321 research outputs found
Searching for tetraquarks on the lattice
We address the question whether the lightest scalar mesons sigma and kappa
are tetraquarks. We present a search for possible light tetraquark states with
J^PC=0^++ and I=0, 1/2, 3/2, 2 in the dynamical and the quenched lattice
simulations using tetraquark interpolators. In all the channels, we unavoidably
find lowest scattering states pi(k)pi(-k) or K(k)pi(-k) with back-to-back
momentum k=0,2*pi/L,.. . However, we find an additional light state in the I=0
and I=1/2 channels, which may be related to the observed resonances sigma and
kappa with a strong tetraquark component. In the exotic repulsive channels I=2
and I=3/2, where no resonance is observed, we find no light state in addition
to the scattering states.Comment: 3 pages, 1 figure, proceedings of Lepton-Photon 2009, Hambur
Effective chiral restoration in the rho'-meson in lattice QCD
In simulations with dynamical quarks it has been established that the ground
state rho in the infrared is a strong mixture of the two chiral representations
(0,1)+(1,0) and (1/2,1/2)_b. Its angular momentum content is approximately the
3S1 partial wave which is consistent with the quark model. Effective chiral
restoration in an excited rho-meson would require that in the infrared this
meson couples predominantly to one of the two representations. The variational
method allows one to study the mixing of interpolators with different chiral
transformation properties in the non-perturbatively determined excited state at
different resolution scales. We present results for the first excited state of
the rho-meson using simulations with n_f=2 dynamical quarks. We point out, that
in the infrared a leading contribution to rho'= rho(1450) comes from
(1/2,1/2)_b, in contrast to the rho. Its approximate chiral partner would be a
h_1(1380) state. The rho' wave function contains a significant contribution of
the 3D1 wave which is not consistent with the quark model prediction.Comment: 4 pp, a few short remarks have been added, a reference updated. To
appear in PR
BerufsmobilitÀt und Lebensform: sind berufliche MobilitÀtserfordernisse in Zeiten der Globalisierung noch mit Familie vereinbar?
Mit beruflicher MobilitĂ€t sind neben einigen Vorteilen eine Reihe von Problemen und Belastungen verbunden, die in der Studie untersucht werden. Befragt wurden in ĂŒber 1000 Interviews mobile BerufstĂ€tige und ihre Partnerinnen oder Partner, die in verschiedenen mobilen Arrangements leben (Fernpendler, Umzugsmobile, Wochenendpendler, Varimobile, Fernbeziehungen). Als Vergleichsgruppe wurden auch nicht mobile Personen befragt. Als Faustregel formulieren die VerfasserInnen der Studie: "Je jĂŒnger die Befragten, je höher der Bildungsabschluss und je kleiner der Haushalt, desto mobiler sind sie". MĂ€nner sind auĂerdem weit hĂ€ufiger mobil als Frauen. Untersucht werden die EntscheidungsgrĂŒnde fĂŒr die MobilitĂ€t, die Belastungen, die MobilitĂ€t mit sich bringt, die Auswirkungen auf Familie und Partnerschaft und auf die sozialen Beziehungen insgesamt und der UnterstĂŒtzungsbedarf aus der Sicht der beruflich Mobilen. Die AutorInnen stellen fest, dass Unternehmen mehr als bisher Mitverantwortung auch fĂŒr das Privatleben ihrer BeschĂ€ftigten ĂŒbernehmen sollten und dass Entwicklungspotenziale zur Gewinnung guter Mitarbeiter und Mitarbeiterinnen zukĂŒnftig weniger im materiellen als im nicht-materiellen, familienorientierten Bereich liegen werden. (IAB
Calibration Of The JohnsonâCook Model At High Temperatures For An Ultra-High Strength CrNiMoV Steel
This paper presents a study on the thermo-mechanical behavior of an ultra-high strength CrNiMoV steel at high temperatures and medium strain rates through hot tensile tests. The material was examined in two conditions: as-cast/heat-treated (AC/HT) and as-rolled (AR). Tensile tests were conducted at temperatures of 800,900,1000,1100, and 1200°C, and strain rates of 0.1,1, and 10sâ1. Inclusion and porosity analysis was also performed on the tensile specimens. The results revealed that the flow stress decreased by approximately 70% on average from 800°C to 1200°C, while increasing by approximately 32% on average from 0.1sâ1 to 10sâ1 in strain rate. The elongation exhibited an increase from 16.5% at 800°C to 33% at 1200°C. However, the ductility transition was slower than expected, particularly for the AC/HT conditions. The AC/HT samples exhibited higher levels of inclusions and porosity compared to the AR samples, with porosity significantly affecting the elongation to failure and ultimate tensile strength (UTS) at a strain rate of 1sâ1. Furthermore, calibrated JohnsonâCook parameters were reported and compared, demonstrating excellent agreement between predicted and experimental values with less than 20% variation. The calibrated JohnsonâCook model can be effectively employed for modeling purposes within the studied temperature range, and its application can even be extrapolated for higher strain rates
Tribo-oxidation of a brake friction couple under varying sliding conditions
This study explores a common parameter that is used to describe the energy input into a friction pairing in pin-on-disc investigations, the pv-value. The impacts of multiple sliding speed, v, and contact pressure, p, combinations were investigated while keeping their product, the pv-value at a constant level. The chosen tests for this study consisted of steady-state drag braking applications on a small-scale test bench. The actual contact area on the friction material's surface was measured after the tests and correlated to the steady-state temperature, T, that was reached during testing. The tribological interface showed sensitivity towards the different sliding and loading conditions including a shift in oxidising states of the iron contents of the friction couples. The sliding and loading conditions were reversed after the transition of oxidising states in order to investigate their impact. The results show that the oxidising states dynamically react to the operating conditions, but the overall frictional performance of the system can remain at an altered level due to enduring changes in the actual contact area and the thermal response of the friction couple with the transition in oxidising states
The electric double layer has a life of its own
Using molecular dynamics simulations with recently developed importance
sampling methods, we show that the differential capacitance of a model ionic
liquid based double-layer capacitor exhibits an anomalous dependence on the
applied electrical potential. Such behavior is qualitatively incompatible with
standard mean-field theories of the electrical double layer, but is consistent
with observations made in experiment. The anomalous response results from
structural changes induced in the interfacial region of the ionic liquid as it
develops a charge density to screen the charge induced on the electrode
surface. These structural changes are strongly influenced by the out-of-plane
layering of the electrolyte and are multifaceted, including an abrupt local
ordering of the ions adsorbed in the plane of the electrode surface,
reorientation of molecular ions, and the spontaneous exchange of ions between
different layers of the electrolyte close to the electrode surface. The local
ordering exhibits signatures of a first-order phase transition, which would
indicate a singular charge-density transition in a macroscopic limit
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