3,976 research outputs found
The UV Perspective of Low-Mass Star Formation
The formation of low-mass stars in molecular clouds involves accretion disks
and jets, which are of broad astrophysical interest. Accreting stars represent
the closest examples of these phenomena. Star and planet formation are also
intimately connected, setting the starting point for planetary systems like our
own. The ultraviolet (UV) spectral range is particularly suited to study star
formation, because virtually all relevant processes radiate at temperatures
associated with UV emission processes or have strong observational signatures
in the UV. In this review, we describe how UV observations provide unique
diagnostics for the accretion process, the physical properties of the
protoplanetary disk, and jets and outflows.Comment: 26 pages, 12 figures. Published in Galaxies special issue: "Star
Formation in the UV", ed. Jorick Vin
Huygens' Principle for the Klein-Gordon equation in the de Sitter spacetime
In this article we prove that the Klein-Gordon equation in the de Sitter
spacetime obeys the Huygens' principle only if the physical mass of the
scalar field and the dimension of the spatial variable are tied by
the equation . Moreover, we define the incomplete Huygens'
principle, which is the Huygens' principle restricted to the vanishing second
initial datum, and then reveal that the massless scalar field in the de Sitter
spacetime obeys the incomplete Huygens' principle and does not obey the
Huygens' principle, for the dimensions , only. Thus, in the de Sitter
spacetime the existence of two different scalar fields (in fact, with m=0 and
), which obey incomplete Huygens' principle, is equivalent to
the condition (in fact, the spatial dimension of the physical world). For
these two values of the mass are the endpoints of the so-called in
quantum field theory the Higuchi bound. The value of the
physical mass allows us also to obtain complete asymptotic expansion of the
solution for the large time. Keywords: Huygens' Principle; Klein-Gordon
Equation; de Sitter spacetime; Higuchi Boun
50GHz Ge waveguide electro-absorption modulator integrated in a 220nm SOI photonics platform
We report waveguide-integrated Ge electro-absorption modulators operating at 1615nm wavelength with 3dB bandwidth beyond 50GHz and a capacitance of 10fF, A 2V voltage swing enables 4.6dB DC extinction ratio for 4.1dB insertion loss
Multiple Components of the Luminous Compact X-ray Source at the Edge of Holmberg II observed by ASCA and ROSAT
We report the results of the analysis of ASCA/ROSAT observations of the
compact luminous X-ray source found at the edge of the nearby star-forming
dwarf galaxy Holmberg II (UGC 4305).Our ASCA spectrum revealed that the X-ray
emission extends to the hard band and can be best described by a power-law with
a photon spectral index of 1.9. The ASCA spectrum does not fit with a
multi-color disk blackbody. The joint ASCA-ROSAT spectrum suggests two
components to the spectrum: the hard power-law component and a warm thermal
plasma kT~0.3[keV]. An additional absorption over that of our galaxy is
required. The wobble correction of the ROSAT HRI image has clearly unveiled the
existence of an extended component which amounts to 27+/-5% of the total X-ray
emission.
These observations indicate that there are more than one component in the
X-ray emission. The properties of the point-like component is indicative of an
accretion onto an intermediate mass blackhole, unless a beaming is taking
place. We argue that the extended component does not come from electron
scattering and/or reflection by scattered optically-thick clouds of the central
radiation. Possible explanations of this X-ray source include multiple
supernova remnants feeding an intermediate-mass blackhole. (abridged)Comment: 12 pages, 6 figures accepted to Astronomical Journa
X-ray to NIR emission from AA Tauri during the dim state - Occultation of the inner disk and gas-to-dust ratio of the absorber
AA Tau is a well-studied, nearby classical T Tauri star, which is viewed
almost edge-on. A warp in its inner disk periodically eclipses the central
star, causing a clear modulation of its optical light curve. The system
underwent a major dimming event beginning in 2011 caused by an extra absorber,
which is most likely associated with additional disk material in the line of
sight toward the central source. We present new XMM-Newton X-ray, Hubble Space
Telescope FUV, and ground based optical and near-infrared data of the system
obtained in 2013 during the long-lasting dim phase. The line width decrease of
the fluorescent H disk emission shows that the extra absorber is located at
au. Comparison of X-ray absorption () with dust extinction (),
as derived from measurements obtained one inner disk orbit (eight days) after
the X-ray measurement, indicates that the gas-to-dust ratio as probed by the
to ratio of the extra absorber is compatible with the ISM ratio.
Combining both results suggests that the extra absorber, i.e., material at
au, has no significant gas excess in contrast to the elevated
gas-to-dust ratio previously derived for material in the inner region
(au).Comment: 16 pages, 12 figures, accepted by A&
Equation of State of Oscillating Brans-Dicke Scalar and Extra Dimensions
We consider a Brans-Dicke scalar field stabilized by a general power law
potential with power index at a finite equilibrium value. Redshifting
matter induces oscillations of the scalar field around its equilibrium due to
the scalar field coupling to the trace of the energy momentum tensor. If the
stabilizing potential is sufficiently steep these high frequency oscillations
are consistent with observational and experimental constraints for arbitrary
value of the Brans-Dicke parameter . We study analytically and
numerically the equation of state of these high frequency oscillations in terms
of the parameters and and find the corresponding evolution of the
universe scale factor. We find that the equation of state parameter can be
negative and less than -1 but it is not related to the evolution of the scale
factor in the usual way. Nevertheless, accelerating expansion is found for a
certain parameter range. Our analysis applies also to oscillations of the size
of extra dimensions (the radion field) around an equilibrium value. This
duality between self-coupled Brans-Dicke and radion dynamics is applicable for
where D is the number of extra dimensions.Comment: 10 two-column pages, RevTex4, 8 figures. Added clarifying
discussions, new references. Accepted in Phys. Rev. D (to appear
Short-term outcome after posterior versus lateral surgical approach for total hip arthroplasty - a randomized clinical trial*
<p>Abstract</p> <p>Purpose</p> <p>Currently, total hip replacement (THR) is most commonly performed via a posterior or a direct lateral approach, but the impact of the latter on the invention's outcome has yet not been quantified.</p> <p>Methods</p> <p>We compared the short-term outcome of cementless THR using the both approaches in a prospective, randomized controlled trial. 60 patients with unilateral osteoarthritis were included. Outcome assessment was performed one day before surgery and one week, four weeks, six weeks and 12 weeks after surgery, respectively, using the Harris Hip score as primary objective.</p> <p>Results</p> <p>We found no significant difference in the intraindividual Harris Hip Score improvement at the pre-and three months post-operative assessments between both treatment groups (p = 0.115). However, Harris Hip scores and most functional and psychometric secondary endpoints showed a consistent tendency of a slightly better three months result in patients implanted via the posterior approach. In contrast a significant shorter operating time of the direct lateral approach was recorded (67 minutes versus 76 minutes, p < 0.001).</p> <p>Conclusion</p> <p>In our opinion this slightly better short-term functional outcome after posterior approach is not clinical relevant. However, to make definitive conclusions all clinical relevant factors (i.e. mid- to long-term function, satisfaction, complication rates and long-term survival) have to be taken into account. <it>Level of evidence: </it>I - therapeutic</p
Nonlinear Pseudo-Supersymmetry in the Framework of N-fold Supersymmetry
We recall the importance of recognizing the different mathematical nature of
various concepts relating to PT-symmetric quantum theories. After clarifying
the relation between supersymmetry and pseudo-supersymmetry, we prove
generically that nonlinear pseudo-supersymmetry, recently proposed by Sinha and
Roy, is just a special case of N-fold supersymmetry. In particular, we show
that all the models constructed by these authors have type A 2-fold
supersymmetry. Furthermore, we prove that an arbitrary one-body quantum
Hamiltonian which admits two (local) solutions in closed form belongs to type A
2-fold supersymmetry, irrespective of whether or not it is Hermitian,
PT-symmetric, pseudo-Hermitian, and so on.Comment: 10 pages, no figures; typos correcte
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