215 research outputs found
Three-dimensional writing inside silicon using a 2-µm picosecond fiber laser
International audienc
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
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
Comparison of detachment in Ohmic plasmas with positive and negative triangularity
Detachment is investigated using core density ramps for lower single null
Ohmic L-mode plasmas across a wide range of upper, lower, and total
triangularity () in the TCV tokamak. It is universally found that
detachment is more difficult to access with negative triangularity (NT)
shaping. The outer divertor leg of discharges with could
not be cooled below 5 eV using core density ramps alone. The behavior of the
upstream plasma and geometrical divertor effects (e.g. a reduced connection
length at negative lower triangularity) do not fully explain the challenges of
detaching NT plasmas. Langmuir probe measurements of the target heat flux
widths () remained constant within 30% across an upper triangularity
scan, while the spreading factor was found to be lower by up to 50% in NT,
indicating a generally lower integral SOL width. An interesting pattern has
been observed in the particle balance where the line-averaged core density was
typically higher in NT discharges for a given fuelling rate. Conversely, the
divertor neutral pressure and integrated particle content were typically lower
for the same line-averaged density. This indicates that NT plasmas may be
closer to the sheath-limited regime than their PT counterparts, which could
explain why NT is more challenging to detach
Comparison of high density and nitrogen seeded detachment using SOLPS-ITER simulations of the tokamak á configuration variable
First of a kind SOLPS-ITER simulations on tokamak á configuration variable (TCV) that include nitrogen have been performed to model recent nitrogen seeded detachment experiments. Based on spectroscopic measurements, a nitrogen recycling coefficient RNp ≈ 0.3–0.5 on the graphite walls of TCV is estimated. The experimentally observed decrease of core nitrogen density with increasing plasma density is reproduced and linked to a reduction of the ionisation mean free path in the scrape-off layer. Although the influence of sputtered carbon impurities from TCV’s graphite wall cannot be fully eliminated, seeding nitrogen increases control over the total impurity density. This facilitates disentangling the effect of impurities from that of high upstream density on the main characteristics of detachment, namely target power and ion current reductions and the development of a parallel pressure drop. Increasing the density and the seeding rate reduce the power on the divertor targets in a different way: with density, the ion current increases and the target temperature strongly decreases, whereas seeding impurities decreases the ion current and affects less strongly the temperature. The reduction in ion current when seeding nitrogen is due to a lower ionisation source, which is not related to power limitation nor an increased momentum loss, but to a decrease of the ionisation reaction rate. Impurity seeding leads to less volumetric momentum losses (and hence pressure drop) than density ramps, for the same level of energy flux reduction. Additionally, main chamber sputtering of carbon is identified as a possible explanation for the missing target ion current roll-over during density ramps in the simulations
Exosome release of β-catenin: a novel mechanism that antagonizes Wnt signaling
The tetraspanins CD9 and CD82 suppress Wnt signaling by promoting the discharge of β-catenin from cells
Sialyllactose in Viral Membrane Gangliosides Is a Novel Molecular Recognition Pattern for Mature Dendritic Cell Capture of HIV-1
An accessible sialyllactose moiety on viral membrane gangliosides is shown to be essential for HIV-1 uptake into mature dendritic cells, thereby promoting viral transfer and infection of bystander CD4+ T lymphocytes
Pediatric Measles Vaccine Expressing a Dengue Antigen Induces Durable Serotype-specific Neutralizing Antibodies to Dengue Virus
Dengue disease is an increasing global health problem that threatens one-third of the world's population. Despite decades of efforts, no licensed vaccine against dengue is available. With the aim to develop an affordable vaccine that could be used in young populations living in tropical areas, we evaluated a new strategy based on the expression of a minimal dengue antigen by a vector derived from pediatric live-attenuated Schwarz measles vaccine (MV). As a proof-of-concept, we inserted into the MV vector a sequence encoding a minimal combined dengue antigen composed of the envelope domain III (EDIII) fused to the ectodomain of the membrane protein (ectoM) from DV serotype-1. Immunization of mice susceptible to MV resulted in a long-term production of DV1 serotype-specific neutralizing antibodies. The presence of ectoM was critical to the immunogenicity of inserted EDIII. The adjuvant capacity of ectoM correlated with its ability to promote the maturation of dendritic cells and the secretion of proinflammatory and antiviral cytokines and chemokines involved in adaptive immunity. The protective efficacy of this vaccine should be studied in non-human primates. A combined measles–dengue vaccine might provide a one-shot approach to immunize children against both diseases where they co-exist
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