NARCIS (Netherlands)

    Vergeer, M.L.T.; Lier, R.J. van

    2007-01-01

    We show that the flash-induced fading effect can be influenced by grouping based on colour and shape similarity. In flash-induced fading, peripherally presented elements perceptually disappear after a flash has been presented around or next to the element(s) (Kanai and Kamitani, 2003 Journal of

  5. k– fading channels: a finite state Markov modelling approach

    Indian Academy of Sciences (India)

    C Priyanka

    2018-02-07

    Feb 7, 2018 ... Lognormal distribution is used to describe long-term signal variations, whereas short-term signal variations are described by Rice (Nakagami-n),. Rayleigh, Weibull, Nakagami-m and Hoyt (Nakagami-q) distributions [1]. The k–l fading distribution describes small-scale variations of the fading channel under ...

  6. Autonomous detection of ISO fade point with color laser printers

    Science.gov (United States)

    Yan, Ni; Maggard, Eric; Fothergill, Roberta; Jessome, Renee J.; Allebach, Jan P.

    2015-01-01

    Image quality assessment is a very important field in image processing. Human observation is slow and subjective, it also requires strict environment setup for the psychological test 1. Thus developing algorithms to match desired human experiments is always in need. Many studies have focused on detecting the fading phenomenon after the materials are printed, that is to monitor the persistence of the color ink 2-4. However, fading is also a common artifact produced by printing systems when the cartridges run low. We want to develop an automatic system to monitor cartridge life and report fading defects when they appear. In this paper, we first describe a psychological experiment that studies the human perspective on printed fading pages. Then we propose an algorithm based on Color Space Projection and K-means clustering to predict the visibility of fading defects. At last, we integrate the psychological experiment result with our algorithm to give a machine learning tool that monitors cartridge life.

  7. Secure Path Selection under Random Fading

    Directory of Open Access Journals (Sweden)

    Furqan Jameel

    2017-05-01

    Full Text Available Application-oriented Wireless Sensor Networks (WSNs promises to be one of the most useful technologies of this century. However, secure communication between nodes in WSNs is still an unresolved issue. In this context, we propose two protocols (i.e. Optimal Secure Path (OSP and Sub-optimal Secure Path (SSP to minimize the outage probability of secrecy capacity in the presence of multiple eavesdroppers. We consider dissimilar fading at the main and wiretap link and provide detailed evaluation of the impact of Nakagami-m and Rician-K factors on the secrecy performance of WSNs. Extensive simulations are performed to validate our findings. Although the optimal scheme ensures more security, yet the sub-optimal scheme proves to be a more practical approach to secure wireless links.

  8. Fading prediction in thermoluminescent materials using computerised glow curve deconvolution (CGCD)

    CERN Document Server

    Furetta, C; Weng, P S

    1999-01-01

    The fading of three different thermoluminescent (TL) materials, CaF sub 2 : Tm (TLD-300), manocrystalline LiF : Mg,Ti (DTG-4) and MgB sub 4 O sub 7 : Dy,Na has been studied at room temperature and at 50 deg. C of storage. The evolution as a function of the elapsed time of the whole glow curve as well as of the individual peaks has been analysed using the Computerised Glow Curve Deconvolution (CGCD) program developed at the NTHU. The analysis allows to predict the loss of the dosimetric information and to make any correction is necessary for using the TL dosimeters in practical applications. Furthermore, it is well demonstrated that using CGCD it is not necessary to anneal the peaks having a rapid fading to avoid, then, any interfering effect on the more stable peaks.

  9. Bremsstrahlung analysis through the microwave cutoff and afterglow performances

    CERN Document Server

    Lamoureux, M P; Niimura, M; Kidera, M; Nakagawa, T

    1999-01-01

    Bremsstralung spectra with a very good energy resolution have been obtained for various time slabs of a few ms throughout the microwave cutoff. In a recent work (1) we had noticed+ and explained why the enhancement of the extracted high charge currents by the afterglow effect is more pronounced when the X-ray emission in the heating stage is more intense. In the present communication, we give some additional information deduced from our spectra. We indicate estimates of the temperature parameter and of the density of the hot electron population at various times. For this purpose the method presented in ref.(3) was adapted to argon. We also determine the maximum energy reached by the electrons in the steady state; the spare results seem to follow the scaling law indicated in Geller's book (4).

  10. Gamma-ray burst afterglow plateaus and gravitational waves

    Energy Technology Data Exchange (ETDEWEB)

    Corsi, Alessandra [Universita di Roma Sapienza and INFN-Roma, Piazzale Aldo Moro 2, 00185-Roma (Italy); Meszaros, Peter, E-mail: alessandra.corsi@roma1.infn.i, E-mail: nnp@astro.psu.ed [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States)

    2009-10-21

    The existence of a shallow decay phase in the early x-ray afterglows of gamma-ray bursts is a common feature. We discuss the possibility that such a feature is connected to the formation of a highly magnetized millisecond pulsar, pumping energy into the fireball via magnetic dipole emission, while undergoing a secular bar-mode instability. If this is the case, gravitational wave losses associated with the neutron star's ellipsoidal deformation, would affect the star's spin-down, possibly producing a gravitational wave signal detectable by the advanced LIGO and Virgo. Such a signal, being emitted in association with an observed x-ray light-curve plateau over relatively long timescales, could open a new interesting opportunity for multi-messenger studies to be carried out in coincidence with gamma-ray burst sources. We conclude that the hypothesis proposed here deserves further investigation.

  11. Performance analysis of replication ALOHA for fading mobile communications channels

    Science.gov (United States)

    Yan, Tsun-Yee; Clare, Loren P.

    1986-01-01

    This paper describes an ALOHA random access protocol for fading communications channels. A two-state Markov model is used for the channel error process to account for the channel fading memory. The ALOHA protocol is modified to send multiple contiguous copies of a message at each transmission attempt. Both pure and slotted ALOHA channels are considered. The analysis is applicable to fading environments where the channel memory is short compared to the propagation delay. It is shown that smaller delay may be achieved using replications and, in noisy conditions, can also improve throughput.

  12. Colour Fading of Textile Fabric by Plasma Treatment

    OpenAIRE

    H. F. Cheung; C. W. Kan; C. W. M. YUEN; J. Yip; Law, M.C.

    2013-01-01

    Colour fading of a reactive dye (C.I. Reactive Blue 19) dyed textile fabric was performed by atmospheric pressure plasma (APP) treatment with the use of plasma jet. Under the APP treatment condition of treatment time = 5 sec/mm; ignition power = 160 W; oxygen concentration = 1%; jet distance = 3 mm, significant colour-fading effect was achieved. For comparison purpose, the reactive dye dyed textile fabric was subjected to conventional enzymatic colour-fading process. Experimental results reve...

  13. The Two-User Gaussian Fading Broadcast Channel

    CERN Document Server

    Jafarian, Amin

    2011-01-01

    This paper presents outerbounds for the two-user Gaussian fading broadcast channel. These outerbounds are based on Costa's entropy power inequality (Costa-EPI) and are formulated mathematically as a feasibility problem. For classes of the two-user Gaussian fading broadcast channel where the outerbound is found to have a feasible solution, we find conditions under which a suitable inner and outer bound meet. For all such cases, this paper provides a partial characterization of the capacity region of the Gaussian two-user fading broadcast channel.

  14. Fade detector for the FODA-TDMA access scheme

    Science.gov (United States)

    Celandroni, Nedo; Ferro, Erina; Marzoli, Antonio

    1989-05-01

    The First in first out Ordered Demand Assignment-Time Division Multiple Access (FODA-TDMA) satellite access scheme designed for simultaneous transmissions of real time data, like packetized voice and slow-scan images (stream traffic) and data coming from standard EDP applications, such as bulk data tansfer, interactive computer access, mailing, data base enquiry and updating (datagram traffic) is described. When deep fades are experienced due to rain attenuation, the system is able to counter the fade. Techniques to detect the fade are presented.

  15. Optical and X-ray Afterglows in the Cannonball Model of GRBs

    OpenAIRE

    De Rújula, Alvaro

    2002-01-01

    The Cannonball Model is based on the hypothesis that GRBs and their afterglows are made in supernova explosions by relativistic ejecta similar to the ones observed in quasars and microquasars. Its predictions are simple, and analytical in fair approximations. The model describes well the properties of the $\\gamma$-rays of GRBs. It gives a very simple and extremely successful description of the optical and X-ray afterglows of {\\it all} GRBs of known redshift. The only problem the model has, so...

  16. Fading of Jupiter's South Equatorial Belt

    Science.gov (United States)

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

    2011-01-01

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

  17. PASSING STANDARDIZED ASSESSMENTS WITH FADING PROMPTS

    Directory of Open Access Journals (Sweden)

    Amy Marie GREENE

    2015-11-01

    Full Text Available Introduction: No Child Left Behind Act of 2001 mandates that all students perform at a level of proficient on state assessments. This includes students with learning and intellectual disabilities who are inherently performing below grade level. Given that schools are held accountable for meeting these goals and some states are not allowing students to graduate if they do not pass the assessments, this is a large concern for students, parents, teachers, and administration Method: Forty-five students with a disability in writing or an intellectual disability participated in this quasi-experimental, single-group, pretest-posttest design that evaluated the effectiveness of the Fading Prompts through Graphic Organizers method for students with learning and intellectual disabilities in written expression as measured according to the Pennsylvania System of School Assessment. Results: Data analyses were conducted through the use of four dichotomies for percent differences, which compared teacher administered pretests and posttests, pretests and the state administered PSSA, teacher administered posttests and the PSSA, and the participants’ PSSA and the average state PSSA score. All forty-five students performed at a below basic level during baseline and a proficient level on the posttest. The learned skills generalized to the PSSA with forty-three students earning a passing score of proficient, while two students advanced to basic. Conclusion: Based on the outcomes of this study, it is highly recommended that this program be utilized at least for students with learning and intellectual disabilities until further research can be done.

  18. Capacity and coding in the presence of fading and jamming

    Science.gov (United States)

    Stark, W. E.; McEliece, R. J.

    The capacity of noncoherent FSK in the presence of fading and partial band jamming is presented. It is observed that for both partial band jamming and fading there is an optimal nonzero code rate that minimizes the energy per bit required to achieve reliable communication. For low enough code rates uniform jamming is the best strategy that the jammer can adopt. We also give results for Reed-Solomon codes on the partial-band jamming channel.

  19. Fading Noise Reduction Effect Through the Short Time DFT Compander

    OpenAIRE

    岸, 政七; 袁, 暁輝

    1994-01-01

    Signals transmitted over poor radio channels are interfered by fading noise to be degraded in speech quality. The short time DFT (ST DFT) compander has successfully excluded envelope detection owing to employing concept of instantaneous spectrum instead of employing approximated AM demodulation in realizing the envelope detectors. This ST DFT compander is able to reduce fading noise to improve speech quality over poor radio channels without any distortions. The ST DFT compander is discussed i...

  20. The VLT/X-shooter GRB afterglow legacy survey

    Science.gov (United States)

    Kaper, Lex; Fynbo, Johan P. U.; Pugliese, Vanna; van Rest, Daan

    2017-11-01

    The Swift satellite allows us to use gamma-ray bursts (GRBs) to peer through the hearts of star forming galaxies through cosmic time. Our open collaboration, representing most of the active European researchers in this field, builds a public legacy sample of GRB X-shooter spectroscopy while Swift continues to fly. To date, our spectroscopy of more than 100 GRB afterglows covers a redshift range from 0.059 to about 8 (Tanvir et al. 2009, Nature 461, 1254), with more than 20 robust afterglow-based metallicity measurements (over a redshift range from 1.7 to 5.9). With afterglow spectroscopy (throughout the electromagnetic spectrum from X-rays to the sub-mm) we can hence characterize the properties of star-forming galaxies over cosmic history in terms of redshift, metallicity, molecular content, ISM temperature, UV-flux density, etc.. These observations provide key information on the final evolution of the most massive stars collapsing into black holes, with the potential of probing the epoch of the formation of the first (very massive) stars. VLT/X-shooter (Vernet et al. 2011, A&A 536, A105) is in many ways the ideal GRB follow-up instrument and indeed GRB follow-up was one of the primary science cases behind the instrument design and implementation. Due to the wide wavelength coverage of X-shooter, in the same observation one can detect molecular H2 absorption near the atmospheric cut-off and many strong emission lines from the host galaxy in the near-infrared (e.g., Friis et al. 2015, MNRAS 451, 167). For example, we have measured a metallicity of 0.1 Z ⊙ for GRB 100219A at z = 4.67 (Thöne et al. 2013, MNRAS 428, 3590), 0.02 Z ⊙ for GRB 111008A at z = 4.99 (Sparre et al. 2014, ApJ 785, 150) and 0.05 Z ⊙ for GRB 130606A at z = 5.91 (Hartoog et al. 2015, A&A 580, 139). In the latter, the very high value of [Al/Fe]=2.40 +/- 0.78 might be due to a proton capture process and may be a signature of a previous generation of massive (perhaps even the first) stars

  1. Dynamic Model of Signal Fading due to Swaying Vegetation

    Directory of Open Access Journals (Sweden)

    Torbjörn Ekman

    2009-01-01

    Full Text Available In this contribution, we use fading measurements at 2.45, 5.25, 29, and 60 GHz, and wind speed data, to study the dynamic effects of vegetation on propagating radiowaves. A new simulation model for generating signal fading due to a swaying tree has been developed by utilizing a multiple mass-spring system to represent a tree and a turbulent wind model. The model is validated in terms of the cumulative distribution function (CDF, autocorrelation function (ACF, level crossing rate (LCR, and average fade duration (AFD using measurements. The agreements found between the measured and simulated first- and second-order statistics of the received signals through vegetation are satisfactory. In addition, Ricean K-factors for different wind speeds are estimated from measurements. Generally, the new model has similar dynamical and statistical characteristics as those observed in measurements and can thus be used for synthesizing signal fading due to a swaying tree. The synthesized fading can be used for simulating different capacity enhancing techniques such as adaptive coding and modulation and other fade mitigation techniques.

  2. A new simple model for composite fading channels: Second order statistics and channel capacity

    KAUST Repository

    Yilmaz, Ferkan

    2010-09-01

    In this paper, we introduce the most general composite fading distribution to model the envelope and the power of the received signal in such fading channels as millimeter wave (60 GHz or above) fading channels and free-space optical channels, which we term extended generalized-K (EGK) composite fading distribution. We obtain the second-order statistics of the received signal envelope characterized by the EGK composite fading distribution. Expressions for probability density function, cumulative distribution function, level crossing rate and average fade duration, moments, amount of fading and average capacity are derived. Numerical and computer simulation examples validate the accuracy of the presented mathematical analysis. © 2010 IEEE.

  3. Fireballs and cannonballs confront the afterglow of GRB 991208

    CERN Document Server

    Dado, S; De Rújula, Alvaro; Dado, Shlomo; Dar, Arnon; Rujula, Alvaro De

    2003-01-01

    Galama et al. have recently reported their follow-up measurements of the radio afterglow (AG) of the Gamma Ray Burst (GRB) 991208, up to 293 days after burst, and their reanalysis of the broad-band AG, in the framework of standard fireball models. They advocate a serious revision of their prior analysis and conclusions, based on optical data and on their earlier observations during the first two weeks of the AG. We comment on their work and fill a lacuna: these authors have overlooked the possibility of comparing their new data to the available predictions of the cannonball (CB) model, based --like their incorrect predictions-- on the first round of data. The new data are in good agreement with these CB-model predictions. This is in spite of the fact that, in comparison to the fireball models, the CB model is much simpler, much more predictive, has many fewer parameters, practically no free choices... and it describes well --on a universal basis-- all the measured AGs of GRBs of known redshift.

  4. Short Hard Gamma Ray Bursts And Their Afterglows

    CERN Document Server

    Dado, Shlomo

    2009-01-01

    Long duration gamma ray bursts (GRBs) and X-ray flashes (XRFs) are produced by highly- relativistic jets ejected in core-collapse supernova explosions. The origin of short hard gamma-ray bursts (SHBs) has not been established. They may be produced by highly relativistic jets ejected in various processes: mergers of compact stellar objects; large-mass accretion episodes onto compact stars in close binaries or onto intermediate-mass black holes in dense stellar regions; phase transition of compact stars. Natural environments of such events are the dense cores of globular clusters, superstar clusters and young supernova remnants. We have used the cannonball model of GRBs to analyze all Swift SHBs with a well-sampled X-ray afterglow. We show that their prompt gamma-ray emission can be explained by inverse Compton scattering (ICS) of the progenitor's glory light, and their extended soft emission component by ICS of high density light or synchrotron radiation (SR) in a high density interstellar medium within the cl...

  5. Thermal Electrons in Gamma-Ray Burst Afterglows

    Science.gov (United States)

    Ressler, Sean M.; Laskar, Tanmoy

    2017-08-01

    To date, nearly all multi-wavelength modeling of long-duration γ-ray bursts has ignored synchrotron radiation from the significant population of electrons expected to pass the shock without acceleration into a power-law distribution. We investigate the effect of including the contribution of thermal, non-accelerated electrons to synchrotron absorption and emission in the standard afterglow model, and show that these thermal electrons provide an additional source of opacity to synchrotron self-absorption, and yield an additional emission component at higher energies. The extra opacity results in an increase in the synchrotron self-absorption frequency by factors of 10-100 for fiducial parameters. The nature of the additional emission depends on the details of the thermal population, but is generally observed to yield a spectral peak in the optical brighter than radiation from the nonthermal population by similar factors a few seconds after the burst, remaining detectable at millimeter and radio frequencies several days later.

  6. How Bad or Good Are the External Forward Shock Afterglow Models of Gamma-Ray Bursts?

    Science.gov (United States)

    Wang, Xiang-Gao; Zhang, Bing; Liang, En-Wei; Gao, He; Li, Liang; Deng, Can-Min; Qin, Song-Mei; Tang, Qing-Wen; Kann, D. Alexander; Ryde, Felix; Kumar, Pawan

    2015-07-01

    The external forward shock models have been the standard paradigm to interpret the broadband afterglow data of gamma-ray bursts (GRBs). One prediction of the models is that some afterglow temporal breaks at different energy bands should be achromatic; that is, the break times should be the same in different frequencies. Multiwavelength observations in the Swift era have revealed chromatic afterglow behaviors at least in some GRBs, casting doubts on the external forward shock origin of GRB afterglows. In this paper, using a large sample of GRBs with both X-ray and optical afterglow data, we perform a systematic study to address the question: how bad or good are the external forward shock models? Our sample includes 85 GRBs up to 2014 March with well-monitored X-ray and optical light curves. Based on how well the data abide by the external forward shock models, we categorize them into five grades and three samples. The first two grades (Grade I and II) include 45 of 85 GRBs. They show evidence of, or are consistent with having, an achromatic break. The temporal and spectral behaviors in each afterglow segment are consistent with the predictions (the “closure relations”) of the forward shock models. These GRBs are included in the Gold sample. The next two grades (Grade III and IV) include 37 of 85 GRBs. They are also consistent with having an achromatic break, even though one or more afterglow segments do not comply with the closure relations. These GRBs are included in the Silver sample. Finally, Grade V (3/85) shows direct evidence of chromatic behaviors, suggesting that the external shock models are inconsistent with the data. These are included in the Bad sample. We further perform statistical analyses of various observational properties (temporal index α, spectral index β, break time tb) and model parameters (energy injection index q, electron spectral index p, jet opening angle {θ }j, radiative efficiency ηγ, and so on) of the GRBs in the Gold sample

  7. Relaxation of heavy species and gas temperature in the afterglow of a N2 microwave discharge★

    Science.gov (United States)

    Pintassilgo, Carlos D.; Guerra, Vasco

    2017-10-01

    In this paper we present a self-consistent kinetic model to study the temporal variation of the gas temperature in the afterglow of a 440 Pa microwave nitrogen discharge operating at 433 MHz in a 3.8 cm diameter tube. The initial conditions in the afterglow are determined by a kinetic model that solves the electron Boltzmann equation coupled to the gas thermal balance equation and a system of rate-balance equations for N2(X 1∑g+, v) molecules, electronically excited states of N2, ground and excited states of atomic nitrogen and the main positive ions. Once the initial concentrations of the heavy species and gas temperature are known, their relaxation in the afterglow is obtained from the solutions to the corresponding time-dependent equations. Modelling predictions are found to be in good agreement with previously measured values for the concentrations of N(4S) atoms and N2(A 3∑u+) molecules, and the radially averaged gas temperature Tg along the afterglow of a microwave discharge in N2 under the same working conditions. It is shown that gas heating in the afterglow comes essentially from the energy transfer involving non-resonant vibration-vibration (V-V) collisions between vibrationally excited nitrogen molecules, as well as from energy exchanges in vibration-translation (V-T) on N2-N collisions. Contribution to the topical issue "Plasma Sources and Plasma Processes (PSPP)", edited by Luis Lemos Alves, Thierry Belmonte and Tiberiu Minea

  8. On the optical and X-ray afterglows of gamma ray bursts

    CERN Document Server

    Dado, S; De Rújula, Alvaro; Dado, Shlomo; Dar, Arnon; Rujula, Alvaro De

    2002-01-01

    We severely criticize the consuetudinary analysis of the afterglows of gamma-ray bursts (GRBs) in the conical-ejection fireball scenarios. We argue that, instead, recent observations imply that the long-duration GRBs and their afterglows are produced by highly relativistic jets of cannonballs (CBs) emitted in supernova explosions. The CBs are heated by their collision with the supernova shell. The GRB is the boosted surface radiation the CBs emit as they reach the transparent outskirts of the shell. The exiting CBs further decelerate by sweeping up interstellar matter (ISM). The early afterglow is dominated by thermal bremsstrahlung from the cooling CB, the late afterglow by synchrotron radiation from the ISM electrons swept up by the CBs. We show that this model fits simply and remarkably well all the measured optical afterglows of the 15 GRBs with known redshift. We find that the CBs of GRB 970508 were gravitationally lensed by an intervening star, and moved extremely superluminally for kiloparsecs. The aft...

  9. BER Performance of M-ary FSK Modulation over AWGN and Rayleigh Fading Channels

    Directory of Open Access Journals (Sweden)

    Yazen Saifuldeen Almashhadani

    2017-07-01

    Full Text Available In a mobile communication environment, there is a rising demand of low Bit Error Rate (BER. The channel is not time invariant since the received signal depends on many fast changing factors, and thus it will lead to fading channels. Statistical models are typically used to simulate fading. In this paper, the BER versus Eb/No will simulate the non-faded and faded channels. Using Rayleigh statistical model, the BER of different channel fading types is studied based on time delay spread can have flat fading or frequency selective fading and also based on the Doppler shift can have slow fading or fast fading taking into consideration the M-ary FSK modulation scheme. The overall system is implemented by using MATLAB.

  10. Digital radio link: Multipath fading on a 7 GHz line-of-sight link

    Science.gov (United States)

    Mattsson, Stefan

    1987-11-01

    Propagation measurements on a 7 GHz, 34 Mb/sec 53 km link were made to characterize the radio channel with suitable models during multipath propagation causing frequency selective or flat fading within the actual bandwidth. From the narrow band sweep measurements, the propagation parameters, corresponding to frequency selective events, are extracted by a minimum square fit of a modeled 3-way transfer function to observed transfer functions. The statistical distributions of measured wide band fade depth are estimated for an unprotected and a space diversity channel using antenna separation of 8 m. The statistical distribution of the durations of deep fades are estimated. The optimal choice of vertical antenna separation is discussed, concerning the ability to combat severe frequency selective fading. A three ray model is shown to be appropriate. Measurements of fade duration show that 70 percent of all fading events with fade depths of 34 dB or more have durations below 3 sec. A fit of the CCIR-proposed prediction of mean fade duration to measured mean fade duration shows that the CCIR-model with C=52 is useful for studied conditions. Based on the CCIR-model, the mean fade duration decreases with increasing fade depth. On the actual 53 km path, fading events with fade depths exceeding the flat fade margin 40 dB have a mean duration below 2 sec.

  11. The very red afterglow of GRB 000418: Further evidence for dust extinction in a gamma-ray burst host galaxy

    DEFF Research Database (Denmark)

    Klose, S.; Stecklum, B.; Masetti, N.

    2000-01-01

    We report near-infrared and optical follow-up observations of the afterglow of the GRB 000418 starting 2.5 days after the occurrence of the burst and extending over nearly 7 weeks. GRB 000418 represents the second case for which the afterglow was initially identified by observations in the near-i...

  12. The γ-ray afterglows of tidal disruption events.

    Science.gov (United States)

    Chen, Xian; Gómez-Vargas, Germán Arturo; Guillochon, James

    2016-05-21

    A star wandering too close to a supermassive black hole (SMBH) will be tidally disrupted. Previous studies of such 'tidal disruption event' (TDE) mostly focus on the stellar debris that are bound to the system, because they give rise to luminous flares. On the other hand, half of the stellar debris in principle are unbound and can stream to a great distance, but so far there is no clear evidence that this 'unbound debris stream' (UDS) exists. Motivated by the fact that the circum-nuclear region around SMBHs is usually filled with dense molecular clouds (MCs), here we investigate the observational signatures resulting from the collision between an UDS and an MC, which is likely to happen hundreds of years after a TDE. We focus on γ-ray emission (0.1-10(5) GeV), which comes from the encounter of shock-accelerated cosmic rays with background protons and, more importantly, is not subject to extinction. We show that because of the high proton density inside an MC, the peak γ-ray luminosity, about 10(39) erg s(-1), is at least 100 times greater than that in the case without an MC (only with a smooth interstellar medium). The luminosity decays on a time-scale of decades, depending on the distance of the MC, and about a dozen of these 'TDE afterglows' could be detected within a distance of about 16 Mpc by the future Cherenkov Telescope Array. Without careful discrimination, these sources potentially could contaminate the searches for starburst galaxies, galactic nuclei containing millisecond pulsars or dark matter annihilation signals.

  13. Machine Learning Search for Gamma-Ray Burst Afterglows in Optical Images

    Science.gov (United States)

    Topinka, M.

    2016-06-01

    Thanks to the advances in robotic telescopes, time domain astronomy leads to a large number of transient events detected in images every night. Data mining and machine learning tools used for object classification are presented. The goal is to automatically classify transient events for both further follow-up by a larger telescope and for statistical studies of transient events. Special attention is given to the identification of gamma-ray burst afterglows. Machine learning techniques are used to identify GROND gamma-ray burst afterglow among the astrophysical objects present in the SDSS archival images based on the g'-r', r'-i' and i'-z' color indices. The performance of the support vector machine, random forest and neural network algorithms is compared. A joint meta-classifier, built on top of the individual classifiers, can identify GRB afterglows with the overall accuracy of ≳ 90%.

  14. Study on the Influence Factors of the Luminous Intensity of the Long Afterglow Luminous Paints

    Directory of Open Access Journals (Sweden)

    Zhao Su

    2016-01-01

    Full Text Available In order to extend the time afterglow luminous powder, enhancement the brightness of luminous paint, this study explore affect long afterglow energy storage luminous paints brightness of the main factors. Luminous paints were prepared with rare earth aluminate long afterglow luminescent powder, first is luminous powder surface modification, then investigate the influence of light emitting powder content, calcium carbonate, titanium dioxide, nano alumina and other fillers on the luminescent properties of the paints. It was concluded that the water resistance of the luminescent powder is better and the brightness can be improved after the modification of anhydrous alcohol. The addition of nano-alumina can improve the brightness of the system, and can effectively enhance the hardness of the paints. In the paints, the two kinds of components of carbonate and titanium dioxide have little effect on the luminescent brightness of the painting.

  15. Controlled growth of copper oxide nanostructures by atmospheric pressure micro-afterglow

    Science.gov (United States)

    Altaweel, A.; Filipič, G.; Gries, T.; Belmonte, T.

    2014-12-01

    A large variety of copper oxide nanostructures encompassing nanodots, nanowires and nanowalls, sometimes organized in ;cabbage-like; architectures, are grown locally by direct oxidation of copper thin films using the micro-afterglow of an Ar-O2 microwave plasma operating at atmospheric pressure. Morphology, structure and composition of the oxidized copper thin films are characterized by X-ray diffraction, secondary ion mass spectrometry and scanning electron microscopy. The concentric areas where each kind of nanostructures is found are defined by both their radial position with respect to the afterglow centre and by experimental conditions. A growth mechanism is proposed, based on stress-induced outward migration of copper ions. The development of stress gradients is caused by the formation of a copper oxide scale layer. If copper oxide nanowires can be grown as in thermal oxidation processes, micro-afterglow conditions offer novel nanostructures and nano-architectures.

  16. Electron energy and vibrational distribution functions of carbon monoxide in nanosecond atmospheric discharges and microsecond afterglows

    Science.gov (United States)

    Pietanza, L. D.; Colonna, G.; Capitelli, M.

    2017-12-01

    Nanopulse atmospheric carbon monoxide discharges and corresponding afterglows have been investigated in a wide range of applied reduced electric field (130 kinetics of vibrational and electronic excited states as well as to a simplified plasma chemistry for the different species formed during the activation of CO. The molar fraction of electronically excited states generated in the discharge is sufficient to create structures in the EEDF in the afterglow regime. On the other hand, only for long duration pulses (i.e. 50 ns), non-equilibrium vibrational distributions can be observed especially in the afterglow. The trend of the results for the case study E/N = 200 Td, \\text{pulse}=2$ ns is qualitatively and quantitatively similar to the corresponding case for CO2 implying that the activation of CO2 by cold plasmas should take into account the kinetics of formed CO with the same accuracy as the CO2 itself.

  17. Rayleigh fading effect reduction with wideband DS/CDMA signals

    Science.gov (United States)

    Holtzman, Jack M.; Jalloul, Louay M. A.

    1994-02-01

    Mobile radio fading analyses typically assume a single frequency carrier transmitted through the propagation medium. The results are then used for the case of narrowband transmission. New phenomena occur with wideband transmission. This paper presents an analysis of the mitigation of the Rayleigh fading effect for wideband direct sequence code division multiple access (DS/CDMA) signaling. There are measurements that show this phenomenon. The reduction of the Rayleigh fading effect is an advantage of CDMA over narrowband transmission systems and it eases the burden of CDMA power control. A general expression for the coefficient of variation of the received wideband signal power is derived. It is shown how the coefficient of variation of the received power decreases as the bandwidth spreading increases. This paper also analyzes the time correlation needed for other analyses (e.g., CDMA power control).

  18. Secret Sharing over Fast-Fading MIMO Wiretap Channels

    Directory of Open Access Journals (Sweden)

    Bloch Matthieu

    2009-01-01

    Full Text Available Secret sharing over the fast-fading MIMO wiretap channel is considered. A source and a destination try to share secret information over a fast-fading MIMO channel in the presence of an eavesdropper who also makes channel observations that are different from but correlated to those made by the destination. An interactive, authenticated public channel with unlimited capacity is available to the source and destination for the secret sharing process. This situation is a special case of the "channel model with wiretapper" considered by Ahlswede and Csiszár. An extension of their result to continuous channel alphabets is employed to evaluate the key capacity of the fast-fading MIMO wiretap channel. The effects of spatial dimensionality provided by the use of multiple antennas at the source, destination, and eavesdropper are then investigated.

  19. Secret Sharing over Fast-Fading MIMO Wiretap Channels

    Directory of Open Access Journals (Sweden)

    Tan F. Wong

    2009-01-01

    Full Text Available Secret sharing over the fast-fading MIMO wiretap channel is considered. A source and a destination try to share secret information over a fast-fading MIMO channel in the presence of an eavesdropper who also makes channel observations that are different from but correlated to those made by the destination. An interactive, authenticated public channel with unlimited capacity is available to the source and destination for the secret sharing process. This situation is a special case of the “channel model with wiretapper” considered by Ahlswede and Csiszár. An extension of their result to continuous channel alphabets is employed to evaluate the key capacity of the fast-fading MIMO wiretap channel. The effects of spatial dimensionality provided by the use of multiple antennas at the source, destination, and eavesdropper are then investigated.

  20. GRB 080503 LATE AFTERGLOW RE-BRIGHTENING: SIGNATURE OF A MAGNETAR-POWERED MERGER-NOVA

    Energy Technology Data Exchange (ETDEWEB)

    Gao, He; Ding, Xuan; Wu, Xue-Feng [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China); Dai, Zi-Gao [School of Astronomy and Space Science, Nanjing University, Nanjing 2100093 (China); Zhang, Bing, E-mail: hug18@psu.edu, E-mail: xfwu@pmo.ac.cn, E-mail: dzg@nju.edu.cn, E-mail: zhang@physics.unlv.edu [Department of Physics and Astronomy, University of Nevada Las Vegas, NV 89154 (United States)

    2015-07-10

    GRB 080503 is a short gamma-ray burst (GRB) detected by Swift and has been classified as a GRB originating from a compact star merger. The soft extended emission and the simultaneous late re-brightening in both the X-ray and optical afterglow light curves raise interesting questions regarding its physical origin. We show that the broadband data of GRB 080503 can be well explained within the framework of the double neutron star merger model, provided that the merger remnant is a rapidly rotating massive neutron star with an extremely high magnetic field (i.e., a millisecond magnetar). We show that the late optical re-brightening is consistent with the emission from a magnetar-powered “merger-nova.” This adds one more case to the growing sample of merger-novae associated with short GRBs. The soft extended emission and the late X-ray excess emission are well connected through a magnetar dipole spin-down luminosity evolution function, suggesting that direct magnetic dissipation is the mechanism to produce these X-rays. The X-ray emission initially leaks from a hole in the merger ejecta pierced by the short GRB jet. The hole subsequently closes after the magnetar spins down and the magnetic pressure drops below ram pressure. The X-ray photons are then trapped behind the merger-nova ejecta until the ejecta becomes optically thin at a later time. This explains the essentially simultaneous re-brightening in both the optical and X-ray light curves. Within this model, future gravitational-wave sources could be associated with a bright X-ray counterpart along with the merger-nova, even if the short GRB jet beams away from Earth.

  1. Radio afterglow of the jetted tidal disruption event Swift J1644+57

    Directory of Open Access Journals (Sweden)

    Mimica P.

    2012-12-01

    Full Text Available The recent transient event Swift J1644+57 has been interpreted as resulting from a relativistic outflow, powered by the accretion of a tidally disrupted star onto a supermassive black hole. This discovery of a new class of relativistic transients opens new windows into the study of tidal disruption events (TDEs and offers a unique probe of the physics of relativistic jet formation and the conditions in the centers of distant quiescent galaxies. Unlike the rapidly-varying γ/X-ray emission from Swift J1644+57, the radio emission varies more slowly and is well modeled as synchrotron radiation from the shock interaction between the jet and the gaseous circumnuclear medium (CNM. Early after the onset of the jet, a reverse shock propagates through and decelerates the ejecta released during the first few days of activity, while at much later times the outflow approaches the self-similar evolution of Blandford and McKee. The point at which the reverse shock entirely crosses the earliest ejecta is clearly observed as an achromatic break in the radio light curve at t ≈ 10 days. The flux and break frequencies of the afterglow constrain the properties of the jet and the CNM, including providing robust evidence for a narrowly collimated jet. I briefly discuss the implications of Swift J1644+57 for the fraction of TDEs accompanied by relativistic jets; the physics of jet formation more broadly; and the prospects for detecting off-axis TDE radio emission, either via follow-up observations of TDE candidates discovered at other wavelengths or blindly with upcoming wide-field radio surveys. The radio rebrightening observed months after the onset of the jet remains a major unsolved mystery, the resolution of which may require considering a jet with more complex (temporal or angular structure.

  2. Cooperative Spectrum Sensing over Non-Identical Nakagami Fading Channels

    KAUST Repository

    Rao, Anlei

    2012-09-08

    Previous works in cooperative spectrum sensing assumed that the channels for sensing and reporting are independent identical distributed (i.i.d). A more practical and appropriate assumption, however, should be that the sensing channels and reporting channels are independent but not necessarily identically distributed (i.n.i.d). In this paper, we derive the false-alarm probability and the detection probability of cooperative spectrum sensing with energy fusion over i.n.i.d Nakagami fading channels. Selected numerical results show that cooperative spectrum sensing still gives considerably better performance results even over i.n.i.d fading channels.

  3. The early X-ray afterglows of optically bright and dark Gamma-Ray Bursts

    OpenAIRE

    Lin, Yi-Qing

    2006-01-01

    A systematical study on the early X-ray afterglows of both optically bright and dark gamma-ray bursts (B-GRBs and D-GRBs) observed by Swift has been presented. Our sample includes 25 GRBs. Among them 13 are B-GRBs and 12 are D-GRBs. Our results show that the distributions of the X-ray afterglow fluxes ($F_{X}$), the gamma-ray fluxes ($S_{\\gamma}$), and the ratio ($R_{\\gamma, X}$) for both the D-GRBs and B-GRBs are similar. The differences of these distributions for the two kinds of GRBs shoul...

  4. Optical and X-ray Afterglows in the Cannonball Model of GRBs

    CERN Document Server

    De Rújula, Alvaro

    2003-01-01

    The Cannonball Model is based on the hypothesis that GRBs and their afterglows are made in supernova explosions by relativistic ejecta similar to the ones observed in quasars and microquasars. Its predictions are simple, and analytical in fair approximations. The model describes well the properties of the $\\gamma$-rays of GRBs. It gives a very simple and extremely successful description of the optical and X-ray afterglows of {\\it all} GRBs of known redshift. The only problem the model has, so far, is that it is contrary to staunch orthodox beliefs.

  5. Fading testbed for free-space optical communications

    Science.gov (United States)

    Shrestha, Amita; Giggenbach, Dirk; Mustafa, Ahmad; Pacheco-Labrador, Jorge; Ramirez, Julio; Rein, Fabian

    2016-10-01

    Free-space optical (FSO) communication is a very attractive technology offering very high throughput without spectral regulation constraints, yet allowing small antennas (telescopes) and tap-proof communication. However, the transmitted signal has to travel through the atmosphere where it gets influenced by atmospheric turbulence, causing scintillation of the received signal. In addition, climatic effects like fogs, clouds and rain also affect the signal significantly. Moreover, FSO being a line of sight communication requires precise pointing and tracking of the telescopes, which otherwise also causes fading. To achieve error-free transmission, various mitigation techniques like aperture averaging, adaptive optics, transmitter diversity, sophisticated coding and modulation schemes are being investigated and implemented. Evaluating the performance of such systems under controlled conditions is very difficult in field trials since the atmospheric situation constantly changes, and the target scenario (e.g. on aircraft or satellites) is not easily accessible for test purposes. Therefore, with the motivation to be able to test and verify a system under laboratory conditions, DLR has developed a fading testbed that can emulate most realistic channel conditions. The main principle of the fading testbed is to control the input current of a variable optical attenuator such that it attenuates the incoming signal according to the loaded power vector. The sampling frequency and mean power of the vector can be optionally changed according to requirements. This paper provides a brief introduction to software and hardware development of the fading testbed and measurement results showing its accuracy and application scenarios.

  6. Wireless Energy Harvesting Using Signals from Multiple Fading Channels

    KAUST Repository

    Chen, Yunfei

    2017-08-01

    In this paper, we study the average, the probability density function and the cumulative distribution function of the harvested power. In the study, the signals are transmitted from multiple sources. The channels are assumed to be either Rician fading or Gamma-shadowed Rician fading. The received signals are then harvested by using either a single harvester for simultaneous transmissions or multiple harvesters for transmissions at different frequencies, antennas or time slots. Both linear and nonlinear models for the energy harvester at the receiver are examined. Numerical results are presented to show that, when a large amount of harvested power is required, a single harvester or the linear range of a practical nonlinear harvester are more efficient, to avoid power outage. Further, the power transfer strategy can be optimized for fixed total power. Specifically, for Rayleigh fading, the optimal strategy is to put the total power at the source with the best channel condition and switch off all other sources, while for general Rician fading, the optimum magnitudes and phases of the transmitting waveforms depend on the channel parameters.

  7. Physical Layer Design in Wireless Sensor Networks for Fading Mitigation

    Directory of Open Access Journals (Sweden)

    Nuo Chen

    2013-09-01

    Full Text Available This paper presents the theoretical analysis, simulation results and suggests design in digital technology of a physical layer for wireless sensor networks. The proposed design is able to mitigate fading inside communication channel. To mitigate fading the chip interleaving technique is proposed. For the proposed theoretical model of physical layer, a rigorous mathematical analysis is conducted, where all signals are presented and processed in discrete time domain form which is suitable for further direct processing necessary for devices design in digital technology. Three different channels are used to investigate characteristics of the physical layer: additive white Gaussian noise channel (AWGN, AWG noise and flat fading channel and AWG noise and flat fading channel with interleaver and deinterleaver blocks in the receiver and transmitter respectively. Firstly, the mathematical model of communication system representing physical layer is developed based on the discrete time domain signal representation and processing. In the existing theory, these signals and their processing are represented in continuous time form, which is not suitable for direct implementation in digital technology. Secondly, the expressions for the probability of chip, symbol and bit error are derived. Thirdly, the communication system simulators are developed in MATLAB. The simulation results confirmed theoretical findings.

  8. Fading of radio signals from spaced synchronous satellites ...

    African Journals Online (AJOL)

    ... it depends strongly on the elevation of the source, the lower the elevation the earlier the onset. Plausible explanations for the observations are proffered. Keywords: equatorial ionospheric scintillation; radio signal fading; source coordinate; spaced synchronous satellites. Nigeria Journal of Pure and Applied Physics Vol.

  9. Combining Stimulus Fading, Reinforcement, and Extinction To Treat Food Refusal.

    Science.gov (United States)

    Freeman, Kurt A.; Piazza, Cathleen C.

    1998-01-01

    The food refusal of a 6-year-old girl with autism and destructive behavior was treated using stimulus fading, reinforcement, and escape extinction. Intake increased, and compliance with prompting procedures remained relatively stable despite the increased consumption requirement. (Author/CR)

  10. Use of Texture Fading in the Treatment of Food Selectivity.

    Science.gov (United States)

    Shore, Bridget A.; Babbitt, Roberta L.; Williams, Keith E.; Coe, David A.; Snyder, Angela

    1998-01-01

    A study investigated the efficacy of texture fading in the treatment of food selectivity displayed by four children (ages 2-5). Successful treatment involved the gradual addition of higher textures based on results of periodic probes. Food acceptance and swallowing were reinforced, while food refusal and expulsion were placed on extinction.…

  11. EFFECT OF SHADOWING AND MULTIPATH FADING ON THE ...

    African Journals Online (AJOL)

    The traditional macro-only network have been proved ineffective when communication signal is required for users located in the cell edge and a certain distance away ... Numerical simulation carried out for the macro-femto heterogeneous network using MATLAB shows how the effect of fading and shadowing was reduced.

  12. A study of the thermoluminescence fading characteristics of natural ...

    African Journals Online (AJOL)

    The thermoluminescence (TL) response fading behaviour of natural marble obtained from the South Western Basement Complex of Nigeria for varying gamma irradiation doses were investigated for the purpose of ascertaining if this material can suffice as a TL dosimeter. Irradiation was done using a 60Co gammacell ...

  13. Signal Classification in Fading Channels Using Cyclic Spectral Analysis

    Science.gov (United States)

    2009-07-01

    exist to exploit spacial diversity through the use of multiple receiver antennas. By assuming that the channel fades independently on each antenna, the...International Conference on Cognitive Radio Oriented Wireless Networks and Communications (CROWNCOM 󈧊), 2006. 24. D. Pauluzzi and N. Beaulieu, “A comparison

  14. Enuresis Control through Fading, Escape, and Avoidance Training.

    Science.gov (United States)

    Hansen, Gordon D.

    1979-01-01

    A twin signal device that provides both escape and avoidance conditioning in enuresis control was documented with case studies of two enuretic children (eight and nine years old). In addition, a technique of fading as an adjunct to the process was utilized with one subject. (Author/SBH)

  15. Block-Fading Channels with Delayed CSIT at Finite Blocklength

    DEFF Research Database (Denmark)

    Trillingsgaard, Kasper Fløe; Popovski, Petar

    2014-01-01

    In many wireless systems, the channel state information at the transmitter (CSIT) can not be learned until after a transmission has taken place and is thereby outdated. In this paper, we study the benefits of delayed CSIT on a block-fading channel at finite blocklength. First, the achievable rate...

  16. Gamma-Ray Burst Afterglow Broadband Fitting Based Directly on Hydrodynamics Simulations

    NARCIS (Netherlands)

    van Eerten, H.; van der Horst, A.; MacFadyen, A.

    2012-01-01

    We present a powerful new tool for fitting broadband gamma-ray burst afterglow data, which can be used to determine the burst explosion parameters and the synchrotron radiation parameters. By making use of scale invariance between relativistic jets of different energies and different circumburst

  17. POLARIZATION EVOLUTION OF EARLY OPTICAL AFTERGLOWS OF GAMMA-RAY BURSTS

    Energy Technology Data Exchange (ETDEWEB)

    Lan, Mi-Xiang; Dai, Zi-Gao [School of Astronomy and Space Science, Nanjing University, Nanjing 210093 (China); Wu, Xue-Feng, E-mail: dzg@nju.edu.cn [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)

    2016-01-10

    The central engine and jet composition of gamma-ray bursts (GRBs) remain mysterious. Here we suggest that observations on the polarization evolution of early optical afterglows may shed light on these questions. We first study the dynamics of a reverse shock and a forward shock that are generated during the interaction of a relativistic jet and its ambient medium. The jet is likely magnetized with a globally large-scale magnetic field from the central engine. The existence of the reverse shock requires that the magnetization degree of the jet should not be high (σ ≤ 1), so that the jet is mainly composed of baryons and leptons. We then calculate the light curves and polarization evolution of early optical afterglows and find that when the polarization position angle changes by 90° during the early afterglow, the polarization degree is zero for a toroidal magnetic field but is very likely to be nonzero for an aligned magnetic field. This result would be expected to provide a probe for the central engine of GRBs because an aligned field configuration could originate from a magnetar central engine and a toroidal field configuration could be produced from a black hole via the Blandford–Znajek mechanism. Finally, for such two kinds of magnetic field configurations, we fit the observed data of the early optical afterglow of GRB 120308A equally well.

  18. Can optical afterglows be used to discriminate between Type I and Type II GRBs?

    OpenAIRE

    Kann, D. A.

    2008-01-01

    The precise localization of short/hard (Type I) gamma-ray bursts (GRBs) in recent years has answered many questions but raised even more. I present some results of a systematic study of the optical afterglows of long/soft (Type II) and short/hard (Type I) GRBs, focusing on the optical luminosity as another puzzle piece in the classification of GRBs.

  19. Selective minority-ion heating in the afterglow of an electron cyclotron resonance ion source

    NARCIS (Netherlands)

    Nadzeyka, A; Meyer, D; Barzangy, F; Drentje, AG; Wiesemann, K

    We report first experimental results on selective minority-ion heating in the afterglow mode of electron cyclotron resonance ion sources in Bochum and at the KVI (Groningen) in mixtures of Ar/O/He and in pure nitrogen. In addition we measured time resolved vacuum ultraviolet-line intensities of

  20. On limits of Wireless Communications in a Fading Environment: a General Parameterization Quantifying Performance in Fading Channel

    Directory of Open Access Journals (Sweden)

    Amit Grover

    2014-08-01

    Full Text Available The reliable services along with high throughput can be achieved by using wireless communication systems. These systems also provides a wide coverage because of their features, no doubt MIMO Communication System [1] is one among them. Features provided by these systems ensure the improved system coverage and increased data transmission rate by considering multiple numbers of transmitter and receiver antennas. In this article, the concept of equalization has been considered and finally the performance of the MIMO Systems in Rician flat fading [5] channel is compared with the Rayleigh flat fading channel. It has also been observed that the performance of these Systems in Rician Flat Fading Channel is the best as compare to the Rayleigh Flat Fading Channel [10]. It has been concluded that the successive interference methods provide better performance as compare to others, but their complexity is high. Simulation results shows that ML provides the better performance in comparison to other equalizers but Sphere decoder provides the best performance.

  1. Ultrahigh energy neutrino afterglows of nearby long duration gamma-ray bursts

    Science.gov (United States)

    Thomas, Jessymol K.; Moharana, Reetanjali; Razzaque, Soebur

    2017-11-01

    Detection of ultrahigh energy (UHE, ≳1 PeV ) neutrinos from astrophysical sources will be a major advancement in identifying and understanding the sources of UHE cosmic rays (CRs) in nature. Long duration gamma-ray burst (GRB) blast waves have been considered as potential acceleration sites of UHECRs. These CRs are expected to interact with GRB afterglow photons, which are synchrotron radiation from relativistic electrons coaccelerated with CRs in the blast wave, and naturally produce UHE neutrinos. Fluxes of these neutrinos are uncertain, however, and crucially depend on the observed afterglow modeling. We have selected a sample of 23 long duration GRBs within redshift 0.5 for which adequate electromagnetic afterglow data are available and which could produce high flux of UHE afterglow neutrinos, being nearby. We fit optical, x-ray, and γ -ray afterglow data with an adiabatic blast wave model in a constant density interstellar medium and in a wind environment where the density of the wind decreases as the inverse square of the radius from the center of the GRB. The blast wave model parameters extracted from these fits are then used for calculating UHECR acceleration and p γ interactions to produce UHE neutrino fluxes from these GRBs. We have also explored the detectability of these neutrinos by currently running and upcoming large area neutrino detectors, such as the Pierre Auger Observatory, IceCube Gen-2, and KM3NeT observatories. We find that our realistic flux models from nearby GRBs will be unconstrained in the foreseeable future.

  2. K Coverage Probability of 5G Wireless Cognitive Radio Network under Shadow Fading Effects

    Directory of Open Access Journals (Sweden)

    Ankur S. Kang

    2016-09-01

    Full Text Available Land mobile communication is burdened with typical propagation constraints due to the channel characteristics in radio systems.Also,the propagation characteristics vary form place to place and also as the mobile unit moves,from time to time.Hence,the tramsmission path between transmitter and receiver varies from simple direct LOS to the one which is severely obstructed by buildings,foliage and terrain.Multipath propagation and shadow fading effects affect the signal strength of an arbitrary Transmitter-Receiver due to the rapid fluctuations in the phase and amplitude of signal which also determines the average power over an area of tens or hundreds of meters.Shadowing introduces additional fluctuations,so the received local mean power varies around the area –mean.The present section deals with the performance analysis of fifth generation wireless cognitive radio network on the basis of signal and interference level based k coverage probability under the shadow fading effects.

  3. An Accurate Hardware Sum-of-Cisoids Fading Channel Simulator for Isotropic and Non-Isotropic Mobile Radio Environments

    Directory of Open Access Journals (Sweden)

    L. Vela-Garcia

    2012-01-01

    Full Text Available The rapid technological development in the field of wireless communications calls for devices capable of reproducing and simulating the behavior of the channel under realistic propagation conditions. This paper presents a hardware fading channel simulator that is able to generate stochastic processes characterized by symmetrical and asymmetrical Doppler power spectral densities (PSDs depending on the assumption of isotropic or non-isotropic scattering. The concept of the proposed hardware simulator is based on an implementation of the sum-of-cisoids (SOC method. The hardware simulator is capable of handling any configuration of the cisoid's amplitudes, frequencies, and phases. Each of the cisoids that constitutes the SOC model is implemented using a piecewise polynomial approximation technique. The investigation of the higher-order statistics of the generated fading processes, like the level-crossing rate (LCR and the average duration of fades (ADF, shows that our design is able to reproduce accurately the key features of realistic channel models that are considered as candidates for the latest wireless communication standards.

  4. Radio resource allocation over fading channels under statistical delay constraints

    CERN Document Server

    Le-Ngoc, Tho

    2017-01-01

    This SpringerBrief presents radio resource allocation schemes for buffer-aided communications systems over fading channels under statistical delay constraints in terms of upper-bounded average delay or delay-outage probability. This Brief starts by considering a source-destination communications link with data arriving at the source transmission buffer. The first scenario, the joint optimal data admission control and power allocation problem for throughput maximization is considered, where the source is assumed to have a maximum power and an average delay constraints. The second scenario, optimal power allocation problems for energy harvesting (EH) communications systems under average delay or delay-outage constraints are explored, where the EH source harvests random amounts of energy from renewable energy sources, and stores the harvested energy in a battery during data transmission. Online resource allocation algorithms are developed when the statistical knowledge of the random channel fading, data arrivals...

  5. Diversity Analysis of Peaky FSK Signaling in Fading Channels

    CERN Document Server

    Gursoy, Mustafa Cenk

    2009-01-01

    Error performance of noncoherent detection of on-off frequency shift keying (OOFSK) modulation over fading channels is analyzed when the receiver is equipped with multiple antennas. The analysis is conducted for two cases: 1) the case in which the receiver has the channel distribution knowledge only; and 2) the case in which the receiver perfectly knows the fading magnitudes. For both cases, the maximum a posteriori probability (MAP) detection rule is derived and analytical probability of error expressions are obtained. Numerical and simulation results indicate that for sufficiently low duty cycle values, lower error probabilities with respect to FSK signaling are achieved. Equivalently, when compared to FSK modulation, OOFSK with low duty cycle requires less energy to achieve the same probability of error, which renders this modulation a more energy efficient transmission technique. Also, through numerical results, the impact of number of antennas, antenna correlation, duty cycle values, and unknown channel ...

  6. Further investigations on 'non-fading' in K-Feldspar

    DEFF Research Database (Denmark)

    Jain, Mayank; Buylaert, Jan-Pieter; Thomsen, Kristina Jørkov

    2015-01-01

    We give a theoretical overview of non-fading infrared stimulated luminescence (IRSL) signals in feldspars, followed by intercomparison of potential methods on some sediment extracts. We observe that a more stringent thermal wash on its own is not effective in obtaining a more stable signal......, suggesting that the higher the stimulation temperature in post IR-IRSL methods, the greater the ability to access distant electron hole pairs. We further find that the delayed off-time signal in time-resolved IRSL has immense potential for sampling non-fading signal and should be explored further......; this signal also appears to be well reset in nature and avoids unwanted thermal transfer effects in comparison to the post IR-IRSL signal measured at 290 degrees C. (C) 2014 Elsevier Ltd and INQUA. All rights reserved....

  7. Troxler Fading, Eye Movements, and Retinal Ganglion Cell Properties

    Directory of Open Access Journals (Sweden)

    Romain Bachy

    2014-12-01

    Full Text Available We present four movies demonstrating the effect of flicker and blur on the magnitude and speed of adaptation for foveal and peripheral vision along the three color axes that isolate retinal ganglion cells projecting to magno, parvo, and konio layers of the LGN. The demonstrations support the eye movement hypothesis for Troxler fading for brightness and color, and demonstrate the effects of flicker and blur on adaptation of each class of retinal ganglion cells.

  8. Troxler Fading, Eye Movements, and Retinal Ganglion Cell Properties

    OpenAIRE

    Romain Bachy; Qasim Zaidi

    2014-01-01

    We present four movies demonstrating the effect of flicker and blur on the magnitude and speed of adaptation for foveal and peripheral vision along the three color axes that isolate retinal ganglion cells projecting to magno, parvo, and konio layers of the LGN. The demonstrations support the eye movement hypothesis for Troxler fading for brightness and color, and demonstrate the effects of flicker and blur on adaptation of each class of retinal ganglion cells.

  9. Capacity of Fading Channels in the Low Power Regime

    KAUST Repository

    Benkhelifa, Fatma

    2013-01-01

    The low power regime has attracted various researchers in the information theory and communication communities to understand the performance limits of wireless systems. Indeed, the energy consumption is becoming one of the major limiting factors in wireless systems. As such, energy-efficient wireless systems are of major importance to the next generation wireless systems designers. The capacity is a metric that measures the performance limit of a wireless system. The study of the ergodic capacity of some fading channels in the low power regime is the main subject of this thesis. In our study, we consider that the receiver has always a full knowledge of the channel state information. However, we assume that the transmitter has possibly imperfect knowledge of the channel state information, i.e. he knows either perfectly the channel or only an estimated version of the channel. Both radio frequency and free space optical communication channel models are considered. The main contribution of this work is the explicit characterization of how the capacity scales as function of the signal-to-noise ratio in the low power regime. This allows us to characterize the gain due to the perfect knowledge compared to no knowledge of the channel state information at the transmitter. In particular, we show that the gain increases logarithmically for radio frequency communication. However, the gain increases as log2(Pavg) or log4(Pavg) for free-space optical communication, where Pavg is the average power constraint imposed to the input. Furthermore, we characterize the capacity of cascaded fading channels and we applied the result to Rayleigh-product fading channel and to a free-space optical link over gamma-gamma atmospheric turbulence in the presence of pointing errors. Finally, we study the capacity of Nakagami-m fading channel under quality of service constraints, namely the effective capacity. We have shown that the effective capacity converges to Shannon capacity in the very low

  10. Afterglow Observations Shed New Light on the Nature of X-ray Flashes

    Energy Technology Data Exchange (ETDEWEB)

    Granot, J

    2005-02-17

    X-ray flashes (XRFs) and X-ray rich gamma-ray bursts (XRGRBs) share many observational characteristics with long duration ({approx}> 2 s) GRBs, but the reason for which the spectral energy distribution of their prompt emission peaks at lower photon energies, E{sub p}, is still a subject of debate. Although many different models have been invoked in order to explain the lower values of E{sub p}, their implications for the afterglow emission were not considered in most cases, mainly because observations of XRF afterglows have become available only recently. Here we examine the predictions of the various XRF models for the afterglow emission, and test them against the observations of XRF 030723 and XRGRB 041006, the events with the best monitored afterglow light curves in their respective class. We show that most existing XRF models are hard to reconcile with the observed afterglow light curves, which are very flat at early times. Such light curves are, however, naturally produced by a roughly uniform jet with relatively sharp edges that is viewed off-axis (i.e. from outside of the jet aperture). This type of model self consistently accommodates both the observed prompt emission and the afterglow light curves of XRGRB 041006 and XRF 030723, implying viewing angles {theta}{sub obs} from the jet axis of ({theta}{sub obs}-{theta}{sub 0}) {approx} 0.15 {theta}{sub 0} and ({theta}{sub obs}-{theta}{sub 0}) {approx} {theta}{sub 0}, respectively, where {theta}{sub 0} {approx} 3{sup o} is the half-opening angle of the jet. This suggests that GRBs, XRGRBs and XRFs are intrinsically similar relativistic jets viewed from different angles. It is then natural to identify GRBs with {gamma}({theta}{sub obs} - {theta}{sub 0}) {approx}< 1, XRGRBs with 1 {approx}< ({theta}{sub obs} - {theta}{sub 0}) {approx}< a few, and XRFs with {gamma}({theta}{sub obs} - {theta}{sub 0}) {approx}> a few, where {gamma} is the Lorentz factor of the outflow near the edge of the jet from which most of the

  11. Secrecy Capacity Analysis over α−μ Fading Channels

    KAUST Repository

    Lei, Hongjiang

    2017-02-15

    In this work, we study the secrecy capacity of the classic Wyner’s model over the α − μ fading channels, where α and μ specify the nonlinearity and clustering of fading channels, respectively. The average secrecy capacity (ASC) is derived in closed-form by using the extended generalized bivariate Fox’s Hfunction (EGBFHF). Moreover, the asymptotic analysis of ASC in high signal-to-noise ratio (SNR) regime is conducted. The asymptotic results unveil that the ASC follows the scaling law of Θ(ln p), where p stands for the ratio between the average powers of main channels and eavesdropping channels. Moreover, the ASC can be enhanced by increasing the transmit SNR, while there exists a ceiling of ASC as the SNRs at both sides are improved simultaneously. The accuracy of the analytical results is validated by Monte-Carlo simulations. The numerical results show that rigorous fading channels are beneficial to the secrecy performance, that is, serious nonlinearity (small α) and sparse clustering (small μ) will lead to the improvement of ASC.

  12. Analysis of Fade Dynamic at Ku-Band in Malaysia

    Directory of Open Access Journals (Sweden)

    Siat Ling Jong

    2014-01-01

    Full Text Available This work investigates fade dynamics of satellite communication systems in equatorial heavy rain region based on a one year of Ku-band propagation measurement campaign carried out in Universiti Teknologi Malaysia (UTM, Johor, Malaysia. First order statistics of rain attenuation are deduced and the results are found to be in good agreement with those obtained from other beacon measurements gathered within the same area (Kuala Lumpur. Moreover, the fade duration and slope statistics of the satellite signal variations are also carefully derived and subsequently compared with the ITU-R recommendation model. Such information is useful for the system operator and radio communication engineer for the design of appropriate fade mitigation techniques as well as the quality of service that could be offered to the user (according to the time interval for a typical day. Further evaluation on the performances of several ITU-R models in the heavy rain region are needed based on the measurement database available of this climatic region.

  13. Exact Symbol Error Probability of Square M-QAM Signaling over Generalized Fading Channels subject to Additive Generalized Gaussian Noise

    KAUST Repository

    Soury, Hamza

    2013-07-01

    This paper considers the average symbol error probability of square Quadrature Amplitude Modulation (QAM) coherent signaling over flat fading channels subject to additive generalized Gaussian noise. More specifically, a generic closedform expression in terms of the Fox H function and the bivariate Fox H function is offered for the extended generalized-K fading case. Simplifications for some special fading distributions such as generalized-K fading, Nakagami-m fading, and Rayleigh fading and special additive noise distributions such as Gaussian and Laplacian noise are then presented. Finally, the mathematical formalism is illustrated by some numerical examples verified by computer based simulations for a variety of fading and additive noise parameters.

  14. System for Processing Coded OFDM Under Doppler and Fading

    Science.gov (United States)

    Tsou, Haiping; Darden, Scott; Lee, Dennis; Yan, Tsun-Yee

    2005-01-01

    An advanced communication system has been proposed for transmitting and receiving coded digital data conveyed as a form of quadrature amplitude modulation (QAM) on orthogonal frequency-division multiplexing (OFDM) signals in the presence of such adverse propagation-channel effects as large dynamic Doppler shifts and frequency-selective multipath fading. Such adverse channel effects are typical of data communications between mobile units or between mobile and stationary units (e.g., telemetric transmissions from aircraft to ground stations). The proposed system incorporates novel signal processing techniques intended to reduce the losses associated with adverse channel effects while maintaining compatibility with the high-speed physical layer specifications defined for wireless local area networks (LANs) as the standard 802.11a of the Institute of Electrical and Electronics Engineers (IEEE 802.11a). OFDM is a multi-carrier modulation technique that is widely used for wireless transmission of data in LANs and in metropolitan area networks (MANs). OFDM has been adopted in IEEE 802.11a and some other industry standards because it affords robust performance under frequency-selective fading. However, its intrinsic frequency-diversity feature is highly sensitive to synchronization errors; this sensitivity poses a challenge to preserve coherence between the component subcarriers of an OFDM system in order to avoid intercarrier interference in the presence of large dynamic Doppler shifts as well as frequency-selective fading. As a result, heretofore, the use of OFDM has been limited primarily to applications involving small or zero Doppler shifts. The proposed system includes a digital coherent OFDM communication system that would utilize enhanced 802.1la-compatible signal-processing algorithms to overcome effects of frequency-selective fading and large dynamic Doppler shifts. The overall transceiver design would implement a two-frequency-channel architecture (see figure

  15. Constraining chameleon field theories using the GammeV afterglow experiments

    Energy Technology Data Exchange (ETDEWEB)

    Upadhye, A.; /Chicago U., EFI /KICP, Chicago; Steffen, J.H.; /Fermilab; Weltman, A.; /Cambridge U., DAMTP /Cape Town U.

    2009-11-01

    The GammeV experiment has constrained the couplings of chameleon scalar fields to matter and photons. Here we present a detailed calculation of the chameleon afterglow rate underlying these constraints. The dependence of GammeV constraints on various assumptions in the calculation is studied. We discuss GammeV-CHASE, a second-generation GammeV experiment, which will improve upon GammeV in several major ways. Using our calculation of the chameleon afterglow rate, we forecast model-independent constraints achievable by GammeV-CHASE. We then apply these constraints to a variety of chameleon models, including quartic chameleons and chameleon dark energy models. The new experiment will be able to probe a large region of parameter space that is beyond the reach of current tests, such as fifth force searches, constraints on the dimming of distant astrophysical objects, and bounds on the variation of the fine structure constant.

  16. STATISTICAL PROPERTIES OF GRB AFTERGLOW PARAMETERS AS EVIDENCE OF COSMOLOGICAL EVOLUTION OF THEIR HOST GALAXIES

    Directory of Open Access Journals (Sweden)

    Gregory Beskin

    2014-08-01

    Full Text Available The results of a study of 43 peaked R-band light curves of optical counterparts of gamma-ray bursts with known redshifts are presented. The parameters of optical transients were calculated in the comoving frame, and then a search for pair correlations between them was conducted. A statistical analysis showed a strong correlation between the peak luminosity and the redshift both for pure afterglows and for events with residual gamma activity, which cannot be explained as an effect of observational selection.This suggests a cosmological evolution of the parameters of the local interstellar medium around the sources of the gamma-ray burst. In the models of forward and reverse shock waves, a relation between the density of the interstellar medium and the redshift was built for gamma-ray burst afterglows, leading to a power-law dependence of the star-formation rate at regions around GRBs on redshift with a slope of about 6.

  17. The superluminal motion of Gamma-Ray-Burst sources and the complex afterglow of GRB 030329

    CERN Document Server

    Dado, S; De Rújula, Alvaro; Dado, Shlomo; Dar, Arnon

    2004-01-01

    The source of the very bright Gamma-Ray Burst GRB 030329 is close enough to us for there to be a hope to measure or significantly constrain its putative superluminal motion. Such a phenomenon is expected in the ``Cannonball'' (CB) model of GRBs. Recent precise data on the optical and radio afterglow of this GRB --which demonstrated its very complex structure-- allow us to pin down the CB-model's prediction for the afterglow-source position as a function of time. It has been stated that (the unpublished part of) the new radio data ``unequivocably disprove'' the CB model. We show how greatly exaggerated that obituary announcement was, and how precise a refined analysis of the data would have to be, to be still of interest.

  18. Diverse Features of the Multiwavelength Afterglows of Gamma-Ray Bursts: Natural or Special?

    Directory of Open Access Journals (Sweden)

    J. J. Geng

    2016-01-01

    Full Text Available The detection of optical rebrightenings and X-ray plateaus in the afterglows of gamma-ray bursts (GRBs challenges the generic external shock model. Recently, we have developed a numerical method to calculate the dynamics of the system consisting of a forward shock and a reverse shock. Here, we briefly review the applications of this method in the afterglow theory. By relating these diverse features to the central engines of GRBs, we find that the steep optical rebrightenings would be caused by the fall-back accretion of black holes, while the shallow optical rebrightenings are the consequence of the injection of the electron-positron-pair wind from the central magnetar. These studies provide useful ways to probe the characteristics of GRB central engines.

  19. Effect of a Biased Probe on the Afterglow Operation of an ECR4 Ion Source

    CERN Document Server

    Hill, C E; Wenander, F; Wolf, B H

    2000-01-01

    Various experiments have been performed on a 14.5 GHz ECR4 in order to improve the ion yield. The source runs in pulsed afterglow mode, and provides currents ~120 emA of Pb27+ to the CERN Heavy Ion Facility on an operational basis. In the search for higher beam intensities, the effects of a pulsed biased disk on axis at the injection side were investigated with different pulse timing and voltage settings. No proof for absolute higher intensities was seen for any of these modifications. However, the yield from a poorly tuned/low-performing source could be improved and the extracted pulse was less noisy with bias voltage applied. The fast response on the bias implies that increases/decreases are not due to ionisation processes. A good tune for high yield of high charge states during the afterglow coincides with a high plasma potential.

  20. Afterglow chemistry of atmospheric-pressure helium-oxygen plasmas with humid air impurity

    Science.gov (United States)

    Murakami, Tomoyuki; Niemi, Kari; Gans, Timo; O'Connell, Deborah; Graham, William G.

    2014-04-01

    The formation of reactive species in the afterglow of a radio-frequency-driven atmospheric-pressure plasma in a fixed helium-oxygen feed gas mixture (He+0.5%O2) with humid air impurity (a few hundred ppm) is investigated by means of an extensive global plasma chemical kinetics model. As an original objective, we explore the effects of humid air impurity on the biologically relevant reactive species in an oxygen-dependent system. After a few milliseconds in the afterglow environment, the densities of atomic oxygen (O) decreases from 1015 to 1013 cm-3 and singlet delta molecular oxygen (O2(1D)) of the order of 1015 cm-3 decreases by a factor of two, while the ozone (O3) density increases from 1014 to 1015 cm-3. Electrons and oxygen ionic species, initially of the order of 1011 cm-3, recombine much faster on the time scale of some microseconds. The formation of atomic hydrogen (H), hydroxyl radical (OH), hydroperoxyl (HO2), hydrogen peroxide (H2O2), nitric oxide (NO) and nitric acid (HNO3) resulting from the humid air impurity as well as the influence on the afterglow chemistry is clarified with particular emphasis on the formation of dominant reactive oxygen species (ROS). The model suggests that the reactive species predominantly formed in the afterglow are major ROS O2(1D) and O3 (of the order of 1015 cm-3) and rather minor hydrogen- and nitrogen-based reactive species OH, H2O2, HNO3 and NO2/NO3, of which densities are comparable to the O-atom density (of the order of 1013 cm-3). Furthermore, the model quantitatively reproduces the experimental results of independent O and O3 density measurements.

  1. Suppression of Afterglow in Microcolumnar CsI:Tl by Codoping With Sm: Recent Advances.

    Science.gov (United States)

    Nagarkar, Vivek V; Thacker, Samta C; Gaysinskiy, Valeriy; Ovechkina, Lena E; Miller, Stuart R; Cool, Steven; Brecher, Charles

    2009-01-01

    Microcolumnar CsI:Tl remains a highly desirable sensor for digital X-ray imaging due to its superior spatial resolution, bright emission, high absorption efficiency, and ready availability. Despite such obvious advantages, two characteristic properties of CsI:Tl undermine their use in clinical and high speed imaging: a persistent afterglow in its scintillation decay, and a hysteresis effect that distorts the scintillation yield after exposure to high radiation doses.In our earlier work we have discovered that the addition of 0.05 to 0.5 mol percent of Sm(2+) to crystals of CsI:Tl suppresses their afterglow by a factor of up to 50, even when subjected to a very high exposure of 120 R. This additive also diminishes hysteresis by an order of magnitude, which is a major accomplishment. Consequent- ly, our work is now focused on developing codoped microcolumnar CsI:Tl, Sm films that can potentially combine excellent properties of the current state-of-the-art CsI:Tl films with the reduced afterglow and hysteresis observed in codoped crystals. While our earlier attempts in CsI:Tl, Sm film fabrication, reported at the previous IEEE meeting, demonstrated obvious advantages of the approach, the recent work has succeeded in producing films that show improvement by at least a factor of 7 in afterglow and 150% in brightness compared to the standard CsI:Tl films. We report these important results in this paper, along with other recent advances in film growth and new imaging results.

  2. A Leptonic-Hadronic Model for the Afterglow of Gamma-Ray Burst 090510

    Science.gov (United States)

    2010-11-20

    rights reserved. Printed in the U.S.A. A LEPTONIC– HADRONIC MODEL FOR THE AFTERGLOW OF GAMMA-RAY BURST 090510 Soebur Razzaque1 Space Science Division...combined leptonic– hadronic model of synchrotron radiation from an adiabatic blast wave. High-energy, !100 MeV, emission in our model is dominated by...escape the blast wave at early time, and their detection can provide evidence of a hadronic emission component dominating at high energies. Key words

  3. Preparation and properties of silicone fouling release coatings with long-life afterglow fluorescent

    Directory of Open Access Journals (Sweden)

    Zhang Zhanping

    2017-01-01

    Full Text Available Based on polydimethylsiloxane, three-component coatings were prepared with different content of luminescence powder. The results showed that the illuminance of coatings increases with the content of luminescence powder, decays exponentially with the afterglow time, increases exponentially with the increase of exposure time. The afterglow illuminance augments with irradiated light illuminance. All coatings are hydrophobic and oleophilic. Surface free energy decreases with the increase of luminescence powder. They have highest impact-resistance and bend flexibility. The luminescence powder does not change obviously the shore hardness, tensile breaking strength, breaking elongation rate, elastic modular and roughness of coatings. The static test panels in sea generally could be covered obviously by biofouling including sponges, bryophytes and mussels, hydra, kelp, green algae after 2 months of immersion during growing season. But it never found that the barnacle attached on the coating surface during 4 years of immersion test. The static anti-fouling ability of the coatings is very limited. In addition, the sea creatures attached on the coating surface can be easily removed; even attached organisms will fall off and expose again the smooth coating surface. Consequently, all coatings with long-life afterglow fluorescent have a significant effect on preventing adhesion of barnacle and fouling-release performance.

  4. Observations of gamma-ray burst afterglows with the AEOS Burst Camera

    Science.gov (United States)

    Flewelling, Heather Anne

    Gamma-ray bursts (GRBs), are variable bursts of gamma-ray radiation, that lasts from milliseconds to hundreds of seconds. These bursts of gamma rays are detected in other wavelengths (optical, IR, radio, X-ray), because the afterglow lasts much longer, and this enables us to learn more about GRBs. The AEOS Burst Camera (ABC) is a 6'x6' field of view camera designed to observe the optical afterglows of GRBs, and is mounted on the 3.67m Advanced Electro- Optical System (AEOS) telescope, located at 10,000ft on Haleakala, Hawaii. There are 45 hours of Target of Opportunity (ToO) time to observe GRBs detected by Swift and other GRB satellites. Observations are started within minutes after a suitable GRB is detected, and continue for an hour or two. During this project, 21 GRBs were observed, and of those, 10 had detected afterglows, and 4 had interesting limits. About half of the bursts fit the fireball model, and half did not, which is similar to what ROTSE has found. Roughly half of the ABC bursts fall in the dark category, with b ox Akerlof Sr, Swan (2007) found, that roughly 70% of all GRBs brighter than 22nd mag at 1000s should be detectable.

  5. Afterglow Population Studies from Swift Follow-Up Observations of Fermi LAT GRBs

    Science.gov (United States)

    Racusin, Judith L.; Oates, S. R.; McEnery, J.; Vasileiou, V.; Troja, E.; Gehrels, N.

    2010-01-01

    The small population of Fermi LAT detected GRBs discovered over the last year has been providing interesting and unexpected clues into GRB prompt and afterglow emission mechanisms. Over the last 5 years, it has been Swift that has provided the robust data set of UV/optical and X-ray afterglow observations that opened many windows into other components of GRB emission structure. We explore the new ability to utilize both of these observatories to study the same GRBs over 10 orders of magnitude in energy, although not always concurrently. Almost all LAT GRBs that have been followed-up by Swift within 1-day have been clearly detected and carefully observed. We will present the context of the lower-energy afterglows of this special subset of GRBs that has > 100 MeV emission compared to the hundreds in the Swift database that may or may not have been observed by LAT, and theorize upon the relationship between these properties and the origin of the high energy gamma-ray emission.

  6. Rates of short-GRB afterglows in association with binary neutron star mergers

    Science.gov (United States)

    Saleem, M.; Pai, Archana; Misra, Kuntal; Resmi, L.; Arun, K. G.

    2018-03-01

    Assuming all binary neutron star (BNS) mergers produce short gamma-ray bursts, we combine the merger rates of BNS from population synthesis studies, the sensitivities of advanced gravitational wave (GW) interferometer networks, and of the electromagnetic (EM) facilities in various wavebands, to compute the detection rate of associated afterglows in these bands. Using the inclination angle measured from GWs as a proxy for the viewing angle and assuming a uniform distribution of jet opening angle between 3° and 30°, we generate light curves of the counterparts using the open access afterglow hydrodynamics package BOXFIT for X-ray, optical, and radio bands. For different EM detectors, we obtain the fraction of EM counterparts detectable in these three bands by imposing appropriate detection thresholds. In association with BNS mergers detected by five (three) detector networks of advanced GW interferometers, assuming a BNS merger rate of 0.6-774 Gpc-3 yr-1 from population synthesis models, we find the afterglow detection rates (per year) to be 0.04-53 (0.02-27), 0.03-36 (0.01-19), and 0.04-47 (0.02-25) in the X-ray, optical, and radio bands, respectively. Our rates represent maximum possible detections for the given BNS rate since we ignore effects of cadence and field of view in EM follow-up observations.

  7. Hydrothermal synthesis and afterglow luminescence properties of hollow SnO{sub 2}:Sm{sup 3+},Zr{sup 4+} spheres for potential application in drug delivery

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Pengfei; Zhang, Jiachi, E-mail: zhangjch@lzu.edu.cn; Qin, Qingsong; Hu, Rui; Wang, Yuhua

    2014-02-01

    Highlights: • We designed a novel afterglow labeling material SnO{sub 2}:Sm{sup 3+},Zr{sup 4+} for the first time. • Hollow SnO{sub 2}:Sm{sup 3+},Zr{sup 4+} spheres with afterglow were prepared by hydrothermal method. • Hollow SnO{sub 2}:Sm{sup 3+},Zr{sup 4+} is a potential afterglow labeling medium for drug delivery. - Abstract: A novel afterglow labeling material SnO{sub 2}:Sm{sup 3+},Zr{sup 4+} with hollow sphere shape and intense afterglow luminescence is prepared by hydrothermal method at 180 °C for the first time. The morphology and the sphere growth process of this material are investigated by scanning electron microscopy in detail. The afterglow measurement shows that this hydrothermal obtained material exhibits obvious red afterglow luminescence (550–700 nm) of Sm{sup 3+} which can last for 542 s (0.32 mcd/m{sup 2}). The depth of traps in this hydrothermal obtained material is calculated to be as shallow as 0.58 eV. The results demonstrate that although it is necessary to further improve the afterglow performance of the hydrothermal derived hollow SnO{sub 2}:Sm{sup 3+},Zr{sup 4+} spheres, it still can be regarded as a potential afterglow labeling medium for drug delivery.

  8. Compensating for Channel Fading in DS-CDMA Communication Systems Employing ICA Neural Network Detectors

    Directory of Open Access Journals (Sweden)

    David Overbye

    2005-06-01

    Full Text Available In this paper we examine the impact of channel fading on the bit error rate of a DS-CDMA communication system. The system employs detectors that incorporate neural networks effecting methods of independent component analysis (ICA, subspace estimation of channel noise, and Hopfield type neural networks. The Rayleigh fading channel model is used. When employed in a Rayleigh fading environment, the ICA neural network detectors that give superior performance in a flat fading channel did not retain this superior performance. We then present a new method of compensating for channel fading based on the incorporation of priors in the ICA neural network learning algorithms. When the ICA neural network detectors were compensated using the incorporation of priors, they give significantly better performance than the traditional detectors and the uncompensated ICA detectors. Keywords: CDMA, Multi-user Detection, Rayleigh Fading, Multipath Detection, Independent Component Analysis, Prior Probability Hebbian Learning, Natural Gradient

  9. PERFORMANCE OF MIMO OFDM SYSTEMS IN FADING CHANNELS

    Directory of Open Access Journals (Sweden)

    C. Kokkonis

    2008-05-01

    Full Text Available The performance of OFDM based systems isseriously affected by imperfections in systemimplementation. To gain a beter understanding of theinfluence of these impairments on the performance ofmultiple antenna OFDM systems, this paper studies azero-forcing based MIMO OFDM system withimperfections modeled as additive error sources in bothtransmitter (TX and receiver (RX. Based on this model,expressions are derived for the probability of error ofuncoded impaired MIMO systems in fading and nonfadingenvironments. These results allow for insightfulcomparison between the influence of TX and RXimpairments. It is concluded that the influence of RXimperfections decreases with an increasing number of RXbranches, while this is not the case for TX deficiencies.

  10. Fade statistics of M-turbulent optical links

    DEFF Research Database (Denmark)

    Jurado-Navas, Antonio; Maria Garrido-Balsells, Jose; Castillo-Vazquez, Miguel

    2017-01-01

    A new and generalized statistical model, called Malaga or simply M distribution, has been derived recently to characterize the irradiance fluctuations of an unbounded optical wavefront propagating through a turbulent medium under all irradiance fluctuation conditions. The aforementioned model...... extends and unifies in a simple analytical closed-form expression most of the proposed statistical models for free-space optical (FSO) communications widely employed until now in the scientific literature. Based on that M model, we have studied some important features associated to its fade statistics...

  11. OPRA capacity bounds for selection diversity over generalized fading channels

    KAUST Repository

    Hanif, Muhammad Fainan

    2014-05-01

    Channel side information at the transmitter can increase the average capacity by enabling optimal power and rate adaptation. The resulting optimal power and rate adaptation (OPRA) capacity rarely has a closed-form analytic expression. In this paper, lower and upper bounds on OPRA capacity for selection diversity scheme are presented. These bounds hold for variety of fading channels including log-normal and generalized Gamma distributed models and have very simple analytic expressions for easy evaluation even for kth best path selection. Some selected numerical results show that the newly proposed bounds closely approximate the actual OPRA capacity. © 2014 IEEE.

  12. Formation of Pyrylium from Aromatic Systems with a Helium:Oxygen Flowing Atmospheric Pressure Afterglow (FAPA) Plasma Source

    Science.gov (United States)

    Badal, Sunil P.; Ratcliff, Tyree D.; You, Yi; Breneman, Curt M.; Shelley, Jacob T.

    2017-06-01

    The effects of oxygen addition on a helium-based flowing atmospheric pressure afterglow (FAPA) ionization source are explored. Small amounts of oxygen doped into the helium discharge gas resulted in an increase in abundance of protonated water clusters by at least three times. A corresponding increase in protonated analyte signal was also observed for small polar analytes, such as methanol and acetone. Meanwhile, most other reagent ions (e.g., O2 +·, NO+, etc.) significantly decrease in abundance with even 0.1% v/v oxygen in the discharge gas. Interestingly, when analytes that contained aromatic constituents were subjected to a He:O2-FAPA, a unique (M + 3)+ ion resulted, while molecular or protonated molecular ions were rarely detected. Exact-mass measurements revealed that these (M + 3)+ ions correspond to (M - CH + O)+, with the most likely structure being pyrylium. Presence of pyrylium-based ions was further confirmed by tandem mass spectrometry of the (M + 3)+ ion compared with that of a commercially available salt. Lastly, rapid and efficient production of pyrylium in the gas phase was used to convert benzene into pyridine. Though this pyrylium-formation reaction has not been shown before, the reaction is rapid and efficient. Potential reactant species, which could lead to pyrylium formation, were determined from reagent-ion mass spectra. Thermodynamic evaluation of reaction pathways was aided by calculation of the formation enthalpy for pyrylium, which was found to be 689.8 kJ/mol. Based on these results, we propose that this reaction is initiated by ionized ozone (O3 +·), proceeds similarly to ozonolysis, and results in the neutral loss of the stable CHO2 · radical. [Figure not available: see fulltext.

  13. Formation of Pyrylium from Aromatic Systems with a Helium:Oxygen Flowing Atmospheric Pressure Afterglow (FAPA) Plasma Source.

    Science.gov (United States)

    Badal, Sunil P; Ratcliff, Tyree D; You, Yi; Breneman, Curt M; Shelley, Jacob T

    2017-06-01

    The effects of oxygen addition on a helium-based flowing atmospheric pressure afterglow (FAPA) ionization source are explored. Small amounts of oxygen doped into the helium discharge gas resulted in an increase in abundance of protonated water clusters by at least three times. A corresponding increase in protonated analyte signal was also observed for small polar analytes, such as methanol and acetone. Meanwhile, most other reagent ions (e.g., O 2 +· , NO + , etc.) significantly decrease in abundance with even 0.1% v/v oxygen in the discharge gas. Interestingly, when analytes that contained aromatic constituents were subjected to a He:O 2 -FAPA, a unique (M + 3) + ion resulted, while molecular or protonated molecular ions were rarely detected. Exact-mass measurements revealed that these (M + 3) + ions correspond to (M - CH + O) + , with the most likely structure being pyrylium. Presence of pyrylium-based ions was further confirmed by tandem mass spectrometry of the (M + 3) + ion compared with that of a commercially available salt. Lastly, rapid and efficient production of pyrylium in the gas phase was used to convert benzene into pyridine. Though this pyrylium-formation reaction has not been shown before, the reaction is rapid and efficient. Potential reactant species, which could lead to pyrylium formation, were determined from reagent-ion mass spectra. Thermodynamic evaluation of reaction pathways was aided by calculation of the formation enthalpy for pyrylium, which was found to be 689.8 kJ/mol. Based on these results, we propose that this reaction is initiated by ionized ozone (O 3 +· ), proceeds similarly to ozonolysis, and results in the neutral loss of the stable CHO 2 · radical. Graphical Abstract ᅟ.

  14. Dependence of (anomalous) fading of infra-red stimulated luminescence on trap occupancy in feldspars

    DEFF Research Database (Denmark)

    Morthekai, P.; Jain, Mayank; Gach, Grzegorz

    2013-01-01

    Dose dependency of anomalous fading of infra-red stimulated luminescence (IRSL) from feldspars has been investigated using radiations of different ionisation qualities. The rate of fading of the IRSL signal after proton irradiation (9.4–30%/decade) is on an average almost twice compared to that a......Dose dependency of anomalous fading of infra-red stimulated luminescence (IRSL) from feldspars has been investigated using radiations of different ionisation qualities. The rate of fading of the IRSL signal after proton irradiation (9.4–30%/decade) is on an average almost twice compared...

  15. A Simulation Model for Nakagmi-m Fading Channel with m>1

    OpenAIRE

    Sandeep Sharma; Rajesh Mishra

    2015-01-01

    In this paper, we propose a model to simulate a wireless fading channel based on Nakagami-m distribution with m>1. The Nakagami-m fading channel is the most generalized distribution as it can generate one-sided Gaussian distribution, Rayleigh distribution and Rician distribution for m equals to 0.5, 1 and >1 respectively. In this work we have proposed a method to generate a wireless fading channel based on Nakagami-m distribution as this distribution fits to a wide class of fading channel con...

  16. An MGF-based capacity analysis of equal gain combining over fading channels

    KAUST Repository

    Yilmaz, Ferkan

    2010-09-01

    Exact average capacity results for L-branch coherent equal-gain combining (EGC) in correlated and uncorrelated fading channels are not known. This paper develops a novel framework (approach) for capacity analysis of L-branch EGC in generalized fading channels. In addition, Gamma shadowed generalized Nakagami-m fading model is proposed in order to statistically model the fading environments in high frequencies such as 60 GHz and above. Some simulations are carried out and then the obtained results are accentuated by means of numerical analysis based on the proposed framework. Numerical and simulation results, performed to verify the correctness of the proposed framework, are in perfect agreement. ©2010 IEEE.

  17. Slowly fading super-luminous supernovae that are not pair-instability explosions.

    Science.gov (United States)

    Nicholl, M; Smartt, S J; Jerkstrand, A; Inserra, C; McCrum, M; Kotak, R; Fraser, M; Wright, D; Chen, T-W; Smith, K; Young, D R; Sim, S A; Valenti, S; Howell, D A; Bresolin, F; Kudritzki, R P; Tonry, J L; Huber, M E; Rest, A; Pastorello, A; Tomasella, L; Cappellaro, E; Benetti, S; Mattila, S; Kankare, E; Kangas, T; Leloudas, G; Sollerman, J; Taddia, F; Berger, E; Chornock, R; Narayan, G; Stubbs, C W; Foley, R J; Lunnan, R; Soderberg, A; Sanders, N; Milisavljevic, D; Margutti, R; Kirshner, R P; Elias-Rosa, N; Morales-Garoffolo, A; Taubenberger, S; Botticella, M T; Gezari, S; Urata, Y; Rodney, S; Riess, A G; Scolnic, D; Wood-Vasey, W M; Burgett, W S; Chambers, K; Flewelling, H A; Magnier, E A; Kaiser, N; Metcalfe, N; Morgan, J; Price, P A; Sweeney, W; Waters, C

    2013-10-17

    Super-luminous supernovae that radiate more than 10(44) ergs per second at their peak luminosity have recently been discovered in faint galaxies at redshifts of 0.1-4. Some evolve slowly, resembling models of 'pair-instability' supernovae. Such models involve stars with original masses 140-260 times that of the Sun that now have carbon-oxygen cores of 65-130 solar masses. In these stars, the photons that prevent gravitational collapse are converted to electron-positron pairs, causing rapid contraction and thermonuclear explosions. Many solar masses of (56)Ni are synthesized; this isotope decays to (56)Fe via (56)Co, powering bright light curves. Such massive progenitors are expected to have formed from metal-poor gas in the early Universe. Recently, supernova 2007bi in a galaxy at redshift 0.127 (about 12 billion years after the Big Bang) with a metallicity one-third that of the Sun was observed to look like a fading pair-instability supernova. Here we report observations of two slow-to-fade super-luminous supernovae that show relatively fast rise times and blue colours, which are incompatible with pair-instability models. Their late-time light-curve and spectral similarities to supernova 2007bi call the nature of that event into question. Our early spectra closely resemble typical fast-declining super-luminous supernovae, which are not powered by radioactivity. Modelling our observations with 10-16 solar masses of magnetar-energized ejecta demonstrates the possibility of a common explosion mechanism. The lack of unambiguous nearby pair-instability events suggests that their local rate of occurrence is less than 6 × 10(-6) times that of the core-collapse rate.

  18. Tackling capacity fading in vanadium flow batteries with amphoteric membranes

    Science.gov (United States)

    Oldenburg, Fabio J.; Schmidt, Thomas J.; Gubler, Lorenz

    2017-11-01

    Capacity fading and poor electrolyte utilization caused by electrolyte imbalance effects are major drawbacks for the commercialization of vanadium flow batteries (VFB). The influence of membrane type (cationic, anionic, amphoteric) on these effects is studied by determining the excess and net flux of each vanadium ion in an operating VFB assembled with a cation exchange membrane (CEM), Nafion® NR212, an anion exchange membrane (AEM), Fumatech FAP-450, and an amphoteric ion exchange membrane (AIEM) synthesized in-house. It is shown that the net vanadium flux, accompanied by water transport, is directed towards the positive side for the CEM and towards the negative side for the AEM. The content of cation and anion exchange groups in the AIEM is adjusted via radiation grafting to balance the vanadium flux between the two electrolyte sides. With the AIEM the net vanadium flux is significantly reduced and capacity fading due to electrolyte imbalances can be largely eliminated. The membrane's influence on electrolyte imbalance effects is characterized and quantified in one single charge-discharge cycle by analyzing the content of the four different vanadium species in the two electrolytes. The experimental data recorded herewith conclusively explains the electrolyte composition after 80 cycles.

  19. Color transplant for reverse ageing of faded artworks

    Science.gov (United States)

    Del Mastio, A.; Piva, A.; Barni, M.; Cappellini, V.; Stefanini, L.

    2008-02-01

    Nowadays, photographs are one of the most used media for communication. Images are used for the representation of documents, Cultural goods, and so on: they are used to pass on a wedge of historical memory of the society. Since its origin, the photographic technique has got several improvements; nevertheless, photos are liable to several damages, both concerning the physical support and concerning the colors and figures which are depicted in it: for example, think about scratches or rips happened to a photo, or think about the fading or red (or yellow) toning concerning the colors of a photo. In this paper, we propose a novel method which is able to assess the original beauty of digital reproductions of aged photos, as well as digital reproductions of faded goods. The method is based on the comparison of the degraded image with a not-degraded one showing similar contents; thus, the colors of the not-degraded image can be transplanted in the degraded one. The key idea is a dualism between the analytical mechanics and the color theory: for each of the degraded and not-degraded images we compute first a scatter plot of the x and y normalized coordinates of their colors; these scatter diagrams can be regarded as a system of point masses, thus provided of inertia axes and an inertia ellipsoid. Moving the scatter diagram of the degraded image over the one belonging to the not-degraded image, the colors of the degraded image can be restored.

  20. Efficient incremental relaying for packet transmission over fading channels

    KAUST Repository

    Fareed, Muhammad Mehboob

    2014-07-01

    In this paper, we propose a novel relaying scheme for packet transmission over fading channels, which improves the spectral efficiency of cooperative diversity systems by utilizing limited feedback from the destination. Our scheme capitalizes on the fact that relaying is only required when direct transmission suffers deep fading. We calculate the packet error rate for the proposed efficient incremental relaying (EIR) scheme with both amplify and forward and decode and forward relaying. We compare the performance of the EIR scheme with the threshold-based incremental relaying (TIR) scheme. It is shown that the efficiency of the TIR scheme is better for lower values of the threshold. However, the efficiency of the TIR scheme for higher values of threshold is outperformed by the EIR. In addition, three new threshold-based adaptive EIR are devised to further improve the efficiency of the EIR scheme. We calculate the packet error rate and the efficiency of these new schemes to provide the analytical insight. © 2014 IEEE.

  1. A 100 kpc nebula associated with the `Teacup' fading quasar

    Science.gov (United States)

    Villar-Martín, M.; Cabrera-Lavers, A.; Humphrey, A.; Silva, M.; Ramos Almeida, C.; Piqueras-López, J.; Emonts, B.

    2018-02-01

    We report the discovery of an ˜100 kpc ionized nebula associated with the radio-quiet type 2 quasar (QSO2) nicknamed the `Teacup' (z = 0.085). The giant nebula is among the largest known around active galaxies at any z. We propose that it is part of the circumgalactic medium (CGM) of the QSO2 host, which has been populated with tidal debris by galactic interactions. This rich gaseous medium has been rendered visible due to the illumination by the powerful active nucleus (AGN). Subsolar abundances (˜0.5 Z⊙) are tentatively favoured by AGN photoionization models. We also report the detection of coronal emission (Fe+6) from the NE bubble, at ˜9 kpc from the AGN. The detection of coronal lines at such large distances from the AGN and the [N II] λ6583/Hα, [S II] λλ6716,6731/Hα, [O I] λ6300/Hα optical emission-line ratios of the giant nebula are consistent with the fading quasar scenario proposed by Gagne et al. The fading rate appears to have been faster in the last ˜46 000 yr. Deep wide field integral field spectroscopy of giant nebulae around powerful AGN such as the `Teacup's' with instruments such as MUSE on VLT opens up a way to detect and study the elusive material from the CGM around massive active galaxies thanks to the illumination by the luminous AGN.

  2. Synthesis of ZnS:Ag,Co water-soluble blue afterglow nanoparticles and application in photodynamic activation.

    Science.gov (United States)

    Ma, Lun; Zou, Xiaoju; Hossu, Marius; Chen, Wei

    2016-08-05

    Silver and cobalt co-doped ZnS (ZnS:Ag,Co) water-soluble afterglow nanoparticles were synthesized using a wet chemistry method followed by aging at room temperature. The nanoparticles had a cubic zinc blende structure with average sizes of approximately 4 nm and emitted a blue fluorescence emission centered at 441 nm due to radiative transitions from surface defects to Ag(+) luminescent centers. Intense afterglow emission peaking at 475 nm from the obtained nanoparticles was observed and was red-shifted compared to the fluorescence emission peak. X-ray photoelectron spectroscopy revealed a large increase of O/S ratio, indicating a surface oxidation process during aging. The S vacancies produced accordingly may contribute to form more electron traps and enhance afterglow. The ZnS:Ag,Co afterglow nanoparticles have a very low dark-toxicity and are applied as a light source for photodynamic therapy activation by conjugating with protoporphyrin together. Our preliminary study has shown that the ZnS:Ag,Co afterglow nanoparticles can significantly reduce the x-ray dosage used in activation and thus may be a very promising candidate for future x-ray excited photodynamic therapy in deep cancer treatment.

  3. Synthesis of ZnS:Ag,Co water-soluble blue afterglow nanoparticles and application in photodynamic activation

    Science.gov (United States)

    Ma, Lun; Zou, Xiaoju; Hossu, Marius; Chen, Wei

    2016-08-01

    Silver and cobalt co-doped ZnS (ZnS:Ag,Co) water-soluble afterglow nanoparticles were synthesized using a wet chemistry method followed by aging at room temperature. The nanoparticles had a cubic zinc blende structure with average sizes of approximately 4 nm and emitted a blue fluorescence emission centered at 441 nm due to radiative transitions from surface defects to Ag+ luminescent centers. Intense afterglow emission peaking at 475 nm from the obtained nanoparticles was observed and was red-shifted compared to the fluorescence emission peak. X-ray photoelectron spectroscopy revealed a large increase of O/S ratio, indicating a surface oxidation process during aging. The S vacancies produced accordingly may contribute to form more electron traps and enhance afterglow. The ZnS:Ag,Co afterglow nanoparticles have a very low dark-toxicity and are applied as a light source for photodynamic therapy activation by conjugating with protoporphyrin together. Our preliminary study has shown that the ZnS:Ag,Co afterglow nanoparticles can significantly reduce the x-ray dosage used in activation and thus may be a very promising candidate for future x-ray excited photodynamic therapy in deep cancer treatment.

  4. Average bit error probability of binary coherent signaling over generalized fading channels subject to additive generalized gaussian noise

    KAUST Repository

    Soury, Hamza

    2012-06-01

    This letter considers the average bit error probability of binary coherent signaling over flat fading channels subject to additive generalized Gaussian noise. More specifically, a generic closed form expression in terms of the Fox\\'s H function is offered for the extended generalized-K fading case. Simplifications for some special fading distributions such as generalized-K fading and Nakagami-m fading and special additive noise distributions such as Gaussian and Laplacian noise are then presented. Finally, the mathematical formalism is illustrated by some numerical examples verified by computer based simulations for a variety of fading and additive noise parameters. © 2012 IEEE.

  5. Evidence for a Canonical GRB Afterglow Light Curve in the Swift/XRT Data

    Energy Technology Data Exchange (ETDEWEB)

    Nousek, J.A.; Kouveliotou, C.; Grupe, D.; Page, K.; Granot, J.; Ramirez-Ruiz, E.; Patel, S.K.; Burrows, D.N.; Mangano, V.; Barthelmy, S.; Beardmore, A.P.; Campana, S.; Capalbi, M.; Chincarini, G.; Cusumano, G.; Falcone, A.D.; Gehrels, N.; Giommi, P.; Goad, M.; Godet, O.; Hurkett, C.; /Penn State U., Astron. Astrophys. /NASA, Marshall /Leicester

    2005-08-17

    We present new observations of the early X-ray afterglows of the first 27 gamma-ray bursts (GRBs) detected with the Swift X-ray Telescope (XRT). The early X-ray afterglows show a canonical behavior, where the light curve broadly consists of three distinct power law segments: (1) an initial very steep decay ({infinity} t{sup -a} with 3 {approx}< a{sub 1} {approx}< 5) , followed by (2) a very shallow decay (0.2 {approx}< a{sub 2} {approx}< 0.8), and finally (3) a somewhat steeper decay (1 {approx}< a{sub 3} {approx}< 1.5). These power law segments are separated by two corresponding break times, 300 s {approx}< t{sub break,1} {approx}< 500 s and 10{sup 3} s {approx}< t{sub break,2} {approx}< 10{sup 4} s. On top of this canonical behavior of the early X-ray light curve, many events have superimposed X-ray flares, which are most likely caused by internal shocks due to long lasting sporadic activity of the central engine, up to several hours after the GRB. We find that the initial steep decay is consistent with it being the tail of the prompt emission, from photons that are radiated at large angles relative to our line of sight. The first break in the light curve (t{sub break,1}) takes place when the forward shock emission becomes dominant, with the intermediate shallow flux decay (a{sub 2}) likely caused by the continuous energy injection into the external shock. When this energy injection stops, a second break is then observed in the light curve (t{sub break,2}). This energy injection increases the energy of the afterglow shock by at least a factor of f {approx}> 4, and augments the already severe requirements for the efficiency of the prompt gamma-ray emission.

  6. The Supercritical Pile Gamma-Ray Burst Model: The GRB Afterglow Steep Decline and Plateau Phase

    Science.gov (United States)

    Sultana, Joseph; Kazanas, D.; Mastichiadis, A.

    2013-01-01

    We present a process that accounts for the steep decline and plateau phase of the Swift X-Ray Telescope (XRT) light curves, vexing features of gamma-ray burst (GRB) phenomenology. This process is an integral part of the "supercritical pile" GRB model, proposed a few years ago to account for the conversion of the GRB kinetic energy into radiation with a spectral peak at E(sub pk) is approx. m(sub e)C(exp 2). We compute the evolution of the relativistic blast wave (RBW) Lorentz factor Gamma to show that the radiation-reaction force due to the GRB emission can produce an abrupt, small (approx. 25%) decrease in Gamma at a radius that is smaller (depending on conditions) than the deceleration radius R(sub D). Because of this reduction, the kinematic criticality criterion of the "supercritical pile" is no longer fulfilled. Transfer of the proton energy into electrons ceases and the GRB enters abruptly the afterglow phase at a luminosity smaller by approx. m(sub p)/m(sub e) than that of the prompt emission. If the radius at which this slow-down occurs is significantly smaller than R(sub D), the RBW internal energy continues to drive the RBW expansion at a constant (new) Gamma and its X-ray luminosity remains constant until R(sub D) is reached, at which point it resumes its more conventional decay, thereby completing the "unexpected" XRT light curve phase. If this transition occurs at R is approx. equal to R(sub D), the steep decline is followed by a flux decrease instead of a "plateau," consistent with the conventional afterglow declines. Besides providing an account of these peculiarities, the model suggests that the afterglow phase may in fact begin before the RBW reaches R is approx. equal to R(sub D), thus providing novel insights into GRB phenomenology.

  7. Parent-Implemented Script Fading to Promote Play-Based Verbal Initiations in Children with Autism

    Science.gov (United States)

    Reagon, Kara A.; Higbee, Thomas S.

    2009-01-01

    We trained 3 mothers of children with autism to create, implement, and systematically fade scripts to promote vocal initiations during play. All 3 children's scripted and unscripted initiations increased after the introduction and fading of scripts, and unscripted initiations were maintained at the 2-week follow-up. The results indicate that…

  8. An attempt to correct for the fading in million year old basaltic rocks

    DEFF Research Database (Denmark)

    Morthekai, P.; Jain, Mayank; Cunha, Pedro P.

    2011-01-01

    The use of feldspar for luminescence dating has been restricted because of anomalous fad-ing. This has made its application to several important geological problems such as volcanic terrains difficult. Presently, two correction procedures are used to correct for anomalous fading. The present study...

  9. Spoon Distance Fading with and without Escape Extinction as Treatment for Food Refusal

    Science.gov (United States)

    Rivas, Kristi D.; Piazza, Cathleen C.; Patel, Meeta R.; Bachmeyer, Melanie H.

    2010-01-01

    Little is known about the characteristics of meals that serve as motivating operations (MOs) for escape behavior. In the current investigation, we showed that the distance at which a therapist held a spoon from a child's lips served as an MO for escape behavior. Based on these results, we implemented spoon distance fading, compared fading with and…

  10. The Impact of Reading Material's Lexical Accessibility on Text Fading Effects in Children's Reading Performance

    Science.gov (United States)

    Nagler, Telse; Lonnemann, Jan; Linkersdörfer, Janosch; Hasselhorn, Marcus; Lindberg, Sven

    2014-01-01

    The "acceleration phenomenon" (AP) is defined by improvements in reading speed and reading comprehension, induced by an artificial text fading procedure corresponding to the previously determined fastest individual reading rate. Recent results, however, indicated that fading that is slower than the self-paced reading rate can produce…

  11. The FADE mass-stat: A technique for inserting or deleting particles in molecular dynamics simulations

    Energy Technology Data Exchange (ETDEWEB)

    Borg, Matthew K., E-mail: matthew.borg@strath.ac.uk [Department of Mechanical and Aerospace Engineering, University of Strathclyde, Glasgow G1 1XJ (United Kingdom); Lockerby, Duncan A., E-mail: duncan.lockerby@warwick.ac.uk [School of Engineering, University of Warwick, Coventry CV4 7AL (United Kingdom); Reese, Jason M., E-mail: jason.reese@ed.ac.uk [School of Engineering, University of Edinburgh, Edinburgh EH9 3JL (United Kingdom)

    2014-02-21

    The emergence of new applications of molecular dynamics (MD) simulation calls for the development of mass-statting procedures that insert or delete particles on-the-fly. In this paper we present a new mass-stat which we term FADE, because it gradually “fades-in” (inserts) or “fades-out” (deletes) molecules over a short relaxation period within a MD simulation. FADE applies a time-weighted relaxation to the intermolecular pair forces between the inserting/deleting molecule and any neighbouring molecules. The weighting function we propose in this paper is a piece-wise polynomial that can be described entirely by two parameters: the relaxation time scale and the order of the polynomial. FADE inherently conserves overall system momentum independent of the form of the weighting function. We demonstrate various simulations of insertions of atomic argon, polyatomic TIP4P water, polymer strands, and C{sub 60} Buckminsterfullerene molecules. We propose FADE parameters and a maximum density variation per insertion-instance that restricts spurious potential energy changes entering the system within desired tolerances. We also demonstrate in this paper that FADE compares very well to an existing insertion algorithm called USHER, in terms of accuracy, insertion rate (in dense fluids), and computational efficiency. The USHER algorithm is applicable to monatomic and water molecules only, but we demonstrate that FADE can be generally applied to various forms and sizes of molecules, such as polymeric molecules of long aspect ratio, and spherical carbon fullerenes with hollow interiors.

  12. Combined diversity and improved energy detection in cooperative spectrum sensing with faded reporting channels

    Directory of Open Access Journals (Sweden)

    Srinivas Nallagonda

    2016-04-01

    Full Text Available In this paper we evaluate the performance of cooperative spectrum sensing (CSS where each cognitive radio (CR employs an improved energy detector (IED with multiple antennas and uses selection combining (SC for detecting the primary user (PU in noisy and faded sensing (S channels. We derive an expression for the probability of false alarm and expressions for probability of missed detection in non-faded (AWGN and Rayleigh faded sensing environments in terms of cumulative distribution function (CDF. Each CR transmits its decision about PU via noisy and faded reporting (R channel to fusion center (FC. In this paper we assume that S-channels are noisy and Rayleigh faded while several cases of fading are considered for R-channels such as: (i Hoyt (or Nakagami-q, (ii Rayleigh, (iii Rician (or Nakagami-n, and (iv Weibull. A Binary Symmetric channel (BSC with a fixed error probability (r in the R-channel is also considered. The impact of fading in R-channel, S-channel and several network parameters such as IED parameter, normalized detection threshold, number of CRs, and number of antennas on missed detection and total error probability is assessed. The effects of Hoyt, Rician, and Weibull fading parameters on overall performance of IED-CSS are also highlighted.

  13. Laboratory fading rates of various luminescence signals from feldspar-rich sediment extracts

    DEFF Research Database (Denmark)

    Thomsen, Kristina Jørkov; Murray, A.S.; Jain, Mayank

    2008-01-01

    region of the spectrum. In contrast, we have determined fading rates for various sedimentary feldspar samples using different stimulation and detection windows. If the initial part of the OSL signal is used the lowest fading rate is observed with post-IR blue stimulation (UV detection), but if a later...

  14. Constraints on an Optical Afterglow and on Supernova Light Following the Short Burst GRB 050813

    NARCIS (Netherlands)

    Ferrero, P.; Sanchez, S.F.; Kann, D.A.; Klose, S.; Greiner, J.; Gorosabel, J.; Hartmann, D.H.; Henden, A.A.; Møller, P.; Palazzi, E.; Rau, A.; Stecklum, B.; Castro-Tirado, A.J.; Fynbo, J.P.U.; Hjorth, J.; Jakobsson, P.; Kouveliotou, C.; Masetti, N.; Pian, E.; Tanvir, N.R.; Wijers, R.A.M.J.

    2007-01-01

    We report early follow-up observations of the error box of the short burst GRB 050813 using the telescopes at Calar Alto and Observatorio Sierra Nevada, followed by deep VLT FORS2 I-band observations obtained under very good seeing conditions 5.7 and 11.7 days after the event. Neither a fading

  15. Luminosity--time and luminosity--luminosity correlations for GRB prompt and afterglow plateau emissions

    OpenAIRE

    Dainotti, M. G.; Petrosian, V.; Willingale, R.; P. O'Brien(Univ. Leicester); Ostrowski, M.; Nagataki, S.

    2015-01-01

    We present an analysis of 123 Gamma-ray bursts (GRBs) with known redshifts possessing an afterglow plateau phase. We reveal that $L_a-T^{*}_a$ correlation between the X-ray luminosity $L_a$ at the end of the plateau phase and the plateau duration, $T^*_a$, in the GRB rest frame has a power law slope different, within more than 2 $\\sigma$, from the slope of the prompt $L_{f}-T^{*}_{f}$ correlation between the isotropic pulse peak luminosity, $L_{f}$, and the pulse duration, $T^{*}_{f}$, from t...

  16. Nitric oxide kinetics in the afterglow of a diffuse plasma filament

    Science.gov (United States)

    Burnette, D.; Montello, A.; Adamovich, I. V.; Lempert, W. R.

    2014-08-01

    A suite of laser diagnostics is used to study kinetics of vibrational energy transfer and plasma chemical reactions in a nanosecond pulse, diffuse filament electric discharge and afterglow in N2 and dry air at 100 Torr. Laser-induced fluorescence of NO and two-photon absorption laser-induced fluorescence of O and N atoms are used to measure absolute, time-resolved number densities of these species after the discharge pulse, and picosecond coherent anti-Stokes Raman spectroscopy is used to measure time-resolved rotational temperature and ground electronic state N2(v = 0-4) vibrational level populations. The plasma filament diameter, determined from plasma emission and NO planar laser-induced fluorescence images, remains nearly constant after the discharge pulse, over a few hundred microseconds, and does not exhibit expansion on microsecond time scale. Peak temperature in the discharge and the afterglow is low, T ≈ 370 K, in spite of significant vibrational nonequilibrium, with peak N2 vibrational temperature of Tv ≈ 2000 K. Significant vibrational temperature rise in the afterglow is likely caused by the downward N2-N2 vibration-vibration (V-V) energy transfer. Simple kinetic modeling of time-resolved N, O, and NO number densities in the afterglow, on the time scale longer compared to relaxation and quenching time of excited species generated in the plasma, is in good agreement with the data. In nitrogen, the N atom density after the discharge pulse is controlled by three-body recombination and radial diffusion. In air, N, NO and O concentrations are dominated by the reverse Zel'dovich reaction, N + NO → N2 + O, and ozone formation reaction, O + O2 + M → O3 + M, respectively. The effect of vibrationally excited nitrogen molecules and excited N atoms on NO formation kinetics is estimated to be negligible. The results suggest that NO formation in the nanosecond pulse discharge is dominated by reactions of excited electronic states of nitrogen, occurring on

  17. Semantic Security with Practical Transmission Schemes over Fading Wiretap Channels

    Directory of Open Access Journals (Sweden)

    Linda Senigagliesi

    2017-09-01

    Full Text Available We propose and assess an on–off protocol for communication over wireless wiretap channels with security at the physical layer. By taking advantage of suitable cryptographic primitives, the protocol we propose allows two legitimate parties to exchange confidential messages with some chosen level of semantic security against passive eavesdroppers, and without needing either pre-shared secret keys or public keys. The proposed method leverages the noisy and fading nature of the channel and exploits coding and all-or-nothing transforms to achieve the desired level of semantic security. We show that the use of fake packets in place of skipped transmissions during low channel quality periods yields significant advantages in terms of time needed to complete transmission of a secret message. Numerical examples are provided considering coding and modulation schemes included in the WiMax standard, thus showing that the proposed approach is feasible even with existing practical devices.

  18. Asymptotic analysis of multicell massive MIMO over Rician fading channels

    KAUST Repository

    Sanguinetti, Luca

    2017-06-20

    This work considers the downlink of a multicell massive MIMO system in which L base stations (BSs) of N antennas each communicate with K single-antenna user equipments randomly positioned in the coverage area. Within this setting, we are interested in evaluating the sum rate of the system when MRT and RZF are employed under the assumption that each intracell link forms a MIMO Rician uncorrelated fading channel. The analysis is conducted assuming that N and K grow large with a non-trivial ratio N/K under the assumption that the data transmission in each cell is affected by channel estimation errors, pilot contamination, and an arbitrary large scale attenuation. Numerical results are used to validate the asymptotic analysis in the finite system regime and to evaluate the network performance under different settings. The asymptotic results are also instrumental to get insights into the interplay among system parameters.

  19. Asymptotic analysis of downlink MISO systems over Rician fading channels

    KAUST Repository

    Falconet, Hugo

    2016-06-24

    In this work, we focus on the ergodic sum rate in the downlink of a single-cell large-scale multi-user MIMO system in which the base station employs N antennas to communicate with K single-antenna user equipments. A regularized zero-forcing (RZF) scheme is used for precoding under the assumption that each link forms a spatially correlated MIMO Rician fading channel. The analysis is conducted assuming N and K grow large with a non trivial ratio and perfect channel state information is available at the base station. Recent results from random matrix theory and large system analysis are used to compute an asymptotic expression of the signal-to-interference-plus-noise ratio as a function of the system parameters, the spatial correlation matrix and the Rician factor. Numerical results are used to evaluate the performance gap in the finite system regime under different operating conditions. © 2016 IEEE.

  20. Decentralized Detection in Wireless Sensor Networks with Channel Fading Statistics

    Directory of Open Access Journals (Sweden)

    Bin Liu

    2006-12-01

    Full Text Available Existing channel aware signal processing design for decentralized detection in wireless sensor networks typically assumes the clairvoyant case, that is, global channel state information (CSI is known at the design stage. In this paper, we consider the distributed detection problem where only the channel fading statistics, instead of the instantaneous CSI, are available to the designer. We investigate the design of local decision rules for the following two cases: (1 fusion center has access to the instantaneous CSI; (2 fusion center does not have access to the instantaneous CSI. As expected, in both cases, the optimal local decision rules that minimize the error probability at the fusion center amount to a likelihood ratio test (LRT. Numerical analysis reveals that the detection performance appears to be more sensitive to the knowledge of CSI at the fusion center. The proposed design framework that utilizes only partial channel knowledge will enable distributed design of a decentralized detection wireless sensor system.

  1. Decentralized Detection in Wireless Sensor Networks with Channel Fading Statistics

    Directory of Open Access Journals (Sweden)

    Liu Bin

    2007-01-01

    Full Text Available Existing channel aware signal processing design for decentralized detection in wireless sensor networks typically assumes the clairvoyant case, that is, global channel state information (CSI is known at the design stage. In this paper, we consider the distributed detection problem where only the channel fading statistics, instead of the instantaneous CSI, are available to the designer. We investigate the design of local decision rules for the following two cases: (1 fusion center has access to the instantaneous CSI; (2 fusion center does not have access to the instantaneous CSI. As expected, in both cases, the optimal local decision rules that minimize the error probability at the fusion center amount to a likelihood ratio test (LRT. Numerical analysis reveals that the detection performance appears to be more sensitive to the knowledge of CSI at the fusion center. The proposed design framework that utilizes only partial channel knowledge will enable distributed design of a decentralized detection wireless sensor system.

  2. Streaming Transmitter over Block-Fading Channels with Delay Constraint

    CERN Document Server

    Cocco, Giuseppe; Ibars, Christian

    2012-01-01

    Data streaming transmission, in which the data arrives at the transmitter gradually over time is studied. It is assumed that the transmitter receives a new message at each channel block at a constant rate which is fixed by an underlying application, and tries to broadcast these messages to users within a certain deadline. The channels are assumed to be block fading and independent over blocks and users. The performance measure is the average total rate of received information at the users within the transmission deadline. Three different encoding schemes are proposed and compared with an informed transmitter upper bound in terms of the average total rate for a set of users with varying channel qualities. Analytical upper bounds on the average total rate are derived for all the proposed schemes. It is shown that no single transmission strategy dominates the others at all channel settings, and the best transmitter streaming scheme depends on the distribution of the average channel conditions over the users.

  3. Space-Time Coding over Fading Channels with Stable Noise

    CERN Document Server

    Lee, Junghoon

    2011-01-01

    This paper addresses the performance of space-time coding over fading channels with impulsive noise which is known to accurately capture network interference. We use the symmetric alpha stable noise distribution and adopt two models which assume dependent and independent noise components across receive antennas. We derive pairwise error probability (PEP) of orthogonal space-time block codes (STBC) with a benchmark genie-aided receiver (GAR), or the minimum distance receiver (MDR) which is optimal in the Gaussian case. For general space-time codes we propose a maximum-likelihood (ML) receiver, and its approximation at high signal-to-noise ratio (SNR). The resulting asymptotically optimal receiver (AOR) does not depend on noise parameters and is computationally simple. Monte-Carlo simulations are used to supplement our analytical results and compare the performance of the receivers.

  4. Atropine and ODQ antagonize tetanic fade induced by L-arginine in cats

    Directory of Open Access Journals (Sweden)

    J.M. Cruciol-Souza

    1999-10-01

    Full Text Available Although it has been demonstrated that nitric oxide (NO released from sodium nitrite induces tetanic fade in the cat neuromuscular preparations, the effect of L-arginine on tetanic fade and its origin induced by NO have not been studied in these preparations. Furthermore, atropine reduces tetanic fade induced by several cholinergic and anticholinergic drugs in these preparations, whose mechanism is suggested to be mediated by the interaction of acetylcholine with inhibitory presynaptic muscarinic receptors. The present study was conducted in cats to determine the effects of L-arginine alone or after pretreatment with atropine or 1H-[1,2,4]oxadiazole [4,3-a]quinoxalin-1-one (ODQ on neuromuscular preparations indirectly stimulated at high frequency. Drugs were injected into the middle genicular artery. L-arginine (2 mg/kg and S-nitroso-N-acetylpenicillamine (SNAP; 16 µg/kg induced tetanic fade. The Nw-nitro-L-arginine (L-NOARG; 2 mg/kg alone did not produce any effect, but reduced the tetanic fade induced by L-arginine. D-arginine (2 mg/kg did not induce changes in tetanic fade. The tetanic fade induced by L-arginine or SNAP was reduced by previous injection of atropine (1.0 µg/kg or ODQ (15 µg/kg. ODQ alone did not change tetanic fade. The data suggest that the NO-synthase-GC pathway participates in the L-arginine-induced tetanic fade in cat neuromuscular preparations. The tetanic fade induced by L-arginine probably depends on the action of NO at the presynaptic level. NO may stimulate guanylate cyclase increasing acetylcholine release and thereby stimulating presynaptic muscarinic receptors.

  5. Peer-Monitoring vs. Micro-Script Fading for Enhancing Knowledge Acquisition when Learning in Computer-Supported Argumentation Environments

    Science.gov (United States)

    Bouyias, Yannis; Demetriadis, Stavros

    2012-01-01

    Research on computer-supported collaborative learning (CSCL) has strongly emphasized the value of providing student support with micro-scripts, which should withdraw (fade-out) allowing students to practice the acquired skills. However, research on fading shows conflicting results and some researchers suggest that the impact of fading is enhanced…

  6. Emissive sheath measurements in the afterglow of a radio frequency plasma

    Energy Technology Data Exchange (ETDEWEB)

    Sheehan, J. P., E-mail: sheehanj@umich.edu; Hershkowitz, N. [Nuclear Engineering and Engineering Physics, University of Wisconsin—Madison, Madison, Wisconsin 53706 (United States); Barnat, E. V.; Weatherford, B. R. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Kaganovich, I. D. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08540 (United States)

    2014-01-15

    The difference between the plasma potential and the floating potential of a highly emissive planar surface was measured in the afterglow of a radio frequency discharge. A Langmuir probe was used to measure the electron temperature and an emissive probe was used to measure the spatial distribution of the potential using the inflection point in the limit of zero emission technique. Time-resolved measurements were made using the slow-sweep method, a technique for measuring time-resolved current-voltage traces. This was the first time the inflection point in the limit of zero emission was used to make time-resolved measurements. Measurements of the potential profile of the presheath indicate that the potential penetrated approximately 50% farther into the plasma when a surface was emitting electrons. The experiments confirmed a recent kinetic theory of emissive sheaths, demonstrating that late in the afterglow as the plasma electron temperature approached the emitted electron temperature, the emissive sheath potential shrank to zero. However, the difference between the plasma potential and the floating potential of a highly emissive planar surface data appeared to be much less sensitive to the electron temperature ratio than the theory predicts.

  7. VLT/X-shooter spectroscopy of the GRB 120327A afterglow

    DEFF Research Database (Denmark)

    D'Elia, V.; Fynbo, Johan Peter Uldall; Goldoni, P.

    2014-01-01

    -25000AA) of the optical afterglow of GRB 120327A, taken with X-shooter at the VLT 2.13 and 27.65 hr after the GRB trigger. The first epoch spectrum shows that the ISM in the GRB host galaxy at z = 2.8145 is extremely rich in absorption features, with three components contributing to the line profiles...... we used to derive information on the distance between the host absorbing gas and the site of the GRB explosion. The variability of the FeI\\lambda2396 excited line between the two epochs proves that these features are excited by the GRB UV flux. Moreover, the distance of component I is found to be d......We present a study of the environment of the Swift long gamma-ray burst GRB 120327A at z ~2.8 through optical spectroscopy of its afterglow. We analyzed medium-resolution, multi-epoch spectroscopic observations (~7000 - 12000, corresponding to ~ 15 - 23 km/s, S/N = 15- 30 and wavelength range 3000...

  8. Growth of graphene-based films using afterglow of inductively coupled plasma

    Science.gov (United States)

    Hiramatsu, Mineo; Tomatsu, Masakazu; Kondo, Hiroki; Hori, Masaru

    2014-10-01

    Plasma-enhanced CVD (PECVD) employing methane/hydrogen gases has been used to grow diamond and carbon nanostructures. In the case of graphene growth using PECVD, excessive supply of carbon precursors and ion bombardment on the growing surface would cause secondary nuclei, resulting in small size of graphene grain and degradation in crystallinity. To overcome this issue, in this work, afterglow of inductively coupled plasma (ICP) was used for the growth of graphene. The CVD system is simple and consists of a reaction chamber and a remote radical source that uses an ICP in cylindrical geometry. Methane/hydrogen gases were fed through a quartz tube of 26 mm inner diameter and 20 cm in length. A five-turn rf (13.56 MHz) coil was mounted on the quartz tube. Substrates (Ni-coated Si and Cu foil) were located in the afterglow region of ICP. Growth experiments were carried out for 1-10 min at temperature of 700 C, rf power of 400 W, and total pressure of 100 mTorr. We have successfully fabricated graphene-based films, which was confirmed by the Raman spectrum and SEM image of deposit. We will discuss the planar graphene growth mechanism in terms of precursors and their surface reaction, in conjunction with the growth experiments using microwave plasma and ICP in planar geometry.

  9. THE UNUSUAL RADIO AFTERGLOW OF THE ULTRA-LONG GAMMA-RAY BURST GRB 130925A

    Energy Technology Data Exchange (ETDEWEB)

    Horesh, Assaf [Benoziyo Center for Astrophysics, Weizmann Institute of Science, 76100 Rehovot (Israel); Cenko, S. Bradley [Astrophysics Science Division, NASA Goddard Space Flight Center, Mail Code 661, Greenbelt, MD 20771 (United States); Perley, Daniel A.; Kulkarni, S. R.; Hallinan, Gregg; Bellm, Eric [Cahill Center for Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)

    2015-10-10

    GRB 130925A is one of the recent additions to the growing family of ultra-long gamma-ray bursts (GRBs; T90 ≳1000 s). While the X-ray emission of ultra-long GRBs have been studied extensively in the past, no comprehensive radio data set has been obtained so far. We report here the early discovery of an unusual radio afterglow associated with the ultra-long GRB 130925A. The radio emission peaks at low-frequencies (∼7 GHz) at early times, only 2.2 days after the burst occurred. More notably, the radio spectrum at frequencies above 10 GHz exhibits a rather steep cut-off, compared to other long GRB radio afterglows. This cut-off can be explained if the emitting electrons are either mono-energetic or originate from a rather steep, dN/dE ∝ E{sup −4}, power-law energy distribution. An alternative electron acceleration mechanism may be required to produce such an electron energy distribution. Furthermore, the radio spectrum exhibits a secondary underlying and slowly varying component. This may hint that the radio emission we observed is comprised of emission from both a reverse and a forward shock. We discuss our results in comparison with previous works that studied the unusual X-ray spectrum of this event and discuss the implications of our findings on progenitor scenarios.

  10. The redshift and afterglow of the extremely energetic gamma-ray burst GRB 080916C

    CERN Document Server

    Greiner, J.; Kruehler, T.; Kienlin, A.v.; Rau, A.; Sari, R.; Fox, Derek B.; Kawai, N.; Afonso, P.; Ajello, M.; Berger, E.; Cenko, S.B.; Cucchiara, A.; Filgas, R.; Klose, S.; Yoldas, A.Kuepue; Lichti, G.G.; Loew, S.; McBreen, S.; Nagayama, T.; Rossi, A.; Sato, S.; Szokoly, G.; Yoldas, A.; Zhang, X.-L.

    2009-01-01

    The detection of GeV photons from gamma-ray bursts (GRBs) has important consequences for the interpretation and modelling of these most-energetic cosmological explosions. The full exploitation of the high-energy measurements relies, however, on the accurate knowledge of the distance to the events. Here we report on the discovery of the afterglow and subsequent redshift determination of GRB 080916C, the first GRB detected by the Fermi Gamma-Ray Space Telescope with high significance detection of photons at >0.1 GeV. Observations were done with 7-channel imager GROND at the 2.2m MPI/ESO telescope, the SIRIUS instrument at the Nagoya-SAAO 1.4m telescope in South Africa, and the GMOS instrument at Gemini-S. The afterglow photometric redshift of z=4.35+-0.15, based on simultaneous 7-filter observations with the Gamma-Ray Optical and Near-infrared Detector (GROND), places GRB 080916C among the top 5% most distant GRBs, and makes it the most energetic GRB known to date. The detection of GeV photons from such a dista...

  11. Metastable atomic species in the N{sub 2} flowing afterglow

    Energy Technology Data Exchange (ETDEWEB)

    Levaton, J. [Laboratorio Nacional de Ciencia e Tecnologia do Bioetanol - CTBE/CNPEM, Caixa Postal 6170, 13083-970 Campinas, Sao Paulo (Brazil); Amorim, J., E-mail: jayr.amorim@bioetanol.org.br [Laboratorio Nacional de Ciencia e Tecnologia do Bioetanol - CTBE/CNPEM, Caixa Postal 6170, 13083-970 Campinas, Sao Paulo (Brazil)

    2012-03-13

    Graphical abstract: Calculated N({sup 4}S), N({sup 2}D) and N({sup 2}P) absolute densities as a function of the afterglow time. Highlights: Black-Right-Pointing-Pointer Nitrogen flowing post-discharge. Black-Right-Pointing-Pointer N({sup 4}S) and N({sup 2}D) densities. Black-Right-Pointing-Pointer Kinetic numerical model of the nitrogen afterglow. - Abstract: We have studied by optical emission spectroscopy the post-discharge of a pure N{sub 2} DC flowing discharge in such experimental conditions that the pink afterglow and the Lewis-Rayleigh afterglow occur. The emission profiles originated from the N{sub 2}(B{sup 3}{Pi}{sub g}), N{sub 2}(C{sup 3}{Pi}{sub u}) and N{sub 2}{sup +}(B{sup 2}{Sigma}{sub u}{sup +}) states and the N{sub 2}(B{sup 3}{Pi}{sub g},6{<=}v{<=}12) and N{sub 2}(C{sup 3}{Pi}{sub u},0{<=}v{<=}4) vibrational distributions were obtained in the post-discharge region. With basis on the works of Bockel et al. [S. Bockel, A.M. Diamy, A. Ricard, Surf. Coat. Tech. 74 (1995) 474] and Amorim and Kiohara [J. Amorim, V. Kiohara, Chem. Phys. Lett. 385 (2004) 268], we have obtained the experimental N({sup 4}S) and N({sup 2}D) relative densities along the post-discharge. A numerical model, previously developed to describe the neutral atomic, molecular and ionic species in the afterglow, was improved to include the kinetics of N({sup 2}D) and N({sup 2}P) states. Several kinetic mechanisms leading to the production of N({sup 2}D) in the post-discharge have been studied in order to explain the experimental data. We have determined that the dominant one is the reaction N{sub 2}(X{sup 1}{Sigma}{sub g}{sup +},v>8)+N({sup 4}S){yields}N{sub 2}(X{sup 1}{Sigma}{sub g}{sup +})+N({sup 2}D) with an estimated rate constant of 7 Multiplication-Sign 10{sup -14} cm{sup 3} s{sup -1}. Also, the fit of the numerical density profiles of N{sub 2}(C{sup 3}{Pi}{sub u}) and N{sub 2}{sup +}(B{sup 2}{Sigma}{sub u}{sup +}) to the experimental ones has provided the rate constant for reaction

  12. Analysis of capacity fading effect on Lithium Cobalt cells caused by pulse current technique in fast charging methods

    Science.gov (United States)

    Hafiz, S.; Arianto, S.; Yunaningsih, R. Y.; Majid, N.; Prihandoko, B.

    2017-04-01

    Charging a battery in a short time is important for portable devices. Many techniques have been developed to find out the proper method for fast charging. One of those techniques that has been patented in several fast charging methods is pulse current technique. This technique implements pulse current with adjusting pulse wide and voltage threshold in a certain values. In this paper, the capacity fading effects caused by the current pulse in lithium cobalt cells were investigated. The experiment was done by applying pulse current at high-level SOC to charge four cylindrical lithium cobalt cells. The Capacity of each cell was checked every 50 charge-discharge cycles. The experiment result shows that the changing capacity in each cell forms patterns alike. As if there was a slight increament on their capacities at first checking but rapidly decreasing at the next check. Then, their capacities continue to decrease slowly but the more often the charge-discharge cycling, the battery lifetime decreased. This research has provided analysis of pulse current effect on lithium cobalt capacity fading that should be noted as a reference in applying current pulse for fast charging methods.

  13. VLT identification of the optical afterglow of the gamma-ray burst GRB 000131 at z=4.50

    DEFF Research Database (Denmark)

    Andersen, M. I.; Hjorth, J.; Pedersen, H.

    2000-01-01

    We report the discovery of the gamma-ray burst GRB 000131 and its optical afterglow. The optical identification was made with the VLT 84 hours after the burst following a BATSE detection and an Inter Planetary Network localization. GRB 000131 was a bright, long-duration GRB, with an apparent prec...

  14. VLT identification of the optical afterglow of the gamma-ray burst GRB000131 at z=4.50

    DEFF Research Database (Denmark)

    Andersen, M.I.; Hjorth, J.; Jesen, B.L.

    2000-01-01

    We report the discovery of the gamma-ray burst GRB 000131 and its optical afterglow. The optical identification was made with the VLT 84 hours after the burst following a BATSE detection and an Inter Planetary Network localization. GRB 000131 was a bright, long-duration GRB, with an apparent prec...

  15. The Growth, Polarization, and Motion of the Radio Afterglow from the Giant Flare from SGR 1806-20

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, G

    2005-04-20

    The extraordinary giant flare (GF) of 2004 December 27 from the soft gamma repeater (SGR) 1806-20 was followed by a bright radio afterglow. We present an analysis of VLA observations of this radio afterglow from SGR1806-20, consisting of previously reported 8.5 GHz data covering days 7 to 20 after the GF, plus new observations at 8.5 and 22 GHz from day 24 to 81. For a symmetric outflow, we find a deceleration in the expansion, from {approx}4.5 mas/day to <2.5 mas/day. The time of deceleration is roughly coincident with the rebrightening in the radio light curve, as expected to result when the ejecta from the GF sweeps up enough of the external medium, and transitions from a coasting phase to the Sedov-Taylor regime. The radio afterglow is elongated and maintains a 2:1 axis ratio with an average position angle of -40{sup o} (north through east), oriented perpendicular to the average intrinsic linear polarization angle. We also report on the discovery of motion in the flux centroid of the afterglow, at an average velocity of 0.26 {+-} 0.03 c (assuming a distance of 15 kpc) at a position angle of -45{sup o}. This motion, in combination with the growth and polarization measurements, suggests an initially asymmetric outflow, mainly from one side of the magnetar.

  16. On the "canonical behaviour" of the X-ray afterglows of the Gamma Ray Bursts observed with Swift's XRT

    CERN Document Server

    Dado, S; De Rújula, Alvaro; Dado, Shlomo; Dar, Arnon

    2006-01-01

    The "canonical behaviour" of the early X-ray afterglows of long-duration Gamma-Ray Bursts (GRBs) --observed by the X-Ray Telescope of the SWIFT satellite-- is precisely the one predicted by the Cannonball model of GRBs.

  17. ON THE LATE-TIME SPECTRAL SOFTENING FOUND IN X-RAY AFTERGLOWS OF GAMMA-RAY BURSTS

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yuan-Zhu; Liang, En-Wei; Lu, Zu-Jia [GXU-NAOC Center for Astrophysics and Space Sciences, Department of Physics, Guangxi University, Nanning 530004 (China); Zhao, Yinan [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Shao, Lang, E-mail: lshao@hebtu.edu.cn [Department of Space Sciences and Astronomy, Hebei Normal University, Shijiazhuang 050024 (China)

    2016-02-20

    Strong spectral softening has been revealed in the late X-ray afterglows of some gamma-ray bursts (GRBs). The scenario of X-ray scattering around the circumburst dusty medium has been supported by previous works due to its overall successful prediction of both the temporal and spectral evolution of some X-ray afterglows. To further investigate the observed feature of spectral softening we now systematically search the X-ray afterglows detected by the X-ray telescope aboard Swift and collect 12 GRBs with significant late-time spectral softening. We find that dust scattering could be the dominant radiative mechanism for these X-ray afterglows regarding their temporal and spectral features. For some well-observed bursts with high-quality data, the time-resolved spectra could be well-produced within the scattering scenario by taking into account the X-ray absorption from the circumburst medium. We also find that during spectral softening the power-law index in the high-energy end of the spectra does not vary much. The spectral softening is mainly manifested by the spectral peak energy continually moving to the soft end.

  18. Effect of double frequency heating on the lead afterglow beam currents of an electron cyclotron resonance ion source

    Science.gov (United States)

    Toivanen, V.; Bellodi, G.; Küchler, D.; Wenander, F.; Tarvainen, O.

    2017-10-01

    The effect of double frequency heating on the performance of the CERN GTS-LHC 14.5 GHz Electron Cyclotron Resonance (ECR) ion source in afterglow mode is reported. The source of the secondary microwave frequency was operated both in pulsed and continuous wave (CW) modes within the range of 12-18 GHz. The results demonstrate that the addition of the secondary frequency can significantly impact the extracted beam currents and the temporal stability of the beam during the afterglow discharge. For example, up to a factor of 2.6 increase was achieved for 208Pb 35 and a factor of 3.1 for 208Pb 37+ compared to single frequency afterglow currents. It is shown that these effects are dependent on the choice of the secondary frequency with respect to the primary one and on the temporal synchronization between the two microwave sources. Overall, the results provide new insight into the afterglow discharge supporting the prevailing understanding of the physical processes behind the phenomenon.

  19. Low-Afterglow CsI:Tl microcolumnar films for small animal high-speed microCT.

    Science.gov (United States)

    Thacker, S C; Singh, B; Gaysinskiy, V; Ovechkina, E E; Miller, S R; Brecher, C; Nagarkar, V V

    2009-06-01

    Dedicated high-speed microCT systems are being developed for noninvasive screening of small animals. Such systems require scintillators with high spatial resolution, high light yield, and minimal persistence to ensure ghost free imaging. Unfortunately, the afterglow associated with conventional CsI:Tl microcolumnar films used in current high-speed systems introduces image lag, leading to substantial artifacts in reconstructed images, especially when the detector is operated at several hundreds of frames per second. At RMD, we have discovered that the addition of a second dopant, Eu(2+), to CsI:Tl crystals suppresses the afterglow by as much as a factor of 40 at 2 ms after a short excitation pulse of 20 ns, and by as much as a factor of 15 at 2 ms after a long excitation pulse of 100 ms. Our observations, supported by theoretical modeling, indicate that Eu(2+) ions introduce deep electron traps that alter the decay kinetics of the material, making it suitable for many high-speed imaging applications. Here we report on the fabrication and characterization of CsI:Tl,Eu microcolumnar films to determine if the remarkable afterglow properties of CsI:Tl,Eu crystals are preserved in the CsI:Tl,Eu microcolumnar films. Preliminary results indicate that the codoped microcolumnar films show a factor of 3.5 improvement in the afterglow compared to the standard CsI:Tl films.

  20. Exploring the Behaviour of Long Gamma-Ray Bursts with Intrinsic Afterglow Correlations: log L200s−α>200s

    Directory of Open Access Journals (Sweden)

    Samantha R. Oates

    2017-01-01

    Full Text Available In these proceedings, we summarise the exploration so far of the relationship between the afterglow luminosity (measured at rest frame 200s; log L 200 s and average afterglow decay rate (measured from rest frame 200s onwards, α > 200 s of long duration Gamma-ray Bursts (GRBs, first reported in the optical/UV light curves of GRB afterglows. We show that this correlation is also present in the X-ray afterglows of GRBs as observed by Swift-XRT. We explore how the parameters of the correlation observed in both the X-ray and optical/UV light curves relate to each other and the prompt emission phase and whether these correlations are consistent with predictions of the standard afterglow model. We find that the observed correlations are consistent with a common underlying physical mechanism producing GRBs and their afterglows regardless of the detailed temporal behaviour. However, a basic afterglow model has difficulty explaining all the observed correlations. This leads us to briefly discuss alternative more complex models.

  1. A comparative simulation study on the performance of LDPC coded communication systems over Weibull fading channels

    Directory of Open Access Journals (Sweden)

    Ibrahim Develi

    2016-04-01

    Full Text Available The Weibull distribution is a useful statistical model that can be used to describe the multipath fading in nowadays wireless communication environments. In this paper, the bit error rate (BER performance of Low-Density Parity-Check (LDPC coded communication systems using different decoding rules is presented over Weibull fading channels by means of comparative computer simulations. It is shown that, especially for the case of the Belief Propagation (BP decoding rule, significant performance improvement can be achieved in comparison with uncoded transmission when the channel is assumed to have Weibull fading.

  2. A Unified MGF-Based Capacity Analysis of Diversity Combiners over Generalized Fading Channels

    CERN Document Server

    Yilmaz, Ferkan

    2010-01-01

    Unified exact average capacity results for L-branch coherent diversity receivers including equal-gain combining (EGC) and maximal-ratio combining (MRC) are not known. This paper develops a novel generic framework for the capacity analysis of $L$-branch EGC/MRC over generalized fading channels. The framework is used to derive new results for the Gamma shadowed generalized Nakagami-m fading model which can be a suitable model for the fading environments encountered by high frequency (60 GHz and above) communications. The mathematical formalism is illustrated with some selected numerical and simulation results confirming the correctness of our newly proposed framework.

  3. Fading Losses on the LCRD Free-Space Optical Link Due to Channel Turbulence

    Science.gov (United States)

    Moision, Bruce; Piazzolla, Sabino; Hamkins, Jon

    2013-01-01

    The Laser Communications Relay Demonstration (LCRD) will implement an optical communications link between a pair of Earth terminals via an Earth-orbiting satellite relay. Clear air turbulence over the communication paths will cause random fluctuations, or fading, in the received signal irradiance. In this paper we characterize losses due to fading caused by clear air turbulence. We illustrate the performance of a representative relay link, utilizing a channel interleaver and error-correction-code to mitigate fading, and provide a method to quickly determine the link performance.

  4. Techniques to Reduce the Fading Effect in 3G Mobile Communications Systems

    Directory of Open Access Journals (Sweden)

    S. Popa

    2009-10-01

    Full Text Available Detailed methods used in mobile radio communications sistems WCDMA 3G, to improve the performance of the system working in a fading environement are presented. For system efficiency are used RRM algorithms. To reduce the interference level and provide quality of service (QoS in criticall situations (interference, fading, was used a power control algorithm. To handle the mobility of the Ms across cell boundaries the handover protocol needed in cellular systems. Was drawn some conclusions about third generation WCDMA air interface in interaction with the fading.

  5. A unified MGF-based capacity analysis of diversity combiners over generalized fading channels

    KAUST Repository

    Yilmaz, Ferkan

    2012-03-01

    Unified exact ergodic capacity results for L-branch coherent diversity combiners including equal-gain combining (EGC) and maximal-ratio combining (MRC) are not known. This paper develops a novel generic framework for the capacity analysis of L-branch EGC/MRC over generalized fading channels. The framework is used to derive new results for the gamma-shadowed generalized Nakagami-m fading model which can be a suitable model for the fading environments encountered by high frequency (60 GHz and above) communications. The mathematical formalism is illustrated with some selected numerical and simulation results confirming the correctness of our newly proposed framework. © 2012 IEEE.

  6. Spectrophotometric analysis of gamma-ray burst afterglow extinction curves with X-Shooter

    Science.gov (United States)

    Japelj, J.; Covino, S.; Gomboc, A.; Vergani, S. D.; Goldoni, P.; Selsing, J.; Cano, Z.; D'Elia, V.; Flores, H.; Fynbo, J. P. U.; Hammer, F.; Hjorth, J.; Jakobsson, P.; Kaper, L.; Kopač, D.; Krühler, T.; Melandri, A.; Piranomonte, S.; Sánchez-Ramírez, R.; Tagliaferri, G.; Tanvir, N. R.; de Ugarte Postigo, A.; Watson, D.; Wijers, R. A. M. J.

    2015-07-01

    We use gamma-ray burst (GRB) afterglow spectra observed with the VLT/X-Shooter spectrograph to measure rest-frame extinction in GRB lines-of-sight by modelling the broadband near-infrared (NIR) to X-ray afterglow spectral energy distributions (SEDs). Our sample consists of nine Swift GRBs, of which eight belong to the long-duration and one to the short-duration class. Dust is modelled using the average extinction curves of the Milky Way and the two Magellanic Clouds. We derive the rest-frame extinction of the entire sample, which fall in the range 0 ≲ AV ≲ 1.2. Moreover, the SMC extinction curve is the preferred extinction curve template for the majority of our sample, a result that is in agreement with those commonly observed in GRB lines of sights. In one analysed case (GRB 120119A), the common extinction curve templates fail to reproduce the observed extinction. To illustrate the advantage of using the high-quality, X-Shooter afterglow SEDs over the photometric SEDs, we repeat the modelling using the broadband SEDs with the NIR-to-UV photometric measurements instead of the spectra. The main result is that the spectroscopic data, thanks to a combination of excellent resolution and coverage of the blue part of the SED, are more successful in constraining extinction curves and therefore dust properties in GRB hosts with respect to photometric measurements. In all cases but one the extinction curve of one template is preferred over the others. We show that themodelled values of the extinction AV and the spectral slope, obtained through spectroscopic and photometric SED analysis, can differ significantly for individual events, though no apparent trend in the differences is observed. Finally we stress that, regardless of the resolution of the optical-to-NIR data, the SED modelling gives reliable results only when the fit is performed on a SED covering a broader spectral region (in our case extending to X-rays). Based on observations collected at the European

  7. Cooperative Cognitive Radio Systems over Nakagami-m Fading Channels

    KAUST Repository

    Hyadi, Amal

    2013-05-08

    This thesis aims to investigate the incorporation of cooperative techniques in cognitive radio networks over Nakagami-m fading channels. These last years, spectrum sharing mechanisms has gained a lot of interest in the wireless communication domain. Using cooperation in a cognitive set up make the use of spectrum much more efficient. Moreover, it helps to extend the coverage area of the cognitive network and also to reduce the transmitting power and, thus, the generated interference. In this work, we consider two particular scenarios for cooperative cognitive radio systems. The first scenario consider multihop regenerative relaying in an underlay cognitive set up. The cooperation is performed in the secondary system, in the presence of multiple primary users. Both interference power and peak power constraints are taking into account. Closed-form expressions for the statistical characteristics and multiple end- to-end performance metrics are derived. Different scenarios are presented to illustrate the obtained results and Monte Carlo simulations confirm the accuracy of our analytical derivations. In the second part of this work, we consider an overlay cognitive network with the spectrally efficient two-phase two-way relaying protocol. Two relay selection techniques, optimizing both the primary and the secondary communication, are presented. The overall outage performance is investigated and an optimal power allocation scheme, that ameliorate the outage performance of the system, is proposed. Numerical simulations are presented to illustrate and compare the obtained results.

  8. Distortion outage minimization in Nakagami fading using limited feedback

    Directory of Open Access Journals (Sweden)

    Wang Chih-Hong

    2011-01-01

    Full Text Available Abstract We focus on a decentralized estimation problem via a clustered wireless sensor network measuring a random Gaussian source where the clusterheads amplify and forward their received signals (from the intra-cluster sensors over orthogonal independent stationary Nakagami fading channels to a remote fusion center that reconstructs an estimate of the original source. The objective of this paper is to design clusterhead transmit power allocation policies to minimize the distortion outage probability at the fusion center, subject to an expected sum transmit power constraint. In the case when full channel state information (CSI is available at the clusterhead transmitters, the optimization problem can be shown to be convex and is solved exactly. When only rate-limited channel feedback is available, we design a number of computationally efficient sub-optimal power allocation algorithms to solve the associated non-convex optimization problem. We also derive an approximation for the diversity order of the distortion outage probability in the limit when the average transmission power goes to infinity. Numerical results illustrate that the sub-optimal power allocation algorithms perform very well and can close the outage probability gap between the constant power allocation (no CSI and full CSI-based optimal power allocation with only 3-4 bits of channel feedback.

  9. On the Delay-Energy Tradeoff in Multiuser Fading Channels

    Directory of Open Access Journals (Sweden)

    Ralf R. Müller

    2009-01-01

    Full Text Available We consider the delay-energy tradeoff on a fading channel with multiuser diversity. For fixed arbitrary rates of the users, the total transmitted energy is minimized subject to a delay constraint. To achieve this goal we propose a scheme which schedules a subset of all users simultaneously. The scheduled users are allocated power to guarantee successful separation at the detector by successive decoding. In this way, we can benefit from both multiuser diversity and the near-far situation via scheduling and simultaneous transmission, respectively. We analytically show that when the number of users goes to infinity the energy required to guarantee the required user rates can be made as small as required at the cost of a higher delay “delay-energy tradeoff”. We explicitly compute the delay under the proposed scheduling policy and discuss how delay differentiation can be achieved. We extend the results to multiband multiaccess channel. Finally, all the results can be generalized in a straightforward fashion to broadcast channel due to the Gaussian multiaccess-broadcast channel duality.

  10. On the Delay-Energy Tradeoff in Multiuser Fading Channels

    Directory of Open Access Journals (Sweden)

    Chaporkar Prasanna

    2009-01-01

    Full Text Available We consider the delay-energy tradeoff on a fading channel with multiuser diversity. For fixed arbitrary rates of the users, the total transmitted energy is minimized subject to a delay constraint. To achieve this goal we propose a scheme which schedules a subset of all users simultaneously. The scheduled users are allocated power to guarantee successful separation at the detector by successive decoding. In this way, we can benefit from both multiuser diversity and the near-far situation via scheduling and simultaneous transmission, respectively. We analytically show that when the number of users goes to infinity the energy required to guarantee the required user rates can be made as small as required at the cost of a higher delay "delay-energy tradeoff". We explicitly compute the delay under the proposed scheduling policy and discuss how delay differentiation can be achieved. We extend the results to multiband multiaccess channel. Finally, all the results can be generalized in a straightforward fashion to broadcast channel due to the Gaussian multiaccess-broadcast channel duality.

  11. The thermodynamics of simple materials with fading memory

    CERN Document Server

    Day, William Alan

    1972-01-01

    This Tract gives an account of certain recent attempts to construct a satisfactory theory of thermodynamics for materials which have a memory for the past. Naturally it draws heavily on the writings of those who have made significant contributions to the field. I am particularly grateful to Professor C. A. Truesdell of The lohns Hopkins University for his invitation to write the Tract and to Professor A. E. Green of Oxford for his comments on various parts of the manuscript. Hertford College, Oxford December 1971 W. A. Day Contents Introduction 1 Chapter 1 Preliminaries 5 1. 1 Vector and Tensor Analysis. 5 1. 2 Paths and Line Integrals . 7 1. 3 Kinematics and the Balance Laws 11 1. 4 Simple Materials with Memory 15 21 Chapter 2 A Theory of Thermodynamics . 2. 1 Processes. 21 2. 2 The Thermodynamic Inequality . 23 2. 3 Heat Conduction Inequalities . 24 2. 4 The Conversion of Heat into Mechanical Work 27 31 The Construction of the Entropy Chapter 3 The Clausius Inequality 31 3. 1 3. 2 Fading Memory . 34 3. 3 Th...

  12. Internal tides and deep diel fades in acoustic intensity.

    Science.gov (United States)

    White, Andrew W; Henyey, Frank S; Andrew, Rex K; Mercer, James A; Worcester, Peter F; Dzieciuch, Matthew A; Colosi, John A

    2016-11-01

    A mechanism is presented by which the observed acoustic intensity is made to vary due to changes in the acoustic path that are caused by internal-tide vertical fluid displacements. The position in range and depth of large-scale caustic structure is determined by the background sound-speed profile. Internal tides cause a deformation of the background profile, changing the positions of the caustic structures-which can introduce intensity changes at a distant receiver. Gradual fades in the acoustic intensity occurring over timescales similar to those of the tides were measured during a low-frequency (284-Hz) acoustic scattering experiment in the Philippine Sea in 2009 [White et al., J. Acoust. Soc. Am. 134(4), 3347-3358 (2013)]. Parabolic equation and Hamiltonian ray-tracing calculations of acoustic propagation through a plane-wave internal tide environmental model employing sound-speed profiles taken during the experiment indicate that internal tides could cause significant gradual changes in the received intensity. Furthermore, the calculations demonstrate how large-scale perturbations to the index of refraction can result in variation in the received intensity.

  13. Scalable video transmission over Rayleigh fading channels using LDPC codes

    Science.gov (United States)

    Bansal, Manu; Kondi, Lisimachos P.

    2005-03-01

    In this paper, we investigate an important problem of efficiently utilizing the available resources for video transmission over wireless channels while maintaining a good decoded video quality and resilience to channel impairments. Our system consists of the video codec based on 3-D set partitioning in hierarchical trees (3-D SPIHT) algorithm and employs two different schemes using low-density parity check (LDPC) codes for channel error protection. The first method uses the serial concatenation of the constant-rate LDPC code and rate-compatible punctured convolutional (RCPC) codes. Cyclic redundancy check (CRC) is used to detect transmission errors. In the other scheme, we use the product code structure consisting of a constant rate LDPC/CRC code across the rows of the `blocks' of source data and an erasure-correction systematic Reed-Solomon (RS) code as the column code. In both the schemes introduced here, we use fixed-length source packets protected with unequal forward error correction coding ensuring a strictly decreasing protection across the bitstream. A Rayleigh flat-fading channel with additive white Gaussian noise (AWGN) is modeled for the transmission. The rate-distortion optimization algorithm is developed and carried out for the selection of source coding and channel coding rates using Lagrangian optimization. The experimental results demonstrate the effectiveness of this system under different wireless channel conditions and both the proposed methods (LDPC+RCPC/CRC and RS+LDPC/CRC) outperform the more conventional schemes such as those employing RCPC/CRC.

  14. Chirp-aided power fading mitigation for upstream 100 km full-range long reach PON with DBR DML

    Science.gov (United States)

    Zhang, Kuo; He, Hao; Xin, Haiyun; Hu, Weisheng; Liang, Song; Lu, Dan; Zhao, Lingjuan

    2018-01-01

    The DML is a promising option for cost-sensitive ONUs in optical access networks, but suffers from severe power fading due to dispersion and chirp. In this work, we investigate to mitigate the power fading by optimizing the chirp. Theoretical analysis indicates, a see-saw effect, influenced by the bias, exists between the adiabatic notch-induced fading (A-fading) and the transient notch-induced fading (T-fading). High bias can mitigate T-fading, but causes large A-fading. Low bias can avoid A-fading, but cannot completely mitigate T-fading. For each transmission distance, balance should be achieved to favor transmission. The ∼20 km short distance requires high bias to obtain large adiabatic chirp to counteract the T-fading, while the ∼100 km long distance requires relatively low bias to avoid the A-fading. With this power fading mitigation technique, we conduct upstream transmission experiment of LR-PON. Experiments show that, although signal contamination is inevitable, clear ;1; and ;0; are obtained with this power fading mitigation scheme for any 0 ∼100 km distance with 10 Gb/s OOK signal and DBR DML. The optical power budget penalty induced by 0 ∼100 km fiber is limited within only 2.2 dB, with optimum bias for each distance. More than 10 and 15 dB improvement is achieved when BER is 10-3 and 10-6. A method is also proposed to automatically obtain optimum bias from the ranging procedure of PON protocol.

  15. MGF Approach to the Analysis of Generalized Two-Ray Fading Models

    KAUST Repository

    Rao, Milind

    2015-01-01

    We analyze a class of Generalized Two-Ray (GTR) fading channels that consist of two line of sight (LOS) components with random phase plus a diffuse component. We derive a closedform expression for the moment generating function (MGF) of the signal-to-noise ratio (SNR) for this model, which greatly simplifies its analysis. This expression arises from the observation that the GTR fading model can be expressed in terms of a conditional underlying Rician distribution. We illustrate the approach to derive simple expressions for statistics and performance metrics of interest such as the amount of fading, the level crossing rate, the symbol error rate, and the ergodic capacity in GTR fading channels. We also show that the effect of considering a more general distribution for the phase difference between the LOS components has an impact on the average SNR.

  16. EFFECTS OF RICIAN FADING ON THE OPERATION OF AERONAUTICAL SATELLITE OFDM CHANNEL

    National Research Council Canada - National Science Library

    Volodymyr Kharchenko; Andrii Grekhov; Ismail Ali; Yulia Udod

    2016-01-01

    ... for estimating the parameters of such a channel. Methods: To study the effect of Rician fading on messages transmission via aeronautical satellite OFDM channel with adaptive modulation the original model of the communication channel...

  17. Extended Generalized-K (EGK): A New Simple and General Model for Composite Fading Channels

    CERN Document Server

    Yilmaz, Ferkan

    2010-01-01

    In this paper, we introduce a generalized composite fading distribution (termed extended generalized-K (EGK)) to model the envelope and the power of the received signal in millimeter wave (60 GHz or above) and free-space optical channels. We obtain the first and the second-order statistics of the received signal envelope characterized by the EGK composite fading distribution. In particular, expressions for probability density function, cumulative distribution function, level crossing rate and average fade duration, and fractional moments are derived. In addition performance measures such as amount of fading, average bit error probability, outage probability, average capacity, and outage capacity are offered in closed-form. Selected numerical and computer simulation examples validate the accuracy of the presented mathematical analysis.

  18. Analysis of Coded FHSS Systems with Multiple Access Interference over Generalized Fading Channels

    Directory of Open Access Journals (Sweden)

    Salam A. Zummo

    2009-02-01

    Full Text Available We study the effect of interference on the performance of coded FHSS systems. This is achieved by modeling the physical channel in these systems as a block fading channel. In the derivation of the bit error probability over Nakagami fading channels, we use the exact statistics of the multiple access interference (MAI in FHSS systems. Due to the mathematically intractable expression of the Rician distribution, we use the Gaussian approximation to derive the error probability of coded FHSS over Rician fading channel. The effect of pilot-aided channel estimation is studied for Rician fading channels using the Gaussian approximation. From this, the optimal hopping rate in coded FHSS is approximated. Results show that the performance loss due to interference increases as the hopping rate decreases.

  19. Achievable capacity of a spectrum sharing system over hyper fading channels

    KAUST Repository

    Ekin, Sabit

    2009-11-01

    Cognitive radio with spectrum sharing feature is a promising technique to address the spectrum under-utilization problem in dynamically changing environments. In this paper, achievable capacity gain of spectrum sharing systems over dynamic fading environments is studied. For the analysis, a theoretical fading model called hyper fading model that is suitable to the dynamic nature of cognitive radio channel is proposed. Closed-form expression of probability density function (PDF) and cumulative density function (CDF) of the signal-to-noise ratio (SNR) for secondary users in spectrum sharing systems are derived. In addition, the capacity gains achievable with spectrum sharing systems in high and low power regions are obtained. Numerical simulations are performed to study the effects of different fading figures, average powers, interference temperature, and number of secondary users on the achievable capacity.

  20. X-ray spectral components observed in the afterglow of GRB 130925A

    DEFF Research Database (Denmark)

    Bellm, Eric C.; Barrière, Nicolas M.; Bhalerao, Varun

    2014-01-01

    We have identified spectral features in the late-time X-ray afterglow of the unusually long, slow-decaying GRB 130925A using NuSTAR, Swift/X-Ray Telescope, and Chandra. A spectral component in addition to an absorbed power law is required at >4σ significance, and its spectral shape varies between...... two observation epochs at 2 × 105 and 106 s after the burst. Several models can fit this additional component, each with very different physical implications. A broad, resolved Gaussian absorption feature of several keV width improves the fit, but it is poorly constrained in the second epoch....... An additive blackbody or second power-law component provide better fits. Both are challenging to interpret: the blackbody radius is near the scale of a compact remnant (108 cm), while the second power-law component requires an unobserved high-energy cutoff in order to be consistent with the non...

  1. The Giant Flare From SGR 1806-20 And Its Radio Afterglow

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, G.B.; /New Mexico U. /NRAO, Socorro; Granot, J.; /KIPAC, Menlo Park

    2006-09-26

    The multi-wavelength observations of the 2004 December 27 Giant Flare (GF) from SGR 1806-20 and its long-lived radio afterglow are briefly reviewed. The GF appears to have been produced by a dramatic reconfiguration of the magnetic field near the surface of the neutron star, possibly accompanied by fractures in the crust. The explosive release of over 10{sup 46} erg (isotropic equivalent) powered a one-sided mildly relativistic outflow. The outflow produced a new expanding radio nebula, that is still visible over a year after the GF. Also considered are the constraints on the total energy in the GF, the energy and mass in the outflow, and on the external density, as well as possible implications for short {gamma}-ray bursts and potential signatures in high energy neutrinos, photons, or cosmic rays. Some possible future observations of this and other GFs are briefly discussed.

  2. On the Polarization of Gamma Ray Bursts and their Optical Afterglows

    CERN Document Server

    Dado, S; De Rújula, Alvaro; Dado, Shlomo; Dar, Arnon

    2004-01-01

    The polarization of the optical afterglow (AG) of Gamma-Ray Bursts (GRBs) has only been measured in a few instances at various times after the GRB. In all cases except the best measured one (GRB 030329) the observed polarization and its evolution are simple and easy to explain in the most naive version of the "Cannonball'' model of GRBs: the "intrinsic" AG polarization is small and the observations reflect the "foreground" effects of the host galaxy and ours. The polarization observed in GRB 030329 behaves chaotically, its understanding requires reasonable but ad-hoc ingredients. The polarization of the gamma rays of a GRB has only been measured in the case of GRB 021206. The result is debated, but similar measurements would be crucial to the determination of the GRB-generating mechanism.

  3. The Discovery of a Hyperluminal Source in the Radio Afterglow of GRB 030329

    CERN Document Server

    Dado, Shlomo; De Rújula, Alvaro; Dado, Shlomo; Dar, Arnon

    2004-01-01

    Taylor, Frail, Berger and Kulkarni have made precise VLBI measurements of the size and position of the source of the radio afterglow of GRB 030329. They report a size evolution compatible with standard fireball models, proper motion limits inconsistent with the cannonball model, and a double source, i.e. "an additional compact component" on day 51 after the GRB, totally unexpected in the standard models. We outline a consistent interpretation of the ensemble of the data in the realm of the cannonball model. The observed double source is a radio image of the two cannonballs required in this model to explain the gamma-ray and optical light curves of this GRB; their separation agrees with the expectation. Thus interpreted, the observation of the two sources --separated by a "hyperluminal" distance-- is a major discovery in astrophysics: it pins down the origin of GRBs.

  4. Dust extinction in high-z galaxies with gamma-ray burst afterglow spectroscopy

    DEFF Research Database (Denmark)

    Elíasdóttir, Á.; Fynbo, J. P. U.; Hjorth, J.

    2009-01-01

    in a GRB host galaxy, while several tens of optical afterglow spectra without the bump have been recorded in the past decade. The derived extinction curve gives AV = 0.8-1.5 depending on the assumed intrinsic slope. Of the three local extinction laws, a Large Magellanic Cloud (LMC) type extinction gives......, the spectrum of GRB 070802 is unique for a GRB spectrum in that it shows clear C I absorption features, leading us to propose a correlation between the presence of the bump and C I. The gas-to-dust ratio for the host galaxy is found to be significantly lower than that of other GRB hosts with N(H I)/AV = (2...

  5. High SNR BER comparison of coherent and differentially coherent modulation schemes in lognormal fading channels

    KAUST Repository

    Song, Xuegui

    2014-09-01

    Using an auxiliary random variable technique, we prove that binary differential phase-shift keying and binary phase-shift keying have the same asymptotic bit-error rate performance in lognormal fading channels. We also show that differential quaternary phase-shift keying is exactly 2.32 dB worse than quaternary phase-shift keying over the lognormal fading channels in high signal-to-noise ratio regimes.

  6. Asymptotic SER performance comparison of MPSK and MDPSK in wireless fading channels

    KAUST Repository

    Song, Xuegui

    2015-02-01

    We propose a general framework to investigate asymptotic relative performance between M-ary phase-shift keying (MPSK) and M-ary differential phase-shift keying (MDPSK) in wireless fading channels. Using this framework, we provide an alternative derivation for the closed-form expression of the asymptotic performance loss of MDPSK w.r.t. MPSK in an additive white Gaussian noise channel. The same performance loss is also shown to be true for the lognormal fading channels.

  7. A Large Catalog of Homogeneous Ultra-Violet/Optical GRB Afterglows: Temporal and Spectral Evolution

    Science.gov (United States)

    Roming, Peter W. A.; Koch, T. Scott; Oates, Samantha R.; Porterfield, Blair L.; Bayless, Amanda J.; Breeveld, Alice A.; Gronwall, Caryl; Kuin, N. P. M.; Page, Mat J.; de Pasquale, Massimiliano; Siegel, Michael H.; Swenson, Craig A.; Tobler, Jennifer M.

    2017-02-01

    We present the second Swift Ultra-Violet/Optical Telescope (UVOT) gamma-ray burst (GRB) afterglow catalog, greatly expanding on the first Swift UVOT GRB afterglow catalog. The second catalog is constructed from a database containing over 120,000 independent UVOT observations of 538 GRBs first detected by Swift, the High Energy Transient Explorer 2 (HETE2), the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL), the Interplanetary Network (IPN), Fermi, and Astro-rivelatore Gamma a Immagini Leggero (AGILE). The catalog covers GRBs discovered from 2005 January 17 to 2010 December 25. Using photometric information in three UV bands, three optical bands, and a “white” or open filter, the data are optimally coadded to maximize the number of detections and normalized to one band to provide a detailed light curve. The catalog provides positional, temporal, and photometric information for each burst, as well as Swift Burst Alert Telescope and X-ray Telescope (XRT) GRB parameters. Temporal slopes are provided for each UVOT filter. The temporal slope per filter of almost half the GRBs are fit with a single power law, but one to three breaks are required in the remaining bursts. Morphological comparisons with the X-ray reveal that ˜ 75 % of the UVOT light curves are similar to one of the four morphologies identified by Evans et al. (2009). The remaining ˜ 25 % have a newly identified morphology. For many bursts, redshift- and extinction-corrected UV/optical spectral slopes are also provided at 2 × 103, 2 × 104, and 2 × 105 s.

  8. GAMMA-RAY BURST DYNAMICS AND AFTERGLOW RADIATION FROM ADAPTIVE MESH REFINEMENT, SPECIAL RELATIVISTIC HYDRODYNAMIC SIMULATIONS

    Energy Technology Data Exchange (ETDEWEB)

    De Colle, Fabio; Ramirez-Ruiz, Enrico [Astronomy and Astrophysics Department, University of California, Santa Cruz, CA 95064 (United States); Granot, Jonathan [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); Lopez-Camara, Diego, E-mail: fabio@ucolick.org [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Ap. 70-543, 04510 D.F. (Mexico)

    2012-02-20

    We report on the development of Mezcal-SRHD, a new adaptive mesh refinement, special relativistic hydrodynamics (SRHD) code, developed with the aim of studying the highly relativistic flows in gamma-ray burst sources. The SRHD equations are solved using finite-volume conservative solvers, with second-order interpolation in space and time. The correct implementation of the algorithms is verified by one-dimensional (1D) and multi-dimensional tests. The code is then applied to study the propagation of 1D spherical impulsive blast waves expanding in a stratified medium with {rho}{proportional_to}r{sup -k}, bridging between the relativistic and Newtonian phases (which are described by the Blandford-McKee and Sedov-Taylor self-similar solutions, respectively), as well as to a two-dimensional (2D) cylindrically symmetric impulsive jet propagating in a constant density medium. It is shown that the deceleration to nonrelativistic speeds in one dimension occurs on scales significantly larger than the Sedov length. This transition is further delayed with respect to the Sedov length as the degree of stratification of the ambient medium is increased. This result, together with the scaling of position, Lorentz factor, and the shock velocity as a function of time and shock radius, is explained here using a simple analytical model based on energy conservation. The method used for calculating the afterglow radiation by post-processing the results of the simulations is described in detail. The light curves computed using the results of 1D numerical simulations during the relativistic stage correctly reproduce those calculated assuming the self-similar Blandford-McKee solution for the evolution of the flow. The jet dynamics from our 2D simulations and the resulting afterglow light curves, including the jet break, are in good agreement with those presented in previous works. Finally, we show how the details of the dynamics critically depend on properly resolving the structure of the

  9. Gamma-Ray Burst Dynamics and Afterglow Radiation from Adaptive Mesh Refinement, Special Relativistic Hydrodynamic Simulations

    Science.gov (United States)

    De Colle, Fabio; Granot, Jonathan; López-Cámara, Diego; Ramirez-Ruiz, Enrico

    2012-02-01

    We report on the development of Mezcal-SRHD, a new adaptive mesh refinement, special relativistic hydrodynamics (SRHD) code, developed with the aim of studying the highly relativistic flows in gamma-ray burst sources. The SRHD equations are solved using finite-volume conservative solvers, with second-order interpolation in space and time. The correct implementation of the algorithms is verified by one-dimensional (1D) and multi-dimensional tests. The code is then applied to study the propagation of 1D spherical impulsive blast waves expanding in a stratified medium with ρvpropr -k , bridging between the relativistic and Newtonian phases (which are described by the Blandford-McKee and Sedov-Taylor self-similar solutions, respectively), as well as to a two-dimensional (2D) cylindrically symmetric impulsive jet propagating in a constant density medium. It is shown that the deceleration to nonrelativistic speeds in one dimension occurs on scales significantly larger than the Sedov length. This transition is further delayed with respect to the Sedov length as the degree of stratification of the ambient medium is increased. This result, together with the scaling of position, Lorentz factor, and the shock velocity as a function of time and shock radius, is explained here using a simple analytical model based on energy conservation. The method used for calculating the afterglow radiation by post-processing the results of the simulations is described in detail. The light curves computed using the results of 1D numerical simulations during the relativistic stage correctly reproduce those calculated assuming the self-similar Blandford-McKee solution for the evolution of the flow. The jet dynamics from our 2D simulations and the resulting afterglow light curves, including the jet break, are in good agreement with those presented in previous works. Finally, we show how the details of the dynamics critically depend on properly resolving the structure of the relativistic flow.

  10. Luminosity Correlations for Gamma-Ray Bursts and Implications for Their Prompt and Afterglow Emission Mechanisms

    Science.gov (United States)

    Sultana, J.; Kazanas, D.; Fukumura, K

    2013-01-01

    We present the relation between the (z- and k-corrected) spectral lags, tau, for the standard Swift energy bands 50 - 100 keV and 100 - 200 keV and the peak isotropic luminosity, L(sub iso) (a relation reported first by Norris et al.), for a subset of 12 long Swift GRBs taken from a recent study of this relation by Ukwatta et al. The chosen GRBs are also a subset of the Dainotti et al. sample, a set of Swift GRBs of known redshift, employed in establishing a relation between the (GRB frame) luminosity, L(sub x), of the shallow (or constant) flux portion of the typical XRT GRB-afterglow light curve and the (GRB frame) time of transition to the normal decay rate, T(sub brk). We also present the L(sub x) - T(sub brk) relation using only the bursts common in the two samples. The two relations exhibit a significant degree of correlation (rho = -0.65 for the L(sub iso) - tao and rho = -0.88 for the L(sub x) -T(sub brk) relation) and have surprisingly similar best-fit power law indices (-1.19 +/- 0.17 for L(sub iso) - tau and -1.10 +/- 0.03 for L(sub x) - T(sub brk)). Even more surprisingly, we noted that although tau and T(sub brk) represent different GRB time variables, it appears that the first relation (L(sub iso) - tao) extrapolates into the second one for timescales tau similar to T(sub brk) This fact suggests that these two relations have a common origin, which we conjecture to be kinematic. This relation adds to the recently discovered relations between properties of the prompt and afterglow GRB phases, indicating a much more intimate relation between these two phases than hitherto considered.

  11. Product of the powers of generalized Nakagami-m variates and performance of cascaded fading channels

    KAUST Repository

    Yilmaz, Ferkan

    2009-11-01

    In this paper, we analyze the fading statistics of a generic fading distribution, termed the N-product Generalized Nakagami-m (GNM) distribution (N*GNM distribution), constructed as the product of the power of N statistically independent and non-identically distributed GNM random variables, for the purpose of modeling the cascaded fading channels. In particular, using the Fox\\'s H function, we derive the probability density function, the cumulative distribution function, the moment generating function and the moments of such channels in closed-form. These derived results are a convenient tool to statistically model the cascaded GNM fading channels and to analyze the performance of digital communication systems over these kinds of channels. As such, generic closed-form expressions for the amount of fading, the outage probability, the capacity, the outage capacity and the average bit error probabilities of digital communications systems over cascaded GNM fading channels are presented. Numerical and simulation results, performed to verify the correctness of the proposed formulation, are in perfect agreement.

  12. Capacity limits of spectrum-sharing systems over hyper-fading channels

    KAUST Repository

    Ekin, Sabit

    2011-01-20

    Cognitive radio (CR) with spectrum-sharing feature is a promising technique to address the spectrum under-utilization problem in dynamically changing environments. In this paper, the achievable capacity gain of spectrum-sharing systems over dynamic fading environments is studied. To perform a general analysis, a theoretical fading model called hyper-fading model that is suitable to the dynamic nature of CR channel is proposed. Closed-form expressions of probability density function (PDF) and cumulative density function (CDF) of the signal-to-noise ratio (SNR) for secondary users (SUs) in spectrum-sharing systems are derived. In addition, the capacity gains achievable with spectrum-sharing systems in high and low power regions are obtained. The effects of different fading figures, average fading powers, interference temperatures, peak powers of secondary transmitters, and numbers of SUs on the achievable capacity are investigated. The analytical and simulation results show that the fading figure of the channel between SUs and primary base-station (PBS), which describes the diversity of the channel, does not contribute significantly to the system performance gain. © 2011 John Wiley & Sons, Ltd.

  13. Use of Interrupted Helium Flow in the Analysis of Vapor Samples with Flowing Atmospheric-Pressure Afterglow-Mass Spectrometry

    Science.gov (United States)

    Storey, Andrew P.; Zeiri, Offer M.; Ray, Steven J.; Hieftje, Gary M.

    2017-02-01

    The flowing atmospheric-pressure afterglow (FAPA) source was used for the mass-spectrometric analysis of vapor samples introduced between the source and mass spectrometer inlet. Through interrupted operation of the plasma-supporting helium flow, helium consumption is greatly reduced and dynamic gas behavior occurs that was characterized by schlieren imaging. Moreover, mass spectra acquired immediately after the onset of helium flow exhibit a signal spike before declining and ultimately reaching a steady level. This initial signal appears to be due to greater interaction of sample vapor with the afterglow of the source when helium flow resumes. In part, the initial spike in signal can be attributed to a pooling of analyte vapor in the absence of helium flow from the source. Time-resolved schlieren imaging of the helium flow during on and off cycles provided insight into gas-flow patterns between the FAPA source and the MS inlet that were correlated with mass-spectral data.

  14. THERMAL EMISSIONS SPANNING THE PROMPT AND THE AFTERGLOW PHASES OF THE ULTRA-LONG GRB 130925A

    Energy Technology Data Exchange (ETDEWEB)

    Basak, Rupal [Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw (Poland); Rao, A. R., E-mail: rupal@camk.edu.pl, E-mail: arrao@tifr.res.in [Tata Institute of Fundamental Research, Mumbai-400005, India. (India)

    2015-07-01

    GRB 130925A is an ultra-long gamma-ray burst (GRB), and it shows clear evidence for thermal emission in the soft X-ray data of the Swift/X-ray Telescope (XRT; ∼0.5 keV), lasting until the X-ray afterglow phase. Due to the long duration of the GRB, the burst could be studied in hard X-rays with high-resolution focusing detectors (NuSTAR). The blackbody temperature, as measured by the Swift/XRT, shows a decreasing trend until the late phase (Piro et al.) whereas the high-energy data reveal a significant blackbody component during the late epochs at an order of magnitude higher temperature (∼5 keV) compared to contemporaneous low energy data (Bellm et al.). We resolve this apparent contradiction by demonstrating that a model with two black bodies and a power law (2BBPL) is consistent with the data right from the late prompt emission to the afterglow phase. Both blackbodies show a similar cooling behavior up to late times. We invoke a structured jet, having a fast spine and a slower sheath layer, to identify the location of these blackbodies. Independent of the physical interpretation, we propose that the 2BBPL model is a generic feature of the prompt emission of all long GRBs, and the thermal emission found in the afterglow phase of different GRBs reflects the lingering thermal component of the prompt emission with different timescales. We strengthen this proposal by pointing out a close similarity between the spectral evolutions of this GRB and GRB 090618, a source with significant wide band data during the early afterglow phase.

  15. A Comprehensive Study of Gamma-Ray Burst Optical Emission. III. Brightness Distributions and Luminosity Functions of Optical Afterglows

    Science.gov (United States)

    Wang, Xiang-Gao; Liang, En-Wei; Li, Liang; Lu, Rui-Jing; Wei, Jian-Yan; Zhang, Bing

    2013-09-01

    We continue our systematic statistical study on optical afterglow data of gamma-ray bursts (GRBs). We present the apparent magnitude distributions of early optical afterglows at different epochs (t = 102 s, 103 s, and 1 hr) for the optical light curves of a sample of 93 GRBs (the global sample) and for sub-samples with an afterglow onset bump or a shallow decay segment. For the onset sample and shallow decay sample we also present the brightness distribution at the peak time t p and break time t b, respectively. All the distributions can be fit with Gaussian functions. We further perform Monte Carlo simulations to infer the luminosity function of GRB optical emission at the rest-frame time 103 s, t p, and t b. Our results show that a single power-law luminosity function is adequate to model the data with indices -1.40 ± 0.10, -1.06 ± 0.16, and -1.54 ± 0.22. Based on the derived rest-frame 103 s luminosity function, we generate the intrinsic distribution of the R-band apparent magnitude M R at the observed time 103 s post-trigger, which peaks at M R = 22.5 mag. The fraction of GRBs whose R-band magnitude is fainter than 22 mag and 25 mag and at the observer time 103 s are ~63% and ~25%, respectively. The detection probabilities of the optical afterglows with ground-based robotic telescopes and the UV-Optical Telescope on board Swift are roughly consistent with that inferred from this intrinsic M R distribution, indicating that the variations of the dark GRB fraction among the samples with different telescopes may be due to the observational selection effect, although the existence of an intrinsically dark GRB population cannot be ruled out.

  16. On the Structure of the Burst and Afterglow of Gamma-Ray Bursts I

    Science.gov (United States)

    Ruffini, Remo; Bianco, Carlo Luciano; Xue, She-Sheng; Chardonnet, Pascal; Fraschetti, Federico

    the three different regimes of the afterglow are described within the fully radiative and radial approximations: the ultrarelativistic, the relativistic and the nonrelativistic regimes. The best fit of the theory leads to an unequivocal identification of the "long GRBs" as extended emission occurring at the afterglow peak (E-APE). The relative intensities, the time separation and the hardness ratio of the P-GRB and the E-APE are used as distinctive observational test of the EMBH theory and the excellent agreement between our theoretical predictions and the observations are documented. The afterglow power-law indexes in the EMBH theory are compared and contrasted with the ones in the literature, and no beaming process is found for GRB 991216. Finally, some preliminary results relating the observed time variability of the E-APE to the inhomogeneities in the interstellar medium are presented, as well as some general considerations on the EMBH formation. The issue of the GSTS paradigm will be the object of a forthcoming publication while the relevance of the iron-lines observed in GRB 991216 is shortly reviewed. The general conclusions are then presented based on the three fundamental parameters of the EMBH theory: the dyadosphere energy, the baryonic mass of the remnant, the interstellar medium density. An in depth discussion and comparison of the EMBH theory with alternative theories is presented as well as indications of further developments beyond the radial approximation, which will be the subject of paper II in this series. Future needs for specific GRB observations are outlined.

  17. A burst in a wind bubble and the impact on baryonic ejecta: high-energy gamma-ray flashes and afterglows from fast radio bursts and pulsar-driven supernova remnants

    Science.gov (United States)

    Murase, Kohta; Kashiyama, Kazumi; Mészáros, Peter

    2016-09-01

    Tenuous wind bubbles, which are formed by the spin-down activity of central compact remnants, are relevant in some models of fast radio bursts (FRBs) and superluminous supernovae (SNe). We study their high-energy signatures, focusing on the role of pair-enriched bubbles produced by young magnetars, rapidly rotating neutron stars, and magnetized white dwarfs. (i) First, we study the nebular properties and the conditions allowing for escape of high-energy gamma-rays and radio waves, showing that their escape is possible for nebulae with ages of ≳10-100 yr. In the rapidly rotating neutron star scenario, we find that radio emission from the quasi-steady nebula itself may be bright enough to be detected especially at sub-mm frequencies, which is relevant as a possible counterpart of pulsar-driven SNe and FRBs. (ii) Secondly, we consider the fate of bursting emission in the nebulae. We suggest that an impulsive burst may lead to a highly relativistic flow, which would interact with the nebula. If the shocked nebula is still relativistic, pre-existing non-thermal particles in the nebula can be significantly boosted by the forward shock, leading to short-duration (maybe millisecond or longer) high-energy gamma-ray flashes. Possible dissipation at the reverse shock may also lead to gamma-ray emission. (iii) After such flares, interactions with the baryonic ejecta may lead to afterglow emission with a duration of days to weeks. In the magnetar scenario, this burst-in-bubble model leads to the expectation that nearby (≲10-100 Mpc) high-energy gamma-ray flashes may be detected by the High-Altitude Water Cherenkov Observatory and the Cherenkov Telescope Array, and the subsequent afterglow emission may be seen by radio telescopes such as the Very Large Array. (iv) Finally, we discuss several implications specific to FRBs, including constraints on the emission regions and limits on soft gamma-ray counterparts.

  18. Trellis coded modulation for 4800-9600 bps transmission over a fading mobile satellite channel

    Science.gov (United States)

    Divsalar, D.; Simon, M. K.

    1986-01-01

    The combination of trellis coding and multiple phase-shift-keyed (MPSK) signalling with the addition of asymmetry to the signal set is discussed with regard to its suitability as a modulation/coding scheme for the fading mobile satellite channel. For MPSK, introducing nonuniformity (asymmetry) into the spacing between signal points in the constellation buys a further improvement in performance over that achievable with trellis coded symmetric MPSK, all this without increasing average or peak power, or changing the bandwidth constraints imposed on the system. Whereas previous contributions have considered the performance of trellis coded modulation transmitted over an additive white Gaussian noise (AWGN) channel, the emphasis in the paper is on the performance of trellis coded MPSK in the fading environment. The results will be obtained by using a combination of analysis and simulation. It will be assumed that the effect of the fading on the phase of the received signal is fully compensated for either by tracking it with some form of phase-locked loop or with pilot tone calibration techniques. Thus, results will reflect only the degradation due to the effect of the fading on the amplitude of the received signal. Also, we shall consider only the case where interleaving/deinterleaving is employed to further combat the fading. This allows for considerable simplification of the analysis and is of great practical interest. Finally, the impact of the availability of channel state information on average bit error probability performance is assessed.

  19. EFFECTS OF RICIAN FADING ON THE OPERATION OF AERONAUTICAL SATELLITE OFDM CHANNEL

    Directory of Open Access Journals (Sweden)

    Volodymyr Kharchenko

    2016-06-01

    Full Text Available The aim of this study is to investigate the influence of Rician fading on messages transmission via the aeronautical satellite OFDM channel with adaptive modulation and the development of a method for estimating the parameters of such a channel. Methods: To study the effect of Rician fading on messages transmission via aeronautical satellite OFDM channel with adaptive modulation the original model of the communication channel “Aircraft-Satellite-Ground Station” was built using software package MATLAB Sіmulіnk. The model includes “Aircraft Transmitter”, “Uplink/Downlink Path”, “Satellite Transponder”, and “Ground Station Receiver”. Each modulator block in the modulation bank performs convolutional coding and puncturing using code rates of ½, ²/3, and ¾, data interleaving, BPSK, QPSK, 16-QAM, and 64-QAM modulation. Results: Dependences of Estimated channel SNR on the ratio between the power of the LOS component and the diffuse component, on the downlink gain and delay in the diffuse component for different Doppler spectrum types and Doppler frequency offsets were obtained. A method for estimating the parameters of the satellite channels with fading was proposed. Discussion: The realistic model of aeronautical satellite OFDM link with Rician fading is developed for the first time on a basis of IEEE 802.11a standard and used for channel parameters evaluation. Proposed in this article approach can be considered as a method for estimating parameters of the channel with fading.

  20. On Amplify-and-Forward Relaying Over Hyper-Rayleigh Fading Channels

    Directory of Open Access Journals (Sweden)

    S. H. Alvi

    2014-12-01

    Full Text Available Relayed transmission holds promise for the next generation of wireless communication systems due to the performance gains it can provide over non-cooperative systems. Recently hyper-Rayleigh fading, which represents fading conditions more severe than Rayleigh fading, has received attention in the context of many practical communication scenarios. Though power allocation for Amplify-and-Forward (AF relaying networks has been studied in the literature, a theoretical analysis of the power allocation problem for hyper-Rayleigh fading channels is a novel contribution of this work. We develop an optimal power allocation (OPA strategy for a dual-hop AF relaying network in which the relay-destination link experiences hyper-Rayleigh fading. A new closed-form expression for the average signal-to-noise ratio (SNR at destination is derived and it is shown to provide a new upper-bound on the average SNR at destination, which outperforms a previously proposed upper-bound based on the well-known harmonic-geometric mean inequality. An OPA across the source and relay nodes, subject to a sum-power constraint, is proposed and it is shown to provide measurable performance gains in average SNR and SNR outage at the destination relative to the case of equal power allocation.

  1. Search for stable energy levels in materials exhibiting strong anomalous fading: The case of apatites

    Energy Technology Data Exchange (ETDEWEB)

    Polymeris, George S., E-mail: polymers@auth.gr [Laboratory of Radiation Applications and Archaeological Dating, Department of Archaeometry and Physicochemical Measurements, ‘Athena’—Research and Innovation Center in Information, Communication and Knowledge Technologies, Kimmeria University Campus, GR-67100 Xanthi (Greece); Solid State Physics Section, Aristotle University of Thessaloniki, 54124 Thessaloniki (Greece); Giannoulatou, Valeria; Sfampa, Ioanna K. [Nuclear Physics Laboratory, Aristotle University of Thessaloniki, 54124 Thessaloniki (Greece); Tsirliganis, Nestor C. [Laboratory of Radiation Applications and Archaeological Dating, Department of Archaeometry and Physicochemical Measurements, ‘Athena’—Research and Innovation Center in Information, Communication and Knowledge Technologies, Kimmeria University Campus, GR-67100 Xanthi (Greece); Kitis, George [Nuclear Physics Laboratory, Aristotle University of Thessaloniki, 54124 Thessaloniki (Greece)

    2014-09-15

    The thermally assisted OSL signal resulting from very deep traps was studied in the case of three fluorapatite samples, one chlorapatite as well as one collophanite cryptocrystalline carbonite phosphorite sample of various origins. Intense thermally assisted OSL signal was monitored while stimulating at 200 °C in all samples subjected to the present study, indicating the prevalence of the existence of these very deep traps. Anomalous fading effect is ubiquitous for all TL and OSL signals of all apatite samples subjected to the present study. The anomalous fading of the thermally assisted OSL signal arising from very deep traps is strongly differentiated from the anomalous fading of electron trap excited at temperatures below 500 °C. The thermally assisted OSL signal arising from very deep traps was found to clearly be more stable, showing much less anomalous fading over time. The possible implications of this finding in dating of both apatites and feldspars are also briefly discussed. - Highlights: • All apatite samples of the present study yield strong thermally assisted OSL (TA-OSL) signal. • In all cases, TA-OSL signal is much more stable compared to TL and conventional OSL, based on the corresponding anomalous fading rates. • This experimental feature could be extremely beneficial for luminescence dating.

  2. Bandwidth efficient coding for fading channels - Code construction and performance analysis

    Science.gov (United States)

    Schlegel, Christian; Costello, Daniel J., Jr.

    1989-01-01

    The authors apply a general method of bounding the event error probability of trellis-coded modulation schemes to fading channels and use the effective length and the minimum-squared-product distance to replace the minimum-free-squared-Euclidean distance as code design parameters for Rayleigh and Rician fading channels with a substantial multipath component. They present 8-PSK trellis codes specifically constructed for fading channels that outperform equivalent codes designed for the additive white Gaussian noise channel when v is greater than or equal to 5. For quasiregular trellis codes there exists an efficient algorithm for evaluating event error probability, and numerical results on Pe which demonstrate the importance of the effective length as a code design parameter for fading channels with or without side information have been obtained. This is consistent with the case for binary signaling, where the Hamming distance remains the best code design parameter for fading channels. The authors show that the use of Reed-Solomon block codes with expanded signal sets becomes interesting only for large values of E(s)/N(0), where they begin to outperform trellis codes.

  3. Exact capacity analysis of multihop transmission over amplify-and-forward relay fading channels

    KAUST Repository

    Yilmaz, Ferkan

    2010-09-01

    In this paper, we propose an analytical framework on the exact computation of the average capacity of multihop transmission over amplify-and-forward relay fading channels. Our approach relies on the algebraic combination of Mellin and Laplace transforms to obtain exact single integral expressions which can be easily computed by Gauss-Chebyshev Quadrature (GCQ) rule. As such, the derived results are a convenient tool to analyze the average capacity of multihop transmission over amplify-and-forward relay fading channels. As an application of the analytical framework on the exact computation of the average capacity of multihop transmission, some examples are accentuated for generalized Nakagami-m fading channels. Numerical and simulation results, performed to verify the correctness of the proposed formulation, are in perfect agreement. ©2010 IEEE.

  4. Joint Parameter Estimation for the Two-Wave with Diffuse Power Fading Model

    Directory of Open Access Journals (Sweden)

    Jesus Lopez-Fernandez

    2016-06-01

    Full Text Available Wireless sensor networks deployed within metallic cavities are known to suffer from a very severe fading, even in strong line-of-sight propagation conditions. This behavior is well-captured by the Two-Wave with Diffuse Power (TWDP fading distribution, which shows great fit to field measurements in such scenarios. In this paper, we address the joint estimation of the parameters K and Δ that characterize the TWDP fading model, based on the observation of the received signal envelope. We use a moment-based approach to derive closed-form expressions for the estimators of K and Δ, as well as closed-form expressions for their asymptotic variance. Results show that the estimation error is close to the Cramer-Rao lower bound for a wide range of values of the parameters K and Δ. The performance degradation due to a finite number of observations is also analyzed.

  5. Study of ageing and fading in CR-39 detectors for different storage conditions.

    Science.gov (United States)

    Franci, Daniele; Aureli, Tommaso; Cardellini, Francesco

    2015-12-01

    The aim of this study was to investigate the effect of ageing and fading on PADC detector response, as a function of the storage time and temperature. Several groups of CR-39 detectors provided by Radosys, Ltd. were exposed at the reference radon chamber of the Istituto Nazionale di Metrologia delle Radiazioni Ionizzanti, at the ENEA centre in Casaccia. The results indicate that low-temperature storage inhibits the effect of both ageing and fading. Finally, the overall reduction in CR-39 sensitivity due to the combined ageing/fading effect was estimated. In particular, the sensitivity of the detectors continuously exposed in air at room temperature over 6 and 3 months was reduced, respectively, by 7.5 and 4 %. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  6. Outage Probability for ARQ Decode-and-Forward Relaying under Packet-Rate Fading

    Science.gov (United States)

    Lee, Sangkook; Su, Weifeng; Batalama, Stella; Matyjas, John D.

    In this paper, a new analytical approach is developed for the evaluation of the outage probability of decode-and-forward (DF) automatic-repeat-request (ARQ) relaying under packet-rate fading (fast fading) channels. Based on this approach, a closed-form asymptotically tight (as SNR → ∞) approximation of the outage probability is derived, and the diversity order of the DF cooperative ARQ relay scheme is shown to be equal to 2L - 1, where L is the maximum number of ARQ retransmissions. The closed-form expression clearly shows that the achieved diversity is partially due to the DF cooperative relaying and partially due to the fast fading nature of the channels (temporal diversity). Numerical and simulation studies illustrate the theoretical developments.

  7. Antenna selection for MIMO systems over Weibull–Gamma fading channel

    Directory of Open Access Journals (Sweden)

    Keerti Tiwari

    2016-09-01

    Full Text Available In this paper, multiple-input multiple-output (MIMO system performance is evaluated over composite Weibull–Gamma (WG fading channel using antenna selection (AS techniques. WG fading channel is considered to model multipath and shadowing effects. The capacity and error rate performance can be improved by exploiting channel state information on the transmitter side (CSIT while reducing hardware complexity. Therefore, AS techniques are used to exploit CSIT. Although, optimal AS improves the system performance at the cost of enhanced complexity, sub-optimal AS technique is preferred to improve capacity performance with reduced complexity level. Also, AS is used for orthogonal space time block code (OSTBC to improve error performance of MIMO system over WG fading channel.

  8. Systems implications of L-band fade data statistics for LEO mobile systems

    Science.gov (United States)

    Devieux, Carrie L.

    1993-01-01

    This paper examines and analyzes research data on the role of foliage attenuation in signal fading between a satellite transmitter and a terrestrial vehicle-mounted receiver. The frequency band of measurement, called L-Band, includes the region 1610.0 to 1626.5 MHz. Data from tests involving various combinations of foliage and vehicle movement conditions clearly show evidence of fast fading (in excess of 0.5 dB per millisecond) and fade depths as great or greater than 16 dB. As a result, the design of a communications link power control that provides the level of accuracy necessary for power sensitive systems could be significantly impacted. Specific examples of this include the communications links that employ Code Division Multiple Access (CDMA) as a modulation technique.

  9. Partial relay selection based on shadowing side information over generalized composite fading channels

    KAUST Repository

    Yilmaz, Ferkan

    2011-11-01

    In this paper, in contrast to the relay selection protocols available in the literature, we propose a partial relay selection protocol utilizing only the shadowing side information of the relays instead of their full channel side information in order to select a relay in a dual-hop relaying system through the available limited feedback channels and power budget. We then presented an exact unified performance expression combining the average bit error probability, ergodic capacity, and moments-generating function of the proposed partial relay selection over generalized fading channels. Referring to the unified performance expression introduced in [1], we explicitly offer a generic unified performance expression that can be easily calculated and that is applicable to a wide variety of fading scenarios. Finally, as an illustration of the mathematical formalism, some numerical and simulation results are generated for an extended generalized-K fading environment, and these numerical and simulation results are shown to be in perfect agreement. © 2011 IEEE.

  10. Outage performance of reactive cooperation in Nakagami-m fading channels

    KAUST Repository

    Benjillali, Mustapha

    2010-06-01

    In this paper, we investigate the outage performance of Decode-and-Forward with reactive relaying in dual-hop cooperetive Nakagaml-m fading links. The destination, based on the umque knowledge of local second hop channel state information, selects the best relay to increase the chances of cooperation when the direct link is also available. After deriving the exact distribution of the variables of interest, the outage probability of the system - with and without the direct link - is obtained in closed-form, and the ε-outage capacity is derived in the particular c.se wh.ere the channel model is reduced to a Rayleigh fading. Simulation results confirm the accuracy of our analysis for a large selection of system and fading parameters.

  11. Outage performance of Decode-and-Forward partial selection in Nakagami-m fading channels

    KAUST Repository

    Benjillali, Mustapha

    2010-01-01

    In this paper, we investigate the outage performance of Decode-and-Forward with partial selection relaying in dualhop cooperative Nakagami-m fading links. The source, based on the unique knowledge of local first hop channel state information, selects the best relay to increase the chances of successful decoding and hence the possibility of cooperation when the direct link is also available. After deriving the exact distribution of the sum of two gamma variates with the same shape parameter, the outage probability of the system-with and without the direct link-is obtained in closed-form. We also derive the ε-outage capacity in different particular cases, and the obtained results- when the channel model is reduced to a Rayleigh fading-are either new or correspond to those previously obtained in other works. Simulation results confirm the accuracy of our analysis for a large selection of system and fading parameters. © 2009 IEEE.

  12. On the capacity of Rician fading channels with full channel state information at low SNR

    KAUST Repository

    Rezki, Zouheir

    2012-06-01

    The capacity of flat Rayleigh fading channels with full channel state information (CSI) at the transmitter and at the receiver at asymptotically low SNR has been recently shown to scale essentially as SNR log (1/SNR). In this paper, we investigate the Rician fading channel capacity with full CSI, and show that the capacity of this channel scales essentially as 1/1+K SNR log (1 /SNR), where K is the Rician factor. This characterization includes perfect CSI at both the transmitter and the receiver or noisy CSI at the transmitter and perfect CSI at the receiver. We also show that one-bit CSI at the transmitter is enough to achieve this asymptotic capacity using an On-Off power control scheme. Our framework may be seen as a generalization of previous works as it captures the Rayleigh fading channel as a special case by letting K goes to zero. © 2012 IEEE.

  13. Mapping of the Faded (fe) Gene to a Region between D10mit191 and D10mit44 on Mouse Chromosome 10

    OpenAIRE

    Oh, Seung-Hun; Nam, Yoonyi; Suh, Jun-Gyo

    2011-01-01

    The faded mouse is a coat color mutant that shows faded coat color and age-related loss of pigmentation. This mutation is transmitted by an autosomal recessive gene with 100% penetrance. In the present study, we carried out linkage analysis of the faded (fe) gene using intra-specific backcross panels. Affected faded mice were carefully confirmed by their faded coat color at about 4 weeks of age. In the intra-specific backcross between faded and CBA mice (n=198), the fe gene was mapped to a re...

  14. Prompt and Afterglow Emission Properties of Gamma-Ray Bursts with Spectroscopically Identified Supernovae

    Energy Technology Data Exchange (ETDEWEB)

    Kaneko, Yuki; Ramirez-Ruiz, E.; Granot, J.; Kouveliotou, C.; Woosley, S.E.; Patel, S.K.; Rol, E.; Zand, J.J.M.in' t; a; Wijers, R.A.M.J.; Strom, R.; /USRA, Huntsville

    2006-07-12

    We present a detailed spectral analysis of the prompt and afterglow emission of four nearby long-soft gamma-ray bursts (GRBs 980425, 030329, 031203, and 060218) that were spectroscopically found to be associated with type Ic supernovae, and compare them to the general GRB population. For each event, we investigate the spectral and luminosity evolution, and estimate the total energy budget based upon broadband observations. The observational inventory for these events has become rich enough to allow estimates of their energy content in relativistic and sub-relativistic form. The result is a global portrait of the effects of the physical processes responsible for producing long-soft GRBs. In particular, we find that the values of the energy released in mildly relativistic outflows appears to have a significantly smaller scatter than those found in highly relativistic ejecta. This is consistent with a picture in which the energy released inside the progenitor star is roughly standard, while the fraction of that energy that ends up in highly relativistic ejecta outside the star can vary dramatically between different events.

  15. The 'Supercritical Pile' GRB Model: Afterglows and GRB, XRR, XRF Unification

    Science.gov (United States)

    Kazanas, D.

    2007-01-01

    We present the general notions and observational consequences of the "Supercritical Pile" GRB model; the fundamental feature of this model is a detailed process for the conversion of the energy stored in relativistic protons in the GRB Relativistic Blast Waves (RBW) into relativistic electrons and then into radiation. The conversion is effected through the $p \\, \\gamma \\rightarrow p \\, e circumflex + e circumflex -$ reaction, whose kinematic threshold is imprinted on the GRB spectra to provide a peak of their emitted luminosity at energy \\Ep $\\sim 1$ MeV in the lab frame. We extend this model to include, in addition to the (quasi--)thermal relativistic post-shock protons an accelerated component of power law form. This component guarantees the production of $e circumflex +e circumflex- - $pairs even after the RBW has slowed down to the point that its (quasi-) thermal protons cannot fulfill the threshold of the above reaction. We suggest that this last condition marks the transition from the prompt to the afterglow GRB phase. We also discuss conditions under which this transition is accompanied by a significant drop in the flux and could thus account for several puzzling, recent observations. Finally, we indicate that the same mechanism applied to the late stages of the GRB evolution leads to a decrease in \\Ep $\\propto \\Gamma circumflex 2(t)\\propto t circumflex {-3/4}$, a feature amenable to future observational tests.

  16. 'Jet breaks' and 'missing breaks' in the X-Ray afterglow of Gamma Ray Bursts

    CERN Document Server

    Dado, Shlomo; De Rújula, Alvaro

    2008-01-01

    The X-ray afterglows (AGs) of Gamma-Ray Bursts (GRBs) and X-Ray Flashes (XRFs) have, after the fast decline phase of their prompt emission, a temporal behaviour varying between two extremes. A large fraction of these AGs has a 'canonical' light curve which, after an initial shallow-decay 'plateau' phase, 'breaks smoothly' into a fast power-law decline. Very energetic GRBs, contrariwise, appear not to have a 'break', their AG declines like a power-law from the start of the observations. Breaks and 'missing breaks' are intimately related to the geometry and deceleration of the jets responsible for GRBs. In the frame of the 'cannonball' (CB) model of GRBs and XRFs, we analyze the cited extreme behaviours (canonical and pure power-law) and intermediate cases spanning the observed range of X-ray AG shapes. We show that the entire panoply of X-ray light-curve shapes --measured with Swift and other satellites-- are as anticipated, on very limpid grounds, by the CB model. We test the expected correlations between the...

  17. Simulation of Relativistic Shocks and Associated Self-Consistent Radiation for GRB Prompt Emission and Afterglows

    Science.gov (United States)

    Nishikawa, Ken-Ichi; Niemiec, J.; Medvedev, M.; Zhang, B.; Hardee, P.; Mizuno, Y.; Nordlund, A.; Frederiksen, J.; Sol, H.; Pohl, M.; hide

    2010-01-01

    Plasma instabilities excited in collisionless shocks are responsible for particle acceleration. We have investigated the particle acceleration and shock structure associated with an unmagnetized relativistic electron-positron jet propagating into an unmagnetized electron-positron plasma. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic-like shock structure. In the leading shock, electron density increases by a factor of about 3.5 in the simulation frame. Strong electromagnetic fields are generated in the trailing shock and provide an emission site. This simulation corresponds to a case for gamma-ray burst afterglows. We will simulate colliding shells as an internal shock model for prompt emission. Turbulent magnetic fields generated by a slower shell will be collided by a faster shell. These magnetic fields contribute to the electron s transverse deflection behind the shock. We calculate the radiation from deflected electrons in the turbulent magnetic fields. The properties of this radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts

  18. Composite and Cascaded Generalized-K Fading Channel Modeling and Their Diversity and Performance Analysis

    KAUST Repository

    Ansari, Imran Shafique

    2010-12-01

    The introduction of new schemes that are based on the communication among nodes has motivated the use of composite fading models due to the fact that the nodes experience different multipath fading and shadowing statistics, which subsequently determines the required statistics for the performance analysis of different transceivers. The end-to-end signal-to-noise-ratio (SNR) statistics plays an essential role in the determination of the performance of cascaded digital communication systems. In this thesis, a closed-form expression for the probability density function (PDF) of the end-end SNR for independent but not necessarily identically distributed (i.n.i.d.) cascaded generalized-K (GK) composite fading channels is derived. The developed PDF expression in terms of the Meijer-G function allows the derivation of subsequent performance metrics, applicable to different modulation schemes, including outage probability, bit error rate for coherent as well as non-coherent systems, and average channel capacity that provides insights into the performance of a digital communication system operating in N cascaded GK composite fading environment. Another line of research that was motivated by the introduction of composite fading channels is the error performance. Error performance is one of the main performance measures and derivation of its closed-form expression has proved to be quite involved for certain systems. Hence, in this thesis, a unified closed-form expression, applicable to different binary modulation schemes, for the bit error rate of dual-branch selection diversity based systems undergoing i.n.i.d. GK fading is derived in terms of the extended generalized bivariate Meijer G-function.

  19. Performance of Cooperative Spectrum Sensing over Non-Identical Fading Environments

    KAUST Repository

    Rao, Anlei

    2012-09-08

    Different from previous works in cooperative spec- trum sensing that assumed the sensing channels independent identically distributed (i.i.d.), we investigate in this paper the independent but not identically distributed (i.n.i.d.) situations. In particular, we derive the false-alarm probability and the detection probability of cooperative spectrum sensing with the scheme of energy fusion over i.n.i.d. Rayleigh, Nakagami, and Rician fading channels. From the selected numerical results, we can see that cooperative spectrum sensing still gives considerably better performance even over i.n.i.d. fading environments.

  20. An Empirical Rate Constant Based Model to Study Capacity Fading in Lithium Ion Batteries

    Directory of Open Access Journals (Sweden)

    Srivatsan Ramesh

    2015-01-01

    Full Text Available A one-dimensional model based on solvent diffusion and kinetics to study the formation of the SEI (solid electrolyte interphase layer and its impact on the capacity of a lithium ion battery is developed. The model uses the earlier work on silicon oxidation but studies the kinetic limitations of the SEI growth process. The rate constant of the SEI formation reaction at the anode is seen to play a major role in film formation. The kinetics of the reactions for capacity fading for various battery systems are studied and the rate constants are evaluated. The model is used to fit the capacity fade in different battery systems.

  1. Opportunistic relaying in multipath and slow fading channel: Relay selection and optimal relay selection period

    KAUST Repository

    Sungjoon Park,

    2011-11-01

    In this paper we present opportunistic relay communication strategies of decode and forward relaying. The channel that we are considering includes pathloss, shadowing, and fast fading effects. We find a simple outage probability formula for opportunistic relaying in the channel, and validate the results by comparing it with the exact outage probability. Also, we suggest a new relay selection algorithm that incorporates shadowing. We consider a protocol of broadcasting the channel gain of the previously selected relay. This saves resources in slow fading channel by reducing collisions in relay selection. We further investigate the optimal relay selection period to maximize the throughput while avoiding selection overhead. © 2011 IEEE.

  2. Motion fading and the motion aftereffect share a common process of neural adaptation.

    Science.gov (United States)

    Hsieh, P-J; Tse, P U

    2009-05-01

    After prolonged viewing of a slowly drifting or rotating pattern under strict fixation, the pattern appears to slow down and then momentarily stop. Here, we show that this motion fading occurs not only for slowly moving stimuli, but also for stimuli moving at high speed; after prolonged viewing of high-speed stimuli, the stimuli appear to slow down but not to stop. We report psychophysical evidence that the same neural adaptation process likely gives rise to motion fading and to the motion aftereffect.

  3. Performance of Coded Systems with Generalized Selection Diversity in Nakagami Fading

    Directory of Open Access Journals (Sweden)

    Salam A. Zummo

    2008-04-01

    Full Text Available We investigate the performance of coded diversity systems employing generalized selection combining (GSC over Nakagami fading channels. In particular, we derive a numerical evaluation method for the cutoff rate of the GSC systems. In addition, we derive a new union bound on the bit-error probability based on the code's transfer function. The proposed bound is general to any coding scheme with a known weight distribution such as convolutional and trellis codes. Results show that the new bound is tight to simulation results for wide ranges of diversity order, Nakagami fading parameter, and signal-to-noise ratio (SNR.

  4. Performance of Coded Systems with Generalized Selection Diversity in Nakagami Fading

    Directory of Open Access Journals (Sweden)

    Zummo SalamA

    2008-01-01

    Full Text Available Abstract We investigate the performance of coded diversity systems employing generalized selection combining (GSC over Nakagami fading channels. In particular, we derive a numerical evaluation method for the cutoff rate of the GSC systems. In addition, we derive a new union bound on the bit-error probability based on the code's transfer function. The proposed bound is general to any coding scheme with a known weight distribution such as convolutional and trellis codes. Results show that the new bound is tight to simulation results for wide ranges of diversity order, Nakagami fading parameter, and signal-to-noise ratio (SNR.

  5. Higher order capacity statistics of multi-hop transmission systems over Rayleigh fading channels

    KAUST Repository

    Yilmaz, Ferkan

    2012-03-01

    In this paper, we present an exact analytical expression to evaluate the higher order statistics of the channel capacity for amplify and forward (AF) multihop transmission systems operating over Rayleigh fading channels. Furthermore, we present simple and efficient closed-form expression to the higher order moments of the channel capacity of dual hop transmission system with Rayleigh fading channels. In order to analyze the behavior of the higher order capacity statistics and investigate the usefulness of the mathematical analysis, some selected numerical and simulation results are presented. Our results are found to be in perfect agreement. © 2012 IEEE.

  6. MGF approach to the capacity analysis of Generalized Two-Ray fading models

    KAUST Repository

    Rao, Milind

    2015-09-11

    We propose a class of Generalized Two-Ray (GTR) fading channels that consists of two line of sight (LOS) components with random phase and a diffuse component. Observing that the GTR fading model can be expressed in terms of the underlying Rician distribution, we derive a closed-form expression for the moment generating function (MGF) of the signal-to-noise ratio (SNR) of this model. We then employ this approach to compute the ergodic capacity with receiver side information. The impact of the underlying phase difference between the LOS components on the average SNR of the signal received is also illustrated. © 2015 IEEE.

  7. "Paintings Fade Like Flowers": Pigment Analysis and Digital Reconstruction of a Faded Pink Lake Pigment in Vincent van Gogh's Undergrowth with Two Figures.

    Science.gov (United States)

    Fieberg, Jeffrey E; Knutås, Per; Hostettler, Kurt; Smith, Gregory D

    2017-05-01

    Color fading in Vincent van Gogh's Undergrowth with Two Figures was studied chemically to facilitate the creation of a digital reconstruction of fugitive colors . The painting contains a field of white, green, orange, and yellow flowers under a canopy of poplar trees with two central figures-a man and a woman, arms entwined. From Van Gogh's letters, however, it is known that he painted the picture with some pink flowers, which appear to have altered, presumably to white. Raman spectroscopy was applied to microsamples of paint to identify the faded pigment as geranium lake, which in this painting consists of the dye, eosin (2',4',5',7'-tetrabromofluorescein). For the first time, lead(II) sulfate has been specifically identified as the likely inorganic substrate for a geranium lake used by Van Gogh in the last months of his life. Microfocus X-ray fluorescence (MXRF) spectroscopy was subsequently used in situ to analyze the white flowers to identify bromine as a proxy for eosin, thus indicating an original pink coloration. Of the 387 white flowers analyzed, 37.7% contained measurable bromine and were, therefore, originally pink. Several cross-sections from these formerly pink areas were assessed using a combination of visual inspection and microcolorimetry to create a colored mask in Adobe Photoshop to digitally reconstruct a suggestion of the original appearance of the painting with regard to the faded flowers. Additionally, microfadeometry was undertaken for the first time on a painting cross-section sample to understand the actual fading kinetics of the underlying bright pink geranium lake used by Van Gogh. A combination of Raman microspectroscopy, MXRF, and scanning electron microscopy energy dispersive spectroscopy (SEM-EDS) were utilized in situ and on paint microsamples to identify the complete palette used to create Undergrowth with Two Figures.

  8. An Investigation of the Impact of Instructional Fading Using Completion Problems on Student Performance in Principles of Accounting Instruction

    Science.gov (United States)

    Kingry, Mary Ann

    2012-01-01

    The effects of instructional fading using completion problems on student performance were investigated in this study. Instructional fading is the gradual withdrawal of the amount of assistance provided to the student and was accomplished in this study using completion problems. They were used to gradually transition the student from completely…

  9. Using Audio Script Fading and Multiple-Exemplar Training to Increase Vocal Interactions in Children with Autism

    Science.gov (United States)

    Garcia-Albea, Elena; Reeve, Sharon A.; Brothers, Kevin J.; Reeve, Kenneth F.

    2014-01-01

    Script-fading procedures have been shown to be effective for teaching children with autism to initiate and participate in social interactions without vocal prompts from adults. In previous script and script-fading research, however, there has been no demonstration of a generalized repertoire of vocal interactions under the control of naturally…

  10. Effectiveness of a fading emulator in evaluating the performance of MIMO systems by comparison with a propagation test

    DEFF Research Database (Denmark)

    Yamamoto, Atsushi; Sakata, T.; Hayashi, T.

    2010-01-01

    This paper presents a MIMO spatial fading emulator, used to represent a street microcell environment. The fading emulator can reproduce a multipath radio propagation environment with either a uniform or non-uniform angular power spectrum (APS) in the horizontal plane. In this paper, we used...

  11. Influence of Imperfect Cophasing on Performance of MRC Receiver of QPSK Signals Transmitted over Weibull Fading Channel

    Directory of Open Access Journals (Sweden)

    M. S. Marković

    2009-11-01

    Full Text Available This paper presents an analysis of maximum ratio combining (MRC receiver of quaternary phase-shift keying (QPSK signals transmitted over a Weibull fading channel. We determine the influence of imperfect cophasing and branches unbalance on bit error rate dependence on average signal-to-noise ratio. The performance dependence on diversity order and fading severity is also observed.

  12. A study on selective surface nitridation of TiO2 nanocrystals in the afterglows of N2 and N2-O2 microwave plasmas

    Science.gov (United States)

    Jeon, Byungwook; Kim, Ansoon; Ricard, André; Sarrette, Jean-Philippe; Yu, Xiaomei; Kim, Yu Kwon

    2018-02-01

    Surface-selective chemical modification of anatase TiO2 nanocrystals is performed in the post-discharge region of N2 microwave plasma and the chemical bonding states of surface nitrogen species are carefully evaluated using X-ray photoemission spectroscopy (XPS). It is found that the surface treatments in the afterglows induce the formation of stable nitrogen species at or near the surface of TiO2. Interestingly, the detailed bonding structure varies strongly depending on the afterglow condition. In pure N2 afterglows, various N species with a direct Tisbnd N bond are formed on the surface, while the use of N2-O2 mixtures induces the formation of additional oxidized species of NO3- on the surface. This is attributed to the high concentrations of O or NO in the afterglows of N2-O2 plasmas. The incorporation of substitutional N species in the subsurface is also achieved after a prolonged exposure in the early afterglow with a high density of N2+ species. Our results show that the exposure condition can be controlled for a selective chemical modification of TiO2 surface for the control of surface properties in various applications.

  13. A Novel Unified Expression for the Capacity and Bit Error Probability of Wireless Communication Systems over Generalized Fading Channels

    CERN Document Server

    Yilmaz, Ferkan

    2011-01-01

    Analysis of the average binary error probabilities (ABEP) and average capacity (AC) of wireless communications systems over generalized fading channels have been considered separately in the past. This paper introduces a novel moment generating function (MGF)-based \\emph{unified expression} for the ABEP and AC of single and multiple link communication with maximal ratio combining. In addition, this paper proposes the hyper-Fox's H fading model as a unified fading distribution of a majority of the well-known generalized fading models. As such, we offer a generic unified performance expression that can be easily calculated and that is applicable to a wide variety of fading scenarios. The mathematical formalism is illustrated with some selected numerical examples that validate the correctness of our newly derived results.

  14. A novel unified expression for the capacity and bit error probability of wireless communication systems over generalized fading channels

    KAUST Repository

    Yilmaz, Ferkan

    2012-07-01

    Analysis of the average binary error probabilities (ABEP) and average capacity (AC) of wireless communications systems over generalized fading channels have been considered separately in past years. This paper introduces a novel moment generating function (MGF)-based unified expression for the ABEP and AC of single and multiple link communications with maximal ratio combining. In addition, this paper proposes the hyper-Fox\\'s H fading model as a unified fading distribution of a majority of the well-known generalized fading environments. As such, the authors offer a generic unified performance expression that can be easily calculated, and that is applicable to a wide variety of fading scenarios. The mathematical formulism is illustrated with some selected numerical examples that validate the correctness of the authors\\' newly derived results. © 1972-2012 IEEE.

  15. Characterization of the flowing afterglows of an N{sub 2}-O{sub 2} reduced-pressure discharge: setting the operating conditions to achieve a dominant late afterglow and correlating the NO{sub {beta}} UV intensity variation with the N and O atom densities

    Energy Technology Data Exchange (ETDEWEB)

    Boudam, M K [Groupe de Physique des Plasmas, Universite de Montreal, CP 6128, Succursale Centre-Ville, Montreal H3C 3J7, Quebec (Canada); Saoudi, B [Groupe de Physique des Plasmas, Universite de Montreal, CP 6128, Succursale Centre-Ville, Montreal H3C 3J7, Quebec (Canada); Moisan, M [Groupe de Physique des Plasmas, Universite de Montreal, CP 6128, Succursale Centre-Ville, Montreal H3C 3J7, Quebec (Canada); Ricard, A [Centre de Physique Atomique de Toulouse (CPAT), 118, route de Narbonne, Universite Paul Sabatier, 31062-Toulouse (France)

    2007-03-21

    The flowing afterglow of an N{sub 2}-O{sub 2} discharge in the 0.6-10 Torr range is examined in the perspective of achieving sterilization of medical devices (MDs) under conditions ensuring maximum UV intensity with minimum damage to polymer-based MDs. The early afterglow is shown to be responsible for creating strong erosion damage, requiring that the sterilizer be operated in a dominant late-afterglow mode. These two types of afterglow can be characterized by optical emission spectroscopy: the early afterglow is distinguished by an intense emission from the N{sub 2}{sup +} 1st negative system (band head at 391.4 nm) while the late afterglow yields an overpopulation of the v' = 11 ro-vibrational level of the N{sub 2}(B) state, indicating a reduced contribution from the early afterglow N{sub 2} metastable species. We have studied the influence of operating conditions (pressure, O{sub 2} content in the N{sub 2}-O{sub 2} mixture, distance of the discharge from the entrance to the afterglow (sterilizer) chamber) in order to achieve a dominant late afterglow that also ensures maximum and almost uniform UV intensity in the sterilization chamber. As far as operating conditions are concerned, moving the plasma source sufficiently far from the chamber entrance is shown to be a practical means for significantly reducing the density of the characteristic species of the early afterglow. Using the NO titration method, we obtain the (absolute) densities of N and O atoms in the afterglow at the NO injection inlet, a few cm before the chamber entrance: the N atom density goes through a maximum at approximately 0.3-0.5% O{sub 2} and then decreases, while the O atom density increases regularly with the O{sub 2} percentage. The spatial variation of the N atom (relative) density in the chamber is obtained by recording the emission intensity from the 1st positive system at 580 nm: in the 2-5 Torr range, this density is quite uniform everywhere in the chamber. The (relative

  16. Script Fading to Promote Unscripted Bids for Joint Attention in Children with Autism

    Science.gov (United States)

    Pollard, Joy S.; Betz, Alison M.; Higbee, Thomas S.

    2012-01-01

    We used a script-fading procedure to teach 3 children with autism to initiate bids for joint attention. We examined the effects of (a) scripts, (b) varied adult scripted responses, and (c) multiple-exemplar script training on promoting unscripted language during bids for joint attention. All 3 participants learned to initiate bids for joint…

  17. Script Fading for Children with Autism: Generalization of Social Initiation Skills from School to Home

    Science.gov (United States)

    Wichnick, Alison Marie

    2013-01-01

    A critical component of teaching social skills to people with autism is the generalization of behavior change across a variety of untrained situations during which social skills are appropriate. The script-fading procedure is an effective technology for teaching social skills to people with autism, but few researchers have established cues in the…

  18. INTERFERENCE REJECTION OF SIGNALS BY ADAPTIVE MINIMUM MEAN SQUARE ERROR CRITERION OVER RAYLEIGH FADING CHANNELS

    Directory of Open Access Journals (Sweden)

    AMITA SONI

    2009-03-01

    Full Text Available Channel time-variation (or fading is the major source of impairment in digital wireless communications. This occurs due to mobility of the user or of the objects in the propagation environment. The limited spectral bandwidth necessitates the use of resource sharing schemes between multiple users. As the transmission medium is shared between the users, this leads to interference between the users. Sharing of resource results in interference such as multiple access interference. This paper deals with methods to study and mitigate such interference considering Rayleigh fading channels. There are various classes of fading conditions. The use of CDMA is under active research as a viable alternative to TDMA and FDMA. Performance in this system is limited by narrowband and multiple access interference. Various methods are used to mitigate them. But here, linear MMSE detector is considered. MMSE technique results in interference rejection. Its adaptive form is applied to Rayleigh fading channels, which are reflective and nondispersive. It results into better results than before.

  19. On Channel Estimation for OFDM/TDM Using MMSE-FDE in a Fast Fading Channel

    Directory of Open Access Journals (Sweden)

    Gacanin Haris

    2009-01-01

    Full Text Available Abstract MMSE-FDE can improve the transmission performance of OFDM combined with time division multiplexing (OFDM/TDM, but knowledge of the channel state information and the noise variance is required to compute the MMSE weight. In this paper, a performance evaluation of OFDM/TDM using MMSE-FDE with pilot-assisted channel estimation over a fast fading channel is presented. To improve the tracking ability against fast fading a robust pilot-assisted channel estimation is presented that uses time-domain filtering on a slot-by-slot basis and frequency-domain interpolation. We derive the mean square error (MSE of the channel estimator and then discuss a tradeoff between improving the tracking ability against fading and the noise reduction. The achievable bit error rate (BER performance is evaluated by computer simulation and compared with conventional OFDM. It is shown that the OFDM/TDM using MMSE-FDE achieves a lower BER and a better tracking ability against fast fading in comparison with conventional OFDM.

  20. Different types of inks having certain medicolegal importance: Deciphering the faded and physically erased handwriting

    Directory of Open Access Journals (Sweden)

    Manal Abd-ElAziz Abd-ElZaher

    2014-06-01

    Full Text Available Disappearing ink is a type of ink which could be used to forge documents as it will fade away without any trace within 40–65 h. Erasable ink is another type of ink easily removed by certain rubbers incorporated in each pen. Both types of inks were applied separately on different types of papers (checks, standard white foolscap, and plain white A4 paper. For vanishing ink, it was observed visually in the first 6 h and then every 6 h. It was found that the vanishing ink disappeared completely within 2 h on checks, 36 h on standard white foolscap paper, and 40 h on plain white A4 paper. For erasable ink, the written strokes were manipulated manually using the incorporated eraser. Deciphering the faded writing failed by the conventional methods, but oblique light can reveal the indentation marks. The faded writing became visible when treated with weak alkaline (NaOH solutions. Erasable ink was deciphered with the aid of infra-red radiation combined with VSC-6000 as clear white traces against red fluorescence. It was concluded that the use of a weak (NaOH solution is an effective method for revealing the faded writing, and the infra-red illumination is also effective.

  1. CONCENTRATION-DEPENDENCE OF FADING OF THE OPEN FORM OF 6'-NITROINDOLINOSPIROPYRAN IN A POLYMER MATRIX

    NARCIS (Netherlands)

    DRABE, KE; DEBOER, S; WIERSMA, DA

    1991-01-01

    The concentration dependence of the fading process of the open form of 6'-nitroindolinospiropyran (BIPS) in PMMA has been studied by fluorescence lifetime measurements at 77 K. At sufficiently high concentrations, the fluorescence decay becomes bi-exponential which indicates that energy transfer

  2. Outage Probability of MRC for κ-μ Shadowed Fading Channels under Co-Channel Interference.

    Directory of Open Access Journals (Sweden)

    Changfang Chen

    Full Text Available In this paper, exact closed-form expressions are derived for the outage probability (OP of the maximal ratio combining (MRC scheme in the κ-μ shadowed fading channels, in which both the independent and correlated shadowing components are considered. The scenario assumes the received desired signals are corrupted by the independent Rayleigh-faded co-channel interference (CCI and background white Gaussian noise. To this end, first, the probability density function (PDF of the κ-μ shadowed fading distribution is obtained in the form of a power series. Then the incomplete generalized moment-generating function (IG-MGF of the received signal-to-interference-plus-noise ratio (SINR is derived in the closed form. By using the IG-MGF results, closed-form expressions for the OP of MRC scheme are obtained over the κ-μ shadowed fading channels. Simulation results are included to validate the correctness of the analytical derivations. These new statistical results can be applied to the modeling and analysis of several wireless communication systems, such as body centric communications.

  3. Differences in the dynamic properties of rain fade between temperate and tropical regions

    Science.gov (United States)

    Chodkaveekityada, Peeramed; Fukuchi, Hajime

    2017-03-01

    Understanding the dynamic properties of rain attenuation is important for designing effective attenuation mitigation methods, especially for Ka-band frequencies, which are particularly sensitive to degradation by rain attenuation. In this paper, the fade duration and fade slope are estimated using satellite data from Thailand and Japan, to investigate the characteristics of rain attenuation in tropical and temperate regions, respectively. For the tropical region, data from the Thaicom 2 and 3 satellites are used, and data from a Japanese communication satellite (CS) are used for the temperate area. Due to the different operating frequencies of the Thaicom 2 and 3 and the CS satellites, the scaling formula from the International Telecommunications Union (ITU) R P.618-12 is used to standardize the data. The Thaicom satellite frequencies of 12.57 (Thaicom 2) and 12.59 (Thaicom 3) GHz in the Ku-band are scaled up to 19.45 GHz, the operating frequency of the CS satellite. Finally, differences of the fade duration and fade slope property in tropical and temperate areas are found and it is confirmed that the rain attenuation effect in tropical areas is more serious than in temperate areas.

  4. Chebyshev-based technique for automated restoration of digital copies of faded photographic prints

    Science.gov (United States)

    Uchaev, Dmitry V.; Uchaev, Denis V.; Malinnikov, Vasiliy A.

    2017-01-01

    We present a technique for automated restoration of digital images obtained from faded photographic prints. The proposed defading technique uses our early proposed image contrast enhancement algorithm based on a contrast measure of images in the Chebyshev moment transform domain. Obtained experimental results demonstrate some advantages of the technique as compared to other widely used image enhancement methods.

  5. A Large Catalog of Multiwavelength GRB Afterglows. I. Color Evolution and Its Physical Implication

    Science.gov (United States)

    Li, Liang; Wang, Yu; Shao, Lang; Wu, Xue-Feng; Huang, Yong-Feng; Zhang, Bing; Ryde, Felix; Yu, Hoi-Fung

    2018-02-01

    The spectrum of gamma-ray burst (GRB) afterglows can be studied with color indices. Here, we present a large comprehensive catalog of 70 GRBs with multiwavelength optical transient data on which we perform a systematic study to find the temporal evolution of color indices. We categorize them into two samples based on how well the color indices are evaluated. The Golden sample includes 25 bursts mostly observed by GROND, and the Silver sample includes 45 bursts observed by other telescopes. For the Golden sample, we find that 96% of the color indices do not vary over time. However, the color indices do vary during short periods in most bursts. The observed variations are consistent with effects of (i) the cooling frequency crossing the studied energy bands in a wind medium (43%) and in a constant-density medium (30%), (ii) early dust extinction (12%), (iii) transition from reverse-shock to forward-shock emission (5%), or (iv) an emergent SN emission (10%). We also study the evolutionary properties of the mean color indices for different emission episodes. We find that 86% of the color indices in the 70 bursts show constancy between consecutive ones. The color index variations occur mainly during the late GRB–SN bump, the flare, and early reverse-shock emission components. We further perform a statistical analysis of various observational properties and model parameters (spectral index {β }o{CI}, electron spectral indices p CI, etc.) using color indices. Overall, we conclude that ∼90% of colors are constant in time and can be accounted for by the simplest external forward-shock model, while the varying color indices call for more detailed modeling.

  6. Ag/BiOBr Film in a Rotating-Disk Reactor Containing Long-Afterglow Phosphor for Round-the-Clock Photocatalysis.

    Science.gov (United States)

    Yin, Haibo; Chen, Xiaofang; Hou, Rujing; Zhu, Huijuan; Li, Shiqing; Huo, Yuning; Li, Hexing

    2015-09-16

    Ag/BiOBr film coated on the glass substrate was synthesized by a solvothermal method and a subsequent photoreduction process. Such a Ag/BiOBr film was then adhered to a hollow rotating disk filled with long-afterglow phosphor inside the chamber. The Ag/BiOBr film exhibited high photocatalytic activity for organic pollutant degradation owing to the improved visible-light harvesting and the separation of photoinduced charges. The long-afterglow phosphor could absorb the excessive daylight and emit light around 488 nm, activating the Ag/BiOBr film to realize round-the-clock photocatalysis. Because the Ag nanoparticles could extend the light absorbance of the Ag/BiOBr film to wavelengths of around 500 nm via a surface plasma resonance effect, they played a key role in realizing photocatalysis induced by long-afterglow phosphor.

  7. DISCOVERY OF SMOOTHLY EVOLVING BLACKBODIES IN THE EARLY AFTERGLOW OF GRB 090618: EVIDENCE FOR A SPINE–SHEATH JET?

    Energy Technology Data Exchange (ETDEWEB)

    Basak, Rupal; Rao, A. R., E-mail: rupalb@tifr.res.in, E-mail: arrao@tifr.res.in [Tata Institute of Fundamental Research, Mumbai—400005 (India)

    2015-10-20

    GRB 090618 is a bright gamma-ray burst (GRB) with multiple pulses. It shows evidence of thermal emission in the initial pulses as well as in the early afterglow phase. Because high-resolution spectral data from the Swift/X-ray Telescope (XRT) are available for the early afterglow, we investigate the shape and evolution of the thermal component in this phase using data from the Swift/Burst Alert Telescope (BAT), the Swift/XRT, and the Fermi/Gamma-ray Burst Monitor detectors. An independent fit to the BAT and XRT data reveals two correlated blackbodies with monotonically decreasing temperatures. Hence, we investigated the combined data with a model consisting of two blackbodies and a power law (2BBPL), a model suggested for several bright GRBs. We elicit the following interesting features of the 2BBPL model: (1) the same model is applicable from the peak of the last pulse in the prompt emission to the afterglow emission, (2) the ratio of temperatures and the fluxes of the two blackbodies remains constant throughout the observations, (3) the blackbody temperatures and fluxes show a monotonic decrease with time, with the BB fluxes dropping about a factor of two faster than that of the power-law (PL) emission, and (4) attributing the blackbody emission to photospheric emissions, we find that the photospheric radii increase very slowly with time, and the lower-temperature blackbody shows a larger emitting radius than that of the higher-temperature blackbody. We find some evidence that the underlying shape of the nonthermal emission is a cutoff power law rather than a PL. We sketch a spine–sheath jet model to explain our observations.

  8. The radio afterglow of Swift J1644+57 reveals a powerful jet with fast core and slow sheath

    Science.gov (United States)

    Mimica, P.; Giannios, D.; Metzger, B. D.; Aloy, M. A.

    2015-07-01

    We model the non-thermal transient Swift J1644+57 as resulting from a relativistic jet powered by the accretion of a tidally disrupted star on to a supermassive black hole. Accompanying synchrotron radio emission is produced by the shock interaction between the jet and the dense circumnuclear medium, similar to a gamma-ray burst afterglow. An open mystery, however, is the origin of the late-time radio re-brightening, which occurred well after the peak of the jetted X-ray emission. Here, we systematically explore several proposed explanations for this behaviour by means of multidimensional hydrodynamic simulations coupled to a self-consistent radiative transfer calculation of the synchrotron emission. Our main conclusion is that the radio afterglow of Swift J1644+57 is not naturally explained by a jet with a one-dimensional top-hat angular structure. However, a more complex angular structure comprised of an ultrarelativistic core (Lorentz factor Γ ˜ 10) surrounded by a slower (Γ ˜ 2) sheath provides a reasonable fit to the data. Such a geometry could result from the radial structure of the super-Eddington accretion flow or as the result of jet precession. The total kinetic energy of the ejecta that we infer of ˜ few 1053 erg requires a highly efficient jet launching mechanism. Our jet model providing the best fit to the light curve of the on-axis event Swift J1644+57 is used to predict the radio light curves for off-axis viewing angles. Implications for the presence of relativistic jets from tidal disruption events (TDEs) detected via their thermal disc emission, as well as the prospects for detecting orphan TDE afterglows with upcoming wide-field radio surveys and resolving the jet structure with long baseline interferometry, are discussed.

  9. [Priming dose of atracurium: measuring orbicularis oculi muscle fade and tracheal intubation conditions.].

    Science.gov (United States)

    Locks, Giovani de Figueiredo; Almeida, Maria Cristina Simões de

    2003-12-01

    The priming principle consists of administering a low neuromuscular blocker dose, minutes before the total dose for tracheal intubation, to shorten non-depolarizing blockers onset. There is, however, the risk for muscle fade and bronchoaspiration. Laryngeal muscles are of especial interest for tracheal intubation maneuvers and airway protection. Since their direct monitoring imposes technical difficulties, it has been reported that orbicularis oculi correlates with laryngeal muscles in terms of sensitivity to neuromuscular blocks. This study aimed at evaluating the presence of orbicularis oculi muscle fade after priming atracurium dose and at comparing clinical tracheal intubation conditions after two priming dose intervals. Participated in this study 35 adult patients, physical status ASA I or II, without risk factors for bronchoaspiration and submitted to elective surgeries. General anesthesia was induced with alfentanil and propofol and patients were manually ventilated under mask. Surface electrodes were then positioned on the temporal branch of the facial nerve, and the acceleration transducer was placed on the orbicularis oculi. Priming atracurium dose (0.02 mg.kg-1) was administered and T4/T1 ratio was evaluated every minute during 5 minutes in 20 cases (G1) and during 7 minutes in 13 cases (G2). After this interval, complementary atracurium dose (0.5 mg.kg-1) was administered and tracheal intubation was performed one minute later. Fade was defined as T4/T1 ratio below 0.9. There has been no fade in any patient during the monitoring interval. In 80% and 69% of G1 or G2 patients, respectively, tracheal intubation was classified as clinically acceptable (p > 0.05). Priming atracurium dose (0.02 mg.kg-1) does not determine orbicularis oculi fade and there is no difference between 5 or 7 minutes priming intervals.

  10. A New Model for Iron Emission Lines and Re-Burst in GRB X-Ray Afterglows

    OpenAIRE

    Gao, W. H.; Wei, D. M.

    2005-01-01

    Recently iron emission features have been observed in several X-ray afterglows of GRBs. It is found that the energy obtained from the illuminating continuum which produces the emission lines is much higher than that of the main burst.The observation of SN-GRB association indicates a fallback disk should be formed after the supernovae explosion. The disk is optically thick and advection-dominated and dense. We suggest that the delayed injection energy after the initial main burst, much higher ...

  11. Ultrasensitive Ambient Mass Spectrometric Analysis with a Pin-to-Capillary Flowing Atmospheric-Pressure Afterglow Source

    Science.gov (United States)

    Shelley, Jacob T.; Wiley, Joshua S.; Hieftje, Gary M.

    2011-01-01

    The advent of ambient desorption/ionization mass spectrometry has resulted in a strong interest in ionization sources that are capable of direct analyte sampling and ionization. One source that has enjoyed increasing interest is the Flowing Atmospheric-Pressure Afterglow (FAPA). FAPA has been proven capable of directly desorbing/ionizing samples in any phase (solid, liquid, or gas) and with impressive limits of detection (explosives. A detection limit of 4 amol was found for the direct determination of the agrochemical ametryn, and appears to be spectrometer-limited. The ability to quickly screen for analytes in bulk liquid samples with the pin-to-capillary FAPA is also shown. PMID:21627097

  12. First-Order Statistical Characteristics of Macrodiversity System with Three Microdiversity MRC Receivers in the Presence of k-µ Short-Term Fading and Gamma Long-Term Fading

    Directory of Open Access Journals (Sweden)

    Branimir Jaksic

    2016-01-01

    Full Text Available Macrodiversity system with macrodiversity SC receiver and three microdiversity MRC (maximum ratio combining receivers is considered. Independent k-μ short-term fading and correlated Gamma long-term fading are present at the inputs of microdiversity MRC receivers. For this model, the probability density function and the cumulative density function of microdiversity MRC receivers and macrodiversity SC receiver output signal envelopes are calculated. Influences of Gamma shadowing severity, k-μ multipath fading severity, Rician factor and correlation coefficient at probability density function, and cumulative density function of macrodiversity SC receiver output signal envelopes are graphically presented.

  13. Dependence of fading patterns of photo-stimulated luminescence from imaging plates on radiation, energy, and image reader

    CERN Document Server

    Ohuchi, H

    2002-01-01

    We have been investigating the fading characteristics of imaging plates (IPs) as integral type detectors. The dependence on alpha, beta, and gamma ray radiation and their energies of the fading effect was measured using three types of IPs (BAS-UR, BAS-TR, and BAS-MS). The functions to correct the fading were determined by using the method reported in a previous paper. In all types of IPs, we confirmed that the fading effect is independent of the energy of the incident particles of beta and gamma rays and also independent of radiation except for the first component, which fades out in a very short time after irradiation with alpha rays. These results are very useful in the utilization of IPs as integral detectors in practical radiation fields. Empirically, the fading pattern is known to change when the IP is scanned by different types of image readers. The differences in the fading patterns obtained with two types of image readers, the BAS-1000 and the BAS-5000 (Fuji Film Co.), is discussed. Development of an ...

  14. Performance analysis of the ALOHA protocol with replication in a fading channel for the Mobile Satellite Experiment

    Science.gov (United States)

    Clare, L. P.; Yan, T.-Y.

    1985-01-01

    The analysis of the ALOHA random access protocol for communications channels with fading is presented. The protocol is modified to send multiple contiguous copies of a message at each transmission attempt. Both pure and slotted ALOHA channels are considered. A general two state model is used for the channel error process to account for the channel fading memory. It is shown that greater throughput and smaller delay may be achieved using repetitions. The model is applied to the analysis of the delay-throughput performance in a fading mobile communications environment. Numerical results are given for NASA's Mobile Satellite Experiment.

  15. Ear-to-Ear On-Body Channel Fading in the ISM-band for Tangentially-Polarized Antennas

    DEFF Research Database (Denmark)

    Kvist, Søren Helstrup; Thaysen, Jesper; Jakobsen, Kaj Bjarne

    2011-01-01

    The ear-to-ear on-body channel fading has been studied in the ISM-band. The ear-to-ear path gain was measured on six persons in an indoor environment for a duration of 200 s. The channel fading has been characterized in terms of empirical cumulative distribution functions (CDF), average fade dura...... duration (AFD), and level crossing rate (LCR) for each of the six persons. Seven probability distributions, including Rician and Nakagamim were fitted by the use of maximum likelihood estimation (MLE). The distributions are ranked by their goodness-of-fit to the empirical CDFs....

  16. Protection of oxidative hair color fading from shampoo washing by hydrophobically modified cationic polymers.

    Science.gov (United States)

    Zhou, Y; Foltis, L; Moore, D J; Rigoletto, R

    2009-01-01

    The fading of oxidative color in hair as a result of daily shampoo washing activities has become a common problem and a source of frequent complaints by consumers. The fading occurs primarily through hair dye solubility in water. One aspect of the current study investigates the physical and chemical factors that influence hair color fading during the washing process. This is accomplished by testing hair dye dissolution in water from dyed hair samples with variation of surfactant type, pH, and hair type. Furthermore, a new approach to preventing color fading is developed aiming to provide an effective barrier function for hair dye from dissolving into water. The preliminary investigation of a series of polymers with various functional groups indicates that polymers with hydrophobically modified and cationic functionalities are most effective in preventing hair dye dissolution in water. It is also evident that a synergistic effect of the polymer's hydrophobic moieties and cationic charges are important on hair color protection during shampoo washing processes. A primary example of a polymer within this category is a cationic terpolymer of vinylpyrrolidone, dimethylaminopropyl methacrylamide, and methacryloylaminopropyl lauryldimonium chloride (INCI: Polyquaternium-55). The color protection benefit of this polymer is evaluated using newly developed methodologies for evaluating hair color changes, such as hair color fading tests through multiple shampoo washes with mannequin heads and hair tresses, both derived from human hair, colorimetry, and quantitative digital image analysis. In addition, new infrared spectroscopic imaging techniques are used to detect the hair dye deposition behavior inside hair fibers both with and without the color protection treatment. Both visual and instrumental measurement results indicate that Polyquaternium-55 provides a high level of color protection when formulated in a hair color protection regimen with up to 50% color protection. This

  17. Perspectives of observing the color indices of optical afterglows of gamma-ray bursts with ESA Gaia

    Science.gov (United States)

    Šimon, Vojtěch; Hudec, René; Pizzichini, Graziella

    2017-10-01

    We propose a strategy for detecting and analyzing optical afterglows (OAs) of long gamma-ray bursts (GRBs) without the need to obtain their light curves. This approach is useful for the Gaia satellite, which provides sampled optical ultra-low-dispersion spectroscopic observations of the sky. For this purpose, we show that most OAs of long GRBs display specific values of some of their color indices, representing synchrotron emission of the jet. They are stable in time during the event. These indices, which can be determined from the spectra, are very similar for the ensemble of OAs with redshift z Gaia instruments also gives us a hope to search for the so-called orphan afterglows, which, according to some authors, can be considerably more numerous than OAs of the observed GRBs. We also show how to resolve OAs from other transients in the Gaia data. The color indices and the properties of the quiescent sources (host galaxies of OAs detectable later by the large ground-based telescopes at the co-ordinates of the OA determined by Gaia) would tell us which one, among transients detected by Gaia, is a GRB OA.

  18. Film formation from HMDSO: comparison of direct plasma injection with afterglow injection using an atmospheric pressure dielectric barrier discharge

    Science.gov (United States)

    Wallimann, Roger; Oberbossel, Gina; Butscher, Denis; Rudolf von Rohr, Philipp

    2017-07-01

    The afterglow of a dielectric barrier discharge plasma was used for the film formation from Hexamethyldisiloxane (HMDSO) on silicon wafers. The process gas was argon with varying admixtures of HMDSO and oxygen. The silicon wafers were analyzed using white light interferometry and ATR-FTIR to characterize film volume and composition, respectively. The topology of deposited films was compared to a flow model to link the film thickness to flow velocity. Results show that deposition only occurs where flow velocity is low. Maximum film volume was observed at an oxygen admixture of 0.05 vol.%, while oxygen depletion for lower admixtures and plasma quenching at higher oxygen contents reduce the film formation. Additionally, film deposition depends on the residence time in the region where active species promote dissociation and on the density of active species in this region. Afterglow injection of HMDSO yields film deposition comparable to direct plasma injection with respect to volume and composition, eliminating the need of direct plasma treatment and preventing unwanted reactor deposition. Contribution to the topical issue "The 15th International Symposium on High Pressure Low Temperature Plasma Chemistry (HAKONE XV)", edited by Nicolas Gherardi and Tomáš Hoder

  19. Classification, Follow-up, and Analysis of GRBs and their Early-time NIR/Optical Afterglows

    Science.gov (United States)

    Morgan, Adam; Bloom, J. S.; Perley, D. A.; Christian, P.; Richards, J.; Cenko, S. B.; Klein, C. R.

    2014-01-01

    In the study of astronomical transients, achieving knowledge from discovery is a multifaceted process which includes real-time classification to identify new events of interest, deep, multi-wavelength follow-up of individual events, and the global analysis of multi-event catalogs. Here we present a body of work encompassing each of these steps as applied to the study of gamma-ray bursts (GRBs). First, we present our work on utilizing machine-learning algorithms on early-time metrics from the Swift satellite to inform the resource allocation of follow-up telescopes in order to optimize time spent on high-redshift GRB candidates. Next, we show broadband observations and analysis of the early-time afterglow of GRB 120119A, which exhibits extreme red-to-blue color change in the first few minutes after the trigger. Model fits of this color change reveal among the best support yet for the direct detection of dust destruction in the local environment of a GRB. Finally, we present results from the PAIRITEL early-time near-infrared (NIR) afterglow catalog. The 1.3 meter PAIRITEL has autonomously observed 15 GRBs in under 4 minutes after the trigger, yielding a homogenous sample of early-time JHKs light curves. Our analysis of these events provides constraints on the NIR GRB luminosity function, direct measurements of early-time NIR color change, and constraints on burst energetics.

  20. Electron energy distribution function, effective electron temperature, and dust charge in the temporal afterglow of a plasma

    Energy Technology Data Exchange (ETDEWEB)

    Denysenko, I. B.; Azarenkov, N. A. [School of Physics and Technology, V. N. Karazin Kharkiv National University, Svobody sq. 4, 61022 Kharkiv (Ukraine); Kersten, H. [Institut für Experimentelle und Angewandte Physik, Leibnizstr. 19, Kiel D-24098 (Germany)

    2016-05-15

    Analytical expressions describing the variation of electron energy distribution function (EEDF) in an afterglow of a plasma are obtained. Especially, the case when the electron energy loss is mainly due to momentum-transfer electron-neutral collisions is considered. The study is carried out for different EEDFs in the steady state, including Maxwellian and Druyvesteyn distributions. The analytical results are not only obtained for the case when the rate for momentum-transfer electron-neutral collisions is independent on electron energy but also for the case when the collisions are a power function of electron energy. Using analytical expressions for the EEDF, the effective electron temperature and charge of the dust particles, which are assumed to be present in plasma, are calculated for different afterglow durations. An analytical expression for the rate describing collection of electrons by dust particles for the case when the rate for momentum-transfer electron-neutral collisions is independent on electron energy is also derived. The EEDF profile and, as a result, the effective electron temperature and dust charge are sufficiently different in the cases when the rate for momentum-transfer electron-neutral collisions is independent on electron energy and when the rate is a power function of electron energy.

  1. Thermal components in the early X-ray afterglows of GRBs: likely cocoon emission and constraints on the progenitors

    Science.gov (United States)

    Valan, Vlasta; Larsson, Josefin; Ahlgren, Björn

    2018-02-01

    The early X-ray afterglows of gamma-ray bursts (GRBs) are usually well described by absorbed power laws. However, in some cases, additional thermal components have been identified. The origin of this emission is debated, with proposed explanations including supernova shock breakout, emission from a cocoon surrounding the jet, as well as emission from the jet itself. A larger sample of detections is needed in order to place constraints on these different models. Here, we present a time-resolved spectral analysis of 74 GRBs observed by Swift X-ray Telescope in a search for thermal components. We report six detections in our sample, and also confirm an additional three cases that were previously reported in the literature. The majority of these bursts have a narrow range of blackbody radii around ˜2 × 1012 cm, despite having a large range of luminosities (Lpeak ˜ 1047-1051 erg s-1). This points to an origin connected to the progenitor stars, and we suggest that emission from a cocoon breaking out from a thick wind may explain the observations. For two of the bursts in the sample, an explanation in terms of late prompt emission from the jet is instead more likely. We also find that these thermal components are preferentially detected when the X-ray luminosity is low, which suggests that they may be hidden by bright afterglows in the majority of GRBs.

  2. Ignition and afterglow dynamics of a high pressure nanosecond pulsed helium micro-discharge: II. Rydberg molecules kinetics

    Science.gov (United States)

    Carbone, Emile A. D.; Schregel, Christian-Georg; Czarnetzki, Uwe

    2016-10-01

    In this paper, we discuss the experimental results presented in Schregel et al (2016 Plasma Sources Sci. Technol. 25 054003) on a high pressure micro-discharge operated in helium and driven by nanosecond voltage pulses. A simple global plasma chemistry model is developed to describe the ions, excited atomic and molecular species dynamics in the ignition and early afterglow regimes. The existing experimental data on high pressure helium kinetics is reviewed and critically discussed. It is highlighted that several inconsistencies in the branching ratio of neutral assisted associative and dissociative processes currently exist in the literature and need further clarification. The model allows to pinpoint the mechanisms responsible for the large amounts of Rydberg molecules produced in the discharge and for the helium triplet metastable state in the afterglow. The main losses of electrons are also identified. The fast quenching of excited He (n  >  3) states appears to be a significant source of Rydberg molecules which has been previously neglected. The plasma model finally draws a simplified, but still accurate description of high pressure helium discharges based on available experimental data for ion and neutral helium species.

  3. Happy Birthday Swift: Ultra-long GRB 141121A and Its Broadband Afterglow

    Science.gov (United States)

    Cucchiara, A.; Veres, P.; Corsi, A.; Cenko, S. B.; Perley, D. A.; Lien, A.; Marshall, F. E.; Pagani, C.; Toy, V. L.; Capone, J. I.; Frail, D. A.; Horesh, A.; Modjaz, M.; Butler, N. R.; Littlejohns, O. M.; Watson, A. M.; Kutyrev, A. S.; Lee, W. H.; Richer, M. G.; Klein, C. R.; Fox, O. D.; Prochaska, J. X.; Bloom, J. S.; Troja, E.; Ramirez-Ruiz, E.; de Diego, J. A.; Georgiev, L.; González, J.; Román-Zúñiga, C. G.; Gehrels, N.; Moseley, H.

    2015-10-01

    We present our extensive observational campaign on the Swift-discovered GRB 141121A, almost 10 years after its launch. Our observations cover radio through X-rays and extend for more than 30 days after discovery. The prompt phase of GRB 141121A lasted 1410 s and, at the derived redshift of z = 1.469, the isotropic energy is Eγ,iso = 8.0 × 1052 erg. Due to the long prompt duration, GRB 141121A falls into the recently discovered class of ultra-long GRBs (UL-GRBs). Peculiar features of this burst are (1) a flat early-time optical light curve and (2) a radio-to-X-ray rebrightening around three days after the burst. The latter is followed by a steep optical-to-X-ray decay and a much shallower radio fading. We analyze GRB 141121A in the context of the standard forward-reverse shock (FS, RS) scenario and we disentangle the FS and RS contributions. Finally, we comment on the puzzling early-time (t ≲ 3 days) behavior of GRB 141121A, and suggest that its interpretation may require a two-component jet model. Overall, our analysis confirms that the class of UL-GRBs represents our best opportunity to firmly establish the prominent emission mechanisms in action during powerful gamma-ray burst explosions, and future missions (like SVOM, XTiDE, or ISS-Lobster) will provide many more of such objects.

  4. HAPPY BIRTHDAY SWIFT: ULTRA-LONG GRB 141121A AND ITS BROADBAND AFTERGLOW

    Energy Technology Data Exchange (ETDEWEB)

    Cucchiara, A. [Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Veres, P. [The George Washington University, Department of Physics, 725 21st, NW Washington, DC 20052 (United States); Corsi, A. [Physics Department, Texas Tech University, Box 41051, Lubbock, TX 79409 (United States); Cenko, S. B.; Marshall, F. E.; Kutyrev, A. S. [Astrophysics Science Division, NASA Goddard Space Flight Center, MC 661, Greenbelt, MD 20771 (United States); Perley, D. A.; Horesh, A. [Department of Astronomy, California Institute of Technology, MC 249-17, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Lien, A. [Center for Research and Exploration in Space Science and Technology (CRESST) and NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Pagani, C. [Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom); Toy, V. L.; Capone, J. I. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Frail, D. A. [National Radio Astronomy Observatory P.O. Box 0. Socorro, NM (United States); Modjaz, M. [Center for Cosmology and Particle Physics, New York University, 4 Washington Place, New York, NY 10003 (United States); Butler, N. R.; Littlejohns, O. M. [School of Earth and Space Exploration, Arizona State University, AZ 85287 (United States); Watson, A. M.; Lee, W. H.; Richer, M. G. [Instituto de Astronomía, Universidad Nacional Autónoma de México, Apartado Postal 70-264, 04510 México, D. F., México (Mexico); Klein, C. R., E-mail: antonino.cucchiara@nasa.gov [Astronomy Department, University of California, Berkeley, CA 94720-7450 (United States); and others

    2015-10-20

    We present our extensive observational campaign on the Swift-discovered GRB 141121A, almost 10 years after its launch. Our observations cover radio through X-rays and extend for more than 30 days after discovery. The prompt phase of GRB 141121A lasted 1410 s and, at the derived redshift of z = 1.469, the isotropic energy is E{sub γ,iso} = 8.0 × 10{sup 52} erg. Due to the long prompt duration, GRB 141121A falls into the recently discovered class of ultra-long GRBs (UL-GRBs). Peculiar features of this burst are (1) a flat early-time optical light curve and (2) a radio-to-X-ray rebrightening around three days after the burst. The latter is followed by a steep optical-to-X-ray decay and a much shallower radio fading. We analyze GRB 141121A in the context of the standard forward–reverse shock (FS, RS) scenario and we disentangle the FS and RS contributions. Finally, we comment on the puzzling early-time (t ≲ 3 days) behavior of GRB 141121A, and suggest that its interpretation may require a two-component jet model. Overall, our analysis confirms that the class of UL-GRBs represents our best opportunity to firmly establish the prominent emission mechanisms in action during powerful gamma-ray burst explosions, and future missions (like SVOM, XTiDE, or ISS-Lobster) will provide many more of such objects.

  5. What can we learn from "internal plateaus"? The peculiar afterglow of GRB 070110

    Science.gov (United States)

    Beniamini, P.; Mochkovitch, R.

    2017-09-01

    Context. The origin of the prompt emission of gamma-ray bursts is highly debated. Proposed scenarios involve various dissipation processes (shocks, magnetic reconnection, and inelastic collisions) above or below the photosphere of an ultra-relativistic outflow. Aims: We search for observational features that could help to favour one scenario over the others by constraining the dissipation radius, the magnetization of the outflow, or by indicating the presence of shocks. Bursts showing peculiar behaviours can emphasize the role of a specific physical ingredient, which becomes more apparent under certain circumstances. Methods: We study GRB 070110, which exhibited several remarkable features during its early afterglow; I.e. a very flat plateau terminated by an extremely steep drop and immediately followed by a bump. We modelled the plateau as the photospheric emission from a long-lasting outflow of moderate Lorentz factor (Γ 20), which lags behind an ultra-relativistic (Γ > 100) ejecta that is responsible for the prompt emission. We computed the dissipation of energy in the forward and reverse shocks resulting from the deceleration of this ejecta by the external medium (uniform or stellar wind). Results: We find that photospheric emission from the long-lasting outflow can account for the plateau properties (luminosity and spectrum) assuming that some dissipation takes place in the flow. The geometrical timescale at the photospheric radius is so short that the observed decline at the end of the plateau likely corresponds to the actual shutdown of the activity in the central engine. The bump that follows results from the power dissipated in the reverse shock, which develops when the material making the plateau catches up with the initially fast shell in front, after the fast shell has decelerated. Conclusions: The proposed interpretation suggests that the prompt phase results from dissipation above the photosphere while the plateau has a photospheric origin. If the

  6. Performance analysis of power-efficient adaptive interference cancelation in fading channels

    KAUST Repository

    Radaydeh, Redha Mahmoud Mesleh

    2010-12-01

    This paper analyzes the performance of a -steering scheme for highly correlated receive antennas in the presence of statistically unordered co-channel interferers over multipath fading channels. An adaptive activation of receive antennas according to the interfering signals fading conditions is considered in the analysis. Analytical expressions for various system performance measures, including the outage probability, average error probability of different signaling schemes, and raw moments of the combined signal-to-interference-plus-noise ratio (SINR) are obtained in exact forms. Numerical and simulation results for the performance-complexity tradeoff of this scheme is presented and then compared with that of full-size arbitrary interference cancelation and no cancelation scenarios. ©2010 IEEE.

  7. Transmit selection for imperfect threshold-based receive MRC in Rayleigh fading channels

    KAUST Repository

    Radaydeh, Redha Mahmoud Mesleh

    2010-01-01

    The performance of multiple-antenna diversity systems in which the receiver combines signal replicas per thresholdbased maximal ratio combining (MRC) and the transmitter uses only a single antenna according to receive combined signal strength is studied. The impact of imperfect channel estimation is considered when the received signal replicas undergo independent and flat multipath fading. The analysis is applicable for arbitrary transmit antenna selection when the multiple-antenna channels experience identically distributed and non-identically distributed Rayleigh fading conditions. New closed-form expressions for the combined SNR statistics and some performance measures are presented. The system models adopted herein and the presented analytical results can be used to study the performance of different system architectures under various channel conditions when the implementation complexity is of interest. © 2009 IEEE.

  8. Distributed detection in UWB sensor networks under non-orthogonal Nakagami-m fading

    KAUST Repository

    Mehbodniya, Abolfazl

    2011-09-01

    Several attractive features of ultra wideband (UWB) communications make it a good candidate for physical-layer of wireless sensor networks (WSN). These features include low power consumption, low complexity and low cost of implementation. In this paper, we present an opportunistic power assignment strategy for distributed detection in parallel fusion WSNs, considering a Nakagami-m fading model for the communication channel and time-hopping (TH) UWB for the transmitter circuit of the sensor nodes. In a parallel fusion WSN, local decisions are made by local sensors and transmitted through wireless channels to a fusion center. The fusion center processes the information and makes the final decision. Simulation results are provided for the global probability of detection error and relative performance gain to evaluate the efficiency of the proposed power assignment strategy in different fading environments. © 2011 IEEE.

  9. Experimental and theoretical studies of perceptible color fading of decorative paints consisting of mixed pigments

    Science.gov (United States)

    Auger, Jean-Claude; McLoughlin, Daragh

    2017-01-01

    We study the color fading of paints films composed of mixtures of white rutile titanium dioxide and yellow arylide pigments dispersed in two polymer binders at different volume concentrations. The samples were exposed to ultraviolet radiations in an accelerated weathering tester during three weeks. The measured patterns in color variations appeared to be independent of the chemistry of the binders. We then developed a theoretical framework, based on the Radiative transfer Equation of light and the One Particle T-Matrix formalism to simulate the color fading process. The loss of color is correlated to the progressive decrease of the original colored pigment volume-filling fraction as the destructive UV radiations penetrate deeper into the films. The calculated patterns of color variations of paints film composed by mixtures of white pigments with yellow Cadmium Sulfate (CdS) and red Cerium Sulfide (Ce2S3) pigments showed the same trend as that seen experimentally.

  10. Design and Performance Analysis of MISO-ORM-DCSK System over Rayleigh Fading Channels

    Directory of Open Access Journals (Sweden)

    Gang Zhang

    2016-01-01

    Full Text Available A novel chaotic communication system, named Orthogonality-based Reference Modulated-Differential Chaos Shift Keying (ORM-DCSK, is proposed to enhance the performance of RM-DCSK. By designing an orthogonal chaotic generator (OCG, the intrasignal interference components in RM-DCSK are eliminated. Also, the signal frame format is expanded so the average bit energy is reduced. As a result, the proposed system has less interference in decision variables. Furthermore, to investigate the bit error rate (BER performance over Rayleigh fading channels, the MISO-ORM-DCSK is studied. The BER expressions of the new system are derived and analyzed over AWGN channel and multipath Rayleigh fading channel. All simulation results not only show that the proposed system can obtain significant improvement but also verify the analysis in theory.

  11. On Outage Performance of Spectrum-Sharing Communication over M-Block Fading

    KAUST Repository

    Alabbasi, AbdulRahman

    2015-12-06

    In this paper, we consider a cognitive radio system in which a block-fading channel is assumed. Each transmission frame consists of M blocks and each block undergoes a different channel gain. Instantaneous channel state information about the interference links remains unknown to the primary and secondary users. We minimize the secondary user\\'s targeted outage probability over the block-fading channels. To protect the primary user, a statistical constraint on its targeted outage probability is enforced. The secondary user\\'s targeted outage region and the corresponding optimal power are derived. We also propose two sub-optimal power strategies and derive compact expressions for the corresponding outage probabilities. These probabilities are shown to be asymptotic lower and upper bounds on the outage probability. Utilizing these bounds, we derive the exact diversity order of the secondary user outage probability. Selected numerical results are presented to characterize the system\\'s behavior.

  12. Electrochemical capacity fading of polyaniline electrode in supercapacitor: An XPS analysis

    Directory of Open Access Journals (Sweden)

    Jinxing Deng

    2017-04-01

    Full Text Available To understand the electrochemical capacity fading of the polyaniline (PANI electrodes in supercapacitors, for the first time, their chemical structure change during electrochemical cycles was traced with XPS analysis after the HCl doped PANI electrodes were subjected to the cyclic voltammetry test in 1.0 M H2SO4 electrolyte for different cycle numbers. The results showed that the chlorine disappeared in the electrode surface, while the surface element contents of sulfur and oxygen increased with the electrochemical cycles increased. It demonstrated that the hydrolytic degradation of the PANI chains and exchange of dopant occurred during the electrochemical cycling, causing the fading in the mechanical and electrochemical performance of the PANI electrodes. This understanding should lead to better design of the conductive polymer-based energy storage devices.

  13. Free Probability based Capacity Calculation of Multiantenna Gaussian Fading Channels with Cochannel Interference

    CERN Document Server

    Chatzinotas, Symeon

    2010-01-01

    During the last decade, it has been well understood that communication over multiple antennas can increase linearly the multiplexing capacity gain and provide large spectral efficiency improvements. However, the majority of studies in this area were carried out ignoring cochannel interference. Only a small number of investigations have considered cochannel interference, but even therein simple channel models were employed, assuming identically distributed fading coefficients. In this paper, a generic model for a multi-antenna channel is presented incorporating four impairments, namely additive white Gaussian noise, flat fading, path loss and cochannel interference. Both point-to-point and multiple-access MIMO channels are considered, including the case of cooperating Base Station clusters. The asymptotic capacity limit of this channel is calculated based on an asymptotic free probability approach which exploits the additive and multiplicative free convolution in the R- and S-transform domain respectively, as ...

  14. Mutual Information of IID Complex Gaussian Signals on Block Rayleigh-faded Channels

    CERN Document Server

    Rusek, Fredrik; Jindal, Nihar

    2010-01-01

    We present a method to compute, quickly and efficiently, the mutual information achieved by an IID (independent identically distributed) complex Gaussian input on a block Rayleigh-faded channel without side information at the receiver. The method accommodates both scalar and MIMO (multiple-input multiple-output) settings. Operationally, the mutual information thus computed represents the highest spectral efficiency that can be attained using standard Gaussian codebooks. Examples are provided that illustrate the loss in spectral efficiency caused by fast fading and how that loss is amplified by the use of multiple transmit antennas. These examples are further enriched by comparisons with the channel capacity under perfect channel-state information at the receiver, and with the spectral efficiency attained by pilot-based transmission.

  15. Turbo coding, turbo equalisation and space-time coding for transmission over fading channels

    CERN Document Server

    Hanzo, L; Yeap, B

    2002-01-01

    Against the backdrop of the emerging 3G wireless personal communications standards and broadband access network standard proposals, this volume covers a range of coding and transmission aspects for transmission over fading wireless channels. It presents the most important classic channel coding issues and also the exciting advances of the last decade, such as turbo coding, turbo equalisation and space-time coding. It endeavours to be the first book with explicit emphasis on channel coding for transmission over wireless channels. Divided into 4 parts: Part 1 - explains the necessary background for novices. It aims to be both an easy reading text book and a deep research monograph. Part 2 - provides detailed coverage of turbo conventional and turbo block coding considering the known decoding algorithms and their performance over Gaussian as well as narrowband and wideband fading channels. Part 3 - comprehensively discusses both space-time block and space-time trellis coding for the first time in literature. Par...

  16. Multilevel Codes for OFDM-Like Modulation over Underspread Fading Channels

    Directory of Open Access Journals (Sweden)

    Mallik Siddhartha

    2006-01-01

    Full Text Available We study the problem of modulation and coding for doubly dispersive, that is, time and frequency selective, fading channels. Using the recent result that underspread linear systems are approximately diagonalized by biorthogonal Weyl-Heisenberg bases, we arrive at a canonical formulation of modulation and code design. For coherent reception with maximum-likelihood decoding, we derive the code design criteria as a function of the channel's scattering function. We use ideas from generalized concatenation to design multilevel codes for this canonical channel model. These codes are based on partitioning a constellation carved out from the integer lattice. Utilizing the block fading interpretation of the doubly dispersive channel, we adapt these partitioning techniques to the richness of the channel. We derive an algebraic framework which enables us to partition in arbitrarily large dimensions.

  17. A unified simulation approach for the fast outage capacity evaluation over generalized fading channels

    KAUST Repository

    Rached, Nadhir B.

    2015-06-14

    The outage capacity (OC) is among the most important performance metrics of communication systems over fading channels. The evaluation of the OC, when Equal Gain Combining (EGC) or Maximum Ratio Combining (MRC) diversity techniques are employed, boils down to computing the Cumulative Distribution Function (CDF) of the sum of channel envelopes (equivalently amplitudes) for EGC or channel gain (equivalently squared enveloped/amplitudes) for MRC. Closed-form expressions of the CDF of the sum of many generalized fading variates are generally unknown and constitute open problems. In this paper, we develop a unified hazard rate twisting Importance Sampling (IS) based approach to efficiently estimate the CDF of the sum of independent arbitrary variates. The proposed IS estimator is shown to achieve an asymptotic optimality criterion, which clearly guarantees its efficiency. Some selected simulation results are also shown to illustrate the substantial computational gain achieved by the proposed IS scheme over crude Monte-Carlo simulations.

  18. Joint Frequency Ambiguity Resolution and Accurate Timing Estimation in OFDM Systems with Multipath Fading

    Directory of Open Access Journals (Sweden)

    Ouyang Shan

    2006-01-01

    Full Text Available A serious disadvantage of orthogonal frequency-division multiplexing (OFDM is its sensitivity to carrier frequency offset (CFO and timing offset (TO. For many low-complexity algorithms, the estimation ambiguity exists when the CFO is greater than one or two subcarrier spacing, and the estimated TO is also prone to exceeding the ISI-free interval within the cyclic prefix (CP. This paper presents a method for joint CFO ambiguity resolution and accurate TO estimation in multipath fading. Maximum-likelihood (ML principle is employed and only one pilot symbol is needed. Frequency ambiguity is resolved and accurate TO can be obtained simultaneously by using the fast Fourier transform (FFT and one-dimensional (1D search. Both known and unknown channel order cases are considered. Computer simulations show that the proposed algorithm outperforms some others in the multipath fading channels.

  19. LDPC concatenated space-time block coded system in multipath fading environment: Analysis and evaluation

    Directory of Open Access Journals (Sweden)

    Surbhi Sharma

    2011-06-01

    Full Text Available Irregular low-density parity-check (LDPC codes have been found to show exceptionally good performance for single antenna systems over a wide class of channels. In this paper, the performance of LDPC codes with multiple antenna systems is investigated in flat Rayleigh and Rician fading channels for different modulation schemes. The focus of attention is mainly on the concatenation of irregular LDPC codes with complex orthogonal space-time codes. Iterative decoding is carried out with a density evolution method that sets a threshold above which the code performs well. For the proposed concatenated system, the simulation results show that the QAM technique achieves a higher coding gain of 8.8 dB and 3.2 dB over the QPSK technique in Rician (LOS and Rayleigh (NLOS faded environments respectively.

  20. On the Computation of the Higher Order Statistics of the Channel Capacity over Generalized Fading Channels

    CERN Document Server

    Yilmaz, Ferkan

    2012-01-01

    The higher-order statistics (HOS) of the channel capacity $\\mu_n=\\mathbb{E}[\\log^n(1+\\gamma_{end})]$, where $n\\in\\mathbb{N}$ denotes the order of the statistics, has received relatively little attention in the literature, due in part to the intractability of its analysis. In this letter, we propose a novel and unified analysis, which is based on the moment generating function (MGF) technique, to exactly compute the HOS of the channel capacity. More precisely, our mathematical formalism can be readily applied to maximal-ratio-combining (MRC) receivers operating in generalized fading environments. The mathematical formalism is illustrated by some numerical examples focussing on the correlated generalized fading environments.

  1. On the capacity of cognitive radio under limited channel state information over fading channels

    KAUST Repository

    Rezki, Zouheir

    2011-06-01

    A spectrum-sharing communication system where the secondary user is aware of the instantaneous channel state information (CSI) of the secondary link, but knows only the statistics and an estimated version of the secondary transmitter-primary receiver (ST-PR) link, is investigated. The optimum power profile and the ergodic capacity of the secondary link are derived for general fading channels (with continuous probability density function) under average and peak transmit-power constraints and with respect to two different interference constraints: an interference outage constraint and a signal-to-interference (SI) outage constraint. When applied to Rayleigh fading channels, our results show, for instance, that the interference constraint is harmful at high-power regime, whereas at low-power regime, it has a marginal impact and no-interference performance may be achieved. © 2011 IEEE.

  2. On the outage capacity of the block fading channel at low-power regime

    KAUST Repository

    Rezki, Zouheir

    2014-06-01

    Outage performance of the M-block fading with additive white Gaussian noise (BF-AWGN) is investigated at low-power regime. We consider delay-constrained constant-rate communications with perfect channel state information (CSI) at both the transmitter and the receiver (CSI-TR), under a short-term power constraint. We show that selection diversity that allocates all the power to the strongest block is asymptotically optimal. Then, we provide a simple characterization of the outage probability in the regime of interest. We quantify the reward due to CSI-TR over the constant-rate constant-power scheme and show that this reward increases with the delay constraint. For instance, for Rayleigh fading, we find that a power gain up to 4.3 dB is achievable. © 2014 IEEE.

  3. Capacity of spectrum sharing Cognitive Radio systems over Nakagami fading channels at low SNR

    KAUST Repository

    Sboui, Lokman

    2013-06-01

    In this paper, we study the ergodic capacity of Cognitive Radio (CR) spectrum sharing systems at low power regime. We focus on Nakagami fading channels. We formally define the low power regime and present closed form expressions of the capacity in the low power regime under various types of interference and/or power constraints, depending on the available channel state information (CSI) of the cross link (CL) between the secondary user transmitter and the primary user receiver. We explicitly characterize two regimes where either the interference constraint or the power constraint dictates the optimal power profile. Our framework also highlights the effects of different fading parameters on the secondary link ergodic capacity. Interestingly, we show that the low power regime analysis provides a specific insight on the capacity behavior of CR that has not been reported by previous studies. © 2013 IEEE.

  4. A Unified Simulation Approach for the Fast Outage Capacity Evaluation over Generalized Fading Channels

    KAUST Repository

    Rached, Nadhir B.

    2016-01-06

    The outage capacity (OC) is among the most important performance metrics of communication systems over fading channels. The evaluation of the OC, when equal gain combining (EGC) or maximum ratio combining (MRC) diversity techniques are employed, boils down to computing the cumulative distribution function (CDF) of the sum of channel envelopes (equivalently amplitudes) for EGC or channel gains (equivalently squared enveloped/ amplitudes) for MRC. Closed-form expressions of the CDF of the sum of many generalized fading variates are generally unknown and constitute open problems. We develop a unified hazard rate twisting Importance Sampling (IS) based approach to efficiently estimate the CDF of the sum of independent arbitrary variates. The proposed IS estimator is shown to achieve an asymptotic optimality criterion, which clearly guarantees its efficiency. Some selected simulation results are also shown to illustrate the substantial computational gain achieved by the proposed IS scheme over crude Monte Carlo simulations.

  5. Improved Detection Performance of Cognitive Radio Networks in AWGN and Rayleigh Fading Environments

    Directory of Open Access Journals (Sweden)

    Mahamod Ismail

    2013-06-01

    Full Text Available Cognitive radios (CRs have been recently emerging as prime candidates to enhance spectral efficiency by exploitingspectrum-aware systems which can reliably monitor licensed users’ activities. CR users monitor such activities byperforming spectrum sensing to detect potential white spaces. However, this process of local sensing might be achallenging task in fading environments. The inefficiency of spectrum sensing might cause interference to licensees ifthey are miss-detected by CR users. Thus, cooperative spectrum sensing is proposed as a means to combat fading andimprove the detection performance. However, the detection performance does not improve by such cooperation whenlow-SNR environment is considered. In this paper, cooperative spectrum sensing with PSO-based threshold adaptationis presented to address the aforementioned problem. Simulation results show that the detection performance with PSObasedadaptive detection threshold is improved, particularly, in low-SNR environment.

  6. Mitigation of signal fading in radio over fiber transmission using fiber nonlinearity.

    Science.gov (United States)

    Maeda, Joji; Kusama, Kazutoyo; Fukuchi, Yutaka

    2009-03-16

    Radio over fiber systems in a microwave/millimeter wave band experience a severe signal fading due to fiber dispersion. However, parametric amplification in transmission fibers, known as modulation instability, can compensate for the signal fading. In this paper, we experimentally demonstrate radio over fiber transmission of 111.689 Mbps BPSK signal with a carrier frequency of 10.804 GHz, and measure bit error rates varying the optical transmission power. For the fiber launched power of 0 dBm, we observe a power penalty of 5.8 dB in the transmission over a 25 km fiber, though by increasing the fiber launched power up to +10 dBm, we successfully reduce the power penalty by 1.1 dB. (c) 2009 Optical Society of America

  7. Adaptive Modulation with Best User Selection over Non-Identical Nakagami Fading Channels

    KAUST Repository

    Rao, Anlei

    2012-09-08

    In this paper, we analyze the performance of adaptive modulation with single-cell multiuser scheduling over independent but not identical distributed (i.n.i.d.) Nakagami fading channels. Closed-form expressions are derived for the average channel capacity, spectral efficiency, and bit-error-rate (BER) for both constant-power variable-rate and variable-power variable-rate uncoded M-ary quadrature amplitude modulation (M-QAM) schemes. We also study the impact of time delay on the average BER of adaptive M-QAM. Selected numerical results show that the multiuser diversity brings a considerably better performance even over i.n.i.d. fading environments.

  8. Multiuser Diversity with Adaptive Modulation in Non-Identically Distributed Nakagami Fading Environments

    KAUST Repository

    Rao, Anlei

    2012-09-08

    In this paper, we analyze the performance of adaptive modulation with single-cell multiuser scheduling over independent but not identical distributed (i.n.i.d.) Nakagami fading channels. Closed-form expressions are derived for the average channel capacity, spectral efficiency, and bit-error-rate (BER) for both constant-power variable-rate and variable-power variable-rate uncoded/coded M-ary quadrature amplitude modulation (M-QAM) schemes. We also study the impact of time delay on the average BER of adaptive M-QAM. Selected numerical results show that the multiuser diversity brings a considerably better performance even over i.n.i.d. fading environments.

  9. A Bayesian Game-Theoretic Approach for Distributed Resource Allocation in Fading Multiple Access Channels

    Directory of Open Access Journals (Sweden)

    Gaoning He

    2010-01-01

    Full Text Available A Bayesian game-theoretic model is developed to design and analyze the resource allocation problem in K-user fading multiple access channels (MACs, where the users are assumed to selfishly maximize their average achievable rates with incomplete information about the fading channel gains. In such a game-theoretic study, the central question is whether a Bayesian equilibrium exists, and if so, whether the network operates efficiently at the equilibrium point. We prove that there exists exactly one Bayesian equilibrium in our game. Furthermore, we study the network sum-rate maximization problem by assuming that the users coordinate according to a symmetric strategy profile. This result also serves as an upper bound for the Bayesian equilibrium. Finally, simulation results are provided to show the network efficiency at the unique Bayesian equilibrium and to compare it with other strategies.

  10. Delay-limited capacity of fading multiple access and broadcast channels in the low power regime

    KAUST Repository

    Rezki, Zouheir

    2015-09-11

    We study delay-limited (also called zero-outage) capacity region of the fading multi-access channel (MAC) with Gaussian noise and perfect channel state information (CSI) at the receiver and at the transmitters (CSI-TR), in the low-power regime. We show that for fading channels where the MAC capacity region is strictly positive, it has a multidimensional rectangle structure and thus is simply characterized by single user capacity points. More specifically, we show that at low power, the boundary surface of the capacity region shrinks to a single point corresponding to the sum-rate maximizer and that the coordinates of this point coincide with single user capacity bounds. Using the duality of the Gaussian MAC and broadcast channels (BC), we show that time-sharing (or time division multiple access (TDMA)) is asymptotically optimal. © 2015 IEEE.

  11. Improved Detection Performance of Cognitive Radio Networks in AWGN and Rayleigh Fading Environments

    Directory of Open Access Journals (Sweden)

    Ying Loong Lee

    2013-06-01

    Full Text Available Cognitive radios (CRs have been recently emerging as prime candidates to enhance spectral efficiency by exploiting spectrum-aware systems which can reliably monitor licensed users’ activities. CR users monitor such activities by performing spectrum sensing to detect potential white spaces. However, this process of local sensing might be a challenging task in fading environments. The inefficiency of spectrum sensing might cause interference to licensees if they are miss-detected by CR users. Thus, cooperative spectrum sensing is proposed as a means to combat fading and improve the detection performance. However, the detection performance does not improve by such cooperation when low-SNR environment is considered. In this paper, cooperative spectrum sensing with PSO-based threshold adaptation is presented to address the aforementioned problem. Simulation results show that the detection performance with PSO-based adaptive detection threshold is improved, particularly, in low-SNR environment.

  12. Gamma-Ray Burst Afterglows as Probes of Environment and Blast Wave Physics. I. Absorption by Host-Galaxy Gas and Dust

    NARCIS (Netherlands)

    Starling, R.L.C.; Wijers, R.A.M.J.; Wiersema, K.; Rol, E.; Curran, P.A.; Kouveliotou, C.; van der Horst, A.J.; Heemskerk, M.H.M.

    2007-01-01

    We use a new approach to obtain limits on the absorbing columns toward an initial sample of 10 long gamma-ray bursts observed with BeppoSAX and selected on the basis of their good optical and near-infrared (NIR) coverage, from simultaneous fits to NIR, optical, and X-ray afterglow data, in count

  13. THE NEEDLE IN THE 100 deg{sup 2} HAYSTACK: UNCOVERING AFTERGLOWS OF FERMI GRBs WITH THE PALOMAR TRANSIENT FACTORY

    Energy Technology Data Exchange (ETDEWEB)

    Singer, Leo P. [LIGO Laboratory, California Institute of Technology, Pasadena, CA 91125 (United States); Kasliwal, Mansi M. [Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena CA 91101 (United States); Cenko, S. Bradley; Cucchiara, Antonino; Gehrels, Neil [Astrophysics Science Division, NASA Goddard Space Flight Center, Code 661, Greenbelt, MD 20771 (United States); Perley, Daniel A.; Cao, Yi [Cahill Center for Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Anderson, Gemma E.; Fender, Rob P. [Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH (United Kingdom); Anupama, G. C. [Indian Institute of Astrophysics, Koramangala, Bangalore 560 034 (India); Arcavi, Iair [Las Cumbres Observatory Global Telescope Network, 6740 Cortona Drive, Suite 102, Goleta, CA 93117 (United States); Bhalerao, Varun [Inter-University Centre for Astronomy and Astrophysics (IUCAA), Post Bag 4, Ganeshkhind, Pune 411007 (India); Bue, Brian D. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Connaughton, Valerie [CSPAR and Physics Department, University of Alabama in Huntsville, 320 Sparkman Drive, Huntsville, AL 35899 (United States); Corsi, Alessandra [Texas Tech University, Physics Department, Lubbock, TX 79409-1051 (United States); Fox, Derek B. [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States); Goldstein, Adam [Astrophysics Office, ZP12, NASA Marshall Space Flight Center, Huntsville, AL 35812 (United States); Gorosabel, J. [Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, E-18008, Granada (Spain); Horesh, Assaf, E-mail: leo.p.singer@nasa.gov [Benoziyo Center for Astrophysics, Weizmann Institute of Science, 76100 Rehovot (Israel); and others

    2015-06-10

    The Fermi Gamma-ray Space Telescope has greatly expanded the number and energy window of observations of gamma-ray bursts (GRBs). However, the coarse localizations of tens to a hundred square degrees provided by the Fermi GRB Monitor instrument have posed a formidable obstacle to locating the bursts’ host galaxies, measuring their redshifts, and tracking their panchromatic afterglows. We have built a target-of-opportunity mode for the intermediate Palomar Transient Factory in order to perform targeted searches for Fermi afterglows. Here, we present the results of one year of this program: 8 afterglow discoveries out of 35 searches. Two of the bursts with detected afterglows (GRBs 130702A and 140606B) were at low redshift (z = 0.145 and 0.384, respectively) and had spectroscopically confirmed broad-line Type Ic supernovae. We present our broadband follow-up including spectroscopy as well as X-ray, UV, optical, millimeter, and radio observations. We study possible selection effects in the context of the total Fermi and Swift GRB samples. We identify one new outlier on the Amati relation. We find that two bursts are consistent with a mildly relativistic shock breaking out from the progenitor star rather than the ultra-relativistic internal shock mechanism that powers standard cosmological bursts. Finally, in the context of the Zwicky Transient Facility, we discuss how we will continue to expand this effort to find optical counterparts of binary neutron star mergers that may soon be detected by Advanced LIGO and Virgo.

  14. NuSTARobservations of grb 130427a establish a single component synchrotron afterglow origin for the late optical to multi-gev emission

    DEFF Research Database (Denmark)

    Kouveliotou, C.; Granot, J.; Racusin, J. L.

    2013-01-01

    GRB 130427A occurred in a relatively nearby galaxy; its prompt emission had the largest GRB fluence ever recorded. The afterglow of GRB 130427A was bright enough for the Nuclear Spectroscopic Telescope ARray (NuSTAR) to observe it in the 3-79 keV energy range long after its prompt emission (simil...

  15. Packaging materials for plasma sterilization with the flowing afterglow of an N2-O2 discharge: damage assessment and inactivation efficiency of enclosed bacterial spores

    Science.gov (United States)

    Levif, P.; Séguin, J.; Moisan, M.; Soum-Glaude, A.; Barbeau, J.

    2011-10-01

    In conventional sterilization methods (steam, ozone, gaseous chemicals), after their proper cleaning, medical devices are wrapped/enclosed in adequate packaging materials, then closed/sealed before initiating the sterilization process: these packaging materials thus need to be porous. Gaseous plasma sterilization being still under development, evaluation and comparison of packaging materials have not yet been reported in the literature. To this end, we have subjected various porous packagings used with conventional sterilization systems to the N2-O2 flowing afterglow and also a non-porous one to evaluate and compare their characteristics towards the inactivation of B. atrophaeus endospores deposited on a Petri dish and enclosed in such packagings. Because the sterilization process with the N2-O2 discharge afterglow is conducted under reduced-pressure conditions, non-porous pouches can be sealed only after returning to atmospheric pressure. All the tests were therefore conducted with one end of the packaging freely opened, post-sealing being required. The features of these packaging materials, namely mass loss, resistance, toxicity to human cells as well as some characteristics specific to the plasma method used such as ultraviolet transparency, were examined before and after exposure to the flowing afterglow. All of our results show that the non-porous packaging considered is much more suitable than the conventionally used porous ones as far as ensuring an efficient and low-damage sterilization process with an N2-O2 plasma-afterglow is concerned.

  16. Attractors for a Class of Abstract Evolution Equations with Fading Memory

    Directory of Open Access Journals (Sweden)

    Xuan Wang

    2017-01-01

    Full Text Available In this paper, we study the dynamics of an abstract evolution equation with fading memory with a critical growing nonlinearity. By use of some new methods and asymptotic estimate techniques, we first verify the asymptotic compact of solution semigroup and then prove the existence of global attractors in weak topological space and strong topological space, while the forcing term only belongs to H-1(Ω or L2(Ω, respectively. The results are new and appear to be optimal.

  17. Physical Layer Security for Cooperative Relaying Over Generalized-K Fading Channels

    KAUST Repository

    Wu, Ling

    2018-02-02

    In this letter, we analyze the secrecy performance for a cooperative diversity system with amplify-and-forward (AF) over generalized-K fading channels. More specifically, some lower bounds on the secrecy performance, such as secure outage probability (SOP), average secrecy capacity (ASC), and strictly positive secrecy capacity (SPSC), are derived in closed-form. Finally, we provide simulation results to verify the accuracy of our analytical results.

  18. Cognitive Forwarding Control in Wireless Ad-Hoc Networks with Slow Fading Channels

    OpenAIRE

    Hakami, Vesal; Dehghan, Mehdi

    2014-01-01

    We propose a decentralized stochastic control solution for the broadcast message dissemination problem in wireless ad hoc networks with slow fading channels. We formulate the control problem as a dynamic robust game which is well justified by two key observations; first, the shared nature of the wireless medium which inevitably cross-couples the nodes' forwarding decisions, thus binding them together as strategic players; second, the stochastic dynamics associated with the link qualities whic...

  19. Performance Analysis of a Cooperative Diversity Scheme in Rician Fading Channel

    Directory of Open Access Journals (Sweden)

    P. Petrović

    2009-11-01

    Full Text Available In this paper we consider performance of a cooperative diversity scheme in Rician fading channel. The analytical results obtained in this paper will be comapred to the simulation results published previously, and it will be shown that the results are in great accordance. Besides that, the influence of the number of relay nodes on the performance of the system will be analysed.

  20. Algebraic lattice Codes achieve the capacity of the compound block-fading channel

    OpenAIRE

    Campello, A; Ling, C; Belfiore, JC

    2016-01-01

    We propose a lattice coding scheme that achieves the capacity of the compound block-fading channel. Our lattice construction exploits the multiplicative structure of number fields and their group of units to absorb ill-conditioned channel realizations. To shape the constellation, a discrete Gaussian distribution over the lattice points is applied. A by-product of our results is a refined analysis of the probability of error of the lattice Gaussian distribution in the AWGN channel.

  1. Capacity bounds for kth best path selection over generalized fading channels

    KAUST Repository

    Hanif, Muhammad Fainan

    2014-02-01

    Exact ergodic capacity calculation for fading wireless channels typically involves time-consuming numerical evaluation of infinite integrals. In this paper, lower and upper bounds on ergodic capacity for kth best path are presented. These bounds have simple analytic expressions which allow their fast evaluation. Numerical results show that the newly proposed bounds closely approximate the exact ergodic capacity for a large variety of system configurations. © 1997-2012 IEEE.

  2. Unified Importance Sampling Schemes for Efficient Simulation of Outage Capacity over Generalized Fading Channels

    KAUST Repository

    Rached, Nadhir B.

    2015-11-13

    The outage capacity (OC) is among the most important performance metrics of communication systems operating over fading channels. Of interest in the present paper is the evaluation of the OC at the output of the Equal Gain Combining (EGC) and the Maximum Ratio Combining (MRC) receivers. In this case, it can be seen that this problem turns out to be that of computing the Cumulative Distribution Function (CDF) for the sum of independent random variables. Since finding a closedform expression for the CDF of the sum distribution is out of reach for a wide class of commonly used distributions, methods based on Monte Carlo (MC) simulations take pride of price. In order to allow for the estimation of the operating range of small outage probabilities, it is of paramount importance to develop fast and efficient estimation methods as naive Monte Carlo (MC) simulations would require high computational complexity. In this line, we propose in this work two unified, yet efficient, hazard rate twisting Importance Sampling (IS) based approaches that efficiently estimate the OC of MRC or EGC diversity techniques over generalized independent fading channels. The first estimator is shown to possess the asymptotic optimality criterion and applies for arbitrary fading models, whereas the second one achieves the well-desired bounded relative error property for the majority of the well-known fading variates. Moreover, the second estimator is shown to achieve the asymptotic optimality property under the particular Log-normal environment. Some selected simulation results are finally provided in order to illustrate the substantial computational gain achieved by the proposed IS schemes over naive MC simulations.

  3. The capacity of the cascaded fading channel in the low power regime

    KAUST Repository

    Benkhelifa, Fatma

    2014-04-01

    In this paper, we present a simple way to compute the ergodic capacity of cascaded channels with perfect channel state information at both the transmitter and the receiver. We apply our generic results to the Rayleigh-double fading channel, and to the free-space optical channel in the presence of pointing errors and we express their low signal-to-noise ratio capacities. We mainly focus on the low signal-to-noise ratio range.

  4. FCT and Delay Fading for Elopement with a Child with Autism

    OpenAIRE

    Stevenson, Maria T.; Ghezzi, Patrick M.; Valenton, Kymmo G.

    2015-01-01

    Nearly half of children with autism have eloped from their caregivers. In assessing elopement, the initial functional analytic results of this case study found positive reinforcement in the form of attention and access to tangibles were the maintaining variables. Functional communication training (FCT) in combination with delay fading was utilized to increase communication and decrease elopement. Results indicated that communication was consistent, elopement remained low, and the child learne...

  5. Analytical evaluation of adaptive-modulation-based opportunistic cognitive radio in nakagami-m fading channels

    KAUST Repository

    Chen, Yunfei

    2012-09-01

    The performance of adaptive modulation for cognitive radio with opportunistic access is analyzed by considering the effects of spectrum sensing, primary user (PU) traffic, and time delay for Nakagami- m fading channels. Both the adaptive continuous rate scheme and the adaptive discrete rate scheme are considered. Numerical examples are presented to quantify the effects of spectrum sensing, PU traffic, and time delay for different system parameters. © 1967-2012 IEEE.

  6. Design of a 40/50 GHz satellite ground station for fade mitigation experiments

    Science.gov (United States)

    Koudelka, O.; Schmidt, M.; Ebert, J.

    2013-05-01

    Due to the increasing demand in satellite capacity, driven by applications such as high-definition television (HDTV), 3D-TV and interactive broadband services, higher frequency bands will have to be exploited. The capacity on Ku-band is already becoming scarce and Ka-band systems are more commonly used. It can be expected that 40 and 50 GHz (Q and V band) will have to be used in the future. At these frequencies the wave propagation effects have a significant impact on the performance. The traditional approach of implementing large fade margins in the system design is not suitable as it leads to expensive ground terminals. Fade mitigation by adaptive coding and modulation (ACM) is a cost-efficient method. To investigate the Q/V-band for future commercial exploitation, ESA's ALPHASAT satellite will provide experimental payloads for communications and wave propagation experiments. In Graz a Q/V-band ground station is currently under development. It will be equipped with a 3 m tracking antenna, a 50 W Klystron amplifier and a 290 K LNA. Fade mitigation experiments will be conducted, initially using DVB-S2 modems which allow to vary the modulation scheme, the Forward Error Correction code and the symbol rate under control of the ACM computer. In addition, uplink power control can be combined with the ACM methods. A specially developed signal analyser provides precise measurement of the signal/noise ratio. In addition, propagation data will be available from a beacon receiver, also developed by Joanneum Research. Important goals of the experiment are to investigate the reliability of links under realistic operating conditions using ACM and to develop efficient ACM and signal/noise ratio measurement algorithms which can be later implemented in optimised modems for Q/V-band. The paper describes the ground station design and addresses the planned fade mitigation experiments.

  7. Train of four fade in a child with stiff baby syndrome.

    LENUS (Irish Health Repository)

    Murphy, C

    2012-02-03

    A case is described of a child with stiff baby syndrome who underwent open reduction and femoral shortening of congenital dislocated hip under general anaesthesia. Neuromuscular function was measured electromyographically and demonstrated a great degree of train of four fade (57%) after sevoflurane inhalational induction of anaesthesia. The response to suxamethonium (2 mg x kg(-1)) was normal. The neuromuscular response to volatile anaesthetic agents and suxamethonium may be abnormal in these children with stiff baby syndrome and intraoperative neuromuscular monitoring is recommended.

  8. Apparatus and Method for Elimination of Polarization-Induced Fading in Fiber-optic Sensor System

    Science.gov (United States)

    Chan, Hon Man (Inventor); Parker, Jr., Allen R. (Inventor)

    2015-01-01

    The invention is an apparatus and method of eliminating polarization-induced fading in interferometric fiber-optic sensor system having a wavelength-swept laser optical signal. The interferometric return signal from the sensor arms are combined and provided to a multi-optical path detector assembly and ultimately to a data acquisition and processing unit by way of a switch that is time synchronized with the laser scan sweep cycle.

  9. A note on Cattaneo-Hristov model with non-singular fading memory

    Directory of Open Access Journals (Sweden)

    Alkahtani Badr Saad T.

    2017-01-01

    Full Text Available Using the new trend of fractional differentiation based on the concept of exponential decay law, the Cattaneo model of diffusion in elastic medium was extended by Hristov. This model displays more physical properties than the first version. However no solution of this new equation is suggested in the literature. Therefore, this paper is devoted to the analysis of numerical solution of the Cattaneo-Hristov model with non-singular fading memory.

  10. Advanced Communications Technology Satellite (ACTS) Fade Compensation Protocol Impact on Very Small-Aperture Terminal Bit Error Rate Performance

    Science.gov (United States)

    Cox, Christina B.; Coney, Thom A.

    1999-01-01

    The Advanced Communications Technology Satellite (ACTS) communications system operates at Ka band. ACTS uses an adaptive rain fade compensation protocol to reduce the impact of signal attenuation resulting from propagation effects. The purpose of this paper is to present the results of an analysis characterizing the improvement in VSAT performance provided by this protocol. The metric for performance is VSAT bit error rate (BER) availability. The acceptable availability defined by communication system design specifications is 99.5% for a BER of 5E-7 or better. VSAT BER availabilities with and without rain fade compensation are presented. A comparison shows the improvement in BER availability realized with rain fade compensation. Results are presented for an eight-month period and for 24 months spread over a three-year period. The two time periods represent two different configurations of the fade compensation protocol. Index Terms-Adaptive coding, attenuation, propagation, rain, satellite communication, satellites.

  11. Error Rates of M-PAM and M-QAM in Generalized Fading and Generalized Gaussian Noise Environments

    KAUST Repository

    Soury, Hamza

    2013-07-01

    This letter investigates the average symbol error probability (ASEP) of pulse amplitude modulation and quadrature amplitude modulation coherent signaling over flat fading channels subject to additive white generalized Gaussian noise. The new ASEP results are derived in a generic closed-form in terms of the Fox H function and the bivariate Fox H function for the extended generalized-K fading case. The utility of this new general closed-form is that it includes some special fading distributions, like the Generalized-K, Nakagami-m, and Rayleigh fading and special noise distributions such as Gaussian and Laplacian. Some of these special cases are also treated and are shown to yield simplified results.

  12. On the capacity of nakagami-m fading Channels with full channel state information at low SNR

    KAUST Repository

    Rezki, Zouheir

    2012-06-01

    The capacity of flat Rayleigh fading channels with full channel state information (CSI) at the transmitter and at the receiver at asymptotically low SNR has been recently shown to scale essentially as SNR log(1/SNR)}. In this paper, we investigate the Nakagami-m fading channel capacity with full CSI, and show that the capacity of this channel scales essentially as m/ Omega SNR log(1/SNR), where m is the Nakagami-m fading parameter and where Ω is the channel mean-square. We also show that one-bit CSI at the transmitter is enough to achieve this asymptotic capacity using an On-Off power control scheme. Our framework may be seen as a generalization of previous works as it captures the Rayleigh fading channel as a special case by taking m=1. © 2012 IEEE.

  13. On the low SNR capacity of MIMO fading channels with imperfect channel state information

    KAUST Repository

    Benkhelifa, Fatma

    2014-05-01

    The capacity of Multiple Input Multiple Output (MIMO) Rayleigh fading channels with full knowledge of channel state information (CSI) at both the transmitter and the receiver (CSI-TR) has been shown recently to scale at low Signal-to-Noise Ratio (SNR) essentially as SNR log(1=SNR), independently of the number of transmit and receive antennas. In this paper, we investigate the ergodic capacity of MIMO Rayleigh fading channel with estimated channel state information at the transmitter (CSI-T) and possibly imperfect channel state information at the receiver (CSI-R). Our framework can be seen as a generalization of previous works as it can capture the perfect CSI-TR as a special case when the estimation error variance goes to zero. In our work, we mainly focus on the low SNR regime and we show that the capacity scales as (1-α) SNR log(1=SNR), where α is the estimation error variance. This characterization shows the loss of performance due to error estimation over the perfect channel state information at both the transmitter and the receiver. As a by-product of our new analysis, we show that our framework can also be extended to characterize the capacity of MIMO Rician fading channels at low SNR with possibly imperfect CSI-T and CSI-R. © 2014 IFIP.

  14. Performance Analysis of SSC Diversity Receivers over Correlated Ricean Fading Satellite Channels

    Directory of Open Access Journals (Sweden)

    Petros S. Bithas

    2007-05-01

    Full Text Available This paper studies the performance of switch and stay combining (SSC diversity receivers operating over correlated Ricean fading satellite channels. Using an infinite series representation for the bivariate Ricean probability density function (PDF, the PDF of the SSC output signal-to-noise ratio (SNR is derived. Capitalizing on this PDF, analytical expressions for the corresponding cumulative distribution function (CDF, the moments of the output SNR, the moments generating function (MGF, and the average channel capacity (CC are derived. Furthermore, by considering several families of modulated signals, analytical expressions for the average symbol error probability (ASEP for the diversity receivers under consideration are obtained. The theoretical analysis is accompanied by representative performance evaluation results, including average output SNR (ASNR, amount of fading (AoF, outage probability (Pout, average bit error probability (ABEP, and average CC, which have been obtained by numerical techniques. The validity of some of these performance evaluation results has been verified by comparing them with previously known results obtained for uncorrelated Ricean fading channels.

  15. Faded-example as a Tool to Acquire and Automate Mathematics Knowledge

    Science.gov (United States)

    Retnowati, E.

    2017-04-01

    Students themselves accomplish Knowledge acquisition and automation. The teacher plays a role as the facilitator by creating mathematics tasks that assist students in building knowledge efficiently and effectively. Cognitive load caused by learning material presented by teachers should be considered as a critical factor. While the intrinsic cognitive load is related to the degree of complexity of the material learning ones can handle, the extraneous cognitive load is directly caused by how the material is presented. Strategies to present a learning material in computational learning domains like mathematics are a namely worked example (fully-guided task) or problem-solving (discovery task with no guidance). According to the empirical evidence, learning based on problem-solving may cause high-extraneous cognitive load for students who have limited prior knowledge, conversely learn based on worked example may cause high-extraneous cognitive load for students who have mastered the knowledge base. An alternative is a faded example consisting of the partly-completed task. Learning from faded-example can facilitate students who already acquire some knowledge about the to-be-learned material but still need more practice to automate the knowledge further. This instructional strategy provides a smooth transition from a fully-guided into an independent problem solver. Designs of faded examples for learning trigonometry are discussed.

  16. Energy Efficient Power Allocation for Distributed Antenna System over Shadowed Nakagami Fading Channel

    Directory of Open Access Journals (Sweden)

    Ying Wang

    2015-12-01

    Full Text Available In this paper, the energy efficiency (EE of downlink distributed antenna system (DAS with multiple receive antennas is investigated over composite fading channel that takes the path loss, shadow fading and Nakagami-m fading into account. Our aim is to maximize EE which is defined as the ratio of the transmission rate to the total consumed power under the constraints of maximum transmit power of each remote antenna. According to the definition of EE and using the upper bound of average EE, the optimized objective function is provided. Based on this, utilizing Karush-Kuhn-Tucker (KKT conditions and mathematical derivation, a suboptimal energy efficient power allocation (PA scheme is developed, and closed-form PA coefficients are obtained. The developed scheme has the EE performance close to the existing optimal scheme. Moreover, it has relatively lower complexity than the existing scheme because only the statistic channel information and less iteration are required. Besides, it includes the scheme in composite Rayleigh channel as a special case. Simulation results show the effectiveness of the developed scheme.

  17. Adaptive Estimation of Multiple Fading Factors for GPS/INS Integrated Navigation Systems

    Directory of Open Access Journals (Sweden)

    Chen Jiang

    2017-06-01

    Full Text Available The Kalman filter has been widely applied in the field of dynamic navigation and positioning. However, its performance will be degraded in the presence of significant model errors and uncertain interferences. In the literature, the fading filter was proposed to control the influences of the model errors, and the H-infinity filter can be adopted to address the uncertainties by minimizing the estimation error in the worst case. In this paper, a new multiple fading factor, suitable for the Global Positioning System (GPS and the Inertial Navigation System (INS integrated navigation system, is proposed based on the optimization of the filter, and a comprehensive filtering algorithm is constructed by integrating the advantages of the H-infinity filter and the proposed multiple fading filter. Measurement data of the GPS/INS integrated navigation system are collected under actual conditions. Stability and robustness of the proposed filtering algorithm are tested with various experiments and contrastive analysis are performed with the measurement data. Results demonstrate that both the filter divergence and the influences of outliers are restrained effectively with the proposed filtering algorithm, and precision of the filtering results are improved simultaneously.

  18. Analisis Unjuk Kerja Convolutional Code pada Sistem MIMO MC-DSSS Melalui Kanal Rayleigh Fading

    Directory of Open Access Journals (Sweden)

    Kadek Agus Mahabojana Dwi Prayoga

    2017-08-01

    Full Text Available Kombinasi antara sistem MIMO (multiple input multiple output, OFDM (orthogonal frequency division multiplexing, dan spread spectrum serta adanya teknik pengkodean kanal mampu mengurangi efek fading dan error yang terjadi. Penelitian ini bertujuan untuk mengetahui perbandingan performansi dari sistem MIMO MC-DSSS (multi carrier-direct sequence spread spectrum Uncoded atau tanpa pengkodean kanal dan MIMO MC-DSSS Convolutional Code atau dengan pengkodean kanal Convolutional yang melalui kanal Rayleigh Fading, ditinjau dari nilai dan grafik BER (bit error rate berbanding Eb/No (energy per bit to noise power spectral density ratio. Penelitian ini menggunakan metode simulasi dengan menggunakan program Matlab R2015a. Hasil dari simulasi didapat unjuk kerja sistem MIMO MC-DSSS dengan Convolutional Code memiliki hasil yang lebih baik dari MIMO MC-DSSS. Pada kanal transmisi Rayleigh Fading untuk mencapi nilai BER sebesar 10-3 pada sistem MIMO MC-DSSS dengan Convolutional Code dibutuhkan Eb/No sebesar -7 dB. Sedangkan pada sistem MIMO MC-DSSS dibutuhkan Eb/No sebesar -3 dB.[turnitin 20%, 7-11-2016

  19. Efficient Cooperative Protocols for Full-Duplex Relaying over Nakagami-m Fading Channels

    KAUST Repository

    Khafagy, Mohammad Galal

    2015-02-24

    In this work, efficient protocols are studied for full-duplex relaying (FDR) with loopback interference over Nakagami-m block fading channels. Recently, a selective decodeand- forward (DF) protocol was proposed for FDR, and was shown to outperform existing protocols in terms of outage over Rayleigh-fading channels. In this work, we propose an incremental selective DF protocol that offers additional power savings, yet yields the same outage performance. We evaluate their outage performance over independent non-identically distributed Nakagami-m fading links, and study their relative performance in terms of the signal-to-noise ratio cumulative distribution function via closed-form expressions. The offered diversity gain is also derived. In addition, we study their performance relative to their half-duplex counterparts, as well as known non-selective FDR protocols. We corroborate our theoretical results with simulation, and confirm that selective cooperation protocols outperform the known non-selective protocols in terms of outage. Finally, we show that depending on the loopback interference level, the proposed protocols can outperform their half-duplex counterparts when high spectral efficiencies are targeted.

  20. On the low SNR capacity of MIMO fading channels with imperfect channel state information

    KAUST Repository

    Benkhelifa, Fatma

    2014-06-01

    The capacity of multiple-input multiple-output (MIMO) Rayleigh fading channels with full knowledge of channel state information (CSI) at both the transmitter and the receiver (CSI-TR) has been shown recently to scale at low signal-to-noise ratio (SNR) essentially as SNR log(1/SNR), independently of the number of transmit and receive antennas. In this paper, we investigate the ergodic capacity of MIMO Rayleigh fading channel with estimated channel state information at the transmitter (CSI-T) and possibly imperfect channel state information at the receiver (CSI-R). Our framework can be seen as a generalization of previous works as it can capture the perfect CSI-TR as a special case when the estimation error variance goes to zero. In this paper, we mainly focus on the low SNR regime, and we show that the capacity scales as (1-α) SNR log(1/SNR), where α is the estimation error variance. This characterization shows the loss of performance due to error estimation over the perfect channel state information at both the transmitter and the receiver. As a by-product of our new analysis, we show that our framework can be also extended to characterize the capacity of MIMO Rician fading channels at low SNR with possibly imperfect CSI-T and CSI-R. © 1972-2012 IEEE.

  1. On the capacity of multiaccess fading channels with full channel state information at low power regime

    KAUST Repository

    Rezki, Zouheir

    2013-06-01

    We study the throughput capacity region of the Gaussian multiaccess (MAC) fading channel with perfect channel state information (CSI) at the receiver (CSI-R) and at the transmitters (CSI-T), at low power regime. We show that it has a multidimensional rectangle structure and thus is simply characterized by single user capacity points. More specifically, we show that at low power regime, the boundary surface of the capacity region shrinks to a single point corresponding to the sum rate maximizer and that the coordinates of this point coincide with single user capacity bounds. Inspired from this result, we propose an on-off scheme, compute its achievable rate, and provide a necessary condition on the fading channels under which this scheme achieves single user capacity bounds of the MAC channel at asymptotically low power regime. We argue that this necessary condition characterizes a class of fading that encompasses all known wireless channels, where the capacity region of the MAC channel has a simple expression in terms of users\\' average power constraints only. © 2013 IEEE.

  2. Achievable rate of spectrum sharing cognitive radio systems over fading channels at low-power regime

    KAUST Repository

    Sboui, Lokman

    2014-11-01

    We study the achievable rate of cognitive radio (CR) spectrum sharing systems at the low-power regime for general fading channels and then for Nakagami fading. We formally define the low-power regime and present the corresponding closed-form expressions of the achievable rate lower bound under various types of interference and/or power constraints, depending on the available channel state information of the cross link (CL) between the secondary-user transmitter and the primary-user receiver. We explicitly characterize two regimes where either the interference constraint or the power constraint dictates the optimal power profile. Our framework also highlights the effects of different fading parameters on the secondary link (SL) ergodic achievable rate. We also study more realistic scenarios when there is either 1-bit quantized channel feedback from the CL alone or 2-bit feedback from both the CL and the SL and propose simple power control schemes and show that these schemes achieve the previously achieved rate at the low-power regime. Interestingly, we show that the low-power regime analysis provides a specific insight into the maximum achievable rate behavior of CR that has not been reported by previous studies.

  3. A Greedy Algorithm of Data-Dependent User Selection for Fast Fading Gaussian Vector Broadcast Channels

    CERN Document Server

    Takeuchi, Keigo

    2012-01-01

    User selection (US) with Zero-forcing beamforming (ZF-BF) is considered in fast fading Gaussian vector broadcast channels (VBCs) with perfect channel state information (CSI) at the transmitter. A novel criterion for US is proposed, which depends on both CSI and the data symbols, while the conventional criteria only depend on CSI. Since the optimization of US based on the proposed criterion is infeasible, a greedy algorithm of data-dependent US is proposed to perform the optimization approximately. An overhead issue arises in fast fading channels: On every update of US, the transmitter may inform each user whether he/she has been selected, using a certain fraction of resources. This overhead results in a significant rate loss for fast fading channels. In order to circumvent this overhead issue, iterative detection and decoding schemes are derived on the basis of belief propagation (BP). The proposed iterative schemes require no information about whether each user has been selected. The proposed US scheme is co...

  4. Outage Analysis of low-latency cooperative wireless networks with threshold-based protocol over composite fading

    OpenAIRE

    Zdravkovic, Nemanja

    2017-01-01

    This paper studies a low-latency decode-and-forward cooperative wireless network subject to composite fading. Assuming temporally correlated channel between cooperating nodes and maximal ratio combining at the destination, outage probability(OP)performance is investigated and novel OP expressions are derived when nodes apply a threshold-based protocol for internode communication. The effects of network dimension, multipath fading and shadowing severity parameters, ...

  5. Concentration dependence of fading of the open form of 6’-nitroindolinospiropyran in a polymer matrix

    OpenAIRE

    Drabe, Karel E.; Boer, Steven de; Wiersma, Douwe A.

    1991-01-01

    The concentration dependence of the fading process of the open form of 6’-nitroindolinospiropyran (BIPS) in PMMA has been studied by fluorescence lifetime measurements at 77 K. At sufficiently high concentrations, the fluorescence decay becomes bi-exponential which indicates that energy transfer occurs to molecules absorbing at longer wavelengths. This leads to a blue-shift of the absorption maximum during the fading process. The retardation of the decolouration of BIPS with increasing concen...

  6. Classification, Follow-Up, and Analysis of Gamma-Ray Bursts and their Early-Time Near-Infrared/Optical Afterglows

    Science.gov (United States)

    Morgan, Adam Nolan

    In the study of astronomical transients, deriving knowledge from discovery is a multifaceted process that includes real-time classification to identify new events of interest, deep, multi-wavelength follow-up of individual events, and the global analysis of multi-event catalogs. Here we present a body of work encompassing each of these steps as applied to the study of gamma-ray bursts (GRBs). First, we present our work on utilizing machine-learning algorithms on early-time metrics from the Swift satellite to inform the resource allocation of follow-up telescopes in order to optimize time spent on high-redshift GRB candidates. Next, we show broadband observations and analysis of the early-time afterglow of GRB 120119A, utilizing data obtained with a dozen telescope facilities both in space and on the ground. This event exhibits extreme red-to-blue color change in the first few minutes after the trigger at levels unseen in prior afterglows, and our model fits of this phenomenon reveal the best support yet for the direct detection of dust destruction in the local environment of a GRB. Finally, we present results from the PAIRITEL early-time near-infrared (NIR) afterglow catalog. The 1.3 meter PAIRITEL has autonomously observed 14 GRBs in under 3 minutes after the burst, yielding a homogenous sample of early-time JHKs light curves. Our analysis of these events provides constraints on the early-time NIR GRB afterglow luminosity function and gives insight into the importance of dust extinction in the suppression of some optical afterglows.

  7. Multipath fading analysis of telemetry signals power fluctuations from Universitetsky microsatellite

    Science.gov (United States)

    Shakhparonov, Vladimir; Millán Adán, Espinoza; Vicente Vivas, Esaú

    2012-03-01

    The article deals with the results of the fading fluctuations analysis for telemetry signals in the 2 m and 70 cm bands from the first Moscow State University microsatellite better known as "Universitetsky". Radio telemetry signals were received from the microsatellite for around 2 years, collecting and recording the power signal data of almost 7500 satellite overpasses. The received signals from about 2300 satellite overpasses had a very low signal to noise ratio (SNR) that caused high transmission losses. The rest of the signals had a SNR high enough to complete the transmission without losses. The main objective of this paper was to find the fading fluctuations caused both by diffusion and by the presence of Gaussian and non Gaussian noise in telemetry signal power data. The purpose was both to characterize the communication channel as well as to elaborate solutions both to improve the communication quality as well as to identify no homogeneous zones in the ionosphere environment. The signal power analysis was based in the observation of statistical characteristics from different power signal components, in particular the components influenced by diffusion and non Gaussian noise. The employed methodology follows the next steps: removing the power signal envelope; taking away the Gaussian noise; obtaining the statistical characteristics from non Gaussian noise, Gaussian noise and envelope; finally identifying the LOS and NLOS signal fading components. For this purpose, the wavelet technique was used to perform the signal decomposition. In particular, the discrete wavelet transform DWT was utilized to carry out the signal de-noising. Then, the results were statistically treated in order to obtain a diffusion index for Rician fading, which are associated with fading in atmosphere and ionosphere layers. In this way the communications channel among satellite and ground station was characterized and a BER parameter was obtained for every satellite overpass, which

  8. Jovian temperature and cloud variability during the 2009-2010 fade of the South Equatorial Belt

    Science.gov (United States)

    Fletcher, Leigh N.; Orton, G. S.; Rogers, J. H.; Simon-Miller, A. A.; de Pater, I.; Wong, M. H.; Mousis, O.; Irwin, P. G. J.; Jacquesson, M.; Yanamandra-Fisher, P. A.

    2011-06-01

    Mid-infrared 7-20 μm imaging of Jupiter from ESO's Very Large Telescope (VLT/VISIR) demonstrate that the increased albedo of Jupiter's South Equatorial Belt (SEB) during the 'fade' (whitening) event of 2009-2010 was correlated with changes to atmospheric temperature and aerosol opacity. The opacity of the tropospheric condensation cloud deck at pressures less than 800 mbar increased by 80% between May 2008 and July 2010, making the SEB (7-17°S) as opaque in the thermal infrared as the adjacent equatorial zone. After the cessation of discrete convective activity within the SEB in May 2009, a cool band of high aerosol opacity (the SEB zone at 11-15°S) was observed separating the cloud-free northern and southern SEB components. The cooling of the SEBZ (with peak-to-peak contrasts of 1.0 ± 0.5 K), as well as the increased aerosol opacity at 4.8 and 8.6 μm, preceded the visible whitening of the belt by several months. A chain of five warm, cloud-free 'brown barges' (subsiding airmasses) were observed regularly in the SEB between June 2009 and June 2010, by which time they too had been obscured by the enhanced aerosol opacity of the SEB, although the underlying warm circulation was still present in July 2010. Upper tropospheric temperatures (150-300 mbar) remained largely unchanged during the fade, but the cool SEBZ formation was detected at deeper levels ( p > 300 mbar) within the convectively-unstable region of the troposphere. The SEBZ formation caused the meridional temperature gradient of the SEB to decrease between 2008 and 2010, reducing the vertical thermal windshear on the zonal jets bounding the SEB. The southern SEB had fully faded by July 2010 and was characterised by short-wave undulations at 19-20°S. The northern SEB persisted as a narrow grey lane of cloud-free conditions throughout the fade process. The cool temperatures and enhanced aerosol opacity of the SEBZ after July 2009 are consistent with an upward flux of volatiles (e.g., ammonia-laden air

  9. Study on the Effect of Calcium and Potassium Spray on Date Bunch Fading Disorder

    Directory of Open Access Journals (Sweden)

    Hosein Shekofteh

    2017-02-01

    Full Text Available Introduction: Date bunch fading disorder has been one of the most important problems, which caused economic damage to date plantation area of Iran. It has been first reported on Mozafti cultivar in Kahnuj area, Kerman province. It has often been observed on soft and mid ripening cultivars such as Mozafti, Mordaseng and Kalote. Furthermore, it usually appears on Mozafti cultivar when fruits change from Khalal to Rutab stage. The most important symptoms of this disorder are sudden wilting of fruits and necrotic strips on the upper surface of the main bunch stalk. Incidence and development of these symptoms increase by high temperature, low relative humidity, and hot and dry wind. Several research studies have been carried out on this disorder so far, but the only research about the effect of nutrition on disorder was performed by Rosta (2003. The aim of the present study was to investigate the effect of calcium and potassium spray on date bunch fading and some traits of date fruit in Rigan region, Kerman province. Materials and Methods: The experiment was conducted based on randomized complete block designs with three replicates in Rigan located in east south of Kerman province, Iran, in 2012. Treatments were: T1: control, T2: spray of calcium nitrate at the concentration of 5 ppm, T3: spray of potassium sulfate at the concentration of 5 ppm, and T4: combined spray of calcium nitrate and potassium sulfate at the concentration of 5 ppm. Treatments were applied at Kimri, Hobabok and Khalal stages. Sampling was performed from 3 date palms (3 bunches from each date palm were selected randomly at the second date harvest. Totally, the traits of 200 fruits were measured in each date palm. The traits measured in the present study were: fruit length, fruit diameter, fruit weight, stone weight, stone diameter, and bunch fading percentage. Results and Discussions: According to the data of variance analysis, treatments had a significant effect on wet fruit

  10. Production of Highly Charged Heavy Ions by means of a Hybrid Source in Dc mode and in Afterglow Mode

    Science.gov (United States)

    Gammino, S.; Ciavola, G.; Torrisi, L.; Andò, L.; Celona, L.; Presti, M.; Manciagli, S.; Picciotto, A.; Mezzasalma, A. M.; Krása, J.; Láska, L.; Pfeifer, M.; Wolowski, J.; Woryna, E.; Parys, P.; Shirkov, G. D.; Hitz, D.

    2005-03-01

    The ECLISSE experiment has been carried out by coupling a Laser Ion Source (based on a Nd:YAG laser (0.9 J / 9 ns, laser power densities metal samples without the use of ovens or sputtering technics were obtained in a variety of experimental conditions. The maximum charge states obtained from the ECRIS were 38+ for Ta and 41+ for Au. The peak current was obtained for 25+ and 29+ respectively and it was in the order of some tens of μA. In this work the analysis of some preliminary results obtained in afterglow mode will be also presented. We employed microwave pulse (length 4 msec) and laser pulse (length 9 nsec) with the same frequency (30 Hz) and variable relative phase. For appropriate phase values, a current enhancement of about one order of magnitude was observed.

  11. Computational study of the afterglow in single and sequential pulsing of an atmospheric-pressure plasma jet

    Science.gov (United States)

    Hasan, M. I.; Bradley, J. W.

    2015-10-01

    The spatial distribution of charged species in the afterglow of a helium plasma jet impinging atmospheric air has been computed using a 2D axisymmetric fluid model. The model is solved for two consecutive pulse periods of a rectangular voltage waveform (duration of 60 ns) and for two different frequencies (25 and 50 kHz). The most abundant ionic species in the afterglow are found to be \\text{O}2+ and \\text{O}2- with their concentrations increasing by about an order of magnitude (up to about 1018 m-3 and 1017 m-3 respectively) in the initial 1 μs. In the first pulse, these species form a halo around the diffusing He+ and electron rich central channel, the shape of the former being strongly correlated with the shape of He-air mixing layer computed using a hydrodynamic model. In the next pulse, this general configuration is also observed; however \\text{O}2+ is more concentrated on the axis of the jet, this being due to influence of residual electrons in the central channel. For \\text{O}2- there is little difference in their spatial distribution compared to the initial pulse. For higher frequency pulsing, the higher concentration of residual electrons lowers the necessary ignition electric field reducing the concentrations (by 25%) of charged species in a period of the applied waveform. This work provides new information on the concentration and distribution of ionic species generated by atmospheric-pressure capillary discharges of interest to those developing such sources for range of applications, particularly in the field of plasma medicine.

  12. Relativistic simulations of long-lived reverse shocks in stratified ejecta: the origin of flares in GRB afterglows

    Science.gov (United States)

    Lamberts, A.; Daigne, F.

    2018-02-01

    The X-ray light curves of the early afterglow phase from gamma-ray bursts (GRBs) present a puzzling variability, including flares. The origin of these flares is still debated, and often associated with a late activity of the central engine. We discuss an alternative scenario where the central engine remains short-lived and flares are produced by the propagation of a long-lived reverse shock in a stratified ejecta. Here we focus on the hydrodynamics of the shock interactions. We perform one-dimensional ultrarelativistic hydrodynamic simulations with different initial internal structure in the GRB ejecta. We use them to extract bolometric light curves and compare with a previous study based on a simplified ballistic model. We find a good agreement between both approaches, with similar slopes and variability in the light curves, but identify several weaknesses in the ballistic model: the density is underestimated in the shocked regions, and more importantly, late shock reflections are not captured. With accurate dynamics provided by our hydrodynamic simulations, we confirm that internal shocks in the ejecta lead to the formation of dense shells. The interaction of the long-lived reverse shock with a dense shell then produces a fast and intense increase of the dissipated power. Assuming that the emission is due to the synchrotron radiation from shock-accelerated electrons, and that the external forward shock is radiatively inefficient, we find that this results in a bright flare in the X-ray light curve, with arrival times, shapes, and duration in agreement with the observed properties of X-ray flares in GRB afterglows.

  13. Inactivation of Candida glabrata by a humid DC argon discharge afterglow: dominant contributions of short-lived aqueous active species

    Science.gov (United States)

    Xiong, Qing; Liu, Hongbin; Lu, Weiping; Chen, Qiang; Xu, Le; Wang, Xia; Zhu, Qunlin; Zeng, Xue; Yi, Ping

    2017-05-01

    Plasma medicine applications are currently attracting significant interest all over the world. Bactericidal treatments of Candida glabrata cultured in saline suspension are performed in this study by a room-temperature reactive afterglow of a DC-driven argon discharge. Water vapor was added to the discharge to study the inactivation contributions of reactive hydrolytic species including OH and H2O2 transporting along the gas flow to the treated solutions. The inactivation results indicate that the dominant roles in the bactericidal treatments are played by the short-lived aqueous active species, but not the stable species like H2O2aq (aq indicates an aqueous species). Further analysis shows that the ·OHaq radicals play an important role in the inactivation process. The ·OHaq radicals in the suspension are mostly produced from the direct dissolution of the OH species in the reactive afterglow. With the increase of added water vapor content, the ·OHaq production increases and enhances the inactivation efficiency of C. glabrata. Furthermore, it is found that the ambient air diffusion shows essential effects on the bactericidal activity of the remote humid argon discharge. Higher bactericidal effects can be obtained in open-space treatments compared to in a controlled Ar + H2O gas atmosphere. Key active air-byproduct species are believed to be generated in the suspension during the treatments and contributing to the inactivation process. Based on chemical analysis, the peroxynitrous acid ONOOHaq is considered as the key antimicrobial air-byproduct species. These results indicate the important dependence of plasma biomedical effects on the processing environment, which finally relates to the critical contributions of the key reactive species formed therein.

  14. A performance study of two hop transmission in mixed underlay RF and FSO fading channels

    KAUST Repository

    Ansari, Imran Shafique

    2014-04-01

    In this work, we present the performance analysis of a dual-hop transmission system composed of asymmetric radio frequency (RF) and free-space optical (FSO) links in underlay cognitive networks. For the RF link, we consider an underlay cognitive network where the secondary users share the spectrum with licensed primary users, where indoor femtocells act as a practical example for such networks. More specifically, we assume that the RF link is subject to an interference constraint. The FSO link accounts for pointing errors and both types of detection techniques (i.e. intensity modulation/direct detection (IM/DD) as well as heterodyne detection). On the other hand, RF link is modeled by the Rayleigh fading distribution that applies power control to maintain the interference at the primary network below a specific threshold whereas the FSO link is modeled by a unified Gamma-Gamma fading distribution. With this model, we derive new exact closed-form expressions for the cumulative distribution function, the probability density function, the moment generating function, and the moments of the end-to-end signal-to-interference plus noise ratio of these systems in terms of the Meijer\\'s G functions. We then capitalize on these results to offer new exact closed-form expressions for the outage probability, the higher-order amount of fading, and the average error rate for binary and Mary modulation schemes, all in terms of Meijer\\'s G functions. All our new analytical results are verified via computer-based Monte-Carlo simulations and are illustrated by some selected numerical results.

  15. System Performance of Concatenated STBC and Block Turbo Codes in Dispersive Fading Channels

    Directory of Open Access Journals (Sweden)

    Kam Tai Chan

    2005-05-01

    Full Text Available A new scheme of concatenating the block turbo code (BTC with the space-time block code (STBC for an OFDM system in dispersive fading channels is investigated in this paper. The good error correcting capability of BTC and the large diversity gain characteristics of STBC can be achieved simultaneously. The resulting receiver outperforms the iterative convolutional Turbo receiver with maximum- a-posteriori-probability expectation maximization (MAP-EM algorithm. Because of its ability to perform the encoding and decoding processes in parallel, the proposed system is easy to implement in real time.

  16. Characterization of ten microsatellite loci in midget faded rattlesnake (Crotalus oreganus concolor)

    Science.gov (United States)

    Oyler-McCance, Sara J.; Parker, Joshua M.

    2010-01-01

    Primers for 10 microsatellite loci were developed for midget faded rattlesnake (Crotalus oreganus concolor), a small bodied subspecies of the Western Rattlesnake, which is found in the Colorado Plateau of eastern Utah, western Colorado and southwestern Wyoming. In a screen of 23 individuals from the most northern portion of the subspecies range in southwestern Wyoming, the 10 loci were found to have levels of variability ranging from 4 to 11 alleles. No loci were found to be linked, although one locus revealed significant departures from Hardy–Weinberg equilibrium. These microsatellite loci will be applicable for population genetic analyses, which will ultimately aid in management efforts for this rare subspecies of rattlesnake.

  17. Characterization of microsatellite loci isolated in midget-faded rattlesnakes (Crotalus viridis concolor)

    Science.gov (United States)

    Oyler-McCance, Sara J.; St. John, J.; Parker, J.M.; Anderson, S.H.

    2005-01-01

    Primers for five polymorphic microsatellite loci were developed for the midget faded rattlesnake (Crotalus viridis concolor), a rare subspecies of western rattlesnake (Crotalus viridus) found only in parts of Wyoming, Colorado, and Utah. Five polymorphic microsatellites were isolated, four of which had relatively high levels of diversity (eight to nine alleles). We found only two departures from Hardy–Weinberg equilibrium and they occurred in different loci, so null alleles are likely not a problem. Moreover, we found that no two loci were linked. These loci will be applicable for population genetic analysis and perhaps analysis of paternity and mating systems.

  18. Low-Complexity Adaptive Channel Estimation over Multipath Rayleigh Fading Non-Stationary Channels Under CFO

    CERN Document Server

    Hadei, Sayed A

    2011-01-01

    In this paper, we propose novel low-complexity adaptive channel estimation techniques for mob ile wireless chan- n els in presence of Rayleigh fading, carrier frequency offsets (CFO) and random channel variations. We show that the selective p artial update of the estimated channel tap-weight vector offers a better trade-off between the performance and computational complexity, compared to the full update of the estimated channel tap-weight vector. We evaluate the mean-square weight error of th e proposed methods and demonstrate the usefulness of its via simulation studies.

  19. Statistical Analysis of Multipath Fading Channels Using Generalizations of Shot Noise

    Directory of Open Access Journals (Sweden)

    Djouadi SeddikM

    2008-01-01

    Full Text Available Abstract This paper provides a connection between the shot-noise analysis of Rice and the statistical analysis of multipath fading wireless channels when the received signals are a low-pass signal and a bandpass signal. Under certain conditions, explicit expressions are obtained for autocorrelation functions, power spectral densities, and moment-generating functions. In addition, a central limit theorem is derived identifying the mean and covariance of the received signals, which is a generalization of Campbell_s theorem. The results are easily applicable to transmitted signals which are random and to CDMA signals.

  20. Statistical Analysis of Multipath Fading Channels Using Generalizations of Shot Noise

    Directory of Open Access Journals (Sweden)

    Christos Kourtellaris

    2008-10-01

    Full Text Available This paper provides a connection between the shot-noise analysis of Rice and the statistical analysis of multipath fading wireless channels when the received signals are a low-pass signal and a bandpass signal. Under certain conditions, explicit expressions are obtained for autocorrelation functions, power spectral densities, and moment-generating functions. In addition, a central limit theorem is derived identifying the mean and covariance of the received signals, which is a generalization of Campbell_s theorem. The results are easily applicable to transmitted signals which are random and to CDMA signals.

  1. Effects of fading and spatial correlation on node selection for estimation in Wireless Sensor Networks

    KAUST Repository

    Al-Murad, Tamim M.

    2010-06-01

    In densely deployed sensor networks, correlation among measurements may be high. Spatial sampling through node selection is usually used to minimize this correlation and to save energy consumption. However because of the fading nature of the wireless channels, extra care should be taken when performing this sampling. In this paper, we develop expressions for the distortion which include the channel effects. The asymptotic behavior of the distortion as the number of sensors or total transmit power increase without bound is also investigated. Further, based on the channel and position information we propose and test several node selection schemes.

  2. Performance Analysis of Iterative Decoding Algorithms for PEG LDPC Codes in Nakagami Fading Channels

    Directory of Open Access Journals (Sweden)

    O. Al Rasheed

    2013-11-01

    Full Text Available In this paper we give a comparative analysis of decoding algorithms of Low Density Parity Check (LDPC codes in a channel with the Nakagami distribution of the fading envelope. We consider the Progressive Edge-Growth (PEG method and Improved PEG method for the parity check matrix construction, which can be used to avoid short girths, small trapping sets and a high level of error floor. A comparative analysis of several classes of LDPC codes in various propagation conditions and decoded using different decoding algorithms is also presented.

  3. Outage probability analysis of wireless sensor networks in the presence of channel fading and spatial correlation

    KAUST Repository

    Al-Murad, Tamim M.

    2011-07-01

    Evaluating the reliability of wireless sensor networks is becoming more important as theses networks are being used in crucial applications. The outage probability defined as the probability that the error in the system exceeds a maximum acceptable threshold has recently been used as a measure of the reliability of such systems. In this work we find the outage probability of wireless sensor network in different scenarios of distributed sensing where sensors\\' readings are affected by spatial correlation and in the presence of channel fading. © 2011 IEEE.

  4. Pure-jump processes and constitutive equations for simple thermodinamic bodies with fading memory

    Directory of Open Access Journals (Sweden)

    Adriano Montanaro

    1991-05-01

    Full Text Available Can it be useful to use discontinuous jump-processes in order to formulate a somewhat different thermodynamic theory for a general simple body with fading memory? In this communication I will present the results of paper [9], where the above question is investigated. By means of a certain well defined class of quasi-processes of local pure-jump, there I set up a thermodynamic theory T* for such a body in which only the dynamic part of entropy is assumed to exist.

  5. Performance and stochastic stability of the adaptive fading extended Kalman filter with the matrix forgetting factor

    Directory of Open Access Journals (Sweden)

    Biçer Cenker

    2016-01-01

    Full Text Available In this paper, the stability of the adaptive fading extended Kalman filter with the matrix forgetting factor when applied to the state estimation problem with noise terms in the non–linear discrete–time stochastic systems has been analysed. The analysis is conducted in a similar manner to the standard extended Kalman filter’s stability analysis based on stochastic framework. The theoretical results show that under certain conditions on the initial estimation error and the noise terms, the estimation error remains bounded and the state estimation is stable.

  6. The fading of Cassiopeia A, and improved models for the absolute spectrum of primary radio calibration sources

    Science.gov (United States)

    Trotter, A. S.; Reichart, D. E.; Egger, R. E.; Stýblová, J.; Paggen, M. L.; Martin, J. R.; Dutton, D. A.; Reichart, J. E.; Kumar, N. D.; Maples, M. P.; Barlow, B. N.; Berger, T. A.; Foster, A. C.; Frank, N. R.; Ghigo, F. D.; Haislip, J. B.; Heatherly, S. A.; Kouprianov, V. V.; LaCluyzé, A. P.; Moffett, D. A.; Moore, J. P.; Stanley, J. L.; White, S.

    2017-08-01

    Based on 5 yr of observations with the 40-foot telescope at Green Bank Observatory (GBO), Reichart & Stephens found that the radio source Cassiopeia A had either faded more slowly between the mid-1970s and late 1990s than Baars et al. had found it to be fading between the late 1940s and mid-1970s, or that it had rebrightened and then resumed fading sometime between the mid-1970s and mid-1990s, in the L band (1.4 GHz). Here, we present 15 additional years of observations of Cas A and Cyg A with the 40-foot in the L band, and three and a half additional years of observations of Cas A, Cyg A, Tau A and Vir A with GBO's recently refurbished 20-m telescope in the L and X (9 GHz) bands. We also present a more sophisticated analysis of the 40-foot data, and a reanalysis of the Baars et al. data, which reveals small, but non-negligible differences. We find that overall, between the late 1950s and late 2010s, Cas A faded at an average rate of 0.670 ± 0.019 per cent yr-1 in the L band, consistent with Reichart & Stephens. However, we also find, at the 6.3σ credible level, that it did not fade at a constant rate. Rather, Cas A faded at a faster rate through at least the late 1960s, rebrightened (or at least faded at a much slower rate), and then resumed fading at a similarly fast rate by, at most, the late 1990s. Given these differences from the original Baars et al. analysis, and given the importance of their fitted spectral and temporal models for flux-density calibration in radio astronomy, we update and improve on these models for all four of these radio sources. In doing so, we additionally find that Tau A is fading at a rate of 0.102^{+0.042}_{-0.043} per cent yr-1 in the L band.

  7. Exact Performance Analysis of Dual-Hop Semi-Blind AF Relaying over Arbitrary Nakagami-m Fading Channels

    KAUST Repository

    Xia, Minghua

    2011-10-01

    Relay transmission is promising for future wireless systems due to its significant cooperative diversity gain. The performance of dual-hop semi-blind amplify-and-forward (AF) relaying systems was extensively investigated, for transmissions over Rayleigh fading channels or Nakagami- fading channels with integer fading parameter. For the general Nakagami- fading with arbitrary values, the exact closed-form system performance analysis is more challenging. In this paper, we explicitly derive the moment generation function (MGF), probability density function (PDF) and moments of the end-to-end signal-to-noise ratio (SNR) over arbitrary Nakagami- fading channels with semi-blind AF relay. With these results, the system performance evaluation in terms of outage probability, average symbol error probability, ergodic capacity and diversity order, is conducted. The analysis developed in this paper applies to any semi-blind AF relaying systems with fixed relay gain, and two major strategies for computing the relay gain are compared in terms of system performance. All analytical results are corroborated by simulation results and they are shown to be efficient tools to evaluate system performance.

  8. On the capacity of multiple access and broadcast fading channels with full channel state information at low SNR

    KAUST Repository

    Rezki, Zouheir

    2014-01-01

    We study the throughput capacity region of the Gaussian multi-access (MAC) fading channel with perfect channel state information (CSI) at the receiver and at the transmitters, at low power regime. We show that it has a multidimensional rectangle structure and thus is simply characterized by single user capacity points.More specifically, we show that at low power regime, the boundary surface of the capacity region shrinks to a single point corresponding to the sum rate maximizer and that the coordinates of this point coincide with single user capacity bounds. Inspired from this result, we propose an on-off scheme, compute its achievable rate, and show that this scheme achieves single user capacity bounds of the MAC channel for a wide class of fading channels at asymptotically low power regime. We argue that this class of fading encompasses all known wireless channels for which the capacity region of the MAC channel has even a simpler expression in terms of users\\' average power constraints only. Using the duality of Gaussian MAC and broadcast channels (BC), we deduce a simple characterization of the BC capacity region at low power regime and show that for a class of fading channels (including Rayleigh fading), time-sharing is asymptotically optimal. © 2014 IEEE.

  9. A Power-Efficient Clustering Protocol for Coal Mine Face Monitoring with Wireless Sensor Networks Under Channel Fading Conditions.

    Science.gov (United States)

    Ren, Peng; Qian, Jiansheng

    2016-06-07

    This study proposes a novel power-efficient and anti-fading clustering based on a cross-layer that is specific to the time-varying fading characteristics of channels in the monitoring of coal mine faces with wireless sensor networks. The number of active sensor nodes and a sliding window are set up such that the optimal number of cluster heads (CHs) is selected in each round. Based on a stable expected number of CHs, we explore the channel efficiency between nodes and the base station by using a probe frame and the joint surplus energy in assessing the CH selection. Moreover, the sending power of a node in different periods is regulated by the signal fade margin method. The simulation results demonstrate that compared with several common algorithms, the power-efficient and fading-aware clustering with a cross-layer (PEAFC-CL) protocol features a stable network topology and adaptability under signal time-varying fading, which effectively prolongs the lifetime of the network and reduces network packet loss, thus making it more applicable to the complex and variable environment characteristic of a coal mine face.

  10. A Power-Efficient Clustering Protocol for Coal Mine Face Monitoring with Wireless Sensor Networks Under Channel Fading Conditions

    Directory of Open Access Journals (Sweden)

    Peng Ren

    2016-06-01

    Full Text Available This study proposes a novel power-efficient and anti-fading clustering based on a cross-layer that is specific to the time-varying fading characteristics of channels in the monitoring of coal mine faces with wireless sensor networks. The number of active sensor nodes and a sliding window are set up such that the optimal number of cluster heads (CHs is selected in each round. Based on a stable expected number of CHs, we explore the channel efficiency between nodes and the base station by using a probe frame and the joint surplus energy in assessing the CH selection. Moreover, the sending power of a node in different periods is regulated by the signal fade margin method. The simulation results demonstrate that compared with several common algorithms, the power-efficient and fading-aware clustering with a cross-layer (PEAFC-CL protocol features a stable network topology and adaptability under signal time-varying fading, which effectively prolongs the lifetime of the network and reduces network packet loss, thus making it more applicable to the complex and variable environment characteristic of a coal mine face.

  11. A strong test for the forward shock model in GRBs: the 90 Ms follow up of the X-ray afterglow of GRB 130427A.

    Science.gov (United States)

    De Pasquale, M.; Page, M.; Kann, D.; Oates, S.; Schulze, S.; Zhang, B.; Cano, Z.; Malesani, D.; Troja, E.; Piro, L.

    2017-10-01

    GRB 130427A was the brightest gamma-ray burst detected in 30 years. With an isotropic energy output of 8.5×10^{53} erg and redshift of 0.34, it combined a very high energy release with a relative proximity to Earth in an unprecedented fashion. Sensitive X-ray observatories such as XMM-Newton and Chandra have detected the afterglow of this event for a record-breaking baseline of 90 million seconds. The light curve shows a simple power-law decay over more than three decades in time. In this presentation, we explore the consequences of this result for the scenarios proposed to interpret GRB 130427A, the implication of this outcome in the context of the forward shock model (beaming angle, energetics, surrounding medium), and the scientific prospects of extending GRB afterglow observations for several hundreds of Ms with Athena.

  12. Optical diagnostics and mass spectrometry on the afterglow of an atmospheric pressure Ar/O$_2$ radiofrequency plasma used for polymer surface treatment

    CERN Document Server

    Duluard, Corinne Y; Hubert, Julie; Reniers, François

    2016-01-01

    In the context of polymer surface treatment, the afterglow of an atmospheric pressure Ar/O$_2$ radiofrequency plasma is characterized by optical emission spectroscopy, laser induced fluorescence and mass spectrometry. The influence of the O$_2$ gas flow rate and the source power on the plasma properties (gas temperature, Ar excitation temperature, relative concentrations of O atoms and OH radicals) are evaluated. We show that for plasma torch-to-substrate distances lower than 6 mm, the afterglow creates a protective atmosphere, thus the plasma gas composition interacting with the substrate is well controlled. For higher distances, the influence of ambient air can no longer be neglected and gradients in Ar, O$_2$ and N$_2$ concentrations are measured as a function of axial and vertical position.

  13. Sterilization/disinfection using reduced-pressure plasmas: some differences between direct exposure of bacterial spores to a discharge and their exposure to a flowing afterglow

    Science.gov (United States)

    Moisan, M.; Levif, P.; Séguin, J.; Barbeau, J.

    2014-07-01

    The use of plasma for sterilization or disinfection offers a promising alternative to conventional steam or chemical approaches. Plasma can operate at temperatures less damaging to some heat-sensitive medical devices and, in contrast to chemicals, can be non-toxic and non-polluting for the operator and the environment, respectively. Direct exposure to the gaseous discharge (comprising an electric field and ions/electrons) or exposure to its afterglow (no E-field) can both be envisaged a priori, since these two methods can achieve sterility. However, important issues must be considered besides the sterility goal. Direct exposure to the discharge, although yielding a faster inactivation of microorganisms, is shown to be potentially more aggressive to materials and sometimes subjected to the shadowing effect that precludes the sterilization of complex-form items. These two drawbacks can be successfully minimized with an adequate flowing-afterglow exposure. Most importantly, the current paper shows that direct exposure to the discharge can lead to the dislodgment and release of viable microorganisms from their substratum. Such a phenomenon could be responsible for the recontamination of sterilized devices as well as possible contamination of the ambient surroundings, additionally yielding an erroneous over-appreciation of the inactivation efficiency. The operation of the N2-O2 flowing afterglow system being developed in our group is such that there are no ions and electrons left in the process chamber (late-afterglow regime) in full contrast with their presence in the discharge. The dislodgment and release of spores could be attributed, based on the literature, to their electrostatic charging by electrons, leading to an (outward) electrostatic stress that exceeds the adhesion of the spores on their substrate.

  14. Multi-Sensor Optimal Data Fusion Based on the Adaptive Fading Unscented Kalman Filter

    Directory of Open Access Journals (Sweden)

    Bingbing Gao

    2018-02-01

    Full Text Available This paper presents a new optimal data fusion methodology based on the adaptive fading unscented Kalman filter for multi-sensor nonlinear stochastic systems. This methodology has a two-level fusion structure: at the bottom level, an adaptive fading unscented Kalman filter based on the Mahalanobis distance is developed and serves as local filters to improve the adaptability and robustness of local state estimations against process-modeling error; at the top level, an unscented transformation-based multi-sensor optimal data fusion for the case of N local filters is established according to the principle of linear minimum variance to calculate globally optimal state estimation by fusion of local estimations. The proposed methodology effectively refrains from the influence of process-modeling error on the fusion solution, leading to improved adaptability and robustness of data fusion for multi-sensor nonlinear stochastic systems. It also achieves globally optimal fusion results based on the principle of linear minimum variance. Simulation and experimental results demonstrate the efficacy of the proposed methodology for INS/GNSS/CNS (inertial navigation system/global navigation satellite system/celestial navigation system integrated navigation.

  15. Analytical bounds on the area spectral efficiency of uplink heterogeneous networks over generalized fading channels

    KAUST Repository

    Shakir, Muhammad

    2014-06-01

    Heterogeneous networks (HetNets) are envisioned to enable next-generation cellular networks by providing higher spectral and energy efficiency. A HetNet is typically composed of multiple radio access technologies where several low-power low-cost operators or user-deployed small-cell base stations (SBSs) complement the macrocell network. In this paper, we consider a two-tier HetNet where the SBSs are arranged around the edge of the reference macrocell such that the resultant configuration is referred to as cell-on-edge (COE). Each mobile user in a small cell is considered capable of adapting its uplink transmit power according to a location-based slow power control mechanism. The COE configuration is observed to increase the uplink area spectral efficiency (ASE) and energy efficiency while reducing the cochannel interference power. A moment-generating-function (MGF)-based approach has been exploited to derive the analytical bounds on the uplink ASE of the COE configuration. The derived expressions are generalized for any composite fading distribution, and closed-form expressions are presented for the generalized- K fading channels. Simulation results are included to support the analysis and to show the efficacy of the COE configuration. A comparative performance analysis is also provided to demonstrate the improvements in the performance of cell-edge users of the COE configuration compared with that of macro-only networks (MoNets) and other unplanned deployment strategies. © 2013 IEEE.

  16. Anomalous fading of the TL, Blue-SL and IR-SL signals of fluorapatite

    Energy Technology Data Exchange (ETDEWEB)

    Tsirliganis, N. [Cultural and Educational Technology Institute, Archaeometry Laboratory, Tsimiski 58, 67100 Xanthi (Greece)]. E-mail: tnestor@ceti.gr; Polymeris, G. [Cultural and Educational Technology Institute, Archaeometry Laboratory, Tsimiski 58, 67100 Xanthi (Greece); Aristotle University of Thessaloniki, Nuclear Physics Laboratory, 54124 Thessaloniki (Greece); Loukou, Z. [Cultural and Educational Technology Institute, Archaeometry Laboratory, Tsimiski 58, 67100 Xanthi (Greece); Kitis, G. [Aristotle University of Thessaloniki, Nuclear Physics Laboratory, 54124 Thessaloniki (Greece)

    2006-08-15

    The thermoluminescence (TL), blue stimulated luminescence (BSL) and infrared stimulated luminescence (IRSL) signals of fluorapatite (originating from Durango, Mexico) were measured and found to exhibit strong anomalous fading (AF). The experimentally obtained OSL and IRSL decay curves were transformed into pseudo-linear modulated (pseudo-LM) decay curves. The resulting glow-curve shaped pseudo-LM decay curves were analyzed using a deconvolution analysis, similar to the one used for the glow-curve deconvolution (GCD) of TL glow-curves. It was found that the pseudo-LM OSL and IRSL decay curves consist of two components named fast and slow, respectively, and their individual contribution was estimated. The AF of the remnant TL, BSL and IRSL as a function of the storage time was fitted using the tunneling model equations and the fading rate g, in terms of percentage per decade was evaluated. According to the obtained g values, the AF of the BSL and IRSL is stronger than that of the TL. The AF of the fast component of BSL and IRSL is almost the same. The AF of the slow component of IRSL is, by approximately a factor of 2, stronger than that of the BSL.

  17. Modeling and Simulation of MIMO Mobile-to-Mobile Wireless Fading Channels

    Directory of Open Access Journals (Sweden)

    Gholamreza Bakhshi

    2012-01-01

    Full Text Available Analysis and design of multielement antenna systems in mobile fading channels require a model for the space-time cross-correlation among the links of the underlying multipleinput multiple-output (MIMO Mobile-to-Mobile (M-to-M communication channels. In this paper, we propose the modified geometrical two-ring model, a MIMO channel reference model for M-to-M communication systems. This model is based on the extension of single-bounce two-ring scattering model for flat fading channel under the assumption that the transmitter and the receiver are moving. Assuming single-bounce scattering model in both isotropic and nonisotropic environment, a closed-form expression for the space-time cross-correlation function (CCF between any two subchannels is derived. The proposed model provides an important framework in M-to-M system design, where includes many existing correlation models as special cases. Also, two realizable statistical simulation models are proposed for simulating both isotropic and nonisotropic reference model. The realizable simulation models are based on Sum-of-Sinusoids (SoS simulation model. Finally, the correctness of the proposed simulation models is shown via different simulation scenarios.

  18. Adaptive Space-Time-Spreading-Assisted Wideband CDMA Systems Communicating over Dispersive Nakagami- Fading Channels

    Directory of Open Access Journals (Sweden)

    Yang Lie-Liang

    2005-01-01

    Full Text Available In this contribution, the performance of wideband code-division multiple-access (W-CDMA systems using space-time-spreading- (STS- based transmit diversity is investigated, when frequency-selective Nakagami- fading channels, multiuser interference, and background noise are considered. The analysis and numerical results suggest that the achievable diversity order is the product of the frequency-selective diversity order and the transmit diversity order. Furthermore, both the transmit diversity and the frequency-selective diversity have the same order of importance. Since W-CDMA signals are subjected to frequency-selective fading, the number of resolvable paths at the receiver may vary over a wide range depending on the transmission environment encountered. It can be shown that, for wireless channels where the frequency selectivity is sufficiently high, transmit diversity may be not necessitated. Under this case, multiple transmission antennas can be leveraged into an increased bitrate. Therefore, an adaptive STS-based transmission scheme is then proposed for improving the throughput of W-CDMA systems. Our numerical results demonstrate that this adaptive STS-based transmission scheme is capable of significantly improving the effective throughput of W-CDMA systems. Specifically, the studied W-CDMA system's bitrate can be increased by a factor of three at the modest cost of requiring an extra 0.4 dB or 1.2 dB transmitted power in the context of the investigated urban or suburban areas, respectively.

  19. Outage Analysis of Spectrum-Sharing over M-Block Fading with Sensing Information

    KAUST Repository

    Alabbasi, Abdulrahman

    2016-07-13

    Future wireless technologies, such as, 5G, are expected to support real-time applications with high data throughput, e.g., holographic meetings. From a bandwidth perspective, cognitive radio is a promising technology to enhance the system’s throughput via sharing the licensed spectrum. From a delay perspective, it is well known that increasing the number of decoding blocks will improve the system robustness against errors, while increasing the delay. Therefore, optimally allocating the resources to determine the tradeoff of tuning the length of decoding blocks while sharing the spectrum is a critical challenge for future wireless systems. In this work, we minimize the targeted outage probability over the block-fading channels while utilizing the spectrum-sharing concept. The secondary user’s outage region and the corresponding optimal power are derived, over twoblocks and M-blocks fading channels. We propose two suboptimal power strategies and derive the associated asymptotic lower and upper bounds on the outage probability with tractable expressions. These bounds allow us to derive the exact diversity order of the secondary user’s outage probability. To further enhance the system’s performance, we also investigate the impact of including the sensing information on the outage problem. The outage problem is then solved via proposing an alternating optimization algorithm, which utilizes the verified strict quasiconvex structure of the problem. Selected numerical results are presented to characterize the system’s behavior and show the improvements of several sharing concepts.

  20. Discrete Multiwavelet Critical-Sampling Transform-Based OFDM System over Rayleigh Fading Channels

    Directory of Open Access Journals (Sweden)

    Sameer A. Dawood

    2015-01-01

    Full Text Available Discrete multiwavelet critical-sampling transform (DMWCST has been proposed instead of fast Fourier transform (FFT in the realization of the orthogonal frequency division multiplexing (OFDM system. The proposed structure further reduces the level of interference and improves the bandwidth efficiency through the elimination of the cyclic prefix due to the good orthogonality and time-frequency localization properties of the multiwavelet transform. The proposed system was simulated using MATLAB to allow various parameters of the system to be varied and tested. The performance of DMWCST-based OFDM (DMWCST-OFDM was compared with that of the discrete wavelet transform-based OFDM (DWT-OFDM and the traditional FFT-based OFDM (FFT-OFDM over flat fading and frequency-selective fading channels. Results obtained indicate that the performance of the proposed DMWCST-OFDM system achieves significant improvement compared to those of DWT-OFDM and FFT-OFDM systems. DMWCST improves the performance of the OFDM system by a factor of 1.5–2.5 dB and 13–15.5 dB compared with the DWT and FFT, respectively. Therefore the proposed system offers higher data rate in wireless mobile communications.

  1. On Channel Estimation for Analog Network Coding in a Frequency-Selective Fading Channel

    Directory of Open Access Journals (Sweden)

    Sjödin Tomas

    2011-01-01

    Full Text Available Recently, broadband analog network coding (ANC was introduced for high-speed transmission over the wireless (frequency-selective fading channel. However, ANC requires the knowledge of channel state information (CSI for self-information removal and coherent signal detection. In ANC, the users' pilot signals interfere during the first slot, which renders the relay unable to estimate CSIs of different users, and, consequently, four time-slot pilot-assisted channel estimation (CE is required to avoid interference. Naturally, this will reduce the capacity of ANC scheme. In this paper, we theoretically analyze the bit error rate (BER performance of bi-directional broadband ANC communication based on orthogonal frequency division multiplexing (OFDM radio access. We also theoretically analyze the performance of the channel estimator's mean square error (MSE. The analysis is based on the assumption of perfect timing and frequency synchronization. The achievable BER performance and the estimator's MSE for broadband ANC is evaluated by numerical and computer simulation. We discuss how, and by how much, the imperfect knowledge of CSI affects the BER performance of broadband ANC. It is shown that the CE scheme achieves a slightly higher BER in comparison with ideal CE case for a low and moderate mobile terminal speed in a frequency-selective fading channel.

  2. Progressive transmission of images over fading channels using rate-compatible LDPC codes.

    Science.gov (United States)

    Pan, Xiang; Banihashemi, Amir H; Cuhadar, Aysegul

    2006-12-01

    In this paper, we propose a combined source/channel coding scheme for transmission of images over fading channels. The proposed scheme employs rate-compatible low-density parity-check codes along with embedded image coders such as JPEG2000 and set partitioning in hierarchical trees (SPIHT). The assignment of channel coding rates to source packets is performed by a fast trellis-based algorithm. We examine the performance of the proposed scheme over correlated and uncorrelated Rayleigh flat-fading channels with and without side information. Simulation results for the expected peak signal-to-noise ratio of reconstructed images, which are within 1 dB of the capacity upper bound over a wide range of channel signal-to-noise ratios, show considerable improvement compared to existing results under similar conditions. We also study the sensitivity of the proposed scheme in the presence of channel estimation error at the transmitter and demonstrate that under most conditions our scheme is more robust compared to existing schemes.

  3. Exact capture probability analysis of GSC receivers over i.n.d. Rayleigh fading channels

    KAUST Repository

    Nam, Sungsik

    2013-07-01

    A closed-form expression of the capture probability of generalized selection combining (GSC) RAKE receivers was introduced in [1]. The idea behind this new performance metric is to quantify how the remaining set of uncombined paths affects the overall performance both in terms of loss in power and increase in interference levels. In this previous work, the assumption was made that the fading is both independent and identically distributed from path to path. However, the average strength of each path is different in reality. In order to derive a closed-form expression of the capture probability over independent and non-identically distributed (i.n.d.) fading channels, we need to derive the joint statistics of ordered non-identical exponential variates. With this motivation in mind, we first provide in this paper some new order statistics results in terms of both moment generating function (MGF) and probability density function (PDF) expressions under an i.n.d. assumption and then derive a new exact closed-form expression for the capture probability GSC RAKE receivers in this more realistic scenario. © 2013 IEEE.

  4. Secure Multiple-Antenna Block-Fading Wiretap Channels with Limited CSI Feedback

    KAUST Repository

    Hyadi, Amal

    2017-07-18

    In this paper, we investigate the ergodic secrecy capacity of a block-fading wiretap channel with limited channel knowledge at the transmitter. We consider that the legitimate receiver, the eavesdropper and the transmitter are equipped with multiple antennas and that the receiving nodes are aware of their respective channel matrices. The transmitter, on the other hand, is only provided by a B-bit feedback of the main channel state information. The feedback bits are sent by the legitimate receiver, at the beginning of each fading block, over an error-free public link with limited capacity. The statistics of the main and the eavesdropper channel state information are known at all nodes. Assuming an average transmit power constraint, we establish upper and lower bounds on the ergodic secrecy capacity. Then, we present a framework to design the optimal codebooks for feedback and transmission. In addition, we show that the proposed lower and upper bounds coincide asymptotically as the capacity of the feedback link becomes large, i.e. $B \\ ightarrow \\\\infty$ ; hence, fully characterizing the ergodic secrecy capacity in this case. Besides, we analyze the asymptotic behavior of the presented secrecy rates, at high Signal-to-Noise Ratio (SNR), and evaluate the gap between the bounds.

  5. On the Secrecy Capacity Region of the Block-Fading BCC with Limited CSI Feedback

    KAUST Repository

    Hyadi, Amal

    2017-02-07

    In this work, we examine the secrecy capacity region of the block-fading broadcast channel with confidential messages (BCC) when the transmitter has limited knowledge of the channel. In particular, we consider a two-user communication system where the transmitter has one common message to be transmitted to both users and one confidential message intended to only one of them. The confidential message has to be kept secret from the other user to whom the information is not intended. The transmitter is not aware of the channel state information (CSI) of neither channel and is only provided by limited CSI feedback sent at the beginning of each fading block. Assuming an error-free feedback link, we characterize the secrecy capacity region of this channel and show that even with a 1-bit CSI feedback, a positive secrecy rate can still be achieved. Then, we look at the case where the feedback link is not error- free and is rather a binary erasure channel (BEC). In the latter case, we provide an achievable secrecy rate region and show that as long as the erasure event is not a probability 1 event, the transmitter can still transmit the confidential information with a positive secrecy rate.

  6. BER EVALUATION OF LDPC CODES WITH GMSK IN NAKAGAMI FADING CHANNEL

    Directory of Open Access Journals (Sweden)

    Surbhi Sharma

    2010-06-01

    Full Text Available LDPC codes (Low Density Parity Check Codes have already proved its efficacy while showing its performance near to the Shannon limit. Channel coding schemes are spectrally inefficient as using an unfiltered binary data stream to modulate an RF carrier that will produce an RF spectrum of considerable bandwidth. Techniques have been developed to improve this bandwidth inefficiency or spectral efficiency, and ease detection. GMSK or Gaussian-filtered Minimum Shift Keying uses a Gaussian Filter of an appropriate bandwidth so as to make system spectrally efficient. A Nakagami model provides a better explanation to less and more severe conditions than the Rayleigh and Rician model and provide a better fit to the mobile communication channel data. In this paper we have demonstrated the performance of Low Density Parity Check codes with GMSK modulation (BT product=0.25 technique in Nakagami fading channel. In results it is shown that average bit error rate decreases as the ‘m’ parameter increases (Less fading.

  7. Pragmatic Space-Time Codes for Cooperative Relaying in Block Fading Channels

    Directory of Open Access Journals (Sweden)

    Marco Chiani

    2008-09-01

    Full Text Available We address the problem of construction of space-time codes for cooperative communications in block fading channels. More precisely, we consider a pragmatic approach based on the concatenation of convolutional codes and BPSK/QPSK modulation to obtain cooperative codes for relay networks, for which we derive the pairwise error probability, an asymptotic bound for frame error probability, and a design criterion to optimize both diversity and coding gain. Based on this framework, we set up a code search procedure to obtain a set of good pragmatic space-time codes (P-STCs with overlay construction, suitable for cooperative communication with a variable number of relays in quasistatic channel, which outperform in terms of coding gain other space-time codes (STCs proposed in the literature. We also find that, despite the fact that the implementation of pragmatic space-time codes requires standard convolutional encoders and Viterbi decoders with suitable generators and branch metric, thus having low complexity, they perform quite well in block fading channels, including quasistatic channel, even with a low number of states and relays.

  8. Wireless Power Transfer in Cooperative DF Relaying Networks with Log-Normal Fading

    KAUST Repository

    Rabie, Khaled M.

    2017-02-07

    Energy-harvesting (EH) and wireless power transfer in cooperative relaying networks have recently attracted a considerable amount of research attention. Most of the existing work on this topic however focuses on Rayleigh fading channels which represents outdoor environments. Unlike these studies, in this paper we analyze the performance of wireless power transfer in two-hop decode-and- forward (DF) cooperative relaying systems in indoor channels characterized by log-normal fading. Three well-known EH protocols are considered in our evaluations: a) time switching relaying (TSR), b) power splitting relaying (PSR) and c) ideal relaying receiver (IRR). The performance is evaluated in terms of the ergodic outage probability for which we derive accurate analytical expressions for the three systems under consideration. Results reveal that careful selection of the EH time and power splitting factors in the TSR- and PSR-based system are important to optimize performance. It is also presented that the optimized PSR system has near- ideal performance and that increasing the source transmit power and/or the energy harvester efficiency can further improve performance.

  9. Energy-harvesting in cooperative AF relaying networks over log-normal fading channels

    KAUST Repository

    Rabie, Khaled M.

    2016-07-26

    Energy-harvesting (EH) and wireless power transfer are increasingly becoming a promising source of power in future wireless networks and have recently attracted a considerable amount of research, particularly on cooperative two-hop relay networks in Rayleigh fading channels. In contrast, this paper investigates the performance of wireless power transfer based two-hop cooperative relaying systems in indoor channels characterized by log-normal fading. Specifically, two EH protocols are considered here, namely, time switching relaying (TSR) and power splitting relaying (PSR). Our findings include accurate analytical expressions for the ergodic capacity and ergodic outage probability for the two aforementioned protocols. Monte Carlo simulations are used throughout to confirm the accuracy of our analysis. The results show that increasing the channel variance will always provide better ergodic capacity performance. It is also shown that a good selection of the EH time in the TSR protocol, and the power splitting factor in the PTS protocol, is the key to achieve the best system performance. © 2016 IEEE.

  10. Space-Time Water-Filling for Composite MIMO Fading Channels

    Directory of Open Access Journals (Sweden)

    2006-01-01

    Full Text Available We analyze the ergodic capacity and channel outage probability for a composite MIMO channel model, which includes both fast fading and shadowing effects. The ergodic capacity and exact channel outage probability with space-time water-filling can be evaluated through numerical integrations, which can be further simplified by using approximated empirical eigenvalue and maximal eigenvalue distribution of MIMO fading channels. We also compare the performance of space-time water-filling with spatial water-filling. For MIMO channels with small shadowing effects, spatial water-filling performs very close to space-time water-filling in terms of ergodic capacity. For MIMO channels with large shadowing effects, however, space-time water-filling achieves significantly higher capacity per antenna than spatial water-filling at low to moderate SNR regimes, but with a much higher channel outage probability. We show that the analytical capacity and outage probability results agree very well with those obtained from Monte Carlo simulations.

  11. Maximizing Expected Achievable Rates for Block-Fading Buffer-Aided Relay Channels

    KAUST Repository

    Shaqfeh, Mohammad

    2016-05-25

    In this paper, the long-term average achievable rate over block-fading buffer-aided relay channels is maximized using a hybrid scheme that combines three essential transmission strategies, which are decode-and-forward, compress-and-forward, and direct transmission. The proposed hybrid scheme is dynamically adapted based on the channel state information. The integration and optimization of these three strategies provide a more generic and fundamental solution and give better achievable rates than the known schemes in the literature. Despite the large number of optimization variables, the proposed hybrid scheme can be optimized using simple closed-form formulas that are easy to apply in practical relay systems. This includes adjusting the transmission rate and compression when compress-and-forward is the selected strategy based on the channel conditions. Furthermore, in this paper, the hybrid scheme is applied to three different models of the Gaussian block-fading buffer-aided relay channels, depending on whether the relay is half or full duplex and whether the source and the relay have orthogonal or non-orthogonal channel access. Several numerical examples are provided to demonstrate the achievable rate results and compare them to the upper bounds of the ergodic capacity for each one of the three channel models under consideration.

  12. Performance Analysis of Ad Hoc Dispersed Spectrum Cognitive Radio Networks over Fading Channels

    Directory of Open Access Journals (Sweden)

    Mohammad Muneer

    2011-01-01

    Full Text Available Cognitive radio systems can utilize dispersed spectrum, and thus such approach is known as dispersed spectrum cognitive radio systems. In this paper, we first provide the performance analysis of such systems over fading channels. We derive the average symbol error probability of dispersed spectrum cognitive radio systems for two cases, where the channel for each frequency diversity band experiences independent and dependent Nakagami- fading. In addition, the derivation is extended to include the effects of modulation type and order by considering M-ary phase-shift keying ( -PSK and M-ary quadrature amplitude modulation -QAM schemes. We then consider the deployment of such cognitive radio systems in an ad hoc fashion. We consider an ad hoc dispersed spectrum cognitive radio network, where the nodes are assumed to be distributed in three dimension (3D. We derive the effective transport capacity considering a cubic grid distribution. Numerical results are presented to verify the theoretical analysis and show the performance of such networks.

  13. Performance of Optimum and Suboptimum Combining Diversity Reception for Binary DPSK over Independent, Nonidentical Rayleigh Fading Channels

    CERN Document Server

    Fu, Hua

    2010-01-01

    This paper is concerned with the error performance analysis of binary differential phase shift keying with differential detection over the nonselective, Rayleigh fading channel with combining diversity reception. Space antenna diversity reception is assumed. The diversity branches are independent, but have nonidentically distributed statistics. The fading process in each branch is assumed to have an arbitrary Doppler spectrum with arbitrary Doppler bandwidth. Both optimum diversity reception and suboptimum diversity reception are considered. Results available previously apply only to the case of first and second-order diversity. Our results are more general in that the order of diversity is arbitrary. Moreover, the bit error probability (BEP) result is obtained in an exact, closed-form expression which shows the behavior of the BEP as an explict function of the one-bit-interval fading correlation coefficient at the matched filter output, the mean signal-to-noise ratio per bit per branch and the order of diver...

  14. On the low SNR capacity of maximum ratio combining over rician fading channels with full channel state information

    KAUST Repository

    Benkhelifa, Fatma

    2013-04-01

    In this letter, we study the ergodic capacity of a maximum ratio combining (MRC) Rician fading channel with full channel state information (CSI) at the transmitter and at the receiver. We focus on the low Signal-to-Noise Ratio (SNR) regime and we show that the capacity scales as L ΩK+L SNRx log(1SNR), where Ω is the expected channel gain per branch, K is the Rician fading factor, and L is the number of diversity branches. We show that one-bit CSI feedback at the transmitter is enough to achieve this capacity using an on-off power control scheme. Our framework can be seen as a generalization of recently established results regarding the fading-channels capacity characterization in the low-SNR regime. © 2012 IEEE.

  15. The fading affect bias in the context of emotion activation level, mood, and personal theories of emotion change.

    Science.gov (United States)

    Ritchie, Timothy; Skowronski, John J; Hartnett, Jessica; Wells, Brett; Walker, W Richard

    2009-05-01

    The intensity of emotions associated with memory of pleasant events generally fades more slowly across time than the intensity of emotions associated with memory of unpleasant events, a phenomenon known as the fading affect bias (FAB). Four studies examined variables that might account for, or moderate, the bias. These included the activation level of the emotions, individual differences in dispositional mood, and participant expectations of emotion change across time. Results suggest that (a) although emotion activation level was related to overall fading of affect, it was unrelated to the FAB; (b) dispositional mood moderated the FAB, but could not fully account for it; and (c) although participants' predictions of event-related emotion change across time were somewhat veridical, the FAB emerged even when these predictions were accounted for statistically. Methodological and theoretical implications for research on the affect associated with autobiographical events are discussed.

  16. Absolute ground-state nitrogen atom density in a N{sub 2}/CH{sub 4} late afterglow: TALIF experiments and modelling studies

    Energy Technology Data Exchange (ETDEWEB)

    Es-sebbar, Et; C-Gazeau, M; Benilan, Y; Jolly, A [LISA, Universites Paris-Est Creteil Val de Marne (UPEC) and Paris Denis Diderot, CNRS-UMR 7583, 61, avenue du General de Gaulle, 94010 Creteil Cedex (France); Pintassilgo, C D, E-mail: essebbar@lisa.univ-paris12.f [Instituto de Plasmas e Fusao Nuclear-Laboratorio Associado, Instituto Superior Tecnico, 1049-001 Lisboa (Portugal)

    2010-08-25

    Following a first study on a late afterglow in flowing pure nitrogen post discharge, we report new two-photon absorption laser-induced fluorescence (TALIF) measurements of the absolute ground-state atomic nitrogen density N({sup 4}S) and investigate the influence of methane introduced downstream from the discharge by varying the CH{sub 4} mixing ratio from 0% up to 50%. The N ({sup 4}S) maximum density is about 2.2 x 10{sup 15} cm{sup -3} in pure N{sub 2} for a residence time of 22 ms and does not change significantly for methane mixing ratio up to {approx}15%, while above, a drastic decrease is observed. The influence of the residence time has been studied. A kinetic model has been developed to determine the elementary processes responsible for the evolution of the N ({sup 4}S) density in N{sub 2}/CH{sub 4} late afterglow. This model shows the same decrease as the experimental results even though absolute density values are always larger by about a factor of 3. In the late afterglow three-body recombination dominates the loss of N ({sup 4}S) atoms whatever the CH{sub 4} mixing ratio. For high CH{sub 4} mixing ratio, the destruction process through collisions with CH{sub 3}, H{sub 2}CN and NH becomes important and is responsible for the observed decrease of the N ({sup 4}S) density.

  17. THERMAL EMISSION IN THE EARLY X-RAY AFTERGLOWS OF GAMMA-RAY BURSTS: FOLLOWING THE PROMPT PHASE TO LATE TIMES

    Energy Technology Data Exchange (ETDEWEB)

    Friis, Mette [Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, Dunhagi 5, 107 Reykjavik (Iceland); Watson, Darach, E-mail: mef4@hi.is, E-mail: darach@dark-cosmology.dk [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen O (Denmark)

    2013-07-01

    Thermal radiation, peaking in soft X-rays, has now been detected in a handful of gamma-ray burst (GRB) afterglows and has to date been interpreted as shock break-out of the GRB's progenitor star. We present a search for thermal emission in the early X-ray afterglows of a sample of Swift bursts selected by their brightness in X-rays at early times. We identify a clear thermal component in eight GRBs and track the evolution. We show that at least some of the emission must come from highly relativistic material since two show an apparent super-luminal expansion of the thermal component. Furthermore, we determine very large luminosities and high temperatures for many of the components-too high to originate in a supernova shock break-out. Instead, we suggest that the component may be modeled as late photospheric emission from the jet, linking it to the apparently thermal component observed in the prompt emission of some GRBs at gamma-ray and hard X-ray energies. By comparing the parameters from the prompt emission and the early afterglow emission, we find that the results are compatible with the interpretation that we are observing the prompt quasi-thermal emission component in soft X-rays at a later point in its evolution.

  18. Long-lived plasma and fast quenching of N2(C3Π u ) by electrons in the afterglow of a nanosecond capillary discharge in nitrogen

    Science.gov (United States)

    Lepikhin, N. D.; Klochko, A. V.; Popov, N. A.; Starikovskaia, S. M.

    2016-08-01

    Quenching of electronically excited nitrogen state, {{\\text{N}}2}≤ft({{\\text{C}}3}{{\\Pi}u},{{v}\\prime}=0\\right) , in the afterglow of nanosecond capillary discharge in pure nitrogen is studied. It is found experimentally that an additional collisional mechanism appears and dominates at high specific deposited energies leading to the anomalously fast quenching of the {{\\text{N}}2}≤ft({{\\text{C}}3}{{\\Pi}u}\\right) in the afterglow. On the basis of obtained experimental data and of the analysis of possible quenching agents, it is concluded that the anomalously fast deactivation of the {{\\text{N}}2}≤ft({{\\text{C}}3}{{\\Pi}u}\\right) can be explained by quenching by electrons. Long-lived plasma at time scale of hundreds nanoseconds after the end of the pulse is observed. High electron densities, about 1014 cm-3 at 27 mbar, are sustained by reactions of associative ionization. Kinetic 1D numerical modeling and comparison of calculated results with experimentally measured electric fields in the second high-voltage pulse 250 ns after the initial pulse, and electron density measurements in the afterglow confirm the validity of the suggested mechanism.

  19. Asymptotic Performance Analysis of the k-th Best Link Selection over Wireless Fading Channels: An Extreme Value Theory Approach

    KAUST Repository

    Al-Badarneh, Yazan Hussein

    2018-01-25

    We consider a general selection-diversity (SD) scheme in which the k-th best link is selected from a number of links. We use extreme value theory (EVT) to derive simple closed-form asymptotic expressions for the average throughput, effective throughput and average bit error probability (BEP) for the k-th best link over various channel models that are widely used to characterize fading in wireless communication systems. As an application example, we consider the Weibull fading channel model and verify the accuracy of the derived asymptotic expressions through Monte Carlo simulations.

  20. On the symbol error rate of M-ary MPSK over generalized fading channels with additive Laplacian noise

    KAUST Repository

    Soury, Hamza

    2014-06-01

    This paper considers the symbol error rate of M-ary phase shift keying (MPSK) constellations over extended Generalized-K fading with Laplacian noise and using a minimum distance detector. A generic closed form expression of the conditional and the average probability of error is obtained and simplified in terms of the Fox\\'s H function. More simplifications to well known functions for some special cases of fading are also presented. Finally, the mathematical formalism is validated with some numerical results examples done by computer based simulations. © 2014 IEEE.

  1. A novel framework on exact average symbol error probabilities of multihop transmission over amplify-and-forward relay fading channels

    KAUST Repository

    Yilmaz, Ferkan

    2010-09-01

    In this paper, we propose an analytical framework on the exact computation of the average symbol error probabilities (ASEP) of multihop transmission over generalized fading channels when an arbitrary number of amplify-and-forward relays is used. Our approach relies on moment generating function (MGF) framework to obtain exact single integral expressions which can be easily computed by Gauss-Chebyshev Quadrature (GCQ) rule. As such, the derived results are a convenient tool to analyze the ASEP performance of multihop transmission over amplify-and-forward relay fading channels. Numerical and simulation results, performed to verify the correctness of the proposed formulation, are in perfect agreement. © 2010 IEEE.

  2. On the Symbol Error Rate of M-ary MPSK over Generalized Fading Channels with Additive Laplacian Noise

    KAUST Repository

    Soury, Hamza

    2015-01-07

    This work considers the symbol error rate of M-ary phase shift keying (MPSK) constellations over extended Generalized-K fading with Laplacian noise and using a minimum distance detector. A generic closed form expression of the conditional and the average probability of error is obtained and simplified in terms of the Fox’s H function. More simplifications to well known functions for some special cases of fading are also presented. Finally, the mathematical formalism is validated with some numerical results examples done by computer based simulations [1].

  3. New Exact and Asymptotic Results of Dual-Branch MRC over Correlated Nakagami-m Fading Channels

    KAUST Repository

    Al-Quwaiee, Hessa

    2015-05-01

    We present in this paper a new performance analysis results of dual-branch maximal-ratio combining over correlated Nakagami-m fading channels with arbitrary fading parameter. In particular, we derive exact closed-form expressions of the outage probability, the average bit error rate, and the ergodic capacity in terms of the extended generalized bivariate Meijer G- function. Moreover, we also provide simple closed- form asymptotic expressions in the high signal-to- noise ratio regime of these three fundamental performance measures. © 2015 IEEE.

  4. From Guided to Self-Regulated Performance of Domain-General Skills: The Role of Peer Monitoring during the Fading of Instructional Scripts

    Science.gov (United States)

    Wecker, Christof; Fischer, Frank

    2011-01-01

    The fading of instructional scripts can be regarded as necessary for allowing learners to take over control of their cognitive activities during the acquisition of skills such as argumentation. There is, however, the danger that learners might relapse into novice strategies after script prompts are faded. One possible solution could be monitoring…

  5. Supporting Survey Courses with Lecture-Tutorials and Backwards-Faded Scaffolded Inquiry

    Science.gov (United States)

    Slater, T. F.; Slater, S. J.

    2013-12-01

    In the course of learning science, it is generally accepted that successful science learning experiences should result in learners developing a meaningful understanding of the nature of science as inquiry where: (i) students are engaged in questions; (ii) students are designing plans to pursue data; and (iii) students are generating and defending conclusions based on evidence they have collected. Few of these learning targets can be effectively reached through a professor-centered, information download lecture. In response to national reform movements calling for professors to adopt teaching strategies and learning environments where non-science majors and future teachers can actively engage in scientific discourse, scholars with the CAPER Center for Astronomy & Physics Education Research have leveraged NSF DUE funding over the last decade to develop and systematically field-test two separate instructional approaches. The first of these is called Lecture-Tutorials (NSF 99077755 and NSF 9952232) . These are self-contained, classroom-ready, collaborative group activities. The materials are designed specifically to be easily integrated into the lecture course and directly address the needs of busy and heavily-loaded teaching faculty for effective, student-centered, classroom-ready materials that do not require a drastic course revision for implementation. Students are asked to reason about difficult concepts, while working in pairs, and to discuss their ideas openly. The second of these is a series of computer-mediated, inquiry learning experiences for non-science majoring undergraduates based upon an inquiry-oriented teaching approach framed by the notions of backwards faded-scaffolding as an overarching theme for instruction (NSF 1044482). Backwards faded-scaffolding is a strategy where the conventional and rigidly linear scientific method is turned on its head and students are first taught how to create conclusions based on evidence, then how experimental design

  6. Sterilization/disinfection of medical devices using plasma: the flowing afterglow of the reduced-pressure N2-O2 discharge as the inactivating medium

    Science.gov (United States)

    Moisan, Michel; Boudam, Karim; Carignan, Denis; Kéroack, Danielle; Levif, Pierre; Barbeau, Jean; Séguin, Jacynthe; Kutasi, Kinga; Elmoualij, Benaïssa; Thellin, Olivier; Zorzi, Willy

    2013-07-01

    Potential sterilization/disinfection of medical devices (MDs) is investigated using a specific plasma process developed at the Université de Montréal over the last decade. The inactivating medium of the microorganisms is the flowing afterglow of a reduced-pressure N2-O2 discharge, which provides, as the main biocidal agent, photons over a broad ultraviolet (UV) wavelength range. The flowing afterglow is considered less damaging to MDs than the discharge itself. Working at gas pressures in the 400—700 Pa range (a few torr) ensures, through species diffusion, the uniform filling of large volume chambers with the species outflowing from the discharge, possibly allowing batch processing within them. As a rule, bacterial endospores are used as bio-indicators (BI) to validate sterilization processes. Under the present operating conditions, Bacillus atrophaeus is found to be the most resistant one and is therefore utilized as BI. The current paper reviews the main experimental results concerning the operation and characterization of this sterilizer/disinfector, updating and completing some of our previously published papers. It uses modeling results as guidelines, which are particularly useful when the corresponding experimental data are not (yet) available, hopefully leading to more insight into this plasma afterglow system. The species flowing out of the N2-O2 discharge can be divided into two groups, depending on the time elapsed after they left the discharge zone as they move toward the chamber, namely the early afterglow and the late afterglow. The early flowing afterglow from a pure N2 discharge (also called pink afterglow) is known to be comprised of N2+ and N4+ ions. In the present N2-O2 mixture discharge, NO+ ions are additionally generated, with a lifetime that extends over a longer period than that of the nitrogen molecular ions. We shall suppose that the disappearance of the NO+ ions marks the end of the early afterglow regime, thereby stressing our intent

  7. Influence of ambient air on the flowing afterglow of an atmospheric pressure Ar/O2 radiofrequency plasma

    CERN Document Server

    Duluard, C Y; Hubert, J; Reniers, F

    2016-01-01

    The influence of ambient air on the flowing afterglow of an atmospheric pressure Ar/O2 radiofrequency plasma has been investigated experimentally. Spatially resolved mass spectrometry and laser induced fluorescence on OH radicals were used to estimate the intrusion of air in between the plasma torch and the substrate as a function of the torch-to-substrate separation distance. No air is detected, within the limits of measurement uncertainties, for separation distances smaller than 5 mm. For larger distances, the effect of ambient air can no longer be neglected, and radial gradients in the concentrations of species appear. The Ar 4p population, determined through absolute optical emission spectroscopy, is seen to decrease with separation distance, whereas a rise in emission from the N2(C--B) system is measured. The observed decay in Ar 4p and N2(C) populations for separation distances greater than 9mm is partly assigned to the increasing collisional quenching rate by N2 and O2 molecules from the entrained air....

  8. Long-lived Ar-Hg plasma in the afterglow of a high-current pulsed discharge

    Energy Technology Data Exchange (ETDEWEB)

    Sergeichev, K. F.; Lukina, N. A.; Fesenko, A. A. [Russian Academy of Sciences, Prokhorov General Physics Institute (Russian Federation)

    2013-02-15

    High-density (n > 10{sup 12} cm{sup -3}) argon-mercury plasma produced by a short (t {approx} 20 {mu}s) high-power pulsed discharge in argon with an admixture of mercury vapor at a discharge current of {approx}50 A, an argon pressure of {approx}4 mm Hg, and a mercury vapor pressure of {approx}10{sup -3} mm Hg was studied using optical spectroscopy and radio physics methods. It is found that the lifetime of this plasma after the end of the discharge pulse is up to 10{sup -2} s. It is shown that such an abnormally long lifetime of such an afterglow plasma, as compared to the plasma of an argon discharge without an admixture of mercury vapor, is related to the long residence time of atoms and ions of both argon and mercury in highly excited states due to chemi-ionization processes involving long-lived metastable argon ions. It is suggested that dissociative recombination of highly excited molecular ions of argon play an important role in the transfer of excitation to argon atoms and ions that are close to autoionization states.

  9. Performance of equal gain combining with quantized phases in rayleigh fading channels

    KAUST Repository

    Rizvi, Umar H.

    2011-01-01

    In this paper, we analyze the error probability of equal gain combining with quantized channel phase compensation for binary phase shift keying signalling over Rayleigh fading channels. The probability density and characteristic functions of the combined signal amplitude are derived and used to compute the analytic expressions for the bit error probability in dependance of the number of quantization levels L, the number of diversity branches N-R and the average received signal-to-noise ratio. The analysis is utilized to outline the trade-off between N-R and L and to compare the performance with non-coherent binary frequency shift keying and differential binary phase shift keying schemes under diversity reception. © 2011 IEEE.

  10. How Equalization Techniques Affect the TCP Performance of MC-CDMA Systems in Correlated Fading Channels

    Directory of Open Access Journals (Sweden)

    Giacomo Leonardi

    2007-12-01

    Full Text Available This paper investigates the impact of several equalization techniques for multicarrier code division multiple access systems on the performance at both lower and upper layers (i.e., physical and TCP layers. Classical techniques such as maximal ratio combining, equal gain combining, orthogonality restoring combining, minimum mean square error, as well as a partial equalization (PE are investigated in time- and frequency-correlated fading channels with various numbers of interferers. Their impact on the performance at upper level is then studied. The results are obtained through an integrated simulation platform carefully reproducing all main aspects affecting the quality of service perceived by the final user, allowing an investigation of the real gain produced by signal processing techniques at TCP level.

  11. How Equalization Techniques Affect the TCP Performance of MC-CDMA Systems in Correlated Fading Channels

    Directory of Open Access Journals (Sweden)

    Conti Andrea

    2008-01-01

    Full Text Available Abstract This paper investigates the impact of several equalization techniques for multicarrier code division multiple access systems on the performance at both lower and upper layers (i.e., physical and TCP layers. Classical techniques such as maximal ratio combining, equal gain combining, orthogonality restoring combining, minimum mean square error, as well as a partial equalization (PE are investigated in time- and frequency-correlated fading channels with various numbers of interferers. Their impact on the performance at upper level is then studied. The results are obtained through an integrated simulation platform carefully reproducing all main aspects affecting the quality of service perceived by the final user, allowing an investigation of the real gain produced by signal processing techniques at TCP level.

  12. Error rates of a full-duplex system over EGK fading channels subject to laplacian interference

    KAUST Repository

    Soury, Hamza

    2017-07-31

    This paper develops a mathematical paradigm to study downlink error rates and throughput for half-duplex (HD) terminals served by a full-duplex (FD) base station (BS). Particularly, we study the dominant intra-cell interferer problem that appears between HD users scheduled on the same FD-channel. The distribution of the dominant interference is first characterized via its distribution function, which is derived in closed-form. Assuming Nakagami-m fading, the probability of error for different modulation schemes is studied and a unified closed-form expression for the average symbol error rate is derived. To this end, we show the effective downlink throughput gain, harvested by employing FD communication at a BS that serves HD users, as a function of the signal-to-interference-ratio when compared to an idealized HD interference and noise free BS operation.

  13. Colour changes due to the fading of Prussian blue in Danish Golden Age paintings

    DEFF Research Database (Denmark)

    Filtenborg, Troels Folke; Buti, David; Vila, Anna

    2016-01-01

    Examination of oil paintings by artists from the so-called Danish Golden Age in the first half of the nineteenth century indicates that a significant degree of deterioration and fading has occurred in a number of cases in some of the blue coloured areas. The occurrence was initially suggested...... by the different appearance of the paint along the edges of the paintings where they had been protected from the light. Technical examination of paintings from the Statens Museum for Kunst collection, by artists such as Christen Købke, Nicolai Abildgaard and C.W. Eckersberg, revealed the presence of Prussian blue......, mixed with lead white and calcium carbonate as a component of the paint in the affected areas. Due to its high tinting strength, Prussian blue was often used – mostly in moderate proportions - mixed with other compounds and pigments. It has been demonstrated by experimental studies that the durability...

  14. Consumption Factor Optimization for Multihop Relaying over Nakagami-m Fading channels

    KAUST Repository

    Randrianantenaina, Itsikiantsoa

    2015-10-06

    In this paper, the energy efficiency of multihop relaying over Nakagami-m fading channels is investigated. The “consumption factor”, adopted as a metric to evaluate the energy efficiency, is derived for both amplify-and-forward and decodeand- forward relaying strategies. Then, based on the obtained expressions, we propose a power allocation strategy maximizing the consumption factor. In addition, a sub-optimal, low complexity, power allocation algorithm is proposed and analyzed, and the obtained power allocation scheme is compared in terms of energy efficiency to other power allocation schemes from the literature. Analytical and simulation results confirm the accuracy of our derivations, and assess the performance gains of the proposed approach.

  15. Throughput Analysis of Fading Sensor Networks with Regular and Random Topologies

    Directory of Open Access Journals (Sweden)

    Liu Xiaowen

    2005-01-01

    Full Text Available We present closed-form expressions of the average link throughput for sensor networks with a slotted ALOHA MAC protocol in Rayleigh fading channels. We compare networks with three regular topologies in terms of throughput, transmit efficiency, and transport capacity. In particular, for square lattice networks, we present a sensitivity analysis of the maximum throughput and the optimum transmit probability with respect to the signal-to-interference ratio threshold. For random networks with nodes distributed according to a two-dimensional Poisson point process, the average throughput is analytically characterized and numerically evaluated. It turns out that although regular networks have an only slightly higher average link throughput than random networks for the same link distance, regular topologies have a significant benefit when the end-to-end throughput in multihop connections is considered.

  16. Performance Analysis of 5G Transmission over Fading Channels with Random IG Distributed LOS Components

    Directory of Open Access Journals (Sweden)

    Dejan Jaksic

    2017-01-01

    Full Text Available Mathematical modelling of the behavior of the radio propagation at mmWave bands is crucial to the development of transmission and reception algorithms of new 5G systems. In this study we will model 5G propagation in nondeterministic line-of-sight (LOS conditions, when the random nature of LOS component ratio will be observed as Inverse Gamma (IG distributed process. Closed-form expressions will be presented for the probability density function (PDF and cumulative distribution function (CDF of such random process. Further, closed-form expressions will be provided for important performance measures such as level crossing rate (LCR and average fade duration (AFD. Capitalizing on proposed expressions, LCR and AFD will be discussed in the function of transmission parameters.

  17. A novel reduced-complexity group detection structure in MIMO frequency selective fading channels

    KAUST Repository

    Qaraqe, Khalid A.

    2010-09-01

    In this paper a novel reduced complexity detection method named modified symbol flipping method is introduced and its advantages on reducing the burden of the calculations at the receiver compared to the optimum maximum likelihood detection method on multiple input- multiple output frequency selective fading channels are explained. The initial concept of the symbol flipping method is derived from a preliminary detection scheme named bit flipping which was introduced in [1]. The detection structure employed in this paper is ing, detection, and cancellation. On the detection stage, the proposed method is employed and the results are compared to the group maximum likelihood detection scheme proposed in [2]. Simulation results show that a 6 dB performance gain can be achieved at the expense of a slight increase in complexity in comparison with the conventional symbol flipping scheme. © 2010 Crown.

  18. GPS Multipath Fade Measurements to Determine L-Band Ground Reflectivity Properties

    Science.gov (United States)

    Kavak, Adnan; Xu, Guang-Han; Vogel, Wolfhard J.

    1996-01-01

    In personal satellite communications, especially when the line-of-sight is clear, ground specular reflected signals along with direct signals are received by low gain, almost omni-directional subscriber antennas. A six-channel, C/A code processing, GPS receiver with an almost omni-directional patch antenna was used to take measurements over three types of ground to characterize 1.575 GHz specular ground reflections and ground dielectric properties. Fade measurements were taken over grass, asphalt, and lake water surfaces by placing the antenna in a vertical position at a fixed height from the ground. Electrical characteristics (conductivity and dielectric constant) of these surfaces (grass, asphalt, lake water) were obtained by matching computer simulations to the experimental results.

  19. Swift/XRT monitoring of SN2011dh: evidence for fading

    Science.gov (United States)

    Margutti, R.; Soderberg, A.

    2011-06-01

    We have analyzed 24 ks of Swift/XRT data of SN1011dh (Silverman et al. 2001, Atel #3398; Reiland et al. 2011, CBET #2736) collected in the time period June 3-7. In agreement with Campana & Burrows (2011, Atel #3414) we find that the source is detected at an average level of ~6 E-03 c/s. We furthermore find that the source has faded from ~1.3 E-02 c/s to ~3 E-03 c/s, with a power-law decay index of alpha~ -1.8 (+0.6,-0.6 90% c.l.) The probability of a chance fluctuation is below 0.01% (binomial test), thus we conclude that the observed decay is statistically significant.

  20. A COMPARISON OF TWO METHODS FADING MEMORY FILTER AND ADAPTIVE KALMAN FILTER IN MONITORING CRUSTAL MOVEMENT

    Directory of Open Access Journals (Sweden)

    Cahit Tağı ÇELİK

    2004-01-01

    Full Text Available Monitoring the Crustal Movement in Geodesy is performed by the deformation survey and analysis. If monitoring the crustal movements involves more than two epochs of survey campaign then from the plate tectonic theory, stations do not move randomly from one epoch to the other, therefore Kalman Filter may be suitable to use. However, if sudden movements happened in the crust in particular earthquake happened, the crust moves very fast in a very short period of time. When Kalman Filter used for monitoring these movements, from associated epoch, for a number of epochs the results may be biased. In the paper, comparison of two methods for elimination of the above mentioned biases have been performed. These methods are Fading Memory Filter and Adaptive Kalman Filter for an unknown bias.

  1. An information-guided channel-hopping scheme for block-fading channels with estimation errors

    KAUST Repository

    Yang, Yuli

    2010-12-01

    Information-guided channel-hopping technique employing multiple transmit antennas was previously proposed for supporting high data rate transmission over fading channels. This scheme achieves higher data rates than some mature schemes, such as the well-known cyclic transmit antenna selection and space-time block coding, by exploiting the independence character of multiple channels, which effectively results in having an additional information transmitting channel. Moreover, maximum likelihood decoding may be performed by simply decoupling the signals conveyed by the different mapping methods. In this paper, we investigate the achievable spectral efficiency of this scheme in the case of having channel estimation errors, with optimum pilot overhead for minimum meansquare error channel estimation, when transmitting over blockfading channels. Our numerical results further substantiate the robustness of the presented scheme, even with imperfect channel state information. ©2010 IEEE.

  2. Advanced Fade Countermeasures for DVB-S2 Systems in Railway Scenarios

    Directory of Open Access Journals (Sweden)

    Cristina Párraga Niebla

    2007-07-01

    Full Text Available This paper deals with the analysis of advanced fade countermeasures for supporting DVB-S2 reception by mobile terminals mounted on high-speed trains. Recent market studies indicate this as a potential profitable market for satellite communications, provided that integration with wireless terrestrial networks can be implemented to bridge the satellite connectivity inside railway tunnels and large train stations. In turn, the satellite can typically offer the coverage of around 80% of the railway path with existing space infrastructure. This piece of work, representing the first step of a wider study, is focusing on the modifications which may be required in the DVB-S2 standard (to be employed in the forward link in order to achieve reliable reception in a challenging environment such as the railway one. Modifications have been devised trying to minimize the impact on the existing air interface, standardized for fixed terminals.

  3. Advanced Fade Countermeasures for DVB-S2 Systems in Railway Scenarios

    Directory of Open Access Journals (Sweden)

    Niebla CristinaPárraga

    2007-01-01

    Full Text Available This paper deals with the analysis of advanced fade countermeasures for supporting DVB-S2 reception by mobile terminals mounted on high-speed trains. Recent market studies indicate this as a potential profitable market for satellite communications, provided that integration with wireless terrestrial networks can be implemented to bridge the satellite connectivity inside railway tunnels and large train stations. In turn, the satellite can typically offer the coverage of around 80% of the railway path with existing space infrastructure. This piece of work, representing the first step of a wider study, is focusing on the modifications which may be required in the DVB-S2 standard (to be employed in the forward link in order to achieve reliable reception in a challenging environment such as the railway one. Modifications have been devised trying to minimize the impact on the existing air interface, standardized for fixed terminals.

  4. Transmission errors in companded PCM over Gaussian and Rayleigh fading channels

    Science.gov (United States)

    Steele, R.; Sundberg, C.-E.; Wong, W. C.

    1984-08-01

    Transmission errors in mu-law pulse-code-modulated systems are capable of inflicting considerable distortion in the recovered analog signals. This distortion is analyzed for the case when the transmission is over radio channels, and when either noncoherent frequency shift keying or coherent phase shift keying (CPSK) modulation is employed. Both Gaussian and Rayleigh fading channels are considered, and for the latter, the effect of bit scrambling prior to transmission and two types of diversity are investigated. The gain in overall signal-to-noise ratio due to using the minimum distance code compared to the conventional folded binary code for low values of input signal power is determined. In addition to the theoretical results, computer simulations are presented of mu-law pulse-code-modulated encoded speech transmitted over the same channels, using CPSK modulation, bit scrambling, and diversity where appropriate.

  5. Transmit power optimization for green multihop relaying over Nakagami-m fading channels

    KAUST Repository

    Randrianantenaina, Itsikiantsoa

    2014-03-01

    In this paper, we investigate the optimal transmit power strategy to maximize the energy efficiency of a multihop relaying network. Considering the communication between a source and a destination through multiple Amplify-and-Forward relays, we first give the expression of the total instantaneous system energy consumption. Then, we define the energy efficiency in our context and obtain its expression in closed-form when the communication is over Nakagami-m fading channels. The analysis yields to the derivation of a global transmit power strategy where each individual node is contributing to the end-to-end overall energy efficiency. Numercial results are presented to illustrate the analysis. Comparison with Monte Carlo simulation results confirms the accuracy of our derivations, and assesses the gains of the proposed power optimization strategy. © 2014 IEEE.

  6. Upper and lower bounds for the ergodic capacity of MIMO Jacobi fading channels

    Science.gov (United States)

    Nafkha, Amor; Bonnefoi, Rémi

    2017-05-01

    In multi-(core/mode) optical fiber communication, the transmission channel can be modeled as a complex sub-matrix of the Haar-distributed unitary matrix (complex Jacobi unitary ensemble). In this letter, we present new analytical expressions of the upper and lower bounds for the ergodic capacity of multiple-input multiple-output Jacobi-fading channels. Recent results on the determinant of the Jacobi unitary ensemble are employed to derive a tight lower bound on the ergodic capacity. We use Jensen's inequality to provide an analytical closed-form upper bound to the ergodic capacity at any signal-to-noise ratio (SNR). Closed-form expressions of the ergodic capacity, at low and high SNR regimes, are also derived. Simulation results are presented to validate the accuracy of the derived expressions.

  7. A study of optimization problem for amplify-and-forward relaying over weibull fading channels

    KAUST Repository

    Ikki, Salama Said

    2010-09-01

    This paper addresses the power allocation and relay positioning problems in amplify-and-forward cooperative networks operating in Weibull fading environments. We study adaptive power allocation (PA) with fixed relay location, optimal relay location with fixed power allocation, and joint optimization of the PA and relay location under total transmit power constraint, in order to minimize the outage probability and average error probability at high signal-to-noise ratios (SNR). Analytical results are validated by numerical simulations and comparisons between the different optimization schemes and their performance are provided. Results show that optimum PA brings only coding gain, while optimum relay location yields, in addition to the latter, diversity gains as well. Also, joint optimization improves both, the diversity gain and coding gain. Furthermore, results illustrate that the analyzed adaptive algorithms outperform uniform schemes. ©2010 IEEE.

  8. Joint Power and Resource Allocation for Block-Fading Relay-Assisted Broadcast Channels

    CERN Document Server

    Shaqfeh, Mohammad

    2012-01-01

    We provide the solution for optimizing the power and resource allocation over block-fading relay-assisted broadcast channels in order to maximize the long term average achievable rates region of the users. The problem formulation assumes regenerative (repetition coding) decode-and-forward (DF) relaying strategy, long-term average total transmitted power constraint, orthogonal multiplexing of the users messages within the channel blocks, possibility to use a direct transmission (DT) mode from the base station to the user terminal directly or a relaying (DF) transmission mode, and partial channel state information. We show that our optimization problem can be transformed into an equivalent "no-relaying" broadcast channel optimization problem with each actual user substituted by two virtual users having different channel qualities and multiplexing weights. The proposed power and resource allocation strategies are expressed in closed-form that can be applied practically in centralized relay-assisted wireless netw...

  9. Asymptotic analysis for Nakagami-m fading channels with relay selection

    KAUST Repository

    Zhong, Caijun

    2011-06-01

    In this paper, we analyze the asymptotic outage probability performance of both decode-and-forward (DF) and amplify-and-forward (AF) relaying systems using partial relay selection and the "best" relay selection schemes for Nakagami-m fading channels. We derive their respective outage probability expressions in the asymptotic high signal-to-noise ratio (SNR) regime, from which the diversity order and coding gain are analyzed. In addition, we investigate the impact of power allocation between the source and relay terminals and derive the diversity-multiplexing tradeoff (DMT) for these relay selection systems. The theoretical findings suggest that partial relay selection can improve the diversity of the system and can achieve the same DMT as the "best" relay selection scheme under certain conditions. © 2011 IEEE.

  10. A novel method for combating dispersion induced power fading in dispersion compensating fiber

    DEFF Research Database (Denmark)

    Lebedev, Alexander; Vegas Olmos, Juan José; Iglesias Olmedo, Miguel

    2013-01-01

    We experimentally investigate the performance of 60 GHz double sideband (DSB) radio over fiber (RoF) links that employ dispersion compensating fiber (DCF). Error free transmission of 3 Gbps signals over 1 m of wireless distance is reported. In order to overcome experimentally observed chromatic...... dispersion (CD) induced power fading of radio frequency (RF) signal, we propose a method for improvement of RF carrier-to-noise (C/N) ratio through introduction of a degree of RF frequency tunability. Overall results improve important aspects of directly modulated RoF systems and demonstrate the feasibility...... of high carrier frequency and wide bandwidth RF signals delivery in RoF links including DCF fiber. Error free performance that we obtain for 3 Gbps amplitude shift-keying (ASK) signals enables uncompressed high-definition 1080p video delivery....

  11. MIMO Fading Emulator Development with FPGA and Its Application to Performance Evaluation of Mobile Radio Systems

    Directory of Open Access Journals (Sweden)

    Yoshio Karasawa

    2017-01-01

    Full Text Available We present four new developments for a multiple-input multiple-output (MIMO over-the-air measurement system based on our previous studies. The first two developments relate to the channel model for multipath environment generation. One is a further simplification of the circuit configuration without performance degradation by reducing the number of delay generation units, which dominate the performance limit when implementing the circuit on a field-programmable gate array (FPGA. The other is to realize spatial correlation characteristics among the input ports on the transmission side, whereas the previously proposed channel model did not consider this correlation. The third development involves the details of implementing the MIMO fading emulator on an FPGA as a two-stage scheme. The fourth is the demonstration of application examples of the developed system.

  12. Optimal Training for Time-Selective Wireless Fading Channels Using Cutoff Rate

    Directory of Open Access Journals (Sweden)

    Tong Lang

    2006-01-01

    Full Text Available We consider the optimal allocation of resources—power and bandwidth—between training and data transmissions for single-user time-selective Rayleigh flat-fading channels under the cutoff rate criterion. The transmitter exploits statistical channel state information (CSI in the form of the channel Doppler spectrum to embed pilot symbols into the transmission stream. At the receiver, instantaneous, though imperfect, CSI is acquired through minimum mean-square estimation of the channel based on some set of pilot observations. We compute the ergodic cutoff rate for this scenario. Assuming estimator-based interleaving and -PSK inputs, we study two special cases in-depth. First, we derive the optimal resource allocation for the Gauss-Markov correlation model. Next, we validate and refine these insights by studying resource allocation for the Jakes model.

  13. On the Ergodic Capacity of Dual-Branch Correlated Log-Normal Fading Channels with Applications

    KAUST Repository

    Al-Quwaiee, Hessa

    2015-05-01

    Closed-form expressions of the ergodic capacity of independent or correlated diversity branches over Log-Normal fading channels are not available in the literature. Thus, it is become of an interest to investigate the behavior of such metric at high signal-to-noise (SNR). In this work, we propose simple closed-form asymptotic expressions of the ergodic capacity of dual-branch correlated Log- Normal corresponding to selection combining, and switch-and-stay combining. Furthermore, we capitalize on these new results to find new asymptotic ergodic capacity of correlated dual- branch free-space optical communication system under the impact of pointing error with both heterodyne and intensity modulation/direct detection. © 2015 IEEE.

  14. Outage and Capacity Performance Evaluation of Distributed MIMO Systems over a Composite Fading Channel

    Directory of Open Access Journals (Sweden)

    Wenjie Peng

    2014-01-01

    Full Text Available The exact closed-form expressions regarding the outage probability and capacity of distributed MIMO (DMIMO systems over a composite fading channel are derived. This is achieved firstly by using a lognormal approximation to a gamma-lognormal distribution when a mobile station (MS in the cell is in a fixed position, and the so-called maximum ratio transmission/selected combining (MRT-SC and selected transmission/maximum ratio combining (ST-MRC schemes are adopted in uplink and downlink, respectively. Then, based on a newly proposed nonuniform MS cell distribution model, which is more consistent with the MS cell hotspot distribution in an actual communication environment, the average outage probability and capacity formulas are further derived. Finally, the accuracy of the approximation method and the rationality of the corresponding theoretical analysis regarding the system performance are proven and illustrated by computer simulations.

  15. New Experimental Technique for Nodularity and Mg Fading Control in Compacted Graphite Iron Production on Laboratory Scale

    Science.gov (United States)

    Hernando, Juan Carlos; Domeij, Björn; González, Daniel; Amieva, José Manuel; Diószegi, Attila

    2017-11-01

    The narrow production window for compacted graphite iron material (CGI) drastically reduces the possibilities to produce it in small batches outside an industrial environment. This fact hinders laboratory-scale investigations on CGI solidification. This work presents a solution to that issue by introducing an experimental technique to produce graphitic cast iron of the main three families. Samples of a base hypereutectic spheroidal graphite iron (SGI) were re-melted in a resistance furnace under Ar atmosphere. Varying the holding time at 1723 K (1450 °C), graphitic irons ranging from spheroidal to lamellar were produced. Characterization of the graphite morphology evolution, in terms of nodularity as a function of holding time, is presented. The nodularity decay for the SGI region suggests a linear correlation with the holding time. In the CGI region, nodularity deterioration shows a slower rate, concluding with the sudden appearance of lamellar graphite. The fading process of magnesium, showing agreement with previous researchers, is described by means of empirical relations as a function of holding time and nodularity. The results on nodularity fade and number of nodules per unit area fade suggest that both phenomena occur simultaneously during the fading process of magnesium.

  16. Path Loss, Shadow Fading, and Line-Of-Sight Probability Models for 5G Urban Macro-Cellular Scenarios

    DEFF Research Database (Denmark)

    Sun, Shu; Thomas, Timothy; Rappaport, Theodore S.

    2015-01-01

    This paper presents key parameters including the line-of-sight (LOS) probability, large-scale path loss, and shadow fading models for the design of future fifth generation (5G) wireless communication systems in urban macro-cellular (UMa) scenarios, using the data obtained from propagation measure...

  17. A novel ergodic capacity analysis of diversity combining and multihop transmission systems over generalized composite fading channels

    KAUST Repository

    Yilmaz, Ferkan

    2012-06-01

    Ergodic capacity is an important performance measure associated with reliable communication at the highest rate at which information can be sent over the channel with a negligible probability of error. In the shadow of this definition, diversity receivers (such as selection combining, equal-gain combining and maximal-ratio combining) and transmission techniques (such as cascaded fading channels, amplify-and-forward multihop transmission) are deployed in mitigating various performance impairing effects such as fading and shadowing in digital radio communication links. However, the exact analysis of ergodic capacity is in general not always possible for all of these forms of diversity receivers and transmission techniques over generalized composite fading environments due to it\\'s mathematical intractability. In the literature, published papers concerning the exact analysis of ergodic capacity have been therefore scarce (i.e., only [1] and [2]) when compared to those concerning the exact analysis of average symbol error probability. In addition, they are essentially targeting to the ergodic capacity of the maximal ratio combining diversity receivers and are not readily applicable to the capacity analysis of the other diversity combiners / transmission techniques. In this paper, we propose a novel moment generating function-based approach for the exact ergodic capacity analysis of both diversity receivers and transmission techniques over generalized composite fading environments. As such, we demonstrate how to simultaneously treat the ergodic capacity analysis of all forms of both diversity receivers and multihop transmission techniques. © 2012 IEEE.

  18. Fleeting, fading, or far-reaching? A knowledge-based model of the persistence of framing effects

    NARCIS (Netherlands)

    Baden, C.; Lecheler, S.

    2012-01-01

    The social relevance of framing effects hinges upon their ability to persist. This article develops a theoretical account of the conditions under which framing effects should vanish quickly, fade slowly, or cause permanent changes. It argues that the cognitive processes involved in mediating frame

  19. Concentration dependence of fading of the open form of 6’-nitroindolinospiropyran in a polymer matrix

    NARCIS (Netherlands)

    Drabe, Karel E.; Boer, Steven de; Wiersma, Douwe A.

    1991-01-01

    The concentration dependence of the fading process of the open form of 6’-nitroindolinospiropyran (BIPS) in PMMA has been studied by fluorescence lifetime measurements at 77 K. At sufficiently high concentrations, the fluorescence decay becomes bi-exponential which indicates that energy transfer

  20. Channel and delay estimation for base-station–based cooperative communications in frequency-selective fading channels

    Directory of Open Access Journals (Sweden)

    Hongjun Xu

    2011-07-01

    Full Text Available A channel and delay estimation algorithm for both positive and negative delay, based on the distributed Alamouti scheme, has been recently discussed for base-station–based asynchronous cooperative systems in frequency-flat fading channels. This paper extends the algorithm, the maximum likelihood estimator, to work in frequency-selective fading channels. The minimum mean square error (MMSE performance of channel estimation for both packet schemes and normal schemes is discussed in this paper. The symbol error rate (SER performance of equalisation and detection for both time-reversal space-time block code (STBC and single-carrier STBC is also discussed in this paper. The MMSE simulation results demonstrated the superior performance of the packet scheme over the normal scheme with an improvement in performance of up to 6 dB when feedback was used in the frequency-selective channel at a MSE of 3 x 10–2. The SER simulation results showed that, although both the normal and packet schemes achieved similar diversity orders, the packet scheme demonstrated a 1 dB coding gain over the normal scheme at a SER of 10–5. Finally, the SER simulations showed that the frequency-selective fading system outperformed the frequency-flat fading system.

  1. Delay-distribution-dependent H∞ state estimation for delayed neural networks with (x,v)-dependent noises and fading channels.

    Science.gov (United States)

    Sheng, Li; Wang, Zidong; Tian, Engang; Alsaadi, Fuad E

    2016-12-01

    This paper deals with the H∞ state estimation problem for a class of discrete-time neural networks with stochastic delays subject to state- and disturbance-dependent noises (also called (x,v)-dependent noises) and fading channels. The time-varying stochastic delay takes values on certain intervals with known probability distributions. The system measurement is transmitted through fading channels described by the Rice fading model. The aim of the addressed problem is to design a state estimator such that the estimation performance is guaranteed in the mean-square sense against admissible stochastic time-delays, stochastic noises as well as stochastic fading signals. By employing the stochastic analysis approach combined with the Kronecker product, several delay-distribution-dependent conditions are derived to ensure that the error dynamics of the neuron states is stochastically stable with prescribed H∞ performance. Finally, a numerical example is provided to illustrate the effectiveness of the obtained results. Copyright © 2016 Elsevier Ltd. All rights reserved.

  2. Throughput and Delay Analysis of HARQ with Code Combining over Double Rayleigh Fading Channels

    KAUST Repository

    Chelli, Ali

    2018-01-15

    This paper proposes the use of hybrid automatic repeat request (HARQ) with code combining (HARQ-CC) to offer reliable communications over double Rayleigh channels. The double Rayleigh fading channel is of particular interest to vehicle-to-vehicle communication systems as well as amplify-and-forward relaying and keyhole channels. This work studies the performance of HARQ-CC over double Rayleigh channels from an information theoretic perspective. Analytical approximations are derived for the $\\\\epsilon$-outage capacity, the average number of transmissions, and the throughput of HARQ-CC. Moreover, we evaluate the delay experienced by Poisson arriving packets for HARQ-CC. We provide analytical expressions for the average waiting time, the packets sojourn time, the average consumed power, and the energy efficiency. In our investigation, we take into account the impact of imperfect feedback on different performance metrics. Additionally, we explore the tradeoff between energy efficiency and the throughput. The proposed scheme is shown to maintain the outage probability below a specified threshold $\\\\epsilon$ which ensures the link reliability. Meanwhile, HARQ-CC adapts implicitly the transmission rate to the channel conditions such that the throughput is maximized. Our results demonstrate that HARQ-CC allows improving the achievable communication rate compared to fixed time diversity schemes. To maximize the throughput of HARQ-CC, the rate per HARQ round should be less than the rate required to meet the outage constraint. Our investigation of the performance of HARQ-CC over Rayleigh and double Rayleigh channels shows that double Rayleigh channels have a higher severity of fading and result in a larger degradation of the throughput. Our analysis reveals that HARQ with incremental redundancy (HARQ-IR) achieves a larger throughput compared to HARQ-CC, while HARQ-CC is simpler to implement, has a lower decoding

  3. Repeat-punctured superorthogonal convolutional turbo codes on AWGN and flat Rayleigh fading channels

    Directory of Open Access Journals (Sweden)

    Fambirai Takawira

    2010-10-01

    Full Text Available Repeat-punctured turbo codes, an extension of the conventional turbo-coding scheme, has shown a significant increase in bit-error rate performance at moderate to high signal-to-noise ratios for short frame lengths. Superorthogonal convolutional turbo codes (SCTC makes use of superorthogonal signals to improve the performance of the conventional turbo codes and a coding scheme that applies the repeat-punctured technique into SCTC has shown to perform better. We investigated two new low-rate coding schemes, repeat-punctured superorthogonal convolutional turbo codes (RPSCTC and dual-repeat-punctured superorthogonal convolutional turbo codes (DRPSCTC, that make use of superorthogonal signaling, together with repetition and puncturing, to improve the performance of SCTC for reliable and effective communications. Simulation results in the additive white Gaussian noise (AWGN channel and the frequency non-selective Rayleigh fading channel are presented together with analytical bounds of bit error probabilities, derived from transfer function bounding techniques. From the simulation results and the analytical bounds presented, it is evident that RPSCTC and DRPSCTC offer a more superior performance than SCTC in the AWGN channel, as well as in flat Rayleigh non-line-of-sight fading channels. The distance spectrum is also presented for the new schemes and accounts for the performance improvement rendered in simulations. It is important to note that the improved performance that SCTC, and consequently RPSCTC and DRPSCTC, exhibit is achieved at the expense of bandwidth expansion and complexity and would be ideal for power-limited satellite communication links or interference-limited systems.

  4. Visible Persistence of Single-Transient Random Dot Patterns: Spatial Parameters Affect the Duration of Fading Percepts.

    Directory of Open Access Journals (Sweden)

    Maximilian Bruchmann

    Full Text Available Visible persistence refers to the continuation of visual perception after the physical termination of a stimulus. We studied an extreme case of visible persistence by presenting two matrices of randomly distributed black and white pixels in succession. On the transition from one matrix to the second, the luminance polarity of all pixels within a disk- or annulus-shaped area reversed, physically creating a single second-order transient signal. This transient signal produces the percept of a disk or an annulus with an abrupt onset and a gradual offset. To study the nature of this fading percept we varied spatial parameters, such as the inner and the outer diameter of annuli (Experiment I and the radius and eccentricity of disks (Experiment III, and measured the duration of visible persistence by having subjects adjust the synchrony of the onset of a reference stimulus with the onset or the offset of the fading percept. We validated this method by comparing two modalities of the reference stimuli (Experiment I and by comparing the judgments of fading percepts with the judgments of stimuli that actually fade in luminance contrast (Experiment II. The results show that (i irrespective of the reference modality, participants are able to precisely judge the on- and the offsets of the fading percepts, (ii auditory reference stimuli lead to higher visible persistence durations than visual ones, (iii visible persistence duration increases with the thickness of annuli and the diameter of disks, but decreases with the diameter of annuli, irrespective of stimulus eccentricity. These effects cannot be explained by stimulus energy, which suggests that more complex processing mechanisms are involved. Seemingly contradictory effects of disk and annulus diameter can be unified by assuming an abstract filling-in mechanism that speeds up with the strength of the edge signal and takes more time the larger the stimulus area is.

  5. Hubble space telescope observations of the afterglow, supernova, and host galaxy associated with the extremely bright GRB 130427A

    Energy Technology Data Exchange (ETDEWEB)

    Levan, A. J. [Department of Physics, University of Warwick, Coventry, CV4 7AL (United Kingdom); Tanvir, N. R.; Wiersema, K. [Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH (United Kingdom); Fruchter, A. S.; Hounsell, R. A.; Graham, J. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Hjorth, J.; Fynbo, J. P. U. [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark); Pian, E. [INAF, Trieste Astronomical Observatory, via G.B. Tiepolo 11, I-34143 Trieste (Italy); Mazzali, P. [Astrophysics Research Institute, Liverpool John Moores University, IC2 Liverpool Science Park 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom); Perley, D. A. [Department of Astronomy, California Institute of Technology, MC 249-17, 1200 East California Blvd., Pasadena, CA 91125 (United States); Cano, Z. [Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, Dunhagi 5, 107 Reykjavik (Iceland); Cenko, S. B. [Astrophysics Science Division, NASA Goddard Space Flight Center, Mail Code 661, Greenbelt, MD 20771 (United States); Kouveliotou, C. [Science and Technology Office, ZP12, NASA/Marshall Space Flight Center, Huntsville, AL 35812 (United States); Pe' er, A. [Department of Physics, University College Cork, Cork (Ireland); Misra, K., E-mail: a.j.levan@warwick.ac.uk [Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital-263 002 (India)

    2014-09-10

    We present Hubble Space Telescope (HST) observations of the exceptionally bright and luminous Swift gamma-ray burst (GRB), GRB 130427A. At z = 0.34, this burst affords an excellent opportunity to study the supernova (SN) and host galaxy associated with an intrinsically extremely luminous burst (E {sub iso} > 10{sup 54} erg): more luminous than any previous GRB with a spectroscopically associated SN. We use the combination of the image quality, UV capability, and invariant point-spread function of HST to provide the best possible separation of the afterglow, host, and SN contributions to the observed light ∼17 rest-frame days after the burst, utilizing a host subtraction spectrum obtained one year later. Advanced Camera for Surveys grism observations show that the associated SN, SN 2013cq, has an overall spectral shape and luminosity similar to SN 1998bw (with a photospheric velocity, v {sub ph} ∼ 15, 000 km s{sup –1}). The positions of the bluer features are better matched by the higher velocity SN 2010bh (v {sub ph} ∼ 30, 000 km s{sup –1}), but this SN is significantly fainter and fails to reproduce the overall spectral shape, perhaps indicative of velocity structure in the ejecta. We find that the burst originated ∼4 kpc from the nucleus of a moderately star forming (1 M {sub ☉} yr{sup –1}), possibly interacting disk galaxy. The absolute magnitude, physical size, and morphology of this galaxy, as well as the location of the GRB within it, are also strikingly similar to those of GRB 980425/SN 1998bw. The similarity of the SNe and environment from both the most luminous and least luminous GRBs suggests that broadly similar progenitor stars can create GRBs across six orders of magnitude in isotropic energy.

  6. Hubble Space Telescope Observations of the Afterglow, Supernova and Host Galaxy Associated with the Extremely Bright GRB 130427A

    Science.gov (United States)

    Levan, A.J.; Tanvir, N. R.; Fruchter, A. S.; Hjorth, J.; Pian, E.; Mazzali, P.; Hounsell, R. A.; Perley, D. A.; Cano, Z.; Graham, J.; hide

    2014-01-01

    We present Hubble Space Telescope (HST) observations of the exceptionally bright and luminous Swift gamma-ray burst, GRB 130427A. At z=0.34 this burst affords an excellent opportunity to study the supernova and host galaxy associated with an intrinsically extremely luminous burst (E(sub iso) greater than 10(exp 54) erg): more luminous than any previous GRB with a spectroscopically associated supernova. We use the combination of the image quality, UV capability and and invariant PSF of HST to provide the best possible separation of the afterglow, host and supernova contributions to the observed light approximately 17 rest-frame days after the burst utilising a host subtraction spectrum obtained 1 year later. Advanced Camera for Surveys (ACS) grism observations show that the associated supernova, SN 2013cq, has an overall spectral shape and luminosity similar to SN 1998bw (with a photospheric velocity, vph approximately 15,000 kilometers per second). The positions of the bluer features are better matched by the higher velocity SN 2010bh (vph approximately 30,000 kilometers per second), but SN 2010bh (vph approximately 30,000 kilometers per second but this SN is significantly fainter, and fails to reproduce the overall spectral shape, perhaps indicative of velocity structure in the ejecta. We find that the burst originated approximately 4 kpc from the nucleus of a moderately star forming (1 Solar Mass yr(exp-1)), possibly interacting disc galaxy. The absolute magnitude, physical size and morphology of this galaxy, as well as the location of the GRB within it are also strikingly similar to those of GRB980425SN 1998bw. The similarity of supernovae and environment from both the most luminous and least luminous GRBs suggests broadly similar progenitor stars can create GRBs across six orders of magnitude in isotropic energy.

  7. Project ASTRAL: All-sky Space Telescope to Record Afterglow Locations

    Science.gov (United States)

    Tsarevsky, G.; Bisnovaty-Kogan, G.; Pozanenko, A.; Beskin, G. M.; Bondar, S.; Rumyantsev, V.

    ASTRAL is a project incorporating wide-field optical telescopes on board a small satellite (FedSat or SMEX type) dedicated to the whole-sky detection of a variety of rapid astronomical phenomena, particularly optical flashes associated with gamma ray bursts (GRB). Those flashes only visible optically (so called orphans), as well as those which could precede associated GRBs, cannot be detected in the current triggering mode of the world wide GRB Coordinates Network (GCN). Hence ASTRAL would have a unique opportunity to trigger a follow-up multi-frequency study via GCN. ASTRAL consists of a set of 13 wide-field cameras, each with FOV = 70°, equipped with 4096 × 4096 CCDs. The detection method is based on comparison of sky images with the reference image. Supernovae, novae and nova-like explosions, fast variable AGNs, flare stars, and even new comets would be promptly detected as well. Thus ASTRAL would be an original working prototype of the prospective major space mission to monitor on-line all the sky, a high priority instrument of 21st Century astrophysics. See http://www.atnf.csiro.au/people/Gregory.Tsarevsky for details.

  8. Note: Light output enhanced fast response and low afterglow 6Li glass scintillator as potential down-scattered neutron diagnostics for inertial confinement fusion.

    Science.gov (United States)

    Arikawa, Yasunobu; Yamanoi, Kohei; Nagai, Takahiro; Watanabe, Kozue; Kouno, Masahiro; Sakai, Kohei; Nakazato, Tomoharu; Shimizu, Toshihiko; Cadatal, Marilou Raduban; Estacio, Elmer Surat; Sarukura, Nobuhiko; Nakai, Mitsuo; Norimatsu, Takayoshi; Azechi, Hiroshi; Murata, Takahiro; Fujino, Shigeru; Yoshida, Hideki; Izumi, Nobuhiko; Satoh, Nakahiro; Kan, Hirofumi

    2010-10-01

    The characteristics of an APLF80+3Ce scintillator are presented. Its sufficiently fast decay profile, low afterglow, and an improved light output compared to the recently developed APLF80+3Pr, were experimentally demonstrated. This scintillator material holds promise for applications in neutron imaging diagnostics at the energy regions of 0.27 MeV of DD fusion down-scattered neutron peak at the world's largest inertial confinement fusion facilities such as the National Ignition Facility and the Laser Mégajoule.

  9. Novel MGF-based expressions for the average bit error probability of binary signalling over generalized fading channels

    KAUST Repository

    Yilmaz, Ferkan

    2014-04-01

    The main idea in the moment generating function (MGF) approach is to alternatively express the conditional bit error probability (BEP) in a desired exponential form so that possibly multi-fold performance averaging is readily converted into a computationally efficient single-fold averaging - sometimes into a closed-form - by means of using the MGF of the signal-to-noise ratio. However, as presented in [1] and specifically indicated in [2] and also to the best of our knowledge, there does not exist an MGF-based approach in the literature to represent Wojnar\\'s generic BEP expression in a desired exponential form. This paper presents novel MGF-based expressions for calculating the average BEP of binary signalling over generalized fading channels, specifically by expressing Wojnar\\'s generic BEP expression in a desirable exponential form. We also propose MGF-based expressions to explore the amount of dispersion in the BEP for binary signalling over generalized fading channels.

  10. Exact Outage Probability of Dual-Hop CSI-Assisted AF Relaying Over Nakagami-m Fading Channels

    KAUST Repository

    Xia, Minghua

    2012-10-01

    In this correspondence, considering dual-hop channel state information (CSI)-assisted amplify-and-forward (AF) relaying over Nakagami- m fading channels, the cumulative distribution function (CDF) of the end-to-end signal-to-noise ratio (SNR) is derived. In particular, when the fading shape factors m1 and m2 at consecutive hops take non-integer values, the bivariate H-function and G -function are exploited to obtain an exact analytical expression for the CDF. The obtained CDF is then applied to evaluate the outage performance of the system under study. The analytical results of outage probability coincide exactly with Monte-Carlo simulation results and outperform the previously reported upper bounds in the low and medium SNR regions.

  11. Performance analysis of DS/CDMA with noncoherent M-ary orthogonal modulation in multipath fading channels

    Science.gov (United States)

    Jalloul, Louay M. A.; Holtzman, Jack M.

    1994-06-01

    In this paper, the performance of a DS/CDMA system using M-ary orthogonal modulation with noncoherent demodulation is evaluated. The system operates in a multipath fading channel. A RAKE receiver structure with equal gain combining is used for demodulation. An approximation to the bit error probability is given which depends only on the first- and second-order moments of the multipath energies. The analysis results are compared with the results from computer simulations. It is seen that the approximation is accurate for multipaths energies with realistic coefficient of variation. System performance is also evaluated in terms of the capacity, which is defined as the number of users that can be supported at a given bit error probability. The approximation is used to evaluate the capacity reductions due to power variations caused by multipath fading.

  12. On the computation of the higher-order statistics of the channel capacity over generalized fading channels

    KAUST Repository

    Yilmaz, Ferkan

    2012-12-01

    The higher-order statistics (HOS) of the channel capacity μn=E[logn (1+γ end)], where n ∈ N denotes the order of the statistics, has received relatively little attention in the literature, due in part to the intractability of its analysis. In this letter, we propose a novel and unified analysis, which is based on the moment generating function (MGF) technique, to exactly compute the HOS of the channel capacity. More precisely, our mathematical formalism can be readily applied to maximal-ratio-combining (MRC) receivers operating in generalized fading environments. The mathematical formalism is illustrated by some numerical examples focusing on the correlated generalized fading environments. © 2012 IEEE.

  13. Effects of simultaneous release of trapped carriers and pair production on fading in thermoluminescent materials during storage in radiation fields

    Energy Technology Data Exchange (ETDEWEB)

    Ros, J.M.G.; Delgado, A. [Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas (CIEMAT), Madrid (Spain). Inst. de Investigacion Basica; Furetta, C.; Scacco, A. [La Sapienza Univ., Rome (Italy). Dip. di Fisica

    1996-03-01

    A calculation of fading effects on the trapped charge population in a TL trap is presented when radiation-induced pair production and thermal raising of trapped charges occurs simultaneously. For the calculation, different time-intensity irradiation profiles have been employed, selected with reference to practical situations in radiation dosimetry. Different sets of TL trapping parameters have been employed to investigate the influence of the kinetic parameters (trap activation energy, frequency factor and retrapping-recombination cross-section ratio) on the stability of the trapped charges. The calculations presented here, which exclusively concern fading effects in a variety of practical situations, would help clarify the respective role of trap and charge effects in the stability of practical TL materials. (author).

  14. Exploring the "intensity fading" phenomenon in the study of noncovalent interactions by MALDI-TOF mass spectrometry

    DEFF Research Database (Denmark)

    Yanes, Oscar; Aviles, Francesc X; Roepstorff, Peter

    2007-01-01

    , in which a reduction in the relative signal intensity of low molecular mass binding partners (i.e., protease inhibitors) can be observed when their target protein (i.e., protease) is added to the sample. Here we have performed a systematic study to explore how various experimental conditions affect......The difficulties to detect intact noncovalent complexes involving proteins and peptides by MALDI-TOF mass spectrometry have hindered a widespread use of this approach. Recently, "intensity fading MS" has been presented as an alternative strategy to detect noncovalent interactions in solution...... the intensity fading phenomenon, as well as a comparison with the strategy based on the direct detection of intact complexes by MALDI MS. For this purpose, the study is focused on two different protease-inhibitor complexes naturally occurring in solution, together with a heterogeneous mixture of nonbinding...

  15. Performance analysis of cognitive multihop relaying with m-QAM detect-and-forward in Nakagami-m fading channels

    KAUST Repository

    Benjillali, Mustapha

    2013-09-01

    In this work, we investigate the performance of cognitive multihop regenerative relaying systems in the "underlay" spectrum sharing scenario. The multiple relays perform "detect-and-forward" relaying strategy to convey a message with an order m quadrature amplitude modulation (m-QAM) from the source to the destination over independent but not necessarily identical Nakagami-m fading channels. We adopt a closed-form analysis framework based on univariate and bivariate Meijer G-functions to derive the end-to-end error performance (in terms of bit and symbol error rates), the outage probability, and the ergodic capacity. Various numerical examples are presented to illustrate the results with a large combination of system and fading parameters, and simulation results confirm the accuracy of our closed-form analysis. © 2013 IEEE.

  16. Rapid Prototyping

    Science.gov (United States)

    1999-01-01

    Javelin, a Lone Peak Engineering Inc. Company has introduced the SteamRoller(TM) System as a commercial product. The system was designed by Javelin during a Phase II NASA funded small commercial product. The purpose of the invention was to allow automated-feed of flexible ceramic tapes to the Laminated Object Manufacturing rapid prototyping equipment. The ceramic material that Javelin was working with during the Phase II project is silicon nitride. This engineered ceramic material is of interest for space-based component.

  17. Performance of fading multi-user diversity for underlay cognitive networksy

    KAUST Repository

    Khan, Fahd Ahmed

    2013-05-01

    Having multiple secondary users (SUs) can be exploited to achieve multiuser diversity and improve the throughput of the underlay secondary network. In the cognitive setting, satisfying the interference constraint is essential, and thus, a scheduling scheme is considered where some SUs are preselected based on the low interference power. From this subset, the SU that yields the highest throughput is selected for transmission. This scheduling scheme helps to lower the interference power while giving good throughput. For an independent but not identically distributed Nakagami-m fading channel, we obtain exact closed-form expressions of the capacity of this scheduling scheme. Furthermore, the scheduling time of SUs is characterized and closed-form expressions for the mean time after which a SU is selected for transmission are obtained. Numerical simulations are performed to corroborate the derived analytical results. Our results show that at low interference threshold, increasing transmit power of the SUs is not beneficial and results in reduced capacity. Furthermore, the channel idle time (i.e. time that no user is utilizing the channel) reduces with increasing the number of SUs. © 2013 IEEE.

  18. Energy Efficient and Performance Analysis of Multihop Wireless Communication Over Nakagami-m Fading Channel

    KAUST Repository

    Randrianantenaina, Itsikiantsoa

    2015-06-01

    The concept of multihop communications (where the source communicates with the destination via many intermediate nodes) has been revisited and adapted to mitigate wireless channel impairments and ensure broader coverage. It has been shown in the literature that, in addition to extending coverage, overcoming shadowing and reducing the transmit power, multihop communications can increase the capacity of the network at a low additional cost. On the other hand, the problem of energy efficiency is one of the current biggest challenges towards green radio communications. Morevover, electromagnetic radiation is at its limit in many contexts, while for battery-powered devices, transmit and circuit energy consumption has to be minimized for better battery lifetime and performance. In this work, the performance of multihop communication over Nakagami-m fading is investigated for both cases without and with diversity combining. Closed form expressions of the average ergodic capacity are derived for each of these cases. Then, an expression of the outage probability is obtained using the inverse of Laplace transform and the average bit error rate is bounded using the Moment-Generating-Function approach. The energy efficiency is analyzed using the "consumption factor" as a metric, and it is derived in closed-form. And based on the obtained expressions, we propose a power allocation strategy maximizing this consumption factor.

  19. Exact capture probability analysis of GSC receivers over Rayleigh fading channel

    KAUST Repository

    Nam, Sungsik

    2010-01-01

    For third generation systems and ultrawideband systems, RAKE receivers have been introduced due to the advantage of RAKE receivers which is their ability to combine different replicas of the transmitted signal arriving at different delays in a rich multipath environment. In principle, RAKE receivers combine all resolvable paths which gives the best performance in a rich diversity environment. However, this is usually costly in terms of hardware required as the number of RAKE fingers increases. Therefore, generalized selection combining (GSC) RAKE reception was proposed and has been studied by many researcher as an alternative to the classical two fundamental diversity schemes: maximal ratio combining and selection combining. Previous work on performance analyses of GSC RAKE receivers based on the signal to noise ratio focused on the development of methodologies to derive exact closedform expressions for various performance measures. However, the remaining set of uncombined paths affect the overall performance both in terms of loss in power. Therefore, to have a full understanding of the performance of GSC RAKE receivers, we introduce in this paper the notion of capture probability, which is defined as the ratio of the captured power (essentially combined paths power) to that of the total available power. The major difficulty in these problems is to derive some joint statistics of ordered exponential variates. With this motivation in mind, we capitalize in this paper on some new order statistics results to derive exact closed-form expressions for the capture probability over independent and identically distributed Rayleigh fading channels. © 2010 IEEE.

  20. Light-induced fading of the PSL signal from irradiated herbs and spices

    Energy Technology Data Exchange (ETDEWEB)

    Alberti, A. [ISOF-CNR, Via P. Gobetti 101, 40129 Bologna (Italy); Corda, U. [ISOF-CNR, Via P. Gobetti 101, 40129 Bologna (Italy); Fuochi, P. [ISOF-CNR, Via P. Gobetti 101, 40129 Bologna (Italy)]. E-mail: fuochi@isof.cnr.it; Bortolin, E. [Istituto Superiore di Sanita, Viale Regina Elena 299, 00161 Rome (Italy); Calicchia, A. [Istituto Superiore di Sanita, Viale Regina Elena 299, 00161 Rome (Italy); Onori, S. [Istituto Superiore di Sanita, Viale Regina Elena 299, 00161 Rome (Italy)

    2007-08-15

    Reliability of the photo-stimulated luminescence (PSL) technique, as screening method for irradiated food identification, has been tested with three kinds of herbs and spices (oregano, red pepper and fennel), prepared in two different ways (granular: i.e. seeds and flakes, or powdered), over a long period of storage with different light exposures. The irradiated samples kept in the dark gave always a positive response (the sample is correctly classified as 'irradiated') for the overall examination period. The samples kept under ambient light conditions, in typical commercial glass containers, exhibited a reduction of the PSL signal, more or less pronounced depending on the type of food and packaging. The different PSL response of the irradiated samples is to be related to the quantity and quality of the mineral debris present in the individual food. It was also found that, for the same type of food, the light-induced fading was much stronger for the flaked and seed samples than for the corresponding powder samples, the penetrating capability of light being much more inhibited in powdered than in whole seeds or flaked form samples. The observed light bleaching of the PSL signal in irradiated herbs and spices is of practical relevance since it may lead to false negative classifications.

  1. Full-Duplex Relaying with Improper Gaussian Signaling over Nakagami-m Fading Channels

    KAUST Repository

    Gaafar, Mohamed

    2017-10-04

    We study the potential employment of improper Gaussian signaling (IGS) in full-duplex relaying (FDR) with non-negligible residual self-interference (RSI) under Nakagami- m fading. IGS is recently shown to outperform traditional proper Gaussian signaling (PGS) in several interference-limited settings. In this work, IGS is employed as an attempt to alleviate RSI. We use two performance metrics, namely, the outage probability and the ergodic rate. First, we provide upper and lower bounds for the system performance in terms of the relay transmit power and circularity coefficient, a measure of the signal impropriety. Then, we numerically optimize the relay signal parameters based only on the channel statistics to improve the system performance. Based on the analysis, IGS allows FDR to operate even with high RSI. The results show that IGS can leverage higher power budgets to enhance the performance, meanwhile it relieves RSI impact via tuning the signal impropriety. Interestingly, one-dimensional optimization of the circularity coefficient, with maximum relay power, offers a similar performance as the joint optimization, which reduces the optimization complexity. From a throughput standpoint, it is shown that IGS-FDR can outperform not only PGS-FDR, but also half-duplex relaying with/without maximum ratio combining over certain regions of the target source rate.

  2. On the performance of multiuser scheduling with post-examining under non-identical fading

    KAUST Repository

    Gaaloul, Fakhreddine

    2012-06-11

    We investigate the performance of a multiuser downlink access scheme based on a post-selection switch and examine algorithm. The studied scheme sequentially switches over the users that experience independent and non-identically distributed fading conditions, and selects a single user with an acceptable channel quality as compared to a pre-selected signal-to-noise ratio (SNR) threshold. If no one of the users can satisfy the target channel quality, the base station (BS) takes the advantage of the knowledge of all users channels and serves the user with the best channel quality among all users. This scheme reduces considerably the feedback load but offers a lower average spectral efficiency (ASE) as compared to that of the full feedback system with instantaneous best user selection. On the other hand, it improves the system performances, such as outage probability and average bit error rate (BER), as compared to a system that is based on a standard switching scheme without post-selection. Numerical results for the ASE average BER, and average feed back load, are presented for the cases of outdated and non-outdated rate-adaptive modulation scheme operating over independent and non-identically distributed users.

  3. Stochastic Power Control for Time-Varying Long-Term Fading Wireless Networks

    Directory of Open Access Journals (Sweden)

    Charalambous Charalambos D

    2006-01-01

    Full Text Available A new time-varying (TV long-term fading (LTF channel model which captures both the space and time variations of wireless systems is developed. The proposed TV LTF model is based on a stochastic differential equation driven by Brownian motion. This model is more realistic than the static models usually encountered in the literature. It allows viewing the wireless channel as a dynamical system, thus enabling well-developed tools of adaptive and nonadaptive estimation and identification techniques to be applied to this class of problems. In contrast with the traditional models, the statistics of the proposed model are shown to be TV, but converge in steady state to their static counterparts. Moreover, optimal power control algorithms (PCAs based on the new model are proposed. A centralized PCA is shown to reduce to a simple linear programming problem if predictable power control strategies (PPCS are used. In addition, an iterative distributed stochastic PCA is used to solve for the optimization problem using stochastic approximations. The latter solely requires each mobile to know its received signal-to-interference ratio. Generalizations of the power control problem based on convex optimization techniques are provided if PPCS are not assumed. Numerical results show that there are potentially large gains to be achieved by using TV stochastic models, and the distributed stochastic PCA provides better power stability and consumption than the distributed deterministic PCA.

  4. Hybrid digital-analog coding with bandwidth expansion for correlated Gaussian sources under Rayleigh fading

    Science.gov (United States)

    Yahampath, Pradeepa

    2017-12-01

    Consider communicating a correlated Gaussian source over a Rayleigh fading channel with no knowledge of the channel signal-to-noise ratio (CSNR) at the transmitter. In this case, a digital system cannot be optimal for a range of CSNRs. Analog transmission however is optimal at all CSNRs, if the source and channel are memoryless and bandwidth matched. This paper presents new hybrid digital-analog (HDA) systems for sources with memory and channels with bandwidth expansion, which outperform both digital-only and analog-only systems over a wide range of CSNRs. The digital part is either a predictive quantizer or a transform code, used to achieve a coding gain. Analog part uses linear encoding to transmit the quantization error which improves the performance under CSNR variations. The hybrid encoder is optimized to achieve the minimum AMMSE (average minimum mean square error) over the CSNR distribution. To this end, analytical expressions are derived for the AMMSE of asymptotically optimal systems. It is shown that the outage CSNR of the channel code and the analog-digital power allocation must be jointly optimized to achieve the minimum AMMSE. In the case of HDA predictive quantization, a simple algorithm is presented to solve the optimization problem. Experimental results are presented for both Gauss-Markov sources and speech signals.

  5. Analysis on Human Blockage Path Loss and Shadow Fading in Millimeter-Wave Band

    Directory of Open Access Journals (Sweden)

    Hongmei Zhao

    2017-01-01

    Full Text Available Millimeter-wave (Mm-w is the trend of communication development in the future; users who carry mobile communication equipment could be blocked by others in a crowded population environment. Based on Shooting and Bouncing Ray (SBR method and setting up different orientation receivers (RX, population density, and people fabric property at 28 GHz and 38 GHz, simulating experimental scene similar to station square by Wireless Insite software, we use least square method to do linear-regression analysis for path loss and build path loss model. The result shows that the path loss index has a certain change in the different frequency, orientation receivers, population density, and people fabric. The path loss index of RouteC1 and RouteA2 has an obvious change in the central transmitter (TX. Each route shadow fading obeys Gaussian distribution whose mean is 0. This paper’s result has a theoretical guiding for designing the communication system in a crowded population environment.

  6. Adaptive Transmitter Precoding for Time Division Duplex CDMA in Fading Multipath Channels: Strategy and Analysis

    Directory of Open Access Journals (Sweden)

    Daryl Reynolds

    2003-01-01

    Full Text Available The recently developed blind adaptive techniques for multiuser detection in code division multiple access (CDMA systems offer an attractive compromise of performance and complexity. However, the desire to further reduce complexity at the mobile unit has led to the investigation of techniques that move signal processing from the mobile unit to the base station. In this paper, we investigate transmitter precoding for downlink time division duplex (TDD code division multiple access (CDMA communications. In particular, we develop a linear minimum mean square error precoding strategy using blind channel estimation for fading multipath channels that allows for simple matched filtering at the mobile unit and is easy to make adaptive. We also present a performance analysis using tools developed for the analysis of conventional (receiver-based linear blind multiuser detection in unknown channels. We compare the analytical and simulation results to traditional receiver-based blind multiuser detection. It is seen that transmitter precoding offers a reasonable alternative for TDD-mode CDMA when minimizing computational complexity at the mobile unit is a priority.

  7. Protection of Video Packets over a Wireless Rayleigh Fading Link: FEC versus ARQ

    Directory of Open Access Journals (Sweden)

    Marc Moeneclaey

    2008-07-01

    Full Text Available Video content can be provided to an end user by transmitting video data as a sequence of internet protocol (IP packets over the network. When the network contains a wireless link, packet erasures occur because of occasional deep fades. In order to maintain a sufficient video quality at the end user, video packets must be protected against erasures by means of a suitable form of error control. In this contribution, we investigate two types of error control: (1 forward error correction (FEC, which involves the transmission of parity packets that enables recovery of a limited number of erased video packets, and (2 the use of an automatic repeat request (ARQ protocol, where the receiver requests the retransmission of video packets that have been erased. We point out that FEC and ARQ considerably reduce the probability of unrecoverable packet loss, because both error control techniques provide a diversity gain, as compared to the case where no protection against erasures is applied. We derive a simple analytical expression for the diversity gain resulting from FEC or ARQ, in terms of the channel coherence time, the allowable latency, and (for FEC the allowable overhead or (for ARQ the time interval between (retransmissions of copies of a same packet. In the case of HDTV transmission over a 60 GHz indoor wireless link, ARQ happens to outperform FEC.

  8. Improving 3D-Turbo Code's BER Performance with a BICM System over Rayleigh Fading Channel

    Directory of Open Access Journals (Sweden)

    R. Yao

    2016-12-01

    Full Text Available Classical Turbo code suffers from high error floor due to its small Minimum Hamming Distance (MHD. Newly-proposed 3D-Turbo code can effectively increase the MHD and achieve a lower error floor by adding a rate-1 post encoder. In 3D-Turbo codes, part of the parity bits from the classical Turbo encoder are further encoded through the post encoder. In this paper, a novel Bit-Interleaved Coded Modulation (BICM system is proposed by combining rotated mapping Quadrature Amplitude Modulation (QAM and 3D-Turbo code to improve the Bit Error Rate (BER performance of 3D-Turbo code over Raleigh fading channel. A key-bit protection scheme and a Two-Dimension (2D iterative soft demodulating-decoding algorithm are developed for the proposed BICM system. Simulation results show that the proposed system can obtain about 0.8-1.0 dB gain at BER of 10^{-6}, compared with the existing BICM system with Gray mapping QAM.

  9. Performance Analysis of Beamforming in MU-MIMO Systems for Rayleigh Fading Channels

    KAUST Repository

    Hassan, Ahmad K.

    2017-03-25

    This paper characterizes the performance metrics of MU-MIMO systems under Rayleigh fading channels in the presence of both cochannel interference and additive noise with unknown channel state information and known correlation matrices. In the first task, we derive analytical expressions for the cumulative distribution function of the instantaneous signal-to-interference-plus-noise ratio (SINR) for any deterministic beamvectors. As a second task, exact closed-form expressions are derived for the instantaneous capacity, the upper bound on ergodic capacity, and the Gram-Schmidt orthogonalization-based ergodic capacity for similar intra-cell correlation coefficients. Finally, we present the utility of several structured-diagonalization techniques, which can achieve the tractability for the approximate solution of ergodic capacity for both similar as well as different intra-cell correlation matrices. The novelty of this paper is to formulate the received SINR in terms of indefinite quadratic forms, which allows us to use complex residue theory to characterize the system behavior. The analytical expressions obtained closely match simulation results.

  10. Modeling fade patterns of nipple areola complex tattoos following breast reconstruction.

    Science.gov (United States)

    Levites, Heather A; Fourman, Mitchell S; Phillips, Brett T; Fromm, Indira M; Khan, Sami U; Dagum, Alexander B; Bui, Duc T

    2014-12-01

    Nipple-areolar complex (NAC) tattoos are an effective cosmetic solution for creating a finished look following breast reconstruction procedures. NAC tattoos are prone to significant fading, leading patients to seek revisions. This study was designed to quantify changes in NAC tattoo appearance over time. A total of 71 images of 39 patients were analyzed for NAC tattoo color and shape by 5 blinded medical student graders using a customized scoring system. Subsequently, each image was analyzed using ColorPic software (Iconico, New York, NY). Red/green/blue and hue/saturation/value color parameters were collected. Color quantities were normalized to the individual patient's skin tone to control for variability in lighting. Spearman correlations and nonlinear regressions were calculated utilizing GraphPad Prism 6.0 (GraphPad, La Jolla, CA). The length of time after tattoo placement inversely correlated with color score (P tattoo placement was also inversely correlated with all quantitative color parameters. Each color parameter fit a 1-phase exponential decay model. The decline in qualitative color and shape score agrees with clinical experience of tattoo quality declining over time. The color qualities of the tattoo approach those of the patient's skin over time, ultimately reaching a plateau. This can be modeled using a 1-phase decay equation. In practice, tattoo colors may be selected that compensate for the predictable changes that will occur. The results of this study will help optimize tattoo color and may alleviate the need for NAC tattoo revisions.

  11. Performance and delay analysis of hybrid ARQ with incremental redundancy over double rayleigh fading channels

    KAUST Repository

    Chelli, Ali

    2014-11-01

    In this paper, we study the performance of hybrid automatic repeat request (HARQ) with incremental redundancy over double Rayleigh channels, a common model for the fading amplitude of vehicle-to-vehicle communication systems. We investigate the performance of HARQ from an information theoretic perspective. Analytical expressions are derived for the \\\\epsilon-outage capacity, the average number of transmissions, and the average transmission rate of HARQ with incremental redundancy assuming a maximum number of HARQ rounds. Moreover, we evaluate the delay experienced by Poisson arriving packets for HARQ with incremental redundancy. We provide analytical expressions for the expected waiting time, the packet\\'s sojourn time in the queue, the average consumed power, and the energy efficiency. In our study, the communication rate per HARQ round is adjusted to the average signal-to-noise ratio (SNR) such that a target outage probability is not exceeded. This setting conforms with communication systems in which a quality of service is expected regardless of the channel conditions. Our analysis underscores the importance of HARQ in improving the spectral efficiency and reliability of communication systems. We demonstrate as well that the explored HARQ scheme achieves full diversity. Additionally, we investigate the tradeoff between energy efficiency and spectral efficiency.

  12. The fading behavior of the propagating VLF signal during the recovery time of solar flares.

    Science.gov (United States)

    Bouderba, Yasmina; Tribeche, Mouloud; Nait Amor, Samir

    2016-07-01

    The VLF radio signal propagating in the waveguide delimited by the Earth's surface and the D-layer of the ionosphere undergoes important modifications due to solar flares. In this work we focus on the NRK (37.5 kHz) VLF transmitter signal that propagates along the medium path to Algiers receiver (distance=3495 km). The signal analysis of two different flare classes shows that the perturbation due to a week flare of C2.1 (I _{max}=2.1 x 10 ^{-6} W/m ^{2}) class are less important than the medium one of M3.2 (I _{max}=3.2 x 10 ^{-5} W/m ^{2}) class. This leads to the fast recovery to the normal ionospheric condition after the weak solar flare while the medium solar flare takes more time. Additionally, the study of the signal amplitude behaviors by means of the LWPC code shows that the fading displacement toward the transmitter is more significant in the case of M3.2 flare than C2.1 class.

  13. S0 galaxies are faded spirals: clues from their angular momentum content

    Science.gov (United States)

    Rizzo, Francesca; Fraternali, Filippo; Iorio, Giuliano

    2018-02-01

    The distribution of galaxies in the stellar specific angular momentum versus stellar mass plane (j⋆-M⋆) provides key insights into their formation mechanisms. In this paper, we determine the location in this plane of a sample of ten field/group unbarred lenticular (S0) galaxies from the CALIFA survey. We performed a bulge-disc decomposition both photometrically and kinematically to study the stellar specific angular momentum of the disc components alone and understand the evolutionary links between S0s and other Hubble types. We found that eight of our S0 discs have a distribution in the j⋆-M⋆ plane that is fully compatible with that of spiral discs, while only two have values of j⋆ lower than the spirals. These two outliers show signs of recent merging. Our results suggest that merger and interaction processes are not the dominant mechanisms in S0 formation in low-density environments. Instead, S0s appear to be the result of secular processes and the fading of spiral galaxies after the shutdown of star formation.

  14. Channel allocation and rate adaptation for relayed transmission over correlated fading channels

    KAUST Repository

    Hwang, Kyusung

    2009-09-01

    We consider, in this paper, channel allocation and rate adaptation scheme for relayed transmission over correlated fading channels via cross-layer design. Specifically, jointly considering the data link layer buffer occupancy and channel quality at both the source and relay nodes, we develop an optimal channel allocation and rate adaptation policy for a dual-hop relayed transmission. As such the overall transmit power for the relayed system is minimized while a target packet dropping rate (PDR) due to buffer over flows is guaranteed. In order to find such an optimal policy, the channel allocation and rate adaptation transmission framework is formulated as a constraint Markov decision process (CMDP). The PDR performance of the optimal policy is compared with that of two conventional suboptimal schemes, namely the channel quality based and the buffer occupancy based channel allocation schemes. Numerical results show that for a given power budget, the optimal scheme requires significantly less power than the conventional schemes in order to maintain a target PDR. ©2009 IEEE.

  15. Joint Scheduling for Dual-Hop Block-Fading Broadcast Channels

    KAUST Repository

    Zafar, Ammar

    2012-09-16

    In this paper, we propose joint user-and-hop scheduling over dual-hop block-fading broadcast channels in order to exploit multi-user diversity gains and multi-hop diversity gains all together. To achieve this objective, the first and second hops are scheduled opportunistically based on the channel state information and as a prerequisite we assume that the relay, which is half-duplex and operates using decode-and-forward, is capable of storing the received packets from the source until the channel condition of the destined user becomes good to be scheduled. We formulate the joint scheduling problem as maximizing the weighted sum of the long term achievable rates by the users under a stability constraint, which means that on the long term the rate received by the relay should equal the rate transmitted by it, in addition to constant or variable power constraints. We show that this problem is equivalent to a single-hop broadcast channel by treating the source as a virtual user with an optimal priority weight that maintains the stability constraint. We show how to obtain the source weight either off-line based on channel statistics or on real-time based on channel measurements. Furthermore, we consider special cases including the maximum sum rate scheduler and the proportional fair scheduler. We demonstrate via numerical results that our proposed joint scheduling scheme enlarges the rate region as compared with a scheme that employs multi-user scheduling alone.

  16. Evaluating Color and Fading of Red-Shafted Flicker (Colaptes auratus cafer) Feathers: Technical and Cultural Considerations

    OpenAIRE

    Pearlstein, Ellen; Keene, Lionel

    2010-01-01

    Fading behavior of undyed feathers has not received much attention in conservation literature and as a result feathers are categorized with other natural materials as being fugitive to display lighting, based on anecdotal evidence. The authors investigated Red-shafted Flicker feathers, which have carotenoid-based colorant systems and significance in North American native regalia, to demonstrate how lighting guidelines could be informed by a multivariate approach that considers material sensit...

  17. Power fading mitigation of 40-Gbit/s 256-QAM OFDM carried by colorless laser diode under injection-locking.

    Science.gov (United States)

    Tsai, Cheng-Ting; Chi, Yu-Chieh; Lin, Gong-Ru

    2015-11-02

    The pre-compensation on power fading effect of a colorless laser diode (CLD) carried 40-Gbit/s 256-QAM OFDM transmission during 25-km is demonstrated. By offsetting the DC bias to thrice the threshold (I(th)) and increasing the injection to 0 dBm, the CLD not only enhances its coherence but also suppresses modulation throughput declination and reduces the relative intensity related noise floor to -50 dBm. Modeling the receiving power of the delivered 256-QAM OFDM subcarriers is established, indicating that raising the bias to 3I(th) down-shifts the power fading induced notch to 8.8 GHz. This further degrades the OFDM subcarrier peak power by -2.9 dB after 25-km transmission, and the corresponded signal-to-noise ratio (SNR), error vector magnitude (EVM) and bit-error-rate (BER) are 26.1 dB, 4.9% and 6.5 × 10(-3), respectively. Pre-leveling the OFDM subcarrier as well as the modulation throughput effectively compromises the over-bias enlarged power fading to promote transmission. With a pre-leveled power slope of 1.5 dB/GHz for 256-QAM OFDM data, the modulation throughput declination of the high biased CLD significantly mitigates under BtB transmission, enabling the receiving sensitivity at -7.2 dBm with SNR, EVM and BER of 29.9 dB, 3.1% and 1.5 × 10(-4), respectively. Increasing the pre-leveling slope to 3.2 dB/GHz minimizes the fiber dispersion induced power fading, which improves the receiving SNR, EVM and BER to 27.4 dB, 4.2% and 2.6 × 10(-3), respectively, with receiving sensitivity of -3 dBm and power penalty of 4.2 dB after 25-km SMF transmission.

  18. A fading-based method for checking the presence of closely overlapping peaks in thermoluminescent (TL) materials

    Science.gov (United States)

    Furetta, C.

    The paper describes a method, based on fading experiment, for determining the presence of a complex structure in the thermoluminescent glow curve emission from herbs, e.g. oregano and nopal. Because of the polymineral content of the inorganic part of these herbs, the emitted glow curve is the result of several overlapping glow peaks, each one corresponding to another mineral. The initial rise method is also used for determining the activation energy of each component.

  19. On the performance of free-space optical wireless communication systems over double generalized gamma fading channels

    KAUST Repository

    Al-Quwaiee, Hessa

    2014-03-01

    Starting with the double generalized Gamma (GG) model that was proposed in [1] to describe turbulence-induced fading in free-space optical (FSO) systems, we propose a new unified model which accounts for the impact of pointing errors and type of receiver detector. Based on this new unified model, we study the performance of FSO links operating over these kind of channels. All our analytical results are verified using computer based Monte-Carlo simulations. © 2014 IEEE.

  20. Temporal Evolution of the Gamma-ray Burst Afterglow Spectrum for an Observer: GeV–TeV Synchrotron Self-Compton Light Curve

    Energy Technology Data Exchange (ETDEWEB)

    Fukushima, Takuma; Fujita, Yutaka [Department of Earth and Space Science, Osaka University, Osaka, 560-0043 (Japan); To, Sho; Asano, Katsuaki, E-mail: fukushima@vega.ess.sci.osaka-u.ac.jp, E-mail: fujita@vega.ess.sci.osaka-u.ac.jp, E-mail: tosho@icrr.u-tokyo.ac.jp, E-mail: asanok@icrr.u-tokyo.ac.jp [Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582 (Japan)

    2017-08-01

    We numerically simulate the gamma-ray burst (GRB) afterglow emission with a one-zone time-dependent code. The temporal evolutions of the decelerating shocked shell and energy distributions of electrons and photons are consistently calculated. The photon spectrum and light curves for an observer are obtained taking into account the relativistic propagation of the shocked shell and the curvature of the emission surface. We find that the onset time of the afterglow is significantly earlier than the previous analytical estimate. The analytical formulae of the shock propagation and light curve for the radiative case are also different from our results. Our results show that even if the emission mechanism is switching from synchrotron to synchrotron self-Compton, the gamma-ray light curves can be a smooth power law, which agrees with the observed light curve and the late detection of a 32 GeV photon in GRB 130427A. The uncertainty of the model parameters obtained with the analytical formula is discussed, especially in connection with the closure relation between spectral index and decay index.