Context.
Retrograde-propagating waves of vertical vorticity with longitudinal wavenumbers between 3 and 15 have been observed on the Sun with a dispersion relation close to that of classical sectoral ...Rossby waves. The observed vorticity eigenfunctions are symmetric in latitude, peak at the equator, switch sign near 20°–30°, and decrease at higher latitudes.
Aims.
We search for an explanation that takes solar latitudinal differential rotation into account.
Methods.
In the equatorial
β
plane, we studied the propagation of linear Rossby waves (phase speed
c
< 0) in a parabolic zonal shear flow,
U
= −
U̅
ξ
2
< 0, where
U̅
= 244 m s
−1
, and
ξ
is the sine of latitude.
Results.
In the inviscid case, the eigenvalue spectrum is real and continuous, and the velocity stream functions are singular at the critical latitudes where
U
=
c
. We add eddy viscosity to the problem to account for wave attenuation. In the viscous case, the stream functions solve a fourth-order modified Orr-Sommerfeld equation. Eigenvalues are complex and discrete. For reasonable values of the eddy viscosity corresponding to supergranular scales and above (Reynolds number 100 ≤
Re
≤ 700), all modes are stable. At fixed longitudinal wavenumber, the least damped mode is a symmetric mode whose real frequency is close to that of the classical Rossby mode, which we call the R mode. For
Re
≈ 300, the attenuation and the real part of the eigenfunction is in qualitative agreement with the observations (unlike the imaginary part of the eigenfunction, which has a larger amplitude in the model).
Conclusions.
Each longitudinal wavenumber is associated with a latitudinally symmetric R mode trapped at low latitudes by solar differential rotation. In the viscous model, R modes transport significant angular momentum from the dissipation layers toward the equator.
Resistance-modified acetylcholinesterases have been described in many insect species and sequencing of their genes has allowed several point mutations to be described. Most mutations line the active ...site gorge. Each mutation provides a specific resistance pattern: it confers resistance to one insecticide but may increase sensitivity to another. Most mutations alter hydrolysis of the substrate by decreasing the rate of enzyme deacetylation and by diminishing the stability of the enzyme. Mutations are often found in combination in the same protein. This has several consequences: it increases the level of resistance, it enlarges the spectrum of resistance and it may restore the catalytic efficiency of the enzyme. Natural populations are heterogeneous, composed of a mixture of different alleles.
Mutation-dependent overproduction of intrinsic β-lactamase AmpC is considered the main cause of resistance of clinical strains of Pseudomonas aeruginosa to antipseudomonal penicillins and ...cephalosporins. Analysis of 31 AmpC-overproducing clinical isolates exhibiting a greater resistance to ceftazidime than to piperacillin-tazobactam revealed the presence of 17 mutations in the β-lactamase, combined with various polymorphic amino acid substitutions. When overexpressed in AmpC-deficient P. aeruginosa 4098, the genes coding for 20/23 of these AmpC variants were found to confer a higher (2-fold to >64-fold) resistance to ceftazidime and ceftolozane-tazobactam than did the gene from reference strain PAO1. The mutations had variable effects on the MICs of ticarcillin, piperacillin-tazobactam, aztreonam, and cefepime. Depending on their location in the AmpC structure and their impact on β-lactam MICs, they could be assigned to 4 distinct groups. Most of the mutations affecting the omega loop, the R2 domain, and the C-terminal end of the protein were shared with extended-spectrum AmpCs (ESACs) from other Gram-negative species. Interestingly, two new mutations (F121L and P154L) were predicted to enlarge the substrate binding pocket by disrupting the stacking between residues F121 and P154. We also found that the reported ESACs emerged locally in a variety of clones, some of which are epidemic and did not require hypermutability. Taken together, our results show that P. aeruginosa is able to adapt to efficacious β-lactams, including the newer cephalosporin ceftolozane, through a variety of mutations affecting its intrinsic β-lactamase, AmpC. Data suggest that the rates of ESAC-producing mutants are ≥1.5% in the clinical setting.
Context.
Helioseismology is the study of the Sun’s interior using observations of oscillations at the surface. It suffers from systematic errors, for instance a center-to-limb error in travel-time ...measurements. Understanding these errors requires an adequate understanding of the nontrivial relationship between wave displacement and helioseismic observables (intensity or velocity).
Aims.
The wave displacement causes perturbations in the atmospheric thermodynamical quantities which, in turn, perturb the opacity, the optical depth, the source function, and the local ray geometry, thus affecting the emergent intensity. We aim to establish the most complete relationship achieved to date between the wave displacement and the emergent intensity perturbation by solving the radiative transfer problem in the perturbed atmosphere.
Methods.
We derived an expression for the emergent intensity perturbation caused by acoustic oscillations at any point on the solar disk by applying a first-order perturbation theory. As input perturbations, we considerd adiabatic modes of oscillation of different degrees in a spherically-symmetric solar model. The background and the perturbed intensities are computed by solving the radiative transfer equation considering the main sources of opacity in the continuum (absorption and scattering).
Results.
We find that for all modes, the perturbations to the thermodynamical quantities are not sufficient to model the intensity perturbations: the geometrical effects due to the wave displacement must always be taken into account as they lead to a difference in amplitude and a phase shift between temperature perturbations at the surface and emergent intensity perturbations. The closer to the limb, the greater the differences. For modes with eigenfrequencies around 3 mHz, we found that the radial and horizontal components of the wave displacement are important, in particular, for high-degree modes.
Conclusions.
This work presents improvements for the computation of the intensity perturbations, in particular, for high-degree modes. Here, we explain the differences in intensity computations seen in earlier works. The phase shifts and amplitude differences between the temperature and intensity perturbations increase toward the limb. This should prove helpful when interpreting some of the systematic centre-to-limb effects observed in local helioseismology. The computations are fast (3 s for 2000 positions and one frequency for one core) and can be parallelised. This work can be extended to models of the line-of-sight velocity observable.
Numerous microsurgical training techniques and materials have been developed to reduce animal use and training costs. This systematic review aimed to catalog the available microsurgery learning ...methods on non-living material in order to define an educational program. The PubMed database was searched for English and French articles related to the initial learning of microsurgery with inert, non-living, or digital material and containing the keywords “microsurgery”, “non-living”, “simulation” and “virtual reality”. Among the 488 articles found, 82 were included. This work reports the main microsurgery learning supports. They were classified according to the material used: inert material, cadaveric animal tissues, human cadaver model, virtual reality, and digital technologies. The educational program proposes here is a two-step program that uses non-living material (basic and deepening) before progressing to living models. This initial learning phase teaches basic microsurgical skills (precision, tremor management, and magnification). Then, frequent home training sessions help to maintain the acquired skills. Ethical, organizational, and economic constraints limit access to animal models. Therefore, inert models seem to be ideal support for initial microsurgical learning. The multiplicity of models described makes it possible to achieve progressive learning depending on which models are available.
De nombreux supports pour l’apprentissage de la microchirurgie ont été développés afin de réduire le nombre d’animaux utilisés et les coûts de formation. L’objectif de cette revue de la littérature était de dresser un répertoire des méthodes d’apprentissage sur du matériel non vivant afin de proposer un programme pédagogique. Une recherche sur PubMed a été réalisée permettant d’analyser tous les articles rédigés en anglais et en français relatifs à l’apprentissage initial de la microchirurgie sur matériel inerte et contenant les termes “microchirurgie”; “non vivants”; “simulation” et “réalité virtuelle”. Parmi les 488 articles retrouvés, 82 ont été inclus. Ce travail rapporte les principaux supports pour l’apprentissage de la microchirurgie. Ils ont été classés en fonction du matériel utilisé: matériel inerte, tissus animaux cadavériques, modèle cadavérique humain, réalité virtuelle et technologies numériques. Le programme pédagogique propose un apprentissage en deux étapes de base et d’approfondissement sur matériel non vivant, avant d’envisager le passage au matériel vivant. Cet apprentissage initial permettrait d’acquérir les compétences nécessaires sous microscope sur la gestuelle, la gestion du tremblement et de la magnification. Ensuite, un entraînement fréquent à domicile permettrait d’entretenir les compétences acquises. Les contraintes éthiques, organisationnelles et économiques limitent de plus en plus l’accès à l’expérimentation animale. Ainsi, les modèles inertes semblent être le support idéal dans l’apprentissage initial de la microchirurgie. La multiplicité des modèles décrits permet d’envisager un apprentissage progressif en fonction de la reproductibilité et de l’accès à ces modèles.
•Noise was reduced with TF compared to ASiR-V while maintaining FBP-like noise texture, leading to sharper image appearance.•Low contrast lesion detectability (AUC) was always higher with TF than ...ASIR-V at 60 %.•TrueFidelity at high strength enabled an estimated radiation dose reduction of 33 % without impairing lesion detectability.
To compare deep learning (True Fidelity, TF) and partial model based Iterative Reconstruction (ASiR-V) algorithm for image texture, low contrast lesion detectability and potential dose reduction.
Anthropomorphic phantoms (mimicking non-overweight and overweight patient), containing lesions of 6 mm in diameter with 20HU contrast, were scanned at five different dose levels (2,6,10,15,20 mGy) on a CT system, using clinical routine protocols for liver lesion detection. Images were reconstructed using ASiR-V 0% (surrogate for FBP), 60 % and TF at low, medium and high strength. Noise texture was characterized by computing a normalized Noise Power Spectrum filtered by an eye filter. The similarity against FBP texture was evaluated using peak frequency difference (PFD) and root mean square deviation (RMSD). Low contrast detectability was assessed using a channelized Hotelling observer and the area under the ROC curve (AUC) was used as figure of merit. Potential dose reduction was calculated to obtain the same AUC for TF and ASiR-V.
FBP-like noise texture was more preserved with TF (PFD from -0.043mm-1 to -0.09mm-1, RMSD from 0.12mm-1 to 0.21mm-1) than with ASiR-V (PFD equal to 0.12 mm-1, RMSD equal to 0.53mm-1), resulting in a sharper image. AUC was always higher with TF than ASIR-V. In average, TF compared to ASiR-V, enabled a radiation dose reduction potential of 7%, 25 % and 33 % for low, medium and high strength respectively.
Compared to ASIR-V, TF at high strength does not impact noise texture and maintains low contrast liver lesions detectability at significant lower dose.
Inversion of self‐potential data for source current density, js, in complex volcanic settings, yields hydrological information without the need for a prior groundwater flow model; js contains ...information about pH, pore saturation, and permeability, from which we infer the distribution of liquid and vapor phases. To understand the hydrothermal flow dynamics and hydraulic connectivity between surface thermal features at Mount Tongariro volcano, New Zealand, we undertook a reconnaissance scale self‐potential survey and developed an inversion routine for js, constrained by an existing 3‐D conductivity model from magnetotelluric measurements. The 3‐D distribution of js at Mount Tongariro reveals a discontinuous zero js zone interpreted as vapor or residually saturated pore space, surrounded by low to moderate js interpreted as circulating condensate liquid. Bounding faults act as conduits for down flowing groundwater or condensate, as well as barriers for the hydrothermal system. Localized small‐scale circulation associated with individual surface thermal features, rather than a single circulating system, accounts for the lack of widespread anomalous geochemical observations prior to the 2012 Te Maari eruption.
Plain Language Summary
Volcanologists routinely sample fluids from springs and vents on volcanoes to determine that volcano's state of unrest. Prior to the 2012 Te Maari eruptions at Mount Tongariro, New Zealand, changes in water and gas chemistry that preceded the eruption were found at only a few of the vents and springs sampled, despite evidence for a large hydrothermal system, thought to connect them. We wanted to understand why chemical changes in the water and gas were not observed more widely on the volcano and if it was related to the pattern of underground water movement. Water moving within a rock generates a small electrical charge, measurable on the surface as a voltage. We mapped voltage variations around the hydrothermal system at Mount Tongariro and developed new 3‐D computer software to simulate the subsurface water movement. We found varying degrees of water and steam within the hydrothermal system that is likely controlled by the rock's ability to allow water movement. Importantly, we found no connectivity between individual springs and vents on the volcano, explaining observations of geographically isolated changes in water and gas chemistry prior to the eruptions. This has important implications for how geochemical monitoring of similar multivent volcanoes is undertaken.
Key Points
Three‐dimensional self‐potential inversion model of a vapor‐dominated hydrothermal reservoir yields subsurface flow conditions
Vapor and liquid phases are distinguished by 3‐D source current density distribution
Hydrothermal system fluid flow knowledge is important for successful volcano monitoring strategies
Context.
Large-scale equatorial Rossby modes have been observed on the Sun over the last two solar cycles.
Aims.
We investigate the impact of the time-varying zonal flows on the frequencies of Rossby ...modes.
Methods.
A first-order perturbation theory approach is used to obtain an expression for the expected shift in the mode frequencies due to perturbations in the internal rotation rate.
Results.
Using the time-varying rotation from helioseismic inversions we predict the changes in Rossby mode frequencies with azimuthal orders from
m
= 1 to
m
= 15 over the last two solar cycles. The peak-to-peak frequency change is less than 1 nHz for the
m
= 1 mode, grows with
m
, and reaches 25 nHz for
m
= 15.
Conclusions.
Given the observational uncertainties on mode frequencies due to the finite mode lifetimes, we find that the predicted frequency shifts are near the limit of detectability.
Central to the understanding of high-temperature superconductivity is the evolution of the electronic structure as doping alters the density of charge carriers in the CuO2 planes. Superconductivity ...emerges along the path from a normal metal on the overdoped side to an antiferromagnetic insulator on the underdoped side. This path also exhibits a severe disruption of the overdoped normal metal's Fermi surface. Angle-resolved photoemission spectroscopy (ARPES) on the surfaces of easily cleaved materials such as Bi2Sr2CaCu2O8+δ shows that in zero magnetic field the Fermi surface breaks up into disconnected arcs. However, in high magnetic field, quantum oscillations at low temperatures in YBa2Cu3O6.5 indicate the existence of small Fermi surface pockets. Reconciling these two phenomena through ARPES studies of YBa2Cu3O7−δ (YBCO) has been hampered by the surface sensitivity of the technique. Here, we show that this difficulty stems from the polarity and resulting self-doping of the YBCO surface. Through in situ deposition of potassium atoms on cleaved YBCO, we can continuously control the surface doping and follow the evolution of the Fermi surface from the overdoped to the underdoped regime. The present approach opens the door to systematic studies of high-temperature superconductors, such as creating new electron-doped superconductors from insulating parent compounds.
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