TY  - JOUR
A1  - Verma, Meetu
A1  - Kummerow, P.
A1  - Denker, Carsten
T1  - On the extent of the moat flow in axisymmetric sunspots
JF  - Astronomische Nachrichten = Astronomical notes
N2  - Unipolar, axisymmetric sunspots are figuratively called “theoretician's sunspots” because their simplicity supposedly makes them more suitable for theoretical descriptions or numerical models. On November 18, 2013, a very large specimen (active region NOAA 11899) crossed the central meridian of the sun. The moat flow associated with this very large spot is quantitatively compared to that of a medium and a small sunspot to determine the extent of the moat flow in different environments. We employ continuum images and magnetograms of the Helioseismic and Magnetic Imager (HMI) as well as extreme ultraviolet (EUV) images at λ160 nm of the Atmospheric Imaging Assembly (AIA), both on board the Solar Dynamics Observatory (SDO), to measure horizontal proper motions with Local Correlation Tracking (LCT) and flux transport velocities with the Differential Affine Velocity Estimator (DAVE). We compute time-averaged flow maps (±6 hr around meridian passage) and radial averages of photometric, magnetic, and flow properties. Flow fields of a small- and a medium-sized axisymmetric sunspot provide the context for interpreting the results. All sunspots show outward moat flow and the advection of moving magnetic features (MMFs). However, the extent of the moat flow varies from spot to spot, and a correlation of flow properties with size is tenuous, if at all present. The moat flow is asymmetric and predominantly in the east–west direction, whereby deviations are related to the tilt angle of the sunspot group as well as to the topology and activity level of the trailing plage.
KW  - activity
KW  - data analysis
KW  - image processing
KW  - photosphere
KW  - sunspots
Y1  - 2018
U6  - https://doi.org/10.1002/asna.201813482
SN  - 0004-6337
SN  - 1521-3994
VL  - 339
IS  - 4
SP  - 268
EP  - 276
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Topçu, Çağdaş
A1  - Frühwirth, Matthias
A1  - Moser, Maximilian
A1  - Rosenblum, Michael
A1  - Pikovskij, Arkadij
T1  - Disentangling respiratory sinus arrhythmia in heart rate variability records
JF  - Physiological Measurement
N2  - Objective: Several different measures of heart rate variability, and particularly of respiratory sinus arrhythmia, are widely used in research and clinical applications. For many purposes it is important to know which features of heart rate variability are directly related to respiration and which are caused by other aspects of cardiac dynamics. Approach: Inspired by ideas from the theory of coupled oscillators, we use simultaneous measurements of respiratory and cardiac activity to perform a nonlinear disentanglement of the heart rate variability into the respiratory-related component and the rest. Main results: The theoretical consideration is illustrated by the analysis of 25 data sets from healthy subjects. In all cases we show how the disentanglement is manifested in the different measures of heart rate variability. Significance: The suggested technique can be exploited as a universal preprocessing tool, both for the analysis of respiratory influence on the heart rate and in cases when effects of other factors on the heart rate variability are in focus.
KW  - respiratory sinus arrhythmia
KW  - heart rate variability
KW  - coupled oscillators model
KW  - phase dynamics
KW  - data analysis
Y1  - 2018
U6  - https://doi.org/10.1088/1361-6579/aabea4
SN  - 0967-3334
SN  - 1361-6579
VL  - 39
IS  - 5
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  -