489 research outputs found
Percolation limited magnetic order in Eu1-xCaxB6
Abstract.: We report the results of measurements of the low-temperature specific heat Cp(T) and the ac susceptibility Ïac(T) in low applied magnetic fields for a series of samples of Eu1-xCaxB6. The anomalies in Cp(T), together with the results for Ïac(T) and M(H), confirm the onset of phase transitions to long range magnetic order for x < 0.7 and provide evidence that for x â„ 0.7, the Eu moments, which are captured in large magnetic clusters with magnetic moments of the order of 260 ÎŒB, adopt a spin-glass type ground state. The data set allows to establish the low-temperature [ T,x] phase diagram of this alloy serie
Observations of the Prompt Gamma-Ray Emission of GRB 070125
The long, bright gamma-ray burst GRB 070125 was localized by the
Interplanetary Network. We present light curves of the prompt gamma-ray
emission as observed by Konus-WIND, RHESSI, Suzaku-WAM, and \textit{Swift}-BAT.
We detail the results of joint spectral fits with Konus and RHESSI data. The
burst shows moderate hard-to-soft evolution in its multi-peaked emission over a
period of about one minute. The total burst fluence as observed by Konus is
erg/cm (20 keV--10 MeV). Using the spectroscopic
redshift , we find that the burst is consistent with the ``Amati''
correlation. Assuming a jet opening angle derived from
broadband modeling of the burst afterglow, GRB 070125 is a significant outlier
to the ``Ghirlanda'' correlation. Its
collimation-corrected energy release ergs is
the largest yet observed.Comment: 25 pages, 6 figures; accepted for publication in ApJ. Improved
spectral fits and energetics estimate
Symmetry-dependent Mn-magnetism in Al69.8Pd12.1Mn18.1
Abstract.: We investigated the stability of magnetic moments in Al69.8Pd12.1Mn18.1. This alloy exists in both, the icosahedral (i) and the decagonal (d) quasicrystalline form. The transition from the i- to the d-phase is achieved by a simple heat treatment. We present the results of measurements of the 27Al NMR-response, the dc magnetic susceptibility, and the low-temperature specific heat of both phases. In the icosahedral compound, the majority of the Mn ions carries a magnetic moment. Their number is reduced by approximately a factor of two by transforming the alloy to its decagonal variety. For both compounds, we have indications for two different local environments of the Al nuclei. The first reflects a low density of states of conduction electrons and a weak coupling of the Al nuclei to the Mn-moments. The second type of environment implies a large d-electron density of states at the Fermi level and a strong coupling to the magnetic Mn moments. Spin-glass freezing transitions are observed at Tdecaf=12K for the decagonal, and Ticof=19 K for the icosahedral phas
Strong Electron-Phonon Coupling in Superconducting MgB: A Specific Heat Study
We report on measurements of the specific heat of the recently discovered
superconductor MgB in the temperature range between 3 and 220 K. Based on a
modified Debye-Einstein model, we have achieved a rather accurate account of
the lattice contribution to the specific heat, which allows us to separate the
electronic contribution from the total measured specific heat. From our result
for the electronic specific heat, we estimate the electron-phonon coupling
constant to be of the order of 2, significantly enhanced compared to
common weak-coupling values . Our data also indicate that the
electronic specific heat in the superconducting state of MgB can be
accounted for by a conventional, s-wave type BCS-model.Comment: 4 pages, 4 figure
Magneto-optical Kerr effect in
We have measured the magneto-optical Kerr rotation of ferromagnetic
with x=0.2 and 0.4, as well as of serving as
the non-magnetic reference material. As previously for , we could
identify a feature at 1 in the Kerr response which is related with
electronic transitions involving the localized 4f electron states. The absence
of this feature in the data for confirms the relevance of the
partially occupied 4f states in shaping the magneto-optical features of
-based hexaborides. Disorder by -doping broadens the itinerant charge
carrier contribution to the magneto-optical spectra
Joint analysis of resident complaints, meteorological, acoustic, and ground motion data to establish a robust annoyance evaluation of wind turbine emissions
In order to advance the expansion of onshore wind energy, wind turbines (WTs) must be erected in often complex terrain. The orography and the associated meteorological conditions, as well as the complex propagation of sound and ground motion waves can lead to increased annoyance of residents.
Here a joint investigation of residential noise reports, meteorological, acoustic and ground motion data together with operational parameters of a wind farm in southern Germany is presented, with the objective to assess the annoyance of residents affected by WT emissions. Once strongly annoyed residents had been identified, simultaneous measurements were conducted over a 2-month period while residents used a noise reporting app to document their annoyance. A combination of the data shows that WT-related signals can be detected by acoustic and ground motion measurements in the vicinity of the WTs and, to a lesser extent, at the residential sites. In addition, background noise can be identified well. The app data indicates higher complaint rates in the early morning, evening and night hours. Changes in rotation rate seem to be the cause of annoyance as well as high rotation rates. These findings can be used to adjust WT operation in order to decrease immissions
Lorentz violating electrodynamics
After summarizing the most interesting results in the calculation of
synchrotron radiation in the Myers-Pospelov effective model for Lorentz
invariance violating (LIV) electrodynamics, we present a general unified way of
describing the radiation regime of LIV electrodynamics which include the
following three different models : Gambini-Pullin, Ellis et al. and
Myers-Pospelov. Such unification reduces to the standard approach of radiation
in a dispersive and absortive (in general) medium with a given index of
refraction. The formulation is presented up to second order in the LIV
parameter and it is explicitly applied to the synchrotron radiation case.Comment: 11 pages, extended version of the talk given by L.F. Urrutia in the
VI Mexican School: Approaches to Quantum Gravity, Playa del Carmen, Mexico,
Nov. 2004. Minor chages in the text and added reference
Signatures of photon and axion-like particle mixing in the gamma-ray burst jet
Photons couple to Axion-Like Particles (ALPs) or more generally to any pseudo
Nambu-Goldstone boson in the presence of an external electromagnetic field.
Mixing between photons and ALPs in the strong magnetic field of a Gamma-Ray
Burst (GRB) jet during the prompt emission phase can leave observable imprints
on the gamma-ray polarization and spectrum. Mixing in the intergalactic medium
is not expected to modify these signatures for ALP mass > 10^(-14) eV and/or
for < nG magnetic field. We show that the depletion of photons due to
conversion to ALPs changes the linear degree of polarization from the values
predicted by the synchrotron model of gamma ray emission. We also show that
when the magnetic field orientation in the propagation region is perpendicular
to the field orientation in the production region, the observed synchrotron
spectrum becomes steeper than the theoretical prediction and as detected in a
sizable fraction of GRB sample. Detection of the correlated polarization and
spectral signatures from these steep-spectrum GRBs by gamma-ray polarimeters
can be a very powerful probe to discover ALPs. Measurement of gamma-ray
polarization from GRBs in general, with high statistics, can also be useful to
search for ALPs.Comment: 17 pages, 3 figures. Accepted for publication in JCAP with minor
change
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