2,107 research outputs found
Optimization of quasi-normal eigenvalues for Krein-Nudelman strings
The paper is devoted to optimization of resonances for Krein strings with
total mass and statical moment constraints. The problem is to design for a
given a string that has a resonance on the line \alpha + \i
\R with a minimal possible modulus of the imaginary part. We find optimal
resonances and strings explicitly.Comment: 9 pages, these results were extracted in a slightly modified form
from the earlier e-print arXiv:1103.4117 [math.SP] following an advise of a
journal's refere
Optical Imaging and Spectroscopic Observation of the Galactic Supernova Remnant G85.9-0.6
Optical CCD imaging with H and [SII] filters and spectroscopic
observations of the galactic supernova remnant G85.9-0.6 have been performed
for the first time. The CCD image data are taken with the 1.5m Russian-Turkish
Telescope (RTT150) at TUBITAK National Observatory (TUG) and spectral data are
taken with the Bok 2.3 m telescope on Kitt Peak, AZ.
The images are taken with narrow-band interference filters H, [SII]
and their continuum. [SII]/H ratio image is performed. The ratio
obtained from [SII]/H is found to be 0.42, indicating that the
remnant interacts with HII regions. G85.9-0.6 shows diffuse-shell morphology.
[SII] average flux ratio is calculated from the
spectra, and the electron density is obtained to be 395 . From
[OIII]/H ratio, shock velocity has been estimated, pre-shock density of
, explosion energy of ergs,
interstellar extinction of , and neutral hydrogen column density
of are reported.Comment: 20 pages, 4 tables, 4 figures. Accepted for publication in
Astrophysics & Space Scienc
The transfer of fibres in the carding machine
The problem of understanding the transfer of fibres between carding-machine surfaces is addressed by considering the movement of a single fibre in an airflow. The structure of the aerodynamic flow field predicts how and when fibres migrate between the different process surfaces. In the case of a revolving-flats carding machine the theory predicts a “strong” aerodynamic mechanism between taker-in and cylinder and a “weak” mechanism between cylinder and removal cylinder resulting in effective transfer in the first case and a more limited transfer in the second
Atomic and Electronic Structures of Unreconstructed Polar MgO(111) Thin Film on Ag(111)
Atomic and electronic structures of a polar surface of MgO formed on Ag(111)
was investigated by using reflection high energy electron diffraction (RHEED),
Auger electron spectroscopy, electron energy loss spectroscopy (EELS), and
ultraviolet photoemission spectroscopy (UPS). A rather flat unreconstructed
polar MgO(111) 11 surface could be grown by alternate adsorption of Mg
and O on Ag(111). The stability of the MgO(111) surface was discussed in
terms of interaction between Ag and Mg atoms at the interface, and charge state
of the surface atoms. EELS of this surface did not show a band gap region, and
finite density of states appeared at the Fermi level in UPS. These results
suggest that a polar MgO(111) surface was not an insulating surface but a
semiconducting or metallic surface.Comment: 6 figures, to be published in Phys. Rev.
Multibeam Maser Survey of methanol and excited OH in the Magellanic clouds: new detections and maser abundance estimates
‘The definitive version is available at www.blackwell-synergy.com.’ Copyright Blackwell Publishing DOI: 10.1111/j.1365-2966.2008.12888.xPeer reviewe
What are communities of practice? A comparative review of four seminal works
This paper is a comparative review of four seminal works on communities of practice. It is argued that the ambiguities of the terms community and practice are a source of the concept's reusability allowing it to be reappropriated for different purposes, academic and practical. However, it is potentially confusing that the works differ so markedly in their conceptualizations of community, learning, power and change, diversity and informality. The three earlier works are underpinned by a common epistemological view, but Lave and Wenger's 1991 short monograph is often read as primarily about the socialization of newcomers into knowledge by a form of apprenticeship, while the focus in Brown and Duguid's article of the same year is, in contrast, on improvising new knowledge in an interstitial group that forms in resistance to management. Wenger's 1998 book treats communities of practice as the informal relations and understandings that develop in mutual engagement on an appropriated joint enterprise, but his focus is the impact on individual identity. The applicability of the concept to the heavily individualized and tightly managed work of the twenty-first century is questionable. The most recent work by Wenger – this time with McDermott and Snyder as coauthors – marks a distinct shift towards a managerialist stance. The proposition that managers should foster informal horizontal groups across organizational boundaries is in fact a fundamental redefinition of the concept. However it does identify a plausible, if limited, knowledge management (KM) tool. This paper discusses different interpretations of the idea of 'co-ordinating' communities of practice as a management ideology of empowerment
Eddy diffusivity in convective hydromagnetic systems
An eigenvalue equation, for linear instability modes involving large scales
in a convective hydromagnetic system, is derived in the framework of multiscale
analysis. We consider a horizontal layer with electrically conducting
boundaries, kept at fixed temperatures and with free surface boundary
conditions for the velocity field; periodicity in horizontal directions is
assumed. The steady states must be stable to short (fast) scale perturbations
and possess symmetry about the vertical axis, allowing instabilities involving
large (slow) scales to develop. We expand the modes and their growth rates in
power series in the scale separation parameter and obtain a hierarchy of
equations, which are solved numerically. Second order solvability condition
yields a closed equation for the leading terms of the asymptotic expansions and
respective growth rate, whose origin is in the (combined) eddy diffusivity
phenomenon. For about 10% of randomly generated steady convective hydromagnetic
regimes, negative eddy diffusivity is found.Comment: 18 pages. Added numerical reults. Submitted to European Physical
Journal
Plasma Turbulence in the Local Bubble
Turbulence in the Local Bubble could play an important role in the
thermodynamics of the gas that is there. The best astronomical technique for
measuring turbulence in astrophysical plasmas is radio scintillation.
Measurements of the level of scattering to the nearby pulsar B0950+08 by
Philips and Clegg in 1992 showed a markedly lower value for the line-of-sight
averaged turbulent intensity parameter is smaller than normal for two of them, but is completely nominal for
the third. This inconclusive status of affairs could be improved by
measurements and analysis of ``arcs'' in ``secondary spectra'' of pulsars.Comment: Submitted to Space Science Reviews as contribution to Proceedings of
ISSI (International Space Science Institute) workshop "From the Heliosphere
to the Local Bubble". Refereed version accepted for publicatio
Optical properties of pyrochlore oxide
We present optical conductivity spectra for
single crystal at different temperatures. Among reported pyrochlore ruthenates,
this compound exhibits metallic behavior in a wide temperature range and has
the least resistivity. At low frequencies, the optical spectra show typical
Drude responses, but with a knee feature around 1000 \cm. Above 20000 \cm, a
broad absorption feature is observed. Our analysis suggests that the low
frequency responses can be understood from two Drude components arising from
the partially filled Ru bands with different plasma frequencies and
scattering rates. The high frequency broad absorption may be contributed by two
interband transitions: from occupied Ru states to empty bands
and from the fully filled O 2p bands to unoccupied Ru states.Comment: 4 pages, 6 figure
Soft gluons in Higgs plus two jet production
We investigate the effects of an all order QCD resummation of soft gluon
emissions for Higgs boson production in association with two hard jets. We
consider both the gluon-gluon fusion and weak boson fusion processes and show
how to resum a large part of the leading logarithms in the jet veto scale. Our
resummation improves on previous analyses which also aim to include the effects
of multiple soft gluon radiation. In addition we calculate the interference
between weak boson fusion and gluon-gluon fusion and find that it is small.Comment: 15 pages and 5 figure
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