4,052 research outputs found
ERGEBNISSE DER GEMEINSAMEN FORSCHUNGSARBEITEN ZWISCHEN DER WACKER-CHEMIE GMBH UND DEM LEHRSTUHL FÜR ANORGANISCHE CHEMIE DER TU BUDAPEST
The object of a common researchwork between the Wacker-Chemie GmbH and the In-
stitute of Inorganic Chemistry, Technical University of Budapest has been fixed in a
co-operation contract since 1983. There are results in the following fields:
- preparative and technological examinations,
- new possibilities in the technical applications,
- physico-chemical examinations of different silicone products.
We would like to report on the co-operation in this brief general publication
Evidence for an unconventional magnetic instability in the spin-tetrahedra system Cu_2Te_2O_5Br_2
Thermodynamic experiments as well as Raman scattering have been used to study
the magnetic instabilities in the spin-tetrahedra systems Cu_2Te_2O_5X_2, X=Cl
and Br. While the phase transition observed in the Cl system at T_o=18.2 K is
consistent with 3D AF ordering, the phase transition at T_o=11.3 K in the Br
system has several unusual features. We propose an explanation in terms of
weakly coupled tetrahedra with a singlet-triplet gap and low lying singlets.Comment: 4 pages, 4 figure
Bounds on Dark Matter from the ``Atmospheric Neutrino Anomaly''
Bounds are derived on the cross section, flux and energy density of new
particles that may be responsible for the atmospheric neutrino anomaly. Decay of primordial
homogeneous dark matter can be excluded.Comment: 10 pages, TeX (revtex
Infrared singularities in one-loop amplitudes
In this talk we discuss a purely numerical approach to next-to-leading order
calculations in QCD. We present a simple formula, which provides a local
infrared subtraction term for the integrand of a one-loop amplitude. In
addition we briefly comment on local ultraviolet subtraction terms and on the
required deformation of the contour of integration.Comment: 6 pages, talk given at the conference "Loops and Legs", Woerlitz,
201
Search for particle acceleration in two massive Wolf-Rayet stars using uGMRT observations
Large wind kinetic power of Wolf-Rayet (WR) stars make them ideal targets in
low radio frequencies to search for non-thermal emission due to relativistic
particle acceleration. In this paper, we present observations of two WR stars,
WR 114 and WR 142, in Band 4 (550-950 MHz) and Band 5 (1050-1450 MHz) using the
upgraded Giant Meterwave Radio Telescope (uGMRT). Neither star is detected in
the observed frequency bands, nor extended emission associated with them. The
upper limit to the free-free radio emission from the stellar wind enables us to
constrain the mass-loss rate of WR 114 to ; this is a factor three smaller than previously estimated
using spectroscopic modelling. If we further assume that the WR stars are
binaries, the non-detection of synchrotron emission from the putative wind
collision region implies that the stars are either in very wide binary systems
away from periastron, or that the stars are in close binary systems with an
orbital separation AU for WR 114 and AU for WR 142. The
non-detection of low-frequency radio emission from these two systems thus
provides evidence that narrows their nature, though it does not rule them out
as bonafide particle-accelerating colliding-wind binaries.Comment: 8 pages, 3 figures, accepted for publication in MNRA
The {\eta}'-carbon potential at low meson momenta
The production of mesons in coincidence with forward-going
protons has been studied in photon-induced reactions on C and on a
liquid hydrogen (LH) target for incoming photon energies of 1.3-2.6 GeV at
the electron accelerator ELSA. The mesons have been identified
via the decay
registered with the CBELSA/TAPS detector system. Coincident protons have been
identified in the MiniTAPS BaF array at polar angles of . Under these kinematic constraints the
mesons are produced with relatively low kinetic energy (
150 MeV) since the coincident protons take over most of the momentum of the
incident-photon beam. For the C-target this allows the determination of the
real part of the -carbon potential at low meson momenta by
comparing with collision model calculations of the kinetic energy
distribution and excitation function. Fitting the latter data for
mesons going backwards in the center-of-mass system yields a potential depth of
V = (44 16(stat)15(syst)) MeV, consistent with earlier
determinations of the potential depth in inclusive measurements for average
momenta of 1.1 GeV/. Within the experimental
uncertainties, there is no indication of a momentum dependence of the
-carbon potential. The LH data, taken as a reference to check
the data analysis and the model calculations, provide differential and integral
cross sections in good agreement with previous results for
photoproduction off the free proton.Comment: 9 pages, 13 figures. arXiv admin note: text overlap with
arXiv:1608.0607
The polarization observables T, P, and H and their impact on multipoles
Data on the polarization observables T, P, and H for the reaction are reported. Compared to earlier data from other experiments, our
data are more precise and extend the covered range in energy and angle
substantially. The results were extracted from azimuthal asymmetries measured
using a transversely polarized target and linearly polarized photons. The data
were taken at the Bonn electron stretcher accelerator ELSA with the CBELSA/TAPS
detector. Within the Bonn-Gatchina partial wave analysis, the new polarization
data lead to a significant narrowing of the error band for the multipoles for
neutral-pion photoproduction
Resolving the M2-brane
We construct deformed, T^2 wrapped, rotating M2-branes on a resolved cone
over Q^{1,1,1} and Q^{1,1,1}/Z_2, as well as on a product of two Eguchi-Hanson
instantons. All worldvolume directions of these supersymmetric and regular
solutions are fibred over the transverse space. These constitute gravity duals
of D=3, N=2 gauge theories. In particular, the deformed M2-brane on a resolved
cone over Q^{1,1,1} and the S^1 wrapped M2-brane on a resolved cone over
Q^{1,1,1}/Z_2 provide explicit realizations of holographic renormalization
group flows in M-theory for which both conformal and Lorentz symmetries are
broken in the IR region and restored in the UV limit. These solutions can be
dualized to supersymmetric type IIB pp-waves, which are rendered non-singular
either by additional flux or a twisted time-like direction.Comment: Latex, 23 pages, references adde
Evidence for surface cooling emission in the XMM-Newton spectrum of the X-ray pulsar PSR B2334+61
We report on the first XMM-Newton observation of the Vela-like pulsar PSR
B2334+61. Spectral analysis reveals soft X-ray emission, with the bulk of the
photons emitted at energies below ~1.5 keV. We find that the spectrum has a
thermal origin and is well-fitted with either a blackbody or a magnetized, pure
H atmospheric model. In the latter case, for a neutron star with a radius of 13
km and a magnetic field of 10e13 G, the best-fit gives an hydrogen column
density nH = 0.33 x 10^22 cm^-2 and an effective temperature T_eff^infinity =
0.65 x 10^6 K, as measured at Earth. A comparison of the surface temperature of
PSR B2334+61 obtained from this fit with cooling curves favor a medium mass
neutron star with M ~ 1.45 solar masses or M ~ 1.6 solar masses, depending on
two different models of proton superfluidity in the interior. We do not detect
any pulsed emission from the source, and determine an upper limit of 5% for the
modulation amplitude of the emission on the pulsar's radio frequency.Comment: 14 pages, 1 figure, 1 table, accepted for publication in Ap
The N(1520) 3/2- helicity amplitudes from an energy-independent multipole analysis based on new polarization data on photoproduction of neutral pions
New data on the polarization observables T, P, and H for the reaction are reported. The results are extracted from azimuthal
asymmetries when a transversely polarized butanol target and a linearly
polarized photon beam are used. The data were taken at the Bonn electron
stretcher accelerator ELSA using the CBELSA/TAPS detector. These and earlier
data are used to perform a truncated energy-independent partial wave analysis
in sliced-energy bins. This energy-independent analysis is compared to the
results from energy-dependent partial wave analyses
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