267 research outputs found
Comparison of seismic signatures of flares obtained by SOHO/MDI and GONG instruments
The first observations of seismic responses to solar flares were carried out
using time-distance (TD) and holography techniques applied to SOHO/MDI
Dopplergrams obtained from space and un-affected by terrestrial atmospheric
disturbances. However, the ground-based network GONG is potentially a very
valuable source of sunquake observations, especially in cases where space
observations are unavailable. In this paper we present updated technique for
pre-processing of GONG observations for application of subjacent vantage
holography. Using this method and TD diagrams we investigate several sunquakes
observed in association with M and X-class solar flares and compare the
outcomes with those reported earlier using MDI data. In both GONG and MDI
datasets, for the first time, we also detect the TD ridge associated with the
September 9, 2001 flare. Our results show reassuringly positive identification
of sunquakes from GONG data that can provide further information about the
physics of seismic processes associated with solar flares.Comment: 19 pages, 6 figures, accepted to Astrophysical Journa
Radiative transfer effects on Doppler measurements as sources of surface effects in sunspot seismology
We show that the use of Doppler shifts of Zeeman sensitive spectral lines to
observe wavesn in sunspots is subject to measurement specific phase shifts
arising from, (i) altered height range of spectral line formation and the
propagating character of p mode waves in penumbrae, and (ii) Zeeman broadening
and splitting. We also show that these phase shifts depend on wave frequencies,
strengths and line of sight inclination of magnetic field, and the polarization
state used for Doppler measurements. We discuss how these phase shifts could
contribute to local helioseismic measurements of 'surface effects' in sunspot
seismology.Comment: 12 pages, 4 figures, Accepted for publication in the Astrophysical
Journal Letter
Sound attenuation in the superconducting amorphous alloy ZrTiCuNiBe
The superconducting energy gap and the parameter of the intensity of electron
scattering at two-level systems in amorphous ZrTiCuNiBe are determined from the
results of measurements of sound attenuation. The mechanism of adiabatic
renormalization of the amplitude of coherent tunneling is used for a
quantitative description of the peculiarities of sound absorption in the
vicinity of critical temperature.Comment: 4 pages, LaTeX, 2 Postscript figures corrected, submitted to Low
Temp. Phy
Domain Architectures as an Instrument to Refine Enterprise Architecture
Enterprise architecture is concerned with the fundamental organization of the operating environment of an enterprise. The enterprise architecture is used to plan and control the construction of the systems that populate the operating environment. As the scope covered can be considerable in large enterprises, introducing domain architectures to partition and detail the enterprise architecture is a plausible approach. We formulate prescriptive criteria that consistent domain architectures must meet. By integrating the creation of domain architectures into an extended strategic alignment model we develop a theory that accounts for both the creation, scope-setting and detailing. Based on the creation viewpoint we derive a multi-level classification taxonomy. The primary differentiator is that between domains that are created from business usage viewpoints and those that are created from solution construction viewpoints. Four cases of domain architectures from actual practice are described that illustrate the variety encountered. Domain classifications in all cases conform to the theoretical model. The criteria, the developed theory and the cases have both academic relevance as well as significance for practitioners
Exotic superconductivity in the coexistent phase of antiferromagnetism and superconductivity in CeCu2(Si0.98Ge0.02)2: A Cu-NQR study under hydrostatic pressure
We report a pressure () effect on CeCu(SiGe)
where an antiferromagnetic (AFM) order at 0.75 K coexists with
superconductivity below 0.4 K\@. At pressures exceeding
GPa, the AFM order is suppressed, which demonstrates that the sudden emergence
of AFM order due to the Ge doping is ascribed to the intrinsic lattice
expansion. The exotic superconductivity at GPa is found to evolve into
a typical heavy-fermion one with a line-node gap above GPa\@. We
highlight that the anomalous enhancement in nuclear spin-lattice relaxation
rate that follows a = const. behavior well below at =
0 GPa is characterized by the persistence of low-lying magnetic excitations,
which may be inherent to the coexistent state of antiferromagnetism and
superconductivity.Comment: 5 pages with 4 figures embedded in the text. To be published in J.
Phys. Soc. Jp
Comparison of the thin flux tube approximation with 3D MHD simulations
The structure and dynamics of small vertical photospheric magnetic flux
concentrations has been often treated in the framework of an approximation
based upon a low-order truncation of the Taylor expansions of all quantities in
the horizontal direction, together with the assumption of instantaneous total
pressure balance at the boundary to the non-magnetic external medium. Formally,
such an approximation is justified if the diameter of the structure (a flux
tube or a flux sheet) is small compared to all other relevant length scales
(scale height, radius of curvature, wavelength, etc.). The advent of realistic
3D radiative MHD simulations opens the possibility of checking the consistency
of the approximation with the properties of the flux concentrations that form
in the course of a simulation.
We carry out a comparative analysis between the thin flux tube/sheet models
and flux concentrations formed in a 3D radiation-MHD simulation. We compare the
distribution of the vertical and horizontal components of the magnetic field in
a 3D MHD simulation with the field distribution in the case of the thin flux
tube/sheet approximation. We also consider the total (gas plus magnetic)
pressure in the MHD simulation box. Flux concentrations with
super-equipartition fields are reasonably well reproduced by the second-order
thin flux tube/sheet approximation. The differences between approximation and
simulation are due to the asymmetry and the dynamics of the simulated
structures
Effects of Magnetic Order on the Upper Critical Field of UPt
I present a Ginzburg-Landau theory for hexagonal oscillations of the upper
critical field of UPt near . The model is based on a
representation for the superconducting order parameter,
, coupled to an in-plane AFM order parameter,
. Hexagonal anisotropy of arises from the weak in-plane
anisotropy energy of the AFM state and the coupling of the superconducting
order parameter to the staggered field. The model explains the important
features of the observed hexagonal anisotropy [N. Keller, {\it et al.}, Phys.
Rev. Lett. {\bf 73}, 2364 (1994).] including: (i) the small magnitude, (ii)
persistence of the oscillations for , and (iii) the change in
sign of the oscillations for and (the temperature at the
tetracritical point). I also show that there is a low-field crossover
(observable only very near ) below which the oscillations should vanish.Comment: 9 pages in a RevTex (3.0) file plus 2 postscript figures (uuencoded).
Submitted to Physical Review B (December 20, 1994)
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