5,676 research outputs found
Decay of geodesic acoustic modes due to the combined action of phase mixing and Landau damping
Geodesic acoustic modes (GAMs) are oscillations of the electric field whose
importance in tokamak plasmas is due to their role in the regulation of
turbulence. The linear collisionless damping of GAMs is investigated here by
means of analytical theory and numerical simulations with the global
gyrokinetic particle-in-cell code ORB5. The combined effect of the phase mixing
and Landau damping is found to quickly redistribute the GAM energy in
phase-space, due to the synergy of the finite orbit width of the passing ions
and the cascade in wave number given by the phase mixing. When plasma
parameters characteristic of realistic tokamak profiles are considered, the GAM
decay time is found to be an order of magnitude lower than the decay due to the
Landau damping alone, and in some cases of the same order of magnitude of the
characteristic GAM drive time due to the nonlinear interaction with an ITG
mode. In particular, the radial mode structure evolution in time is
investigated here and reproduced quantitatively by means of a dedicated initial
value code and diagnostics.Comment: Submitted to Phys. Plasma
Dijet Production at Large Rapidity Separation in N=4 SYM
Ratios of azimuthal angle correlations between two jets produced at large
rapidity separation are studied in the N=4 super Yang-Mills theory (MSYM). It
is shown that these observables, which directly prove the SL(2,C) symmetry
present in gauge theories in the Regge limit, exhibit an excellent perturbative
convergence. They are compared to those calculated in QCD for different
renormalization schemes concluding that the momentum-substraction (MOM) scheme
with the Brodsky-Lepage-Mackenzie (BLM) scale-fixing procedure captures the
bulk of the MSYM results.Comment: 13 pages, 7 figure
Effect of turbulence on electron cyclotron current drive and heating in ITER
Non-linear local electromagnetic gyrokinetic turbulence simulations of the
ITER standard scenario H-mode are presented for the q=3/2 and q=2 surfaces. The
turbulent transport is examined in regions of velocity space characteristic of
electrons heated by electron cyclotron waves. Electromagnetic fluctuations and
sub-dominant micro-tearing modes are found to contribute significantly to the
transport of the accelerated electrons, even though they have only a small
impact on the transport of the bulk species. The particle diffusivity for
resonant passing electrons is found to be less than 0.15 m^2/s, and their heat
conductivity is found to be less than 2 m^2/s. Implications for the broadening
of the current drive and energy deposition in ITER are discussed.Comment: Letter, 5 pages, 5 figures, for submission to Nuclear Fusio
Understanding the core density profile in TCV H-mode plasmas
Results from a database analysis of H-mode electron density profiles on the
Tokamak \`a Configuration Variable (TCV) in stationary conditions show that the
logarithmic electron density gradient increases with collisionality. By
contrast, usual observations of H-modes showed that the electron density
profiles tend to flatten with increasing collisionality. In this work it is
reinforced that the role of collisionality alone, depending on the parameter
regime, can be rather weak and in these, dominantly electron heated TCV cases,
the electron density gradient is tailored by the underlying turbulence regime,
which is mostly determined by the ratio of the electron to ion temperature and
that of their gradients. Additionally, mostly in ohmic plasmas, the Ware-pinch
can significantly contribute to the density peaking. Qualitative agreement
between the predicted density peaking by quasi-linear gyrokinetic simulations
and the experimental results is found. Quantitative comparison would
necessitate ion temperature measurements, which are lacking in the considered
experimental dataset. However, the simulation results show that it is the
combination of several effects that influences the density peaking in TCV
H-mode plasmas.Comment: 23 pages, 12 figure
Global gyrokinetic simulations of intrinsic rotation in ASDEX Upgrade Ohmic L-mode plasmas
Non-linear, radially global, turbulence simulations of ASDEX Upgrade (AUG)
plasmas are performed and the nonlinear generated intrinsic flow shows
agreement with the intrinsic flow gradients measured in the core of Ohmic
L-mode plasmas at nominal parameters. Simulations utilising the kinetic
electron model show hollow intrinsic flow profiles as seen in a predominant
number of experiments performed at similar plasma parameters. In addition,
significantly larger flow gradients are seen than in a previous flux-tube
analysis (Hornsby et al {\it Nucl. Fusion} (2017)). Adiabatic electron model
simulations can show a flow profile with opposing sign in the gradient with
respect to a kinetic electron simulation, implying a reversal in the sign of
the residual stress due to kinetic electrons. The shaping of the intrinsic flow
is strongly determined by the density gradient profile. The sensitivity of the
residual stress to variations in density profile curvature is calculated and
seen to be significantly stronger than to neoclassical flows (Hornsby et al
{\it Nucl. Fusion} (2017)). This variation is strong enough on its own to
explain the large variations in the intrinsic flow gradients seen in some AUG
experiments. Analysis of the symmetry breaking properties of the turbulence
shows that profile shearing is the dominant mechanism in producing a finite
parallel wave-number, with turbulence gradient effects contributing a smaller
portion of the parallel wave-vector
AIF-1 gene does not confer susceptibility to Behçet's disease: Analysis of extended haplotypes in Sardinian population
Background BehcEet's disease (BD) is a polygenic immune-mediated disorder characterized by a close association with the HLA-Bâ51 allele. The HLA region has a strong linkage disequilibrium (LD) and carries several genetic variants (e.g. MIC-A, TNF-α genes) identified as associated to BD because of their LD with HLA-Bâ51. In fact, the HLA-Bâ51 is inherited as part of extended HLA haplotypes which are well preserved in patients with BD. Sardinian population is highly differentiated from other Mediterranean populations because of a distinctive genetic structure with very highly preserved HLA haplotypes. Patients and methods In order to identify other genes of susceptibility to BD within the HLA region we investigated the distribution of human Allograft Inflammatory Factor-1 (AIF-1) gene variants among BD patients and healthy controls from Sardinia. Six (rs2736182; rs2259571; rs2269475; rs2857597; rs13195276; rs4711274) AIF-1 single nucleotide polymorphisms (SNPs) and related extended haplotypes have been investigated as well as their LD within the HLA region and with HLA-Bâ51. Overall, 64 BD patients, 43 HLA-Bâ51 positive healthy controls (HC) and 70 random HC were enrolled in the study. Results HLA-Bâ51 was the only allele with significantly higher frequency (pc = 0.0021) in BD patients (40.6%) than in HC (9.8%). The rs2259571TAIF-1 variant had a significantly reduced phenotypic, but not allelic frequency in BD patients (72.1%; pc = 0.014) compared to healthy population (91.3%). That was likely due to the LD between HLA-Bâ51 and rs2259571G(pc= 9E-5), even though the rs2259571Gdistribution did not significantly differ between BD patients and HC. Conclusion No significant difference in distribution of AIF-1 SNPs haplotypes was observed between BD patients and HC and between HLA-Bâ51 positive BD patients and HLA-Bâ51 positive HC. Taken together, these results suggest that AIF-1 gene is not associated with susceptibility to BD in Sardinia
Expression analysis of HLA-E and NKG2A and NKG2C receptors points at a role for natural killer function in ankylosing spondylitis
Background. Ankylosing Spondylitis (AS) is a complex chronic inflammatory disease strongly associated with the majority of HLA-B27 alleles. HLA-E are non-classical MHC class I molecules that specifically interact with the natural killer receptors NKG2A (inhibitory) and NKG2C (activating), and have been recently proposed to be involved in AS pathogenesis. Objectives: To analyze the expression of HLA-E and the CD94/NKG2 pair of receptors in HLA-B27 positive AS patients and healthy controls (HC) bearing the AS-associated, B*2705 and the non-AS-associated, B*2709 allele. Methods: The level of surface expression of HLA-E molecules on CD14 positive peripheral blood mononuclear cell was evaluated in 21 HLA-B*2705 patients with AS, 12 HLA-B*2705 HC, 12 HLA-B*2709 HC and 6 HLA-B27 negative HC, using the monoclonal antibody MEM-E/08 by quantitative cytofluorimetric analysis. The percentage and density of expression of HLA-E ligands NKG2A and NKG2C were also measured on CD3-CD56+ NK cells. Results. HLA-E expression in CD14 positive cells was significantly higher in AS patients (587.0 IQR 424-830) compared to B*2705 HC (389 IQR 251.3-440.5, p=0.0007), B*2709 HC (294.5 IQR 209.5-422, p=0.0004) and HLA-B27 negative HC (380 IQR 197.3-515.0, p=0.01). A higher number of NK cells expressing NKG2A compared to NKG2C was found in all cohort analysed as well as a higher cell surface density. Conclusion: The higher surface level of HLA-E molecules in AS patients compared to HC, concurrently with a prevalent expression of NKG2A, suggests that the crosstalk between these two molecules might play a role in AS pathogenesis accounting for the previously reported association between HLA-E and AS
UHPLC-MS/MS Method for the Analysis of 2,6 Toluene Diisocyanate and 2,4 Toluene Diisocyanate Released from Microa-gglomerated Corks in Wine
Micro-agglomerate corks, made by agglutination of cork granulate through the addition of different adhesives, represent an important slice of the market of cork stoppers. Binder glues which are polyurethane- or butadiene-based have been used since they have strong agglomerating effect. Unfortunately, polyurethane-based glues can have isocyanide end group compounds which can migrate into the wine. 2,4-toluene diisocyanate (2,4-TDI) and 2,6 toluene diisocyanate (2,6-TDI), can be found in adhesive and could migrate into wine. A simple ultrahigh-performance liquid chromatography-mass spectrometry (UHPLC-MS/MS) method for the determination of these active ingredients (a.is.) in wine has been developed. The method has been validated under Eurachem CITAC guidelines (Cooperation on International Traceability in Analytical Chemistry). Instrument limit of detection (LOD) and to a limit of quantification (LOQ) for 2,6 TDI and 2,4 TDI were 0.42 and 0.39 ÎŒg/L, and 1.72 and 1.57 ÎŒg/L, respectively. Four different solvents applied for recoveries showed quite different rates ranging for 2,6 TDI and 2,4 TDI from 17.96 to 88.53 %, and 40.08 to 99.18 %, respectively. Real sample analysis showed low residue levels, especially of 2,6 TDI, with values always below the LOQ. The data reported on real samples allowed to establish that from a risk management purpose, no toxicology risk can be accomplished
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