292 research outputs found
Multiorbital kinetic effects on charge ordering of frustrated electrons on the triangular lattice
The role of the multiorbital effects on the emergence of frustrated
electronic orders on the triangular lattice at half filling is investigated
through an extended spinless fermion Hubbard model. By using two complementary
approaches, unrestricted Hartree-Fock and exact diagonalizations, we unravel a
very rich phase diagram controlled by the strength of both local and off-site
Coulomb interactions and by the interorbital hopping anisotropy ratio .
Three robust unconventional electronic phases, a pinball liquid, an inverse
pinball liquid, and a large-unit-cell droplet
phase, are found to be generic in the triangular geometry, being controlled by
the band structure parameters. The latter are also stabilized in the isotropic
limit of our microscopic model, which recovers the standard SU(2) spinful
extended single-band Hubbard model.Comment: 10 pages, 6 figure
Performance assessment of a tightly baffled, long-legged divertor configuration in TCV with SOLPS-ITER
Numerical simulations explore the possibility to test the tightly baffled,
long-legged divertor (TBLLD) concept in a future upgrade of the Tokamak \`a
configuration variable (TCV). The SOLPS-ITER code package is used to compare
the exhaust performance of several TBLLD configurations with existing unbaffled
and baffled TCV configurations. The TBLLDs feature a range of radial gaps
between the separatrix and the outer leg side walls. All considered TBLLDs are
predicted to lead to a denser and colder plasma in front of the targets and
improve the power handling by factors of 2-3 compared to the present, baffled
divertor and by up to a factor of 12 compared to the original, unbaffled
configuration. The improved TBLLD performance is mainly due to a better neutral
confinement with improved plasma-neutral interactions in the divertor region.
Both power handling capability and neutral confinement increases when reducing
the radial gap. The core compatibility of TBLLDs with nitrogen seeding is also
evaluated and the detachment window with acceptable core pollution for the
proposed TBLLDs is explored, showing a reduction of required upstream impurity
concentration up to 18% to achieve the detachment with thinner radial gap
Geometrical frustration effects on charge-driven quantum phase transitions
The interplay of Coulomb repulsion and geometrical frustration on
charge-driven quantum phase transitions is explored. The ground state phase
diagram of an extended Hubbard model on an anisotropic triangular lattice
relevant to quarter-filled layered organic materials contains homogeneous
metal, 'pinball' and three-fold charge ordered metallic phases. The stability
of the 'pinball' phase occurring for strong Coulomb repulsions is found to be
strongly influenced by geometrical frustration. A comparison with a spinless
model reproduces the transition from the homogeneous metallic phase to a
pinball liquid, which indicates that the spin correlations should play a much
smaller role than the charge correlations in the metallic phase close to the
charge ordering transition. Spin degeneracy is, however, essential to describe
the dependence of the system on geometrical frustration. Based on finite
temperature Lanczos diagonalization we find that the effective Fermi
temperature scale, T*, of the homogeneous metal vanishes at the quantum phase
transition to the ordered metallic phase driven by the Coulomb repulsion. Above
this temperature scale 'bad' metallic behavior is found which is robust against
geometrical frustration in general. Quantum critical phenomena are not found
whenever nesting of the Fermi surface is strong, possibly indicating a first
order transition instead. 'Reentrant' behavior in the phase diagram is
encountered whenever the 2kF-CDW instability competes with the Coulomb driven
three-fold charge order transition. The relevance of our results to the family
of quarter-filled materials: theta-(BEDT-TTF)2X is discussed.Comment: 15 pages, 11 figure
Characterization and transfer of heavy metals in two different urban stormwater infiltration works sediments: an experimental approach
Analysis of wall-embedded Langmuir probe signals in different conditions on the Tokamak à Configuration Variable
Change in quality of life of stage IA lung cancer patients after sublobar resection and lobectomy
© Journal of Thoracic Disease. All rights reserved. Background: Few studies have examined the differential impact of sublobar resection (SL) and lobectomy (L) on quality of life (QoL) during the first postoperative year. Methods: We used a prospective cohort of Stage IA lung cancer patients undergoing video-assisted thoracoscopic surgery (VATS) from the Initiative for Early Lung Cancer Research on Treatment. QoL was measured before surgery, and within 4, 6, and 12 months post-surgery using three validated instruments: SF-12 [physical (PCS) and mental health (MCS)], FACT-LCS (lung-cancer-symptoms), and the PHQ-4 (anxiety and depression subscales). Locally weighted smoothing curve (LOWESS) was fitted to identify the best interval knot for the change in the QoL trend post-surgery. After adjusting for demographic and clinical variables, an adjusted piecewise linear mixed effects model was developed to estimate differences in baseline and 12-month scores, and rates of change for each QoL measure. Results: SL resection was performed in 127 (63.2%) and L in 74 (36.8%) patients. LOWESS plots suggested that the shift of QoL (interval knot) was at 2 months post-surgery. Decreases in PCS scores were less severe for SL than L patients 2 months post-surgery (−0.18 vs. −2.30, P=0.02); while subsequent improvements were observed for both groups (SL: +0.29 vs. L: +0.74, P=0.06). SL patients reported significantly better scores a year post-surgery compared to baseline (P=0.003), while L patients did not. Anxiety decreased at similar rates for both SL and L patients within 2 months post-surgery (P=0.18), then stabilized for the remaining months. MCS and depression scores remained stable in both groups throughout. QoL scores were lower for women than for men, but only significantly worse for the lung-cancer-symptoms (P=0.003) and anxiety (P=0.04). Conclusions: SL patients fared better in physical health and lung cancer symptoms than L patients. The first two postoperative months showed the most significant change which suggests targeting postoperative intervention during that time
Reduction in benefits of total flux expansion on divertor detachment due to parallel flows
The Super-X divertor (SXD) is an alternative divertor configuration
leveraging total flux expansion at the outer strike point (OSP). Key features
for the attractiveness of the SXD are facilitated detachment access and
control, as predicted by the extended 2-point model (2PM). However, parallel
flows are not consistently included in the 2PM. In this work, the 2PM is
refined to overcome this limitation: the role of total flux expansion on the
pressure balance is made explicit, by including the effect of parallel flows.
In consequence, the effect of total flux expansion on detachment access and
control is weakened, compared to predictions of the 2PM. This new model
partially explains discrepancies between the 2PM and experiments performed on
TCV, in ohmic L-mode scenarios, where in core density ramps in lower
single-null (SN) configuration, the impact of the OSP major radius Rt on the
CIII emission front movement in the divertor outer leg - used as a proxy for
the plasma temperature - is substantially weaker than 2PM predictions; and in
OSP sweeps in lower and upper SN configurations, with a constant core density,
the peak parallel particle flux density at the OSP is almost independent of Rt,
while the 2PM predicts a linear dependence. Finally, analytical and numerical
modelling of parallel flows in the divertor is presented, to support the
argument. It is shown that an increase in total flux expansion can favour
supersonic flows at the OSP. Parallel flows are also shown to be relevant by
analysing SOLPS-ITER simulations of TCV
Synergetic effects of collisions, turbulence and sawtooth crashes on impurity transport
This paper investigates the interplay of neoclassical, turbulent and MHD processes, which are simultaneously at play when contributing to impurity transport. It is shown that these contributions are not additive, as assumed sometimes. The interaction between turbulence and neoclassical effects leads to less effective thermal screening, i.e. lowers the outward flux due to temperature gradient. This behavior is attributed to poloidal asymmetries of the flow driven by turbulence. Moreover sawtooth crashes play an important role to determine fluxes across the q = 1 surface. It is found that the density profile of a heavy impurity differs significantly in sawtoothing plasmas from the one predicted by neoclassical theory when neglecting MHD events. Sawtooth crashes impede impurity accumulation, but also weaken the impurity outflux due to the temperature gradient when the latter is dominant
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