Search results for "anisotropy"
showing 10 items of 912 documents
Ligand Design for Heterobimetallic Single-Chain Magnets: Synthesis, Crystal Structures, and Magnetic Properties of MIICuII (M=Mn, Co) Chains with Ste…
2006
Two new series of neutral ox-amato-bridged heterobimetallic chains of general formula [MCu(L x ) 2 ]- m DMSO (m=0-4) (L 1 =N-2-methyl-phenyloxamate, M=Mn (1a) and Co (1 b); L2 = N-2,6-dimethylphenyloxamate, M=Mn (2a) and Co (2b); L 3 = N-2,4,6-trimethylphenyloxamate, M= Mn (3a) and Co (3b)) have been prepared by reaction between the corresponding anionic oxamatocopper(II) complexes [Cu(L x ) 2 ] 2- with Mn 2+ or Co 2+ cations in DMSO. The crystal structures of [CoCu(L 2 ) 2 (H 2 O) 2 ] (2b') and [CoCu(L 3 ) 2 (H 2 O) 2 ]·4H 2 O (3b') have been solved by single-crystal X-ray diffraction methods. Compounds 2b' and 3b' adopt zigzag and linear chain structures, respectively. The intrachain Cu··…
Cosmological bounds on neutrino statistics
2018
We consider the phenomenological implications of the violation of the Pauli exclusion principle for neutrinos, focusing on cosmological observables such as the spectrum of Cosmic Microwave Background anisotropies, Baryon Acoustic Oscillations and the primordial abundances of light elements. Neutrinos that behave (at least partly) as bosonic particles have a modified equilibrium distribution function that implies a different influence on the evolution of the Universe that, in the case of massive neutrinos, can not be simply parametrized by a change in the effective number of neutrinos. Our results show that, despite the precision of the available cosmological data, only very weak bounds can …
Search for patterns by combining cosmic-ray energy and arrival directions at the Pierre Auger Observatory
2015
Energy-dependent patterns in the arrival directions of cosmic rays are searched for using data of the Pierre Auger Observatory. We investigate local regions around the highest-energy cosmic rays with E ≥ 6×1019 eV by analyzing cosmic rays with energies above E ≥ 5×1018 eV arriving within an angular separation of approximately 15∘. We characterize the energy distributions inside these regions by two independent methods, one searching for angular dependence of energy-energy correlations and one searching for collimation of energy along the local system of principal axes of the energy distribution. No significant patterns are found with this analysis. The comparison of these measurements with …
Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter
2010
Data collected by the Pierre Auger Observatory through 31 August 2007 showed evidence for anisotropy in the arrival directions of cosmic rays above the Greisen-Zatsepin-Kuz'min energy threshold, 6 x 10(19) eV. The anisotropy was measured by the fraction of arrival directions that are less than 3.1 degrees from the position of an active galactic nucleus within 75 Mpc (using the Veron-Cetty and Veron 12th catalog). An updated measurement of this fraction is reported here using the arrival directions of cosmic rays recorded above the same energy threshold through 31 December 2009. The number of arrival directions has increased from 27 to 69, allowing a more precise measurement. The correlating…
A search for point sources of EeV neutrons
2012
A thorough search of the sky exposed at the Pierre Auger Cosmic Ray Observatory reveals no statistically significant excess of events in any small solid angle that would be indicative of a flux of neutral particles from a discrete source. The search covers from −90◦ to +15◦ in declination using four different energy ranges above 1 EeV (1018 eV). The method used in this search is more sensitive to neutrons than to photons. The upper limit on a neutron flux is derived for a dense grid of directions for each of the four energy ranges. These results constrain scenarios for the production of ultrahigh energy cosmic rays in the Galaxy.
An Indication of Anisotropy in Arrival Directions of Ultra-high-energy Cosmic Rays through Comparison to the Flux Pattern of Extragalactic Gamma-Ray …
2018
A new analysis of the dataset from the Pierre Auger Observatory provides evidence for anisotropy in the arrival directions of ultra-high-energy cosmic rays on an intermediate angular scale, which is indicative of excess arrivals from strong, nearby sources. The data consist of 5514 events above 20 EeV with zenith angles up to 80 deg recorded before 2017 April 30. Sky models have been created for two distinct populations of extragalactic gamma-ray emitters: active galactic nuclei from the second catalog of hard Fermi-LAT sources (2FHL) and starburst galaxies from a sample that was examined with Fermi-LAT. Flux-limited samples, which include all types of galaxies from the Swift-BAT and 2MASS …
Large-scale Cosmic-Ray Anisotropies above 4 EeV Measured by the Pierre Auger Observatory
2018
We present a detailed study of the large-scale anisotropies of cosmic rays with energies above 4 EeV measured using the Pierre Auger Observatory. For the energy bins [4,8] EeV and $E\geq 8$ EeV, the most significant signal is a dipolar modulation in right ascension at energies above 8 EeV, as previously reported. In this paper we further scrutinize the highest-energy bin by splitting it into three energy ranges. We find that the amplitude of the dipole increases with energy above 4 EeV. The growth can be fitted with a power law with index $\beta=0.79\pm 0.19$. The directions of the dipoles are consistent with an extragalactic origin of these anisotropies at all the energies considered. Addi…
Galactic Cosmic-Ray Anisotropy in the Northern hemisphere from the ARGO-YBJ Experiment during 2008-2012
2018
This paper reports on the observation of the sidereal large-scale anisotropy of cosmic rays using data collected by the ARGO-YBJ experiment over 5 years (2008-2012). This analysis extends previous work limited to the period from 2008 January to 2009 December, near the minimum of solar activity between cycles 23 and 24. With the new data sample, the period of solar cycle 24 from near minimum to maximum is investigated. A new method is used to improve the energy reconstruction, allowing us to cover a much wider energy range, from 4 to 520 TeV. Below 100 TeV, the anisotropy is dominated by two wide regions, the so-called “tail-in” and “loss-cone” features. At higher energies, a dramatic change…
Constraints on neutrino emission from nearby galaxies using the 2MASS redshift survey and IceCube
2020
The distribution of galaxies within the local universe is characterized by anisotropic features. Observatories searching for the production sites of astrophysical neutrinos can take advantage of these features to establish directional correlations between a neutrino dataset and overdensities in the galaxy distribution in the sky. The results of two correlation searches between a seven-year time-integrated neutrino dataset from the IceCube Neutrino Observatory, and the 2MASS Redshift Survey (2MRS) catalog are presented here. The first analysis searches for neutrinos produced via interactions between diffuse intergalactic Ultra-High Energy Cosmic Rays (UHECRs) and the matter contained within …
Anisotropic scaling of tectonic stylolites: A fossilized signature of the stress field?
2010
International audience; [1] Vertical stylolites are pressure solution features, which are considered to be caused by horizontal tectonic loading, with the largest principal compressive stress being (sub-) parallel to the Earth's surface. In the present study we analyze the roughness of such tectonic stylolites from two tectonic settings in southern Germany and northeastern Spain, aiming to investigate their scaling properties with respect to the stress during formation. High-resolution laser profilometry was carried out on opened stylolite surfaces of nine samples. These data sets were then analyzed using one-and two-dimensional Fourier power spectral approaches. We found that tectonic styl…