9,879 research outputs found
Directional acoustic measurements by laser Doppler velocimeters
Laser Doppler velocimeters (LDVs) were used as velocity microphones to measure sound pressure level in the range of 90-130 db, spectral components, and two-point cross correlation functions for acoustic noise source identification. Close agreement between LDV and microphone data is observed. It was concluded that directional sensitivity and the ability to measure remotely make LDVs useful tools for acoustic measurement where placement of any physical probe is difficult or undesirable, as in the diagnosis of jet aircraft noise
The energy of waves in the photosphere and lower chromosphere: III. Inversion setup for Ca II H spectra in local thermal equilibrium
The Ca II H line is one of the strongest lines in the solar spectrum and
provides continuous information on the solar atmosphere from the photosphere to
the lower chromosphere. We describe an inversion approach that reproduces
observed Ca II H spectra assuming LTE. We developed an inversion strategy based
on the SIR code. The approach uses a two-step procedure with an archive of
pre-calculated spectra to fit the line core and a subsequent iterative
modification to improve the fit in the line wing. Simultaneous spectra in the
630nm range can optionally be used to fix the continuum temperature. The method
retrieves 1D temperature stratifications neglecting lateral radiative
transport. LOS velocities are included by an empirical approach. An archive of
about 300.000 pre-calculated spectra is more than sufficient to reproduce the
line core of observed Ca II H spectra both in quiet Sun and in active regions.
The final thermodynamical stratifications match observed and best-fit spectra
to a level of about 0.5 (1) % of Ic in the line wing (core). Inversion schemes
based on pre-calculated spectra allow one a reliable and relatively fast
retrieval of solar properties from observed chromospheric spectra. The approach
can be easily extended to an 1D NLTE case by a simple exchange of the
pre-calculated archive spectra.Comment: 15 pages, 15 figures, accepted for publication in A&A. The animation
will only be provided in the A&A online sectio
Basin stability approach for quantifying responses of multistable systems with parameters mismatch
Acknowledgement This work is funded by the National Science Center Poland based on the decision number DEC-2015/16/T/ST8/00516. PB is supported by the Foundation for Polish Science (FNP).Peer reviewedPublisher PD
Alpha effect due to buoyancy instability of a magnetic layer
A strong toroidal field can exist in form of a magnetic layer in the
overshoot region below the solar convection zone. This motivates a more
detailed study of the magnetic buoyancy instability with rotation. We calculate
the alpha effect due to helical motions caused by a disintegrating magnetic
layer in a rotating density-stratified system with angular velocity Omega
making an angle theta with the vertical. We also study the dependence of the
alpha effect on theta and the strength of the initial magnetic field. We carry
out three-dimensional hydromagnetic simulations in Cartesian geometry. A
turbulent EMF due to the correlations of the small scale velocity and magnetic
field is generated. We use the test-field method to calculate the transport
coefficients of the inhomogeneous turbulence produced by the layer. We show
that the growth rate of the instability and the twist of the magnetic field
vary monotonically with the ratio of thermal conductivity to magnetic
diffusivity. The resulting alpha effect is inhomogeneous and increases with the
strength of the initial magnetic field. It is thus an example of an
"anti-quenched" alpha effect. The alpha effect is nonlocal, requiring around
8--16 Fourier modes to reconstruct the actual EMF based on the actual mean
field.Comment: 14 pages, 19 figures 3 tables (submitted to A & A
Mirror Adaptation in Sensory-Motor Simultaneity
Background:
When one watches a sports game, one may feel her/his own muscles moving in synchrony with the player's. Such parallels between observed actions of others and one's own has been well supported in the latest progress in neuroscience, and coined âmirror system.â It is likely that due to such phenomena, we are able to learn motor skills just by observing an expert's performance. Yet it is unknown whether such indirect learning occurs only at higher cognitive levels, or also at basic sensorimotor levels where sensorimotor delay is compensated and the timing of sensory feedback is constantly calibrated.
Methodology/Principal Findings:
Here, we show that the subject's passive observation of an actor manipulating a computer mouse with delayed auditory feedback led to shifts in subjective simultaneity of self mouse manipulation and auditory stimulus in the observing subjects. Likewise, self adaptation to the delayed feedback modulated the simultaneity judgment of the other subjects manipulating a mouse and an auditory stimulus. Meanwhile, subjective simultaneity of a simple visual disc and the auditory stimulus (flash test) was not affected by observation of an actor nor self-adaptation.
Conclusions/Significance:
The lack of shift in the flash test for both conditions indicates that the recalibration transfer is specific to the action domain, and is not due to a general sensory adaptation. This points to the involvement of a system for the temporal monitoring of actions, one that processes both one's own actions and those of others
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