Articles de revues sur le sujet « Light nuclei spectrum »
Pour voir les autres types de publications sur ce sujet consultez le lien suivant : Light nuclei spectrum.
Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres
Consultez les 50 meilleurs articles de revues pour votre recherche sur le sujet « Light nuclei spectrum ».
À côté de chaque source dans la liste de références il y a un bouton « Ajouter à la bibliographie ». Cliquez sur ce bouton, et nous générerons automatiquement la référence bibliographique pour la source choisie selon votre style de citation préféré : APA, MLA, Harvard, Vancouver, Chicago, etc.
Vous pouvez aussi télécharger le texte intégral de la publication scolaire au format pdf et consulter son résumé en ligne lorsque ces informations sont inclues dans les métadonnées.
Parcourez les articles de revues sur diverses disciplines et organisez correctement votre bibliographie.
1
VARY, JAMES P., PIETER MARIS et ANDREY SHIROKOV. « AB INITIO NO CORE METHODS : APPLICATIONS TO LIGHT NUCLEI ». International Journal of Modern Physics E 17, supp01 (décembre 2008) : 109–21. http://dx.doi.org/10.1142/s0218301308011793.
Texte intégralRésumé :
We introduce a no-core full configuration (NCFC) approach and present results for 4 He , 12 C , 14 F and some other nuclei with the realistic NN interaction, JISP16. We obtain ground state energies and their uncertainties through exponential extrapolations that we demonstrate are reliable in 4 He where fully converged results are obtained. We find 12 C is overbound by 1.7 MeV and we predict the yet-to-be-measured binding energy of 14 F to be 70.2±3.5 MeV. The extrapolated spectrum of 14 F is in reasonable agreement with known features of the 14 B spectrum. Distinctions are drawn between this approach and the no-core shell model (NCSM).
2
Morigaki, Kazuo. « Light-induced defect creation processes and light-induced defects in hydrogenated amorphous silicon ». European Physical Journal Applied Physics 90, no 2 (mai 2020) : 20101. http://dx.doi.org/10.1051/epjap/2020190257.
Texte intégralRésumé :
We have proposed a model of light-induced defect creation processes and light-induced defects. Recently, important results using pulsed electron-nuclear double resonance (ENDOR) by Fehr et al. [M. Fehr, A. Schnegg, C. Teutloff, R. Bittl, O. Astakhov, F. Finger, B. Rech, K. Lips, Phys. Status Solidi A 207, 552 (2010)] have been reported, so that these results are interpreted on the basis of our model. Fehr et al. have observed ENDOR signals due to hydrogen nuclei distributed around a dangling bond. The ENDOR spectra due to hydrogen nuclei being located with distance of r from the dangling bond have been calculated, taking into accounts the dipolar interaction, and also the Fermi-type contact hyperfine interaction for the H-related dangling bond (HDB) that is a dangling bond having hydrogen at a nearby site. The typical features of the observed ENDOR spectra are that the spectrum has a shoulder at the low frequency side from the natural NMR frequency of hydrogen and it has a dip in the central part. The calculated ENDOR spectrum of HDB exhibits such a shoulder. This is consistent with our model of light-induced defects such as HDB. The ENDOR spectra with various values of r are calculated. In this paper, we also deal with the distant ENDOR precisely, using the theory of distant ENDOR by Lambe et al. [J. Lambe, N. Laurance, K.C. McIrvine, R.W. Terhune, Phys. Rev. 122, 1161 (1961)]. The calculated distant ENDOR spectrum shows a dip in the central part. Concerning the dip, Fehr et al. attribute the dip to be due to the suppression of the matrix ENDOR line (this is called the artifact). Thus, it is not obvious whether the dip is due to such an artifact or the central part of the distant ENDOR spectrum.
3
Kalmykov, N. N., G. V. Kulikov, V. P. Sulakov, Yu A. Fomin et V. N. Kalmykov. « On the energy spectrum of light nuclei in primary cosmic rays ». Bulletin of the Russian Academy of Sciences : Physics 73, no 5 (mai 2009) : 558–60. http://dx.doi.org/10.3103/s1062873809050074.
Texte intégral
4
Qinghua Wang, 王清华, 李振华 Zhenhua Li, 来建成 Jiancheng Lai et 贺安之 Anzhi He. « Fourier analysis of elastic light scattering spectrum of epithelial cell nuclei ». Chinese Optics Letters 8, no 3 (2010) : 278–81. http://dx.doi.org/10.3788/col20100803.0278.
Texte intégral
5
Mazur, I. A., A. M. Shirokov, A. I. Mazur, I. J. Shin, Y. Kim, P. Maris et J. P. Vary. « Description of Continuum Spectrum States of Light Nuclei in the Shell Model ». Physics of Particles and Nuclei 50, no 5 (septembre 2019) : 537–43. http://dx.doi.org/10.1134/s1063779619050186.
Texte intégral
6
Pahlavani, M. R., et R. Morad. « Application of AdS/CFT in Nuclear Physics ». Advances in High Energy Physics 2014 (2014) : 1–19. http://dx.doi.org/10.1155/2014/863268.
Texte intégralRésumé :
We review some recent progress in studying the nuclear physics especially nucleon-nucleon (NN) force within the gauge-gravity duality, in context of noncritical string theory. Our main focus is on the holographic QCD model based on the AdS6background. We explain the noncritical holography model and obtain the vector-meson spectrum and pion decay constant. Also, we study the NN interaction in this frame and calculate the nucleonmeson coupling constants. A further topic covered is a toy model for calculating the light nuclei potential. In particular, we calculate the light nuclei binding energies and also excited energies of some available excited states. We compare our results with the results of other nuclear models and also with the experimental data. Moreover, we describe some other issues which are studied using the gauge-gravity duality.
7
VAAGEN, J. S., B. V. DANILIN et S. N. ERSHOV. « CONTINUUM SPECTROSCOPY OF HALO NUCLEI ». International Journal of Modern Physics E 16, no 04 (mai 2007) : 1033–45. http://dx.doi.org/10.1142/s0218301307006484.
Texte intégralRésumé :
Halo nuclei represent a new type of structure found in extremely neutron rich light nuclei, at the limits of nuclear existence. Of particular interest are Borromean nuclei, where none of the binary substructures can bind. Similar structures, Efimov states, have now also been produced in traps in molecular physics. Nuclear physics has in recent years taken further steps to also explore the nature of the halo continuum, in fact the major part of the spectrum since halo nuclei support only one or a few bound states. Since 3 → 3 scattering is prohibitively difficult to perform, the halo continuum has so far been excited in binary collisions, proceeding via the exotic ground state which to various degrees puts its imprint on the result. Below we discuss via examples how to disentangle continuum structures, comparing with recent correlation data. The work involves a consistent treatment of halo structure and reaction theory, and emphasizes the important future role of exclusive observables and complete experiments.
8
Kalmykov, N. N., V. N. Kalmykov, G. V. Kulikov, P. V. Sulakov et Yu A. Fomin. « The light nuclei energy spectrum of primary cosmic rays using EAS MSU array data ». Moscow University Physics Bulletin 63, no 6 (décembre 2008) : 425–27. http://dx.doi.org/10.3103/s0027134908060143.
Texte intégral
9
Wills, Beverley J., D. Wills, N. J. Evans, A. Natta, K. L. Thompson, M. Breger, M. L. Sitko, D. F. Lester, D. R. Garnett et S. R. Sawyer. « Polarization of IRAS Quasars and the Inner Structure of Active Galactic Nuclei ». Symposium - International Astronomical Union 134 (1989) : 325–26. http://dx.doi.org/10.1017/s0074180900141221.
Texte intégralRésumé :
We have found that 4 new, bright IRAS quasars, out of 7 observed, have strong, non-variable, wavelength-dependent polarization. Three show degrees of polarization, pλ, increasing from infrared to UV wavelengths (Fig. 1), which implies a combination of a polarized, scattered spectrum and a much redder, unpolarized spectrum. Detailed IR and optical polarimetry and spectrophotometry of one, IRAS 13349+2438 (Wills et al.), shows a polarized flux spectrum, pλxFλ, (continuum and Pa α, Hα, and Hβ broad hydrogen lines) typical of unreddened, luminous quasars. This suggests that the path of scattered light from a central, luminous quasar is low in dust and that the polarization of the scattered spectrum is wavelength independent. The latter is most easily explained by electron scattering although the data do not exclude dust scattering. When this polarized flux spectrum is subtracted from the total spectrum, we are left with a very reddened line and continuum spectrum, E(B-V) = 0.3 to 0.7, which we attribute to the same luminous quasar seen through a thick dusty torus. The angle of polarization is parallel to the major axis of the r-band image, presumed to be that of the host galaxy. If the torus is in the plane of the galaxy, the axial ratio suggests a viewing angle of 40° to the plane of the torus. Fig. 2 illustrates the geometry. The appearance of the quasar at optical and UV wavelengths will depend strongly on viewing angle, suggesting that present samples of quasars selected by colours, optical flux density, or quasi-stellar appearance, may be seriously biased, with important consequences for studies of the space density and evolution of AGN.
10
BELYAEVA, T. L., et N. S. ZELENSKAYA. « Computation of Nuclear Reactions with Light-Heavy Ions ». International Journal of Modern Physics C 02, no 01 (mars 1991) : 238–42. http://dx.doi.org/10.1142/s012918319100024x.
Texte intégralRésumé :
The computer code OLYMPS for calculation of the inclusive cross sections for nuclear reactions induced by light heavy ions on medium-mass nuclei at beam energies of 10–20 MeV per nucleon is developed. Our calculations are based on the description of the massive transfer reactions in the spectator model. In view of the fact that most of the considered reactions have more than two particles in the final state and require an allowance for the continuum spectrum, the standard distorted wave Born approximation (DWBA) code fails to work. In our method the transition amplitude is witten in a prior-form of exact finite range DWBA and an exact numerical integration over the transfer momentum is carried out. This requires knowledge of the optical potentials between interacting light and heavy ions in a wide energy range. In addition, OLYMPS provides for the alternative ways of calculation of the wave functions of the relative motion of the heavy ions.
11
Elshoukrofy, A. S., L. Sveshnikova, E. Postnikov, I. Astapov, P. Bezyazeekov, V. Boreyko, A. Borodin et al. « Method of Separation Between Light and Heavy Groups of Primary CR Nuclei by LDF of Cherenkov Light in the Range 300–3000 TeV ». KnE Energy 3, no 1 (9 avril 2018) : 136. http://dx.doi.org/10.18502/ken.v3i1.1735.
Texte intégralRésumé :
The problem of chemical composition below the knee in the cosmic-ray energy spectrum has not yet been solved due to low statistics collected from direct experiments. In the HiSCORE experiment the lateral distribution functions (LDF) of Cherenkov light of EASs with energy greater than hundreds of TeV can be measured in detail for millions of individual events. A full steepness of LDF is sensitive to the depth of shower maximum and as a result to primary particle type. In this paper, we developed a parametric method of separation between heavy and light groups of nuclei using the ’knee-like’ approximation of LDF and taking into account measurement uncertainty.
12
Ingram, Adam, Guglielmo Mastroserio, Thomas Dauser, Pieter Hovenkamp, Michiel van der Klis et Javier A. García. « A public relativistic transfer function model for X-ray reverberation mapping of accreting black holes ». Monthly Notices of the Royal Astronomical Society 488, no 1 (21 juin 2019) : 324–47. http://dx.doi.org/10.1093/mnras/stz1720.
Texte intégralRésumé :
ABSTRACTWe present the publicly available model reltrans that calculates the light-crossing delays and energy shifts experienced by X-ray photons originally emitted close to the black hole when they reflect from the accretion disc and are scattered into our line of sight, accounting for all general relativistic effects. Our model is fast and flexible enough to be simultaneously fit to the observed energy-dependent cross-spectrum for a large range of Fourier frequencies, as well as to the time-averaged spectrum. This not only enables better geometric constraints than only modelling the relativistically broadened reflection features in the time-averaged spectrum, but additionally enables constraints on the mass of supermassive black holes in active galactic nuclei and stellar-mass black holes in X-ray binaries. We include a self-consistently calculated radial profile of the disc ionization parameter and properly account for the effect that the telescope response has on the predicted time lags. We find that a number of previous spectral analyses have measured artificially low source heights due to not accounting for the former effect and that timing analyses have been affected by the latter. In particular, the magnitude of the soft lags in active galactic nuclei may have been underestimated, and the magnitude of lags attributed to thermal reverberation in X-ray binaries may have been overestimated. We fit reltrans to the lag-energy spectrum of the Seyfert galaxy Mrk 335, resulting in a best-fitting black hole mass that is smaller than previous optical reverberation measurements (∼7 million compared with ∼14–26 million M⊙).
13
de Carvalho, J. Pacheco, C. F. R. Pacheco et A. D. Reis. « Applications of Nuclear Techniques, Computer Simulation and Microscopy to Depth Profiling of Light Nuclei ». Microscopy and Microanalysis 18, S5 (août 2012) : 83–84. http://dx.doi.org/10.1017/s1431927612013074.
Texte intégralRésumé :
There is a wide range of surface analysis techniques which are, generally, complementary and provide target information for depths near the surface. Nuclear techniques, which are non-destructive, provide for analysis over a few microns close to the surface giving absolute values of concentrations of isotopes and elements. They have been applied in areas such as scientific, technologic, industry, arts and medicine, using MeV ion beams. Nuclear reactions permit tracing of isotopes with high sensitivities. We use ion-ion reactions and the energy analysis method. At a suitable energy of the incident ion beam, an energy spectrum is recorded of ions from the reaction, coming from several depths in the target. Such spectra are computationally predicted, giving target composition and concentration profile information. Elastic scattering is a particular and important case. A computer program has been developed in this context, mainly for flat targets. The non-flat target situation arises as an extension.
14
BALACHANDRAN, A. P., et SACHINDEO VAIDYA. « SKYRMIONS, SPECTRAL FLOW AND PARITY DOUBLES ». International Journal of Modern Physics A 14, no 03 (30 janvier 1999) : 445–61. http://dx.doi.org/10.1142/s0217751x99000221.
Texte intégralRésumé :
It is well-known that the winding number of the Skyrmion can be identified as the baryon number. We show in this paper that this result can also be established using the Atiyah–Singer index theorem and spectral flow arguments. We argue that this proof suggests that there are light quarks moving in the field of the Skyrmion. We then show that if these light degrees of freedom are averaged out, the low energy excitations of the Skyrmion are in fact spinorial. A natural consequence of our approach is the prediction of a [Formula: see text] state and its excitations in addition to the nucleon and delta. Using the recent numerical evidence for the existence of Skyrmions with discrete spatial symmetries, we further suggest that the the low energy spectrum of many light nuclei may possess a parity doublet structure arising from a subtle topological interaction between the slow Skyrmion and the fast quarks. We also present tentative experimental evidence supporting our arguments.
15
Ingram, Adam, Guglielmo Mastroserio, Michiel van der Klis, Edward Nathan, Riley Connors, Thomas Dauser, Javier A. García et al. « On measuring the Hubble constant with X-ray reverberation mapping of active galactic nuclei ». Monthly Notices of the Royal Astronomical Society 509, no 1 (18 octobre 2021) : 619–33. http://dx.doi.org/10.1093/mnras/stab2950.
Texte intégralRésumé :
ABSTRACT We show that X-ray reverberation mapping can be used to measure the distance to type 1 active galactic nuclei (AGNs). This is because X-ray photons originally emitted from the ‘corona’ close to the black hole irradiate the accretion disc and are reemitted with a characteristic ‘reflection’ spectrum that includes a prominent ∼6.4 keV iron emission line. The shape of the reflection spectrum depends on the irradiating flux, and the light-crossing delay between continuum photons observed directly from the corona and the reflected photons constrain the size of the disc. Simultaneously modelling the X-ray spectrum and the time delays between photons of different energies therefore constrains the intrinsic reflected luminosity, and the distance follows from the observed reflected flux. Alternatively, the distance can be measured from the X-ray spectrum alone if the black hole mass is known. We develop a new model of our reltrans X-ray reverberation mapping package, called rtdist, that has distance as a model parameter. We simulate a synthetic observation that we fit with our new model, and find that this technique applied to a sample of ∼25 AGNs can be used to measure the Hubble constant with a 3σ statistical uncertainty of ${\sim} 6\,{\rm km}\,{\rm s}^{-1}\, {\rm Mpc}^{-1}$. Since the technique is completely independent of the traditional distance ladder and the cosmic microwave background radiation, it has the potential to address the current tension between them. We discuss sources of modelling uncertainty, and how they can be addressed in the near future.
16
de Souza, Vitor, et Peter L. s Biermman. « On the correlation of the highest energy cosmic rays with AGNs ». Proceedings of the International Astronomical Union 5, H15 (novembre 2009) : 251–53. http://dx.doi.org/10.1017/s1743921310009087.
Texte intégralRésumé :
AbstractIn this paper we briefly discuss the present status of the cosmic ray astrophysics under the light of the new data from the Pierre Auger Observatory. The measured energy spectrum is used to test the scenario of production in nearby radio galaxies. Within this framework the AGN correlation would require that most of the cosmic rays are heavy nuclei and are widely scattered by intergalactic magnetic fields.
17
Al-Rubaiee, A. A., Uda Hashim, Mohd Khairuddin Md Arshad, A. Rahim Ruslinda, R. M. Ayub, A. S. Ibraheam, M. Wesam Al-Mufti, Y. Al-Douri, Muhammed Ali Abed et Sarah Hussein Ali. « Estimating of Cherenkov Radiation in Extensive Air Showers Using CORSIKA Code for Tunka133 EAS Cherenkov Array ». Applied Mechanics and Materials 754-755 (avril 2015) : 807–11. http://dx.doi.org/10.4028/www.scientific.net/amm.754-755.807.
Texte intégralRésumé :
The simulation of Cherenkov light Lateral distribution function (LDF) in Extensive Air Showers (EAS) initiated primary particles such as primary calcium, argon, proton iron nuclei, neutron and nitrogen have been performed using CORSIKA program for conditions and configurations of Tunka133 EAS Cherenkov array. The simulation was fulfilled at the high energy range 1014-1016eV for four different zenith angles 0o, 10o, 15oand 30o. The results of the simulated Cherenkov light LDF are compared with the measurements of Tunka133 EAS array for the same particles and energy range mentioned above. This comparison may give the good ability to reconstruct the energy spectrum and mass composition of the primary cosmic ray particles in EAS. The main feature of the given approach consists of the possibility to make a library of Cherenkov light LDF samples which could be utilized for analysis of real events which can be detected with different EAS arrays and reconstruction of the primary cosmic rays energy spectrum and mass composition of EAS particles.
18
Al-Rubaiee, A. A., Y. Al-Douri et U. Hashim. « Extension of Cherenkov Light LDF Approximation for Yakutsk EAS Array ». Journal of Astrophysics 2014 (14 août 2014) : 1–6. http://dx.doi.org/10.1155/2014/492814.
Texte intégralRésumé :
The simulation of the Cherenkov light lateral distribution function (LDF) in extensive air showers (EAS) was performed using CORSIKA code for configuration of Yakutsk EAS array at high energy range for different primary particles (p, Fe, and O2) and different zenith angles. Depending on Breit-Wigner function a parameterization of Cherenkov light LDF was reconstructed on the basis of this simulation as a function of primary energy. A comparison of the calculated Cherenkov light LDF with that measured on the Yakutsk EAS array gives the possibility of identification of the particle initiating the shower and determination of its energy in the knee region of the cosmic ray spectrum. The extrapolation of approximated Cherenkov light LDF for high energies was obtained for primary proton and iron nuclei.
19
Lu, Peifen, Junping Wang, Hui Li, Kang Lin, Xiaochun Gong, Qiying Song, Qinying Ji et al. « High-order above-threshold dissociation of molecules ». Proceedings of the National Academy of Sciences 115, no 9 (13 février 2018) : 2049–53. http://dx.doi.org/10.1073/pnas.1719481115.
Texte intégralRésumé :
Electrons bound to atoms or molecules can simultaneously absorb multiple photons via the above-threshold ionization featured with discrete peaks in the photoelectron spectrum on account of the quantized nature of the light energy. Analogously, the above-threshold dissociation of molecules has been proposed to address the multiple-photon energy deposition in the nuclei of molecules. In this case, nuclear energy spectra consisting of photon-energy spaced peaks exceeding the binding energy of the molecular bond are predicted. Although the observation of such phenomena is difficult, this scenario is nevertheless logical and is based on the fundamental laws. Here, we report conclusive experimental observation of high-order above-threshold dissociation of H2 in strong laser fields where the tunneling-ionized electron transfers the absorbed multiphoton energy, which is above the ionization threshold to the nuclei via the field-driven inelastic rescattering. Our results provide an unambiguous evidence that the electron and nuclei of a molecule as a whole absorb multiple photons, and thus above-threshold ionization and above-threshold dissociation must appear simultaneously, which is the cornerstone of the nowadays strong-field molecular physics.
20
Zierold, Karl, Jean Michel, Christine Terryn et Gérard Balossier. « The Distribution of Light Elements in Biological Cells Measured by Electron Probe X-Ray Microanalysis of Cryosections ». Microscopy and Microanalysis 11, no 2 (8 mars 2005) : 138–45. http://dx.doi.org/10.1017/s1431927605050130.
Texte intégralRésumé :
The intracellular distribution of the elements carbon, nitrogen, and oxygen was measured in cultured rat hepatocytes by energy dispersive electron probe X-ray microanalysis of 100-nm-thick freeze-dried cryosections. Electron irradiation with a dose up to 106e/nm2caused no or merely negligible mass loss in mitochondria and in cytoplasm. Cell nuclei lost carbon, nitrogen, and—to a clearly higher extent—oxygen with increasing electron irradiation. Therefore, electron doses less than 3 × 105e/nm2were used to measure the subcellular compartmentation of carbon, nitrogen, and oxygen in cytoplasm, mitochondria, and nuclei of the cells. The subcellular distribution of carbon, nitrogen, and oxygen reflects the intracellular compartmentation of various biomolecules. Cells exposed to inorganic mercury before cryofixation showed an increase of oxygen in nuclei and cytoplasm. Concomitantly the phosphorus/nitrogen ratio decreased in mitochondria. The data suggest mercury-induced production of ribonucleic acid (RNA) and decrease of adenosine triphosphate (ATP). Although biomolecules cannot be identified by X-ray microanalysis, measurements of the whole element spectrum including the light elements carbon, nitrogen, and oxygen can be useful to study specific biomolecular activity in cellular compartments depending on the functional state of the cell.
21
Barioni, A., G. Kaur, J. Alcantara-Nunez, M. Assunção, V. Guimaraes, A. L. Lara, A. Lepine-Szily et al. « Two-neutron transfer as a tool to study pairing correlations in nuclei ». Journal of Physics : Conference Series 2340, no 1 (1 septembre 2022) : 012040. http://dx.doi.org/10.1088/1742-6596/2340/1/012040.
Texte intégralRésumé :
Abstract A feasibility study of two-neutron transfer reactions, using 12C and 19F targets, was performed. In this experiment, a 6He beam at 20 MeV incident energy was delivered by the RIBRAS facility. The main goal of this work was to test the RIBRAS system, operated in a single-solenoid mode, to investigate (6He,α) reactions in light nuclei. The excitation function of the 14C nucleus, populated by the 12C(6He,α) reaction, was extracted from the data. Evidence of nn-transfer reactions populating the ground state and the first 0 1 + state in 14C were observed. However, the present spectrum might have contribution from other reaction channels such as the 6He breakup. Future experiments with the RIBRAS dual-solenoid mode will improve the quality of the data by reducing a significant amount of background.
22
Chiaraluce, E., F. Panessa, G. Bruni, R. D. Baldi, E. Behar, F. Vagnetti, F. Tombesi et I. McHardy. « Hard-X-ray-selected active galactic nuclei – I. A radio view at high frequencies ». Monthly Notices of the Royal Astronomical Society 495, no 4 (22 mai 2020) : 3943–60. http://dx.doi.org/10.1093/mnras/staa1393.
Texte intégralRésumé :
ABSTRACT A thorough study of radio emission in active galactic nuclei (AGNs) is of fundamental importance to understand the physical mechanisms responsible for the emission and the interplay between accretion and ejection processes. High-frequency radio observations can target the nuclear contribution of smaller emitting regions and are less affected by absorption. We present JVLA 22 and 45 GHz observations of 16 nearby (0.003 ≤ z ≤ 0.3) hard-X-ray-selected AGNs at the (sub)-kpc scale with tens μJy beam−1 sensitivity. We detected 15/16 sources, with flux densities ranging from hundreds μJy to tens Jy (specific luminosities from ∼1020 to ${\sim}10^{25}\, \mathrm{ W}\, \mathrm{ Hz}^{-1}$ at 22 GHz). All detected sources host a compact core, with eight being core-dominated at either frequencies, the others exhibiting also extended structures. Spectral indices range from steep to flat/inverted. We interpret this evidence as either due to a core+jet system (6/15), a core accompanied by surrounding star formation (1/15), to a jet oriented close to the line of sight (3/15), to emission from a corona or the base of a jet (1/15), although there might be degeneracies between different processes. Four sources require more data to shed light on their nature. We conclude that, at these frequencies, extended, optically thin components are present together with the flat-spectrum core. The LR/LX ∼ 10−5 relation is roughly followed, indicating a possible contribution to radio emission from a hot corona. A weakly significant correlation between radio core (22 and 45 GHz) and X-ray luminosities is discussed in the light of an accretion–ejection framework.
23
Zhao, Yi, Qiang Yuan, Xiao-Jun Bi, Feng-Rong Zhu et Huan-Yu Jia. « Perspective of detecting very high energy gamma-ray emission from active galactic nuclei with Large High Altitude Air Shower Observatory (LHAASO) ». International Journal of Modern Physics D 25, no 01 (janvier 2016) : 1650006. http://dx.doi.org/10.1142/s0218271816500061.
Texte intégralRésumé :
The detectability of active galactic nuclei (AGN), a major class of [Formula: see text]-ray emitters in the sky, by the newly planned Chinese project, Large High Altitude Air Shower Observatory (LHAASO), is investigated. The expectation is primarily based on the AGN catalog of Fermi Large Area Telescope (Fermi-LAT), with an extrapolation to the very high energy (VHE) range taking into account the absorption effect by the extragalactic background light (EBL). It is found that LHAASO may have the potential to detect more than several tens of the Fermi detected AGN, basically BL Lacertaes, with one-year sky survey. The capability of measuring the energy spectrum and light curve are also discussed.
24
Biasuzzi, B., O. Hervet, D. A. Williams et J. Biteau. « Normalization of the extragalactic background light from high-energy γ-ray observations ». Astronomy & ; Astrophysics 627 (juillet 2019) : A110. http://dx.doi.org/10.1051/0004-6361/201834240.
Texte intégralRésumé :
Extragalactic background light (EBL) plays an important role in cosmology since it traces the history of galaxy formation and evolution. Such diffuse radiation from near-UV to far-infrared wavelengths can interact with γ-rays from distant sources such as active galactic nuclei (AGNs), and is responsible for the high-energy absorption observed in their spectra. However, probing the EBL from γ-ray spectra of AGNs is not trivial due to internal processes that can mimic its effect. Such processes are usually taken into account in terms of curvature of the intrinsic spectrum. Hence, an improper choice of parametrization for the latter can seriously affect EBL reconstruction. In this paper, we propose a statistical approach that avoids a priori assumptions on the intrinsic spectral curvature and that, for each source, selects the best-fit model on a solid statistical basis. By combining the Fermi-LAT observations of 490 blazars, we determine the γ-ray-inferred level of EBL for various state-of-the-art EBL models. We discuss the EBL level obtained from the spectra of both BL Lacs and flat spectrum radio quasars (FSRQ) in order to investigate the impact of internal absorption in different classes of objects. We further scrutinize constraints on the EBL evolution from γ-ray observations by reconstructing the EBL level in four redshift ranges, up to z ∼ 2.5. The approach implemented in this paper, carefully addressing the question of the modeling of the intrinsic emission at the source, can serve as a solid stepping stone for studies of hundreds of high-quality spectra acquired by next-generation γ-ray instruments.
25
Luo, Qing, Bing-qiang Qiao, Wei Liu, Shu-wang Cui et Yi-qing Guo. « Statistical Study of the Optimal Local Sources for Cosmic Ray Nuclei and Electrons ». Astrophysical Journal 930, no 1 (1 mai 2022) : 82. http://dx.doi.org/10.3847/1538-4357/ac6267.
Texte intégralRésumé :
Abstract Local sources, such as the Geminga supernova remnant (SNR), may have played an important role in the anomaly of protons, electrons, and anisotropy in past works. In fact, there exist 12 SNRs around the solar system within 1 kpc. One question is whether other SNRs also possibly contribute to the spectra of nuclei and electrons, and explain the special structure of the anisotropy. In this work, under spatial-dependent propagation, we systematically study the contribution of all local SNRs, within 1 kpc around the solar system, to the spectra of nuclei and electrons, as well as the energy dependence of the anisotropy. As a result, only the Geminga, the Monogem, and the Vela SNRs have quantitative contributions to the nuclei and electron spectra, and the anisotropy. Here, the Geminga SNR is the sole optimal candidate and the Monogem SNR is controversial due to the tension of the anisotropy between the model calculation and the observations. The Vela SNR contributes to a new spectral structure beyond TeV energy, hinted by the HESS, the VERITAS, the DAMPE, and the CALET measurements. More interestingly, the electron anisotropy satisfies the Fermi-LAT limit below TeV energy, but rises greatly and reaches 10% at several TeV. This novel structure will shed new light on verifying our model. We hope that the new structure of the electron spectrum and anisotropy can be observed by the spaceborne DAMPE and HERD, and the ground-based HAWC and LHAASO experiments in the near future.
26
Korochkin, A., A. Neronov et D. Semikoz. « Search for spectral features in extragalactic background light with gamma-ray telescopes ». Astronomy & ; Astrophysics 633 (janvier 2020) : A74. http://dx.doi.org/10.1051/0004-6361/201936262.
Texte intégralRésumé :
Context. Cumulative optical and infrared emission from galaxies accumulated over cosmological time scales, the extragalactic background light (EBL), could be probed by complementary techniques of direct observations and source counting in the visible and infrared as well as via its imprint on the signal of distant active galactic nuclei in γ-rays. Aims. We compare the visible and infrared measurements with the γ-ray constraints and study if the discrepancies of the measurements with different methods could be due to the presence of features in the EBL spectrum that are localised in the micron wavelength range. Methods. We combined data on time-averaged spectra of selected blazars that were obtained by Fermi and ground-based gamma-ray telescopes. We also modelled the effect of absorption on EBL while allowing for the existence of a previously unaccounted spectral feature. Results. We show that a previously reported “excess” in EBL flux in the ∼1 micron wavelength range is consistent with γ-ray measurements, that is, if the excess has the form of a narrow feature of the width δλ < λ and an overall flux of up to 15 nW m−2 sr−1 above the “minimal” EBL, which is estimated from the visible and infrared source counts. Such ’bump-like’ spectral features could originate, for example, from decaying dark-matter particles, or either axions or peculiar astrophysical processes in the course of star-formation history. We discuss the possibilities for the search of spectral features in the EBL with the Cherenkov Telescope Array.
27
Lerner, Eric J. « Plasma model of microwave background and primordial elements : an alternative to the big bang ». Laser and Particle Beams 6, no 3 (août 1988) : 457–69. http://dx.doi.org/10.1017/s0263034600005395.
Texte intégralRésumé :
A plasma model of the origin of the light elements and the microwave background is presented. In contrast to the conventional Big Bang hypothesis, the model assumes that helium, deuterium and the microwave background were all generated by massive stars in the early stages of galaxy formation. The microwave background is scattered and isotropized by multi-GeV electrons trapped in the jets emitted by active galactic nuclei. The model produces reasonable amounts of heavy elements, accurately predicts the gamma-ray background intensity and spectrum, and explains the statistics of quasars, compact and extended radio sources.
28
Nagare, Rohan, Mark S. Rea, Barbara Plitnick et Mariana G. Figueiro. « Effect of White Light Devoid of “Cyan” Spectrum Radiation on Nighttime Melatonin Suppression Over a 1-h Exposure Duration ». Journal of Biological Rhythms 34, no 2 (1 mars 2019) : 195–204. http://dx.doi.org/10.1177/0748730419830013.
Texte intégralRésumé :
The intrinsically photosensitive retinal ganglion cells are the main conduit of the light signal emanating from the retina to the biological clock located in the suprachiasmatic nuclei of the hypothalamus. Lighting manufacturers are developing white light sources that are devoid of wavelengths around 480 nm (“cyan gap”) to reduce their impact on the circadian system. The present study was designed to investigate whether exposure to a “cyan-gap,” 3000 K white light source, spectrally tuned to reduce radiant power between 475 and 495 nm (reducing stimulation of the melanopsin-containing photoreceptor), would suppress melatonin less than a conventional 3000 K light source. The study’s 2 phases employed a within-subjects experimental design involving the same 16 adult participants. In Phase 1, participants were exposed for 1 h to 3 experimental conditions over the course of 3 consecutive weeks: 1) dim light control (<5 lux at the eyes); 2) 800 lux at the eyes of a 3000 K light source; and 3) 800 lux at the eyes of a 3000 K, “cyan-gap” modified (3000 K mod) light source. The same protocol was repeated in Phase 2, but light levels were reduced to 400 lux at the eyes. As hypothesized, there were significant main effects of light level ( F1,12 = 9.1, p < 0.05, ηp² = 0.43) and exposure duration ( F1,12 = 47.7, p < 0.05, ηp² = 0.80) but there was no significant main effect of spectrum ( F1,12 = 0.16, p > 0.05, ηp² = 0.01). There were no significant interactions with spectrum. Contrary to our model predictions, our results showed that short-term exposures (≤ 1 h) to “cyan-gap” light sources suppressed melatonin similarly to conventional light sources of the same CCT and photopic illuminance at the eyes.
29
Sisk-Reynés, Júlia, James H. Matthews, Christopher S. Reynolds, Helen R. Russell, Robyn N. Smith et M. C. David Marsh. « New constraints on light axion-like particles using Chandra transmission grating spectroscopy of the powerful cluster-hosted quasar H1821+643 ». Monthly Notices of the Royal Astronomical Society 510, no 1 (2 décembre 2021) : 1264–77. http://dx.doi.org/10.1093/mnras/stab3464.
Texte intégralRésumé :
ABSTRACT Axion-like particles (ALPs) are predicted by several Beyond the Standard Model theories, in particular, string theory. In the presence of an external magnetic field perpendicular to the direction of propagation, ALPs can couple to photons. Therefore, if an X-ray source is viewed through a magnetized plasma, such as a luminous quasar in a galaxy cluster, we may expect spectral distortions that are well described by photon–ALP oscillations. We present a 571 ks combined high- and low-energy transmission grating Chandra observation of the powerful radio-quiet quasar H1821+643, hosted by a cool-core cluster at redshift 0.3. The spectrum is well described by a double power-law continuum and broad+narrow iron line emission typical of type-1 active galactic nuclei (AGNs), with remaining spectral features ${\lt}2.5{{\ \rm per\ cent}}$. Using a cell-based approach to describe the turbulent cluster magnetic field, we compare our spectrum with photon–ALP mixing curves for 500 field realizations, assuming that the thermal-to-magnetic pressure ratio β remains constant up to the virial radius. At $99.7{{\ \rm per\ cent}}$ credibility and taking β = 100, we exclude all couplings gaγ > 6.3 × 10−13 GeV−1 for most ALP masses <10−12 eV. Our results are moderately more sensitive to constraining ALPs than the best previous result from Chandra observations of the Perseus cluster, albeit with a less constrained field model. We reflect on the promising future of ALP studies with bright AGNs embedded in rich clusters, especially with the upcoming Athena mission.
30
Tadhunter, C., M. Patel et J. Mullaney. « A light echo from the warm outflow in the ULIRG F01004-2237 following a major flare in its optical continuum emission ». Monthly Notices of the Royal Astronomical Society 504, no 3 (22 avril 2021) : 4377–88. http://dx.doi.org/10.1093/mnras/stab1105.
Texte intégralRésumé :
ABSTRACT Emission-line variability studies have the potential to provide key information about the structures of the near-nuclear outflow regions of active galactic nuclei (AGN). Here we present a VLT/Xshooter spectrum of the nucleus of the ULIRG F01004-2237 that was taken in 2018 August, about 8 yr after a major flare in its integrated optical emission. Compared with our WHT/ISIS spectrum from 2015 September, the broad, red wings of the emission lines most closely associated with the flaring event, including He iiλ4686, N iiiλλ4640,4100, and He iλ5876, have substantially declined in flux. In contrast, the broad, blue wings that dominate the [O iii], [Ne iii], [Ne v], and [O i] forbidden lines have increased in flux by a factor 1.4–4.4 (depending on the line). Moreover, the [Fe vii]λ6087 line is detected in the new spectrum for the first time. We interpret these results in terms of a light echo from the outflowing warm gas: the direct emission from the flaring event is continuing to fade, but due to light travel time effects we are only now observing the impact of the flare on the emission from the extended outflow region. Unless the outflow is confined to a small range of angles close to our line of sight, these observations imply that the outflow must be relatively compact (r <50 pc). In terms of the nature of the flare event, we speculate that the properties of the F01004-2237 flare may be the result of a tidal disruption event occurring in an object with pre-existing AGN activity.
31
Walton, N. A., J. R. Walsh et S. R. Pottasch. « Imaging and Spectroscopy of Abell 63 (UU SGE) ». Symposium - International Astronomical Union 155 (1993) : 394. http://dx.doi.org/10.1017/s0074180900171839.
Texte intégralRésumé :
UU Sge, the eclipsing binary central star (Bond et al, 1978) of the low-surface-brightness planetary nebula (PN) Abell 63, has been observed spectroscopically in the visible throughout its 11.2 hour period and especially during the minimum. A spectral determination of the binary system has been made. The primary hot central star is an ‘O’ type PN nucleus of temperature ≈40,000 K, consistent with the low excitation of the nebular spectrum (e.g. no He ii 4686Å nebular emission detected). From the spectrum at minimum light, the secondary star appears to be a cool dwarf star around G7. Measurement of the magnitude of the secondary during the eclipse of the primary enabled the distance to the PN to be directly determined as 3.6 kpc. For this distance the luminosity of the hot star is approximately 4 320 L⊙, in good agreement with evolutionary tracks for (single) PN nuclei. Deep CCD images of Abell 63 show it has a ‘butterfly’ morphology implying that the close binary central system may have had a strong effect on the nebula shaping. The paper describing this work has been submitted (Walton et al, 1992).
32
Springer, Ofer M., et Eran O. Ofek. « Measuring time delays – I. Using a flux time series that is a linear combination of time-shifted light curves ». Monthly Notices of the Royal Astronomical Society 506, no 1 (7 juin 2021) : 864–76. http://dx.doi.org/10.1093/mnras/stab1600.
Texte intégralRésumé :
ABSTRACT Several phenomena in astrophysics generate light curves with time delays. Among these are reverberation mapping and lensed quasars. In these systems, the measurement of the time delay is complicated by the fact that the delayed components are unresolved and that the light curves are generated from a stochastic process. We derive the likelihood function of the observations given a model of either a combination of time-delayed light curves or a single light curve. This likelihood function is different from the auto-correlation-function-based investigated by previous studies. We demonstrate that given a single-band light curve that is a linear combination of two (or more) time-shifted copies of an original light curve, generated from a probability distribution with some roughly known power spectrum, it is possible to test if the total-flux light curve is a composition of time-delayed copies or, alternatively, is consistent with being a single copy of the original light curve. Furthermore, it is possible to measure the time delays between these components even when the flux ratio is about 1/10. In the era of synoptic sky surveys, this method is useful for identifying lensed quasars and simultaneously measuring their time delays, and also for estimating the reverberation time scales of active galactic nuclei. In a companion paper, we derive another method that uses the centre-of-light astrometric position (e.g. of a lensed quasar) along with the combined flux. We also present the proper likelihood function for fitting a power-law model to a power spectrum. We test the new method on simulations and provide python and matlab implementations.
33
Patra, Sayan, M. Germann, J. Ph Karr, M. Haidar, L. Hilico, V. I. Korobov, F. M. J. Cozijn, K. S. E. Eikema, W. Ubachs et J. C. J. Koelemeij. « Proton-electron mass ratio from laser spectroscopy of HD+ at the part-per-trillion level ». Science 369, no 6508 (30 juillet 2020) : 1238–41. http://dx.doi.org/10.1126/science.aba0453.
Texte intégralRésumé :
Recent mass measurements of light atomic nuclei in Penning traps have indicated possible inconsistencies in closely related physical constants such as the proton-electron and deuteron-proton mass ratios. These quantities also influence the predicted vibrational spectrum of the deuterated molecular hydrogen ion (HD+) in its electronic ground state. We used Doppler-free two-photon laser spectroscopy to measure the frequency of the v = 0→9 overtone transition (v, vibrational quantum number) of this spectrum with an uncertainty of 2.9 parts per trillion. By leveraging high-precision ab initio calculations, we converted our measurement to tight constraints on the proton-electron and deuteron-proton mass ratios, consistent with the most recent Penning trap determinations of these quantities. This results in a precision of 21 parts per trillion for the value of the proton-electron mass ratio.
34
Schleicher, Bernd, Axel Arbet-Engels, Dominik Baack, Matteo Balbo, Adrian Biland, Michael Blank, Thomas Bretz et al. « Fractional Variability—A Tool to Study Blazar Variability ». Galaxies 7, no 2 (30 mai 2019) : 62. http://dx.doi.org/10.3390/galaxies7020062.
Texte intégralRésumé :
Active Galactic Nuclei emit radiation over the whole electromagnetic spectrum up to TeV energies. Blazars are one subtype with their jets pointing towards the observer. One of their typical features is extreme variability on timescales, from minutes to years. The fractional variability is an often used parameter for investigating the degree of variability of a light curve. Different detection methods and sensitivities of the instruments result in differently binned data and light curves with gaps. As they can influence the physics interpretation of the broadband variability, the effects of these differences on the fractional variability need to be studied. In this paper, we study the systematic effects of completeness in time coverage and the sampling rate. Using public data from instruments monitoring blazars in various energy ranges, we study the variability of the bright TeV blazars Mrk 421 and Mrk 501 over the electromagnetic spectrum, taking into account the systematic effects, and compare our findings with previous results. Especially in the TeV range, the fractional variability is higher than in previous studies, which can be explained by the much longer (seven years compared to few weeks) and more complete data sample.
35
Pan, Xin, Shuang-Liang Li, Xinwu Cao, Giovanni Miniutti et Minfeng Gu. « A Disk Instability Model for the Quasi-periodic Eruptions of GSN 069 ». Astrophysical Journal Letters 928, no 2 (1 avril 2022) : L18. http://dx.doi.org/10.3847/2041-8213/ac5faf.
Texte intégralRésumé :
Abstract GSN 069 is a recently discovered quasi-periodic eruption (QPE) source recurring about every 9 hr. The mechanism for the QPEs of GSN 069 is still unclear. In this work, a disk instability model is constructed to explain GSN 069 based on Pan et al. (PLC21), where the authors proposed a toy model for the repeating changing-look active galactic nuclei. We improve the work of PLC21 by including a nonzero viscous torque condition on the inner boundary of the disk and adopting a general form for the viscous stress torque in the Kerr metric. It is found that the 0.4–2 keV light curves, the light curves at different energy bands, and the phase-resolved X-ray spectrum of GSN 069 can all be qualitatively reproduced by our model. Furthermore, the profiles of light curves in QPEs can be significantly changed by the parameter μ in the viscous torque equation, which implies that our model may also be applied to other QPEs.
36
Boughelilba, Margot, Anita Reimer et Lukas Merten. « Lepto-hadronic Jet-disk Model for the Multiwavelength SED of M87 ». Astrophysical Journal 938, no 1 (1 octobre 2022) : 79. http://dx.doi.org/10.3847/1538-4357/ac8e64.
Texte intégralRésumé :
Abstract The low-luminosity active galactic nuclei M87, archetype of Fanaroff–Riley I radio galaxies, was observed in a historically quiet state in 2017. While one-zone leptonic jet models alone cannot explain the core radio-to-gamma-ray spectrum, we explore a hybrid jet-disk scenario. In this work, we model the overall spectral energy distribution of M87's core with a dominating one-zone lepto-hadronic jet component, coupled with the contribution from the accretion flow. We find close-to-equipartition parameter sets for which the jet component fits the radio-to-optical data as well as the gamma-ray band, while the accretion flow mainly contributes to the X-ray band. The effects of gamma-ray absorption by the extragalactic background light during the propagation toward Earth are probed and are found to be negligible for this model. The neutrino flux produced by such scenarios is also calculated, but remains below the current instruments’ sensitivity.
37
Dumas, Daniël B., Simona V. Gornati, Youri Adolfs, Tomomi Shimogori, R. Jeroen Pasterkamp et Freek E. Hoebeek. « Anatomical Development of the Cerebellothalamic Tract in Embryonic Mice ». Cells 11, no 23 (27 novembre 2022) : 3800. http://dx.doi.org/10.3390/cells11233800.
Texte intégralRésumé :
The main connection from cerebellum to cerebrum is formed by cerebellar nuclei axons that synapse in the thalamus. Apart from its role in coordinating sensorimotor integration in the adult brain, the cerebello-thalamic tract (CbT) has also been implicated in developmental disorders, such as autism spectrum disorders. Although the development of the cerebellum, thalamus and cerebral cortex have been studied, there is no detailed description of the ontogeny of the mammalian CbT. Here we investigated the development of the CbT at embryonic stages using transgenic Ntsr1-Cre/Ai14 mice and in utero electroporation of wild type mice. Wide-field, confocal and 3D light-sheet microscopy of immunohistochemical stainings showed that CbT fibers arrive in the prethalamus between E14.5 and E15.5, but only invade the thalamus after E16.5. We quantified the spread of CbT fibers throughout the various thalamic nuclei and found that at E17.5 and E18.5 the ventrolateral, ventromedial and parafascicular nuclei, but also the mediodorsal and posterior complex, become increasingly innervated. Several CbT fiber varicosities express vesicular glutamate transporter type 2 at E18.5, indicating cerebello-thalamic synapses. Our results provide the first quantitative data on the developing murine CbT, which provides guidance for future investigations of the impact that cerebellum has on thalamo-cortical networks during development.
38
Kidger, Mark, Staszek Zola, Mauri Valtonen, Anne Lähteenmäki, Emilia Järvelä, Merja Tornikoski, Joni Tammi, Alexis Liakos et Gary Poyner. « Far-infrared photometry of OJ 287 with the Herschel Space Observatory ». Astronomy & ; Astrophysics 610 (février 2018) : A74. http://dx.doi.org/10.1051/0004-6361/201732142.
Texte intégralRésumé :
Context. The blazar OJ 287 has shown a ≈12 year quasi-periodicity over more than a century, in addition to the common properties of violent variability in all frequency ranges. It is the strongest known candidate to have a binary singularity in its central engine. Aim. We aim to better understand the different emission components by searching for correlated variability in the flux over four decades of frequency measurements. Methods. We combined data at frequencies from the millimetric to the visible to characterise the multifrequency light curve in April and May 2010. This includes the only photometric observations of OJ 287 made with the Herschel Space Observatory: five epochs of data obtained over 33 days at 250, 350, and 500 μm with Herschel-SPIRE. Results. Although we find that the variability at 37 GHz on timescales of a few weeks correlates with the visible to near-IR spectral energy distribution, there is a small degree of reddening in the continuum at lower flux levels that is revealed by the decreasing rate of decline in the light curve at lower frequencies. However, we see no clear evidence that a rapid flare detected in the light curve during our monitoring in the visible to near-IR light curve is seen either in the Herschel data or at 37 GHz, suggesting a low-frequency cut-off in the spectrum of such flares. Conclusions.We see only marginal evidence of variability in the observations with Herschel over a month, although this may be principally due to the poor sampling. The spectral energy distribution between 37 GHz and the visible can be characterised by two components of approximately constant spectral index: a visible to far-IR component of spectral index α = −0.95, and a far-IR to millimetric spectral index of α = −0.43. There is no evidence of an excess of emission that would be consistent with the 60 μmdust bump found in many active galactic nuclei.
39
Barua, Samuzal, V. Jithesh, Ranjeev Misra, Gulab C. Dewangan, Rathin Sarma et Amit Pathak. « NuSTAR observation of Ark 564 reveals the variation of coronal temperature with flux ». Monthly Notices of the Royal Astronomical Society 492, no 2 (10 janvier 2020) : 3041–46. http://dx.doi.org/10.1093/mnras/staa067.
Texte intégralRésumé :
ABSTRACT The hard X-ray spectral index of some active galactic nuclei (AGN) has been observed to steepen with the source flux. This has been interpreted in a Comptonization scenario, where an increase in the soft flux decreases the temperature of the corona, leading to steepening of the photon index. However, the variation of the coronal temperature with flux has been difficult to measure due to the presence of complex reflection component in the hard X-rays and the lack of high-quality data at that energy band. Recently, a 200 ks Nuclear Spectroscopic Telescope Array(NuSTAR) observation of Ark 564 in 3–50 keV band revealed the presence of one of the coolest coronae with temperature kTe ∼ 15 keV in the time-averaged spectrum. Here, we reanalyse the data and examined the spectra in four flux levels. Our analysis shows that the coronal temperature decreased from ∼17 to ∼14 keV as the flux increased. The high energy photon index Γ ∼ 2.3 varied by less than 0.1, implying that the optical depth of the corona increased by about 10 per cent as the flux increased. This first reporting of coronal temperature variation with flux shows that further long observation by NuSTAR of this and other sources would shed light on the geometry and dynamics of the inner regions of the accretion flow.
40
Guépin, Claire, Kumiko Kotera, Enrico Barausse, Ke Fang et Kohta Murase. « Ultra-high-energy cosmic rays and neutrinos from tidal disruptions by massive black holes ». Astronomy & ; Astrophysics 616 (août 2018) : A179. http://dx.doi.org/10.1051/0004-6361/201732392.
Texte intégralRésumé :
Tidal disruptions are extremely powerful phenomena that have been designated as candidate sources of ultra-high-energy cosmic rays. The disruption of a star by a black hole can naturally provide protons and heavier nuclei, which can be injected and accelerated to ultra-high energies within a jet. Inside the jet, accelerated nuclei are likely to interact with a dense photon field, leading to a significant production of neutrinos and secondary particles. We model numerically the propagation and interactions of high-energy nuclei in jetted tidal disruption events in order to evaluate consistently their signatures in cosmic rays and neutrinos. We propose a simple model of the light curve of tidal disruption events, consisting of two stages: a high state with bright luminosity and short duration and a medium state, less bright and longer lasting. These two states have different impacts on the production of cosmic rays and neutrinos. In order to calculate the diffuse fluxes of cosmic rays and neutrinos, we model the luminosity function and redshift evolution of jetted tidal disruption events. We find that we can fit the latest ultra-high-energy cosmic-ray spectrum and composition results of the Auger experiment for a range of reasonable parameters. The diffuse neutrino flux associated with this scenario is found to be subdominant, but nearby events can be detected by IceCube or next-generation detectors such as IceCube-Gen2.
41
Mbarek, Rostom, Damiano Caprioli et Kohta Murase. « High-energy Neutrino Emission from Espresso-reaccelerated Ions in Jets of Active Galactic Nuclei ». Astrophysical Journal 942, no 1 (1 janvier 2023) : 37. http://dx.doi.org/10.3847/1538-4357/aca481.
Texte intégralRésumé :
Abstract We present a bottom-up calculation of the flux of ultrahigh-energy cosmic rays (UHECRs) and high-energy neutrinos produced by powerful jets of active galactic nuclei (AGNs). By propagating test particles in 3D relativistic magnetohydrodynamic jet simulations, including a Monte Carlo treatment of sub-grid pitch-angle scattering and attenuation losses due to realistic photon fields, we study the spectrum and composition of the accelerated UHECRs and estimate the amount of neutrinos produced in such sources. We find that UHECRs may not be significantly affected by photodisintegration in AGN jets where the espresso mechanism efficiently accelerates particles, consistent with Auger’s results that favor a heavy composition at the highest energies. Moreover, we present estimates and upper bounds for the flux of high-energy neutrinos expected from AGN jets. In particular, we find that (i) source neutrinos may account for a sizable fraction, or even dominate, the expected flux of cosmogenic neutrinos; (ii) neutrinos from the β-decay of secondary neutrons produced in nucleus photodisintegration end up in the teraelectronvolt to petaelectronvolt band observed by IceCube, but can hardly account for the observed flux; (iii) UHECRs accelerated via the espresso mechanism lead to nearly isotropic neutrino emission, which suggests that nearby radio galaxies may be more promising as potential sources. We discuss our results in light of multimessenger astronomy and current/future neutrino experiments.
42
Lynch, Georgina. « Using Pupillometry to Assess the Atypical Pupillary Light Reflex and LC-NE System in ASD ». Behavioral Sciences 8, no 11 (21 novembre 2018) : 108. http://dx.doi.org/10.3390/bs8110108.
Texte intégralRésumé :
With recent advances in technology, there has been growing interest in use of eye-tracking and pupillometry to assess the visual pathway in autism spectrum disorder (ASD). Within emerging literature, an atypical pupillary light reflex (PLR) has been documented, holding potential for use as a clinical screening biomarker for ASD. This review outlines dominant theories of neuropathology associated with ASD and integrates underlying neuroscience associated with the atypical PLR through a reciprocal model of brainstem involvement and cortical underconnectivity. This review draws from animal models of ASD demonstrating disruption of cranial motor nuclei and brain imaging studies examining arousal and the influence of the locus coeruleus norepinephrine (LC-NE) system on the pupillary response. Pupillometry methods are explained in relation to existing data examining the PLR in ASD and pupillary parameters of constriction latency and tonic pupil diameter as key parameters for investigation. This focused review provides preliminary data toward future work developing pupillometry metrics and offers direction for studies aimed at rigorous study replication using pupillometry with the ASD population. Experimental conditions and testing protocol for capturing pupil parameters with this clinical population are discussed to promote clinical research and translational application.
43
Ray, Ramesh M., Huazhang Guo, Minesh Patel, Shi Jin, Sujoy Bhattacharya et Leonard R. Johnson. « Role of myosin regulatory light chain and Rac1 in the migration of polyamine-depleted intestinal epithelial cells ». American Journal of Physiology-Gastrointestinal and Liver Physiology 292, no 4 (avril 2007) : G983—G995. http://dx.doi.org/10.1152/ajpgi.00356.2006.
Texte intégralRésumé :
We have previously shown that polyamine depletion decreased migration, Rac activation, and protein serine threonine phosphatase 2A activity. We have also shown that polyamine depletion increased cortical F-actin and decreased lamellipodia and stress fibers. In this study, we used staurosporine (STS), a potent, cell-permeable, and broad-spectrum serine/threonine kinase inhibitor, and studied migration. STS concentrations above 100 nM induced apoptosis. However, in polyamine-depleted cells, a lower concentration of STS (5 nM) increased attachment, spreading, Rac1 activation, and, subsequently, migration without causing apoptosis. STS-induced migration was completely prevented by a Rac1 inhibitor (NSC-23766) and dominant negative Rac1. These results imply that STS restores migration in polyamine-depleted cells through Rac1. The most important finding in this study was that polyamine depletion increased the association of phosphorylated myosin regulatory light chain (pThr18/Ser19-MRLC) at the cell periphery, which colocalized with thick cortical F-actin. Localization of pThr18- and pSer19-MRLC was found with stress fibers and nuclei, respectively. STS decreased the phosphorylation of cellular and peripheral pThr18-MRLC without any effect on nuclear pSer19-MRLC, dissolved thick cortical F-actin, and increased lamellipodia and stress fiber formation in polyamine-depleted cells. In control and polyamine-depleted cells, focal adhesion kinase (FAK) colocalized with stress fibers and the actin cortex, respectively. STS reorganized FAK, paxillin, and the cytoskeleton. These results suggest that polyamine depletion prevents the dephosphorylation of MRLC and thereby prevents the dynamic reorganization of the actin cytoskeleton and decreases lamellipodia formation resulting in the inhibition of migration.
44
Sreekumar, P., et D. A. Kniffen. « Diffuse Gamma Rays of Galactic and Extragalactic Origin : Preliminary Results from EGRET ». Symposium - International Astronomical Union 168 (1996) : 279–88. http://dx.doi.org/10.1017/s0074180900110162.
Texte intégralRésumé :
The all-sky survey in high energy gamma rays (E>30 MeV) carried out by the Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory provides for the first time an opportunity to examine in detail diffuse gamma-ray emission of extra-galactic origin. The observed diffuse emission at high galactic latitudes is generally assumed to have a galactic component arising from cosmic-ray interactions with the local interstellar gas and radiation, in addition to an isotropic component presumably of extragalactic origin. The galactic component can be estimated from a model of the interstellar medium and cosmic-ray distribution. Since the derived extragalactic spectrum depends very much on the success of our galactic model, the consistency of the galactic diffuse emission model is examined both spectrally and spatially with existing EGRET observations. In conjunction with this model, EGRET observations of the high latitude emission are used to examine the flux and spectrum of the residual extragalactic emission. This residual emission could be either truly diffuse in origin or could arise from accumulated emission from unresolved sources particularly in the light of EGRET observations showing the presence of numerous gamma-ray bright active galactic nuclei.
45
d’Enterria, David. « Ultrahigh-energy cosmic rays : Anomalies, QCD, and LHC data ». EPJ Web of Conferences 210 (2019) : 02005. http://dx.doi.org/10.1051/epjconf/201921002005.
Texte intégralRésumé :
Measurements of proton and nuclear collisions at the Large Hadron Collider at nucleon-nucleon c.m. energies up to $ \sqrt {S_{NN} } = 13\,{\rm{TeV}} $ have improved our understanding of hadronic interactions at the highest energies reached in collisions of cosmic rays with nuclei in the earth atmosphere, up to $ \sqrt {S_{NN} } $ ≈ 450 TeV. The Monte Carlo event generators (epos, qgsjet, and sibyll) commonly used to describe the air showers generated by ultrahigh-energy cosmic rays (UHECR, with ECR ≈ 1017-1020 eV) feature now, after parameter retuning based on LHC Run-I data, more consistent predictions on the nature of the cosmic rays at the tail of the measured spectrum. However, anomalies persist in the data that cannot be accommodated by the models. Among others, the total number of muons (as well as their maximum production depth) remains significantly underestimated (overestimated) by all models. Comparisons of epos, qgsjet, and sibyll predictions to the latest LHC data, and to collider MC generators such as pythia, indicate that improved description of hard multiple minijet production and nuclear effects may help reduce part of the data-model discrepancies, shed light on the UHECR composition approaching the observed ECR ≈ 1020 eV cutoff, and uncover any potential new physics responsible for the observed anomalies.
46
Skorodko, T., M. Bashkanov, D. Bogoslowsky, H. Calén, F. Cappellaro, H. Clement, L. Demiroers et al. « ππ PRODUCTION IN PROTON-PROTON COLLISIONS ». International Journal of Modern Physics A 22, no 02n03 (30 janvier 2007) : 509–13. http://dx.doi.org/10.1142/s0217751x07035720.
Texte intégralRésumé :
At CELSIUS-WASA the two-pion production in proton-proton collisisons has been measured exclusively from threshold up to the energy regime, where both of the collision partners are expected to be excited to the Δ state. The measurements constitute the first kinematically complete data samples of solid statistics in this energy range. Most of the data have been obtained for the π+π- and π0π0channels. Whereas at near-threshold energies the differential distributions can be succesfully explained by chiral dynamics and Roper excitation, respectively, the data for the π+π- channel in the ΔΔ region can be described only, if the special configuration (ΔΔ)0+ is assumed. The data for the π0π0 channel moreover exhibit a low-mass enhancement in the π0π0 invariant mass spectrum, which is reminiscent of the ABC-effect found in double-pionic fusion to light nuclei.
47
Walter, Peter, Micheal Holmes, Razib Obaid, Lope Amores, Xianchao Cheng, James P. Cryan, James M. Glownia et al. « The DREAM Endstation at the Linac Coherent Light Source ». Applied Sciences 12, no 20 (19 octobre 2022) : 10534. http://dx.doi.org/10.3390/app122010534.
Texte intégralRésumé :
Free-electron lasers (FEL), with their ultrashort pulses, ultrahigh intensities, and high repetition rates at short wavelength, have provided new approaches to Atomic and Molecular Optical Science. One such approach is following the birth of a photo electron to observe ion dynamics on an ultrafast timescale. Such an approach presents the opportunity to decipher the photon-initiated structural dynamics of an isolated atomic and molecular species. It is a fundamental step towards understanding single- and non-linear multi-photon processes and coherent electron dynamics in atoms and molecules, ultimately leading to coherent control following FEL research breakthroughs in pulse shaping and polarization control. A key aspect for exploring photoinduced quantum phenomena is visualizing the collective motion of electrons and nuclei in a single reaction process, as dynamics in atoms/ions proceed at femtosecond (10−15 s) timescales while electronic dynamics take place in the attosecond timescale (10−18 s). Here, we report on the design of a Dynamic Reaction Microscope (DREAM) endstation located at the second interaction point of the Time-Resolved Molecular and Optical (TMO) instrument at the Linac Coherent Light Source (LCLS) capable of following the photon–matter interactions by detecting ions and electrons in coincidence. The DREAM endstation takes advantage of the pulse properties and high repetition rate of LCLS-II to perform gas-phase soft X-ray experiments in a wide spectrum of scientific domains. With its design ability to detect multi-ions and electrons in coincidence while operating in step with the high repetition rate of LCLS-II, the DREAM endstation takes advantage of the inherent momentum conservation of reaction product ions with participating electrons to reconstruct the original X-ray photon–matter interactions. In this report, we outline in detail the design of the DREAM endstation and its functionality, with scientific opportunities enabled by this state-of-the-art instrument.
48
Swiggum, Cameren, Christy Tremonti, Serena Perrotta, Adam Schaefer, Ryan C. Hickox, Alison L. Coil, Paul H. Sell, Aleksandar M. Diamond-Stanic, Jalyn Krause et Gregory Mosby. « Understanding the Nature of an Unusual Post-starburst Quasar with Exceptionally Strong Ne v Emission ». Astrophysical Journal 929, no 1 (1 avril 2022) : 79. http://dx.doi.org/10.3847/1538-4357/ac5c2c.
Texte intégralRésumé :
Abstract We present a z = 0.94 quasar, SDSS J004846.45-004611.9, discovered in the Sloan Digital Sky Survey III (SDSS-III) BOSS survey. A visual analysis of this spectrum reveals highly broadened and blueshifted narrow emission lines, in particular, [Ne v] λ3426 and [O iii] λ5007, with outflow velocities of 4000 km s−1, along with unusually large [Ne v] λ3426/[Ne iii] λ3869 ratios. The gas shows higher ionization at higher outflow velocities, indicating a connection between the powerful outflow and the unusual strength of the high ionization lines. The spectral energy distribution and the i − W3 color of the source reveal that it is likely a core extremely red quasar (ERQ); a candidate population of young active galactic nuclei (AGN) that are violently blowing out gas and dust from their centers. The dominance of host galaxy light in its spectrum and its fortuitous position in the SDSS S82 region allows us to measure its star formation history and investigate variability for the first time in an ERQ. Our analysis indicates that SDSS J004846.45-004611.9 underwent a short-lived starburst phase 400 Myr ago and was subsequently quenched, possibly indicating a time lag between star formation quenching and the onset of AGN activity. We also find that the strong extinction can be uniquely attributed to the AGN and does not persist in the host galaxy, contradicting a scenario where the source has recently transitioned from being a dusty submillimeter galaxy. In our relatively shallow photometric data, the source does not appear to be variable at 0.24–2.4 μm in the rest frame, most likely due to the dominant contribution of host galaxy starlight at these wavelengths.
49
Diaz, Y., P. Arévalo, L. Hernández-García, L. Bassani, A. Malizia, O. González-Martín, C. Ricci et al. « Constraining X-ray reflection in the low-luminosity AGN NGC 3718 using NuSTAR and XMM–Newton ». Monthly Notices of the Royal Astronomical Society 496, no 4 (19 juin 2020) : 5399–413. http://dx.doi.org/10.1093/mnras/staa1762.
Texte intégralRésumé :
ABSTRACT One distinctive feature of low-luminosity active galactic nuclei (LLAGNs) is the relatively weak reflection features they may display in the X-ray spectrum, which can result from the disappearance of the torus with decreasing accretion rates. Some material, however, must surround the active nucleus, i.e. the accretion flow itself and, possibly, a flattened-out or thinned torus. In this work, we study whether reflection is indeed absent or undetectable due to its intrinsically weak features together with the low statistics inherent to LLAGNs. Here, we focus on NGC 3718 (L/LEdd ∼ 10−5) combining observations from XMM–Newton and the deepest to date NuSTAR (0.5–79 keV) spectrum of a LLAGNs, to constrain potential reflectors, and analyse how the fitted coronal parameters depend on the reflection model. We test models representing both an accretion disc (Relxill) and a torus-like (MYTorus and Borus) neutral reflector. From a statistical point of view, reflection is not required, but its inclusion allows to place strong constraints on the geometry and physical features of the surroundings: both neutral reflectors (torus) tested should be Compton thin (NH < 1023.2cm−2) and preferentially cover a large fraction of the sky. If the reflected light instead arises from an ionized reflector, a highly ionized case is preferred. These models produce an intrinsic power-law spectral index in the range [1.81–1.87], where the torus models result in steeper slopes. The cut-off energy of the power-law emission also changes with the inclusion of reflection models, resulting in constrained values for the disc reflectors and unconstrained values for torus reflectors.
50
Korzhik, M. V. « Gadolinium contained scintillation glass for neutron detection in a wide energy range. » Proceedings of the National Academy of Sciences of Belarus. Physics and Mathematics Series 57, no 2 (16 juillet 2021) : 217–23. http://dx.doi.org/10.29235/1561-2430-2021-57-2-217-223.
Texte intégralRésumé :
Inorganic scintillation glasses form a domain of rapidly evolving detector materials used to measure various types of ionizing radiation. The most widespread are lithium-silicate glasses enriched with the 6Li isotope, which are used to register thermal neutrons. At the same time, due to the specificity of the energy dependence of the neutron cross-section of light nuclei, such materials are of little use for the evaluation of epithermal and more highly energetic neutrons. The use of rare earth elements in the composition of glasses makes it possible to increase the sensitivity to neutrons. In the BaO–Gd2O3–SiO2 system, doped with Ce ions, a scintillation glass with a yield of at least 2500 photons / MeV was created for the first time, which permits to create inexpensive detector elements of a significant volume for registering neutrons. It has been shown that a detector based on BaO–Gd2O3–SiO2 glass has satisfactory properties when detecting neutrons in a wide spectrum of their energies.