270 research outputs found
Influence of Yb:YAG laser beam parameters on Haynes 188 weld fusion zone microstructure and mechanical properties
The weldability of 1.2 mm thick Haynes 188 alloy sheets by a disk Yb:YAG laser welding was examined. Butt joints were made, and the influence of parameters such as power, size, and shape of the spot, welding speed, and gas flow has been investigated. Based on an iconographic correlation approach, optimum process parameters were determined. Depending on the distribution of the power density (circular or annular), acceptable welds were obtained. Powers greater than 1700 W, welding speeds higher than 3.8 m mm1, and spot sizes between 160 and 320 lm were needed in the circular (small fiber) configuration. By comparison, the annular (large fiber) configuration required a power as high as 2500 W, and a welding speed less than 3.8 m min�1. The mechanical properties of the welds depended on their shape and microstructure, which in turn depended on the welding conditions. The content of carbides, the proportion of areas consisting of cellular and dendritic substructures, and the size of these substructures were used to explain the welded joint mechanical properties
High-contrast imaging constraints on gas giant planet formation - The Herbig Ae/Be star opportunity
Planet formation studies are often focused on solar-type stars, implicitly
considering our Sun as reference point. This approach overlooks, however, that
Herbig Ae/Be stars are in some sense much better targets to study planet
formation processes empirically, with their disks generally being larger,
brighter and simply easier to observe across a large wavelength range. In
addition, massive gas giant planets have been found on wide orbits around early
type stars, triggering the question if these objects did indeed form there and,
if so, by what process. In the following I briefly review what we currently
know about the occurrence rate of planets around intermediate mass stars,
before discussing recent results from Herbig Ae/Be stars in the context of
planet formation. The main emphasis is put on spatially resolved polarized
light images of potentially planet forming disks and how these images - in
combination with other data - can be used to empirically constrain (parts of)
the planet formation process. Of particular interest are two objects, HD100546
and HD169142, where, in addition to intriguing morphological structures in the
disks, direct observational evidence for (very) young planets has been
reported. I conclude with an outlook, what further progress we can expect in
the very near future with the next generation of high-contrast imagers at 8-m
class telescopes and their synergies with ALMA.Comment: Accepted by Astrophysics and Space Science as invited short review in
special issue about Herbig Ae/Be stars; 12 pages incl. 5 figures, 2 tables
and reference
First Observation and Measurement of the Decay K+- -> pi+- e+ e- gamma
Using the full data set of the NA48/2 experiment, the decay K+- -> pi+- e+ e-
gamma is observed for the first time, selecting 120 candidates with 7.3 +- 1.7
estimated background events. With K+- -> pi+- pi0D as normalisation channel,
the branching ratio is determined in a model-independent way to be Br(K+- ->
pi+- e+ e- gamma, m_eegamma > 260 MeV/c^2) = (1.19 +- 0.12_stat +- 0.04_syst) x
10^-8. This measured value and the spectrum of the e+ e- gamma invariant mass
allow a comparison with predictions of Chiral Perturbation Theory.Comment: 13 pages, 3 figures. Accepted for publication in Phys.Lett.
Empirical parameterization of the K+- -> pi+- pi0 pi0 decay Dalitz plot
As first observed by the NA48/2 experiment at the CERN SPS, the \p0p0
invariant mass (M00) distribution from \kcnn decay shows a cusp-like anomaly
at M00=2m+, where m+ is the charged pion mass. An analysis to extract the pi pi
scattering lengths in the isospin I=0 and I=2 states, a0 and a2, respectively,
has been recently reported. In the present work the Dalitz plot of this decay
is fitted to a new empirical parameterization suitable for practical purposes,
such as Monte Carlo simulations of K+- -> pi+- pi0 pi0 decays.Comment: 9 pages, 3 figures
Search for direct CP-violation in K+- --> pi+-pi0pi0 decays
A search for direct CP-violation in K+- --> pi+-pi0pi0 decays based on 47.14
million events has been performed by the NA48/2 experiment at the CERN SPS. The
asymmetry in the Dalitz plot linear slopes A_g=(g^+ - g^-)/(g^+ + g^-) is
measured to be A_g=(1.8 +- 2.6).10^{-4}. The design of the experiment and the
method of analysis provide good control of instrumental charge asymmetries in
this measurement. The precision of the result is limited by statistics and is
almost one order of magnitude better than that of previous measurements by
other experiments.Comment: 14 page
A new measurement of direct CP violation in two pion decays of the neutral kaon
The NA48 experiment at CERN has performed a new measurement of direct CP
violation, based on data taken in 1997 by simultaneously collecting K_L and K_S
decays into pi0pi0 and pi+pi-. The result for the CP violating parameter
Re(epsilon'/epsilon) is (18.5 +/- 4.5(stat)} +/- 5.8 (syst))x10^{-4}.Comment: 18 pages, 6 figure
Search for the glueball candidates f0(1500) and fJ(1710) in gamma gamma collisions
Data taken with the ALEPH detector at LEP1 have been used to search for gamma
gamma production of the glueball candidates f0(1500) and fJ(1710) via their
decay to pi+pi-. No signal is observed and upper limits to the product of gamma
gamma width and pi+pi- branching ratio of the f0(1500) and the fJ(1710) have
been measured to be Gamma_(gamma gamma -> f0(1500)). BR(f0(1500)->pi+pi-) <
0.31 keV and Gamma_(gamma gamma -> fJ(1710)). BR(fJ(1710)->pi+pi-) < 0.55 keV
at 95% confidence level.Comment: 10 pages, 3 figure
Search for supersymmetry with a dominant R-parity violating LQDbar couplings in e+e- collisions at centre-of-mass energies of 130GeV to 172 GeV
A search for pair-production of supersymmetric particles under the assumption
that R-parity is violated via a dominant LQDbar coupling has been performed
using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV.
The observed candidate events in the data are in agreement with the Standard
Model expectation. This result is translated into lower limits on the masses of
charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for
m_0=500 GeV/c^2 and tan(beta)=sqrt(2) charginos with masses smaller than 81
GeV/c^2 and neutralinos with masses smaller than 29 GeV/c^2 are excluded at the
95% confidence level for any generation structure of the LQDbar coupling.Comment: 32 pages, 30 figure
Two Intermediate-mass Transiting Brown Dwarfs from the TESS Mission
We report the discovery of two intermediate-mass transiting brown dwarfs (BDs), TOI-569b and TOI-1406b, from NASA's Transiting Exoplanet Survey Satellite mission. TOI-569b has an orbital period of P=.55604±0.00016 days, a mass of Mb = 64.1±1.9 MJ, and a radius of Rb = 0.75±0.02 RJ. Its host star, TOI-569, has a mass of Må = 1.21±0.05 M, a radius of Rå = 1.47±0.03 R, [Fe H 0.29 0.09] = + dex, and an effective temperature of Teff = 5768±10K. TOI-1406b has an orbital period of P=10.57415±0.00063 days, a mass of Mb = 46.0± 2.7 MJ, and a radius of Rb = 0.86±0.03 RJ. The host star for this BD has a mass of Må = 1.18±0.09 M, a radius of Rå = 1.35±0.03 R, [Fe/H] =-0.08± 0.09 dex, and an effective temperature of Teff = 6290±100 K. Both BDs are in circular orbits around their host stars and are older than 3 Gyr based on stellar isochrone models of the stars. TOI-569 is one of two slightly evolved stars known to host a transiting BD (the other being KOI-415). TOI-1406b is one of three known transiting BDs to occupy the mass range of 40-50 MJ and one of two to have a circular orbit at a period near 10 days (with the first being KOI-205b). Both BDs have reliable ages from stellar isochrones, in addition to their well-constrained masses and radii, making them particularly valuable as tests for substellar isochrones in the BD mass-radius diagram
Measurement of the Dalitz plot slope parameters of the decay
The distribution of the decays in the Dalitz plot
has been measured by the NA48/2 experiment at the CERN SPS with a sample of
fully reconstructed events. With the standard Particle Data
Group parameterization the following values of the slope parameters were
obtained: , ,
. The quality and statistical accuracy of the data have
allowed an improvement in precision by more than an order of magnitude, and are
such as to warrant a more elaborate theoretical treatment, including pion-pion
rescattering, which is in preparation.Comment: 14 pages, 5 figures. Version submitted to Phys. Lett. B. Slightly
improved analysis and bibliography
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