A tmQCD mixed-action approach to flavour physics

We discuss a mixed-action approach in which sea quarks are regularised using non-perturbatively O(a) improved Wilson fermions, while a fully-twisted tmQCD action is used for valence quarks. In this setup, automatic O(a) improvement is preserved for valence observables, apart from small residual O(a) effects from the sea. A strategy for matching sea and valence is set up, and carried out for Nf = 2 + 1 CLS ensembles with open boundary conditions at several simulation points. The scaling of basic light-quark observables such as the pseudoscalar meson decay constant is studied, as well as the isospin splitting of pseudoscalar meson masses.

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Tidally induced lateral dispersion of the Storfjorden overflow plume

Ocean Science ◽

10.5194/os-9-885-2013 ◽

2013 ◽

Vol 9 (5) ◽

pp. 885-899 ◽

Cited By ~ 5

Author(s):

F. Wobus ◽

G. I. Shapiro ◽

J. M. Huthnance ◽

M. A. M. Maqueda ◽

Y. Aksenov

Keyword(s):

Ocean Circulation ◽

Circulation Model ◽

Bottom Layer ◽

Horizontal Resolution ◽

Open Boundary ◽

Coastal Current ◽

Fram Strait ◽

Open Boundary Conditions ◽

Shear Dispersion ◽

Set Up

Abstract. We investigate the flow of brine-enriched shelf water from Storfjorden (Svalbard) into Fram Strait and onto the western Svalbard Shelf using a regional set-up of NEMO-SHELF, a 3-D numerical ocean circulation model. The model is set up with realistic bathymetry, atmospheric forcing, open boundary conditions and tides. The model has 3 km horizontal resolution and 50 vertical levels in the sh-coordinate system which is specially designed to resolve bottom boundary layer processes. In a series of modelling experiments we focus on the influence of tides on the propagation of the dense water plume by comparing results from tidal and non-tidal model runs. Comparisons of non-tidal to tidal simulations reveal a hotspot of tidally induced horizontal diffusion leading to the lateral dispersion of the plume at the southernmost headland of Spitsbergen which is in close proximity to the plume path. As a result the lighter fractions in the diluted upper layer of the plume are drawn into the shallow coastal current that carries Storfjorden water onto the western Svalbard Shelf, while the dense bottom layer continues to sink down the slope. This bifurcation of the plume into a diluted shelf branch and a dense downslope branch is enhanced by tidally induced shear dispersion at the headland. Tidal effects at the headland are shown to cause a net reduction in the downslope flux of Storfjorden water into the deep Fram Strait. This finding contrasts previous results from observations of a dense plume on a different shelf without abrupt topography.

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Can turbulent reconnection be fast in 2D?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311017911 ◽

2010 ◽

Vol 6 (S271) ◽

pp. 385-386

Author(s):

K. Kulpa-Dybeł ◽

G. Kowal ◽

K. Otmianowska-Mazur ◽

A. Lazarian ◽

E. Vishniac

Keyword(s):

Three Dimensional ◽

Open Boundary ◽

Initial Vector ◽

Spectral Space ◽

Two Dimensional ◽

Open Boundary Conditions ◽

Random Forcing ◽

Potential Perturbation ◽

Set Up ◽

External Driving

AbstractTurbulent reconnection is studied by means of two-dimensional (2D) compressible magnetohydrodynamical numerical calculations. The process of homogeneous turbulence is set up by adding two-dimensional random forcing implemented in the spectral space at small wave numbers with no correlation between velocity and forcing. We apply the initial Harris current sheet configuration together with a density profile calculated from the numerical equilibrium of magnetic and gas pressures. We assume that there is no external driving of the reconnection. The reconnection develops as a result of the initial vector potential perturbation. We use open boundary conditions. Our main goal is to find the dependencies of reconnection rate on the uniform resistivity. We present that the reconnection speed depends on the Lindquist number in 2D in the case of low as well as high resolution. When we apply more powerful turbulence the reconnection is faster, however the speed of reconnection is smaller than in the case of our three-dimensional numerical simulations.

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Tidally-induced lateral dispersion of the Storfjorden overflow plume

Ocean Science Discussions ◽

10.5194/osd-10-691-2013 ◽

2013 ◽

Vol 10 (2) ◽

pp. 691-726

Author(s):

F. Wobus ◽

G. I. Shapiro ◽

J. M. Huthnance ◽

M. A. M. Maqueda ◽

Y. Aksenov

Keyword(s):

Ocean Circulation ◽

Circulation Model ◽

Bottom Layer ◽

Horizontal Resolution ◽

Open Boundary ◽

Coastal Current ◽

Fram Strait ◽

Open Boundary Conditions ◽

Shear Dispersion ◽

Set Up

Abstract. We investigate the flow of brine-enriched shelf water from Storfjorden (Svalbard) into Fram Strait and onto the Western Svalbard Shelf using a regional setup of NEMO-SHELF, a 3-D numerical ocean circulation model. The model is set up with realistic bathymetry, atmospheric forcing, open boundary conditions and tides. The model has 3 km horizontal resolution and 50 vertical levels in the sh-coordinate system which is specially designed to resolve bottom boundary layer processes. In a series of modelling experiments we focus on the influence of tides on the propagation of the dense water plume by comparing results from tidal and non-tidal model runs. Comparisons of non-tidal to tidal simulations reveal a hotspot of tidally-induced horizontal diffusion leading to the lateral dispersion of the plume at the southernmost headland of Spitsbergen which is in close proximity to the plume path. As a result the lighter fractions in the diluted upper layer of the plume are drawn into the shallow coastal current that carries Storfjorden water onto the Western Svalbard Shelf, while the dense bottom layer continues to sink down the slope. This bifurcation of the plume into a diluted shelf branch and a dense downslope branch is enhanced by tidally-induced shear dispersion at the headland. Tidal effects at the headland are shown to cause a net reduction in the downslope flux of Storfjorden water into deep Fram Strait. This finding contrasts previous results from observations of a dense plume on a different shelf without abrupt topography.

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Hydrodynamic and Hydrographic Modeling of Istanbul Strait

10.20944/preprints201908.0299.v1 ◽

2019 ◽

Author(s):

Mehmet Melih Koşucu ◽

Mehmet Cüneyd Demirel ◽

V.S. Ozgur Kirca ◽

Mehmet Özger

Keyword(s):

Mixing Layer ◽

Open Boundary ◽

Roughness Coefficient ◽

Model Parameters ◽

Temperature Profiles ◽

Open Boundary Conditions ◽

Pass Filter ◽

Low Pass Filter ◽

The North ◽

Set Up

The aim of this study is to model hydrodynamic processes of the Istanbul Strait with its stratified flow characteristic and calibrate the most important parameters using local and global search algorithms. For that two open boundary conditions are defined, which are in the North and South part of the Strait. Observed bathymetric, hydrographic, meteorological and water level data are used to set up the Delft3D-FLOW model. First, the sensitivities of model parameters on the numerical model outputs are assessed using PEST toolbox. Then, the model is calibrated based on the objective functions focusing on the flowrates of upper and lower layers. The salinity and temperature profiles of the Strait are only used for model validation. The results show that the calibrated model outputs of Istanbul Strait are reliable and consistent with the in-situ measurements. The sensitivity analysis reveals that the Spatial Low-Pass Filter Coefficient, Horizontal Eddy Viscosity, Prandtl-Schmidt Number, Slope in log-log Spectrum and Manning Roughness Coefficient are most sensitive parameters affecting flowrate performance of the model. The agreement between observed salinity profiles and simulated model outputs is promising whereas the match between observed and simulated temperature profiles is weak showing that the model can be improved particularly for simulating the mixing layer.

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Hydrodynamic and Hydrographic Modeling of Istanbul Strait

Processes ◽

10.3390/pr7100710 ◽

2019 ◽

Vol 7 (10) ◽

pp. 710 ◽

Cited By ~ 1

Author(s):

Mehmet Koşucu ◽

Mehmet Demirel ◽

V.S. Kirca ◽

Mehmet Özger

Keyword(s):

Mixing Layer ◽

Flow Characteristics ◽

Open Boundary ◽

Roughness Coefficient ◽

Model Parameters ◽

Temperature Profiles ◽

Open Boundary Conditions ◽

Pass Filter ◽

Low Pass Filter ◽

Set Up

The aim of this study is to model the hydrodynamic processes of the Istanbul Strait with its stratified flow characteristics, and calibrate the most important parameters using local and global search algorithms. For that, two open boundary conditions are defined, which are in the northern and southern parts of the Strait. Observed bathymetric, hydrographic, meteorological, and water-level data are used to set up the Delft3D-FLOW model. First, the sensitivities of the model parameters on the numerical model outputs are assessed using Parameter EStimation Tool (PEST) toolbox. Then, the model is calibrated based on the objective functions, focusing on the flow rates of the upper and lower layers. The salinity and temperature profiles of the strait are only used for model validation. The results show that the calibrated model outputs of the Istanbul Strait are reliable and consistent with the in situ measurements. The sensitivity analysis reveals that the spatial low-pass filter coefficient, horizontal eddy viscosity, Prandtl–Schmidt number, slope in log–log spectrum, and Manning roughness coefficient are most sensitive parameters affecting the flow rate performance of the model. The agreement between observed salinity profiles and simulated model outputs is promising, whereas the match between observed and simulated temperature profiles is weak, showing that the model can be improved, particularly for simulating the mixing layer.

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Effects of turbulence on magnetic reconnection: 3D numerical simulations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309031536 ◽

2008 ◽

Vol 4 (S259) ◽

pp. 671-674

Author(s):

Katarzyna Otmianowska-Mazur ◽

G. Kowal ◽

A. Lazarian ◽

E. Vishniac

Keyword(s):

Current Sheet ◽

Large Scale ◽

Three Dimensional ◽

Open Boundary ◽

Initial Vector ◽

Spectral Space ◽

Diffusion Region ◽

Open Boundary Conditions ◽

Random Forcing ◽

Set Up

AbstractTurbulent reconnection is studied by means of three dimensional (3D) compressible magnetohydrodynamical numerical calculations. The process of homogeneous turbulence is set up by adding three-dimensional solenoidal random forcing implemented in the spectral space at small wave numbers with no correlation between velocity and forcing. We apply the initial Harris current sheet configuration together with a density profile calculated from the numerical equilibrium of magnetic and gas pressures. We assume that there is no external driving of the reconnection. The reconnection develops as a result of the initial vector potential perturbation. We use open boundary conditions. Our main goal is to find the dependencies of reconnection rate on different properties of turbulence. The results of our simulations show that turbulence significantly affects the topology of magnetic field near the diffusion region. We present that the reconnection speed does not depend on the Reynolds numbers as well the magnetic diffusion. In addition, a fragmentation of current sheet decreases the disparity in inflow/outflow ratios. When we apply the large scale and more powerful turbulence the reconnection is faster.

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Impurity induced scale-free localization

Communications Physics ◽

10.1038/s42005-021-00547-x ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Linhu Li ◽

Ching Hua Lee ◽

Jiangbin Gong

Keyword(s):

Boundary Conditions ◽

Skin Effect ◽

Reciprocal Lattice ◽

Periodic Boundary Conditions ◽

Open Boundary ◽

Open Boundary Conditions ◽

Translational Invariance ◽

Scale Free ◽

Special Cases ◽

Simulation Results

AbstractNon-Hermitian systems have been shown to have a dramatic sensitivity to their boundary conditions. In particular, the non-Hermitian skin effect induces collective boundary localization upon turning off boundary coupling, a feature very distinct from that under periodic boundary conditions. Here we develop a full framework for non-Hermitian impurity physics in a non-reciprocal lattice, with periodic/open boundary conditions and even their interpolations being special cases across a whole range of boundary impurity strengths. We uncover steady states with scale-free localization along or even against the direction of non-reciprocity in various impurity strength regimes. Also present are Bloch-like states that survive albeit broken translational invariance. We further explore the co-existence of non-Hermitian skin effect and scale-free localization, where even qualitative aspects of the system’s spectrum can be extremely sensitive to impurity strength. Specific circuit setups are also proposed for experimentally detecting the scale-free accumulation, with simulation results confirming our main findings.

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