19,063 research outputs found
A Solid State Pulsed Coagulating Diathermy Instrument
Solid state pulsed coagulating diathermy instrumen
The variable stellar wind of Rigel probed at high spatial and spectral resolution
We present a spatially resolved, high-spectral resolution (R=12000) K-band
temporal monitoring of Rigel using AMBER at the VLTI. Rigel was observed in the
Bracket Gamma line and its nearby continuum in 2006-2007, and 2009-2010. These
unprecedented observations were complemented by contemporaneous optical
high-resolution spectroscopy. We analyse the near-IR spectra and visibilities
with the 1D non-LTE radiative-transfer code CMFGEN. The differential and
closure phase signal exhibit asymmetries that are interpreted as perturbations
of the wind. A systematic visibility decrease is observed across the Bracket
Gamma. During the 2006-2007 period the Bracket Gamma and likely the continuum
forming regions were larger than in the 2009-2010 epoch. Using CMFGEN, we infer
a mass-loss rate change of about 20% between the two epochs. We further find
time variations in the differential visibilities and phases. The 2006-2007
period is characterized by noticeable variations of the differential
visibilities in Doppler position and width and by weak variations in
differential and closure phase. The 2009-2010 period is much more quiet with
virtually no detectable variations in the dispersed visibilities but a strong
S-shape signal is observed in differential phase coinciding with a strong
ejection event discernible in the optical spectra. The differential phase
signal that is sometimes detected is reminiscent of the signal computed from
hydrodynamical models of corotating interaction regions. For some epochs the
temporal evolution of the signal suggests the rotation of the circumstellar
structures.Comment: Paper accepted in the A&A journa
The topological classification of one-dimensional symmetric quantum walks
We give a topological classification of quantum walks on an infinite 1D
lattice, which obey one of the discrete symmetry groups of the tenfold way,
have a gap around some eigenvalues at symmetry protected points, and satisfy a
mild locality condition. No translation invariance is assumed. The
classification is parameterized by three indices, taking values in a group,
which is either trivial, the group of integers, or the group of integers modulo
2, depending on the type of symmetry. The classification is complete in the
sense that two walks have the same indices if and only if they can be connected
by a norm continuous path along which all the mentioned properties remain
valid. Of the three indices, two are related to the asymptotic behaviour far to
the right and far to the left, respectively. These are also stable under
compact perturbations. The third index is sensitive to those compact
perturbations which cannot be contracted to a trivial one. The results apply to
the Hamiltonian case as well. In this case all compact perturbations can be
contracted, so the third index is not defined. Our classification extends the
one known in the translation invariant case, where the asymptotic right and
left indices add up to zero, and the third one vanishes, leaving effectively
only one independent index. When two translationally invariant bulks with
distinct indices are joined, the left and right asymptotic indices of the
joined walk are thereby fixed, and there must be eigenvalues at or
(bulk-boundary correspondence). Their location is governed by the third index.
We also discuss how the theory applies to finite lattices, with suitable
homogeneity assumptions.Comment: 36 pages, 7 figure
Dynamical mass of the O-type supergiant in Zeta Orionis A
A close companion of Zeta Orionis A was found in 2000 with the Navy Precision
Optical Interferometer (NPOI), and shown to be a physical companion. Because
the primary is a supergiant of type O, for which dynamical mass measurements
are very rare, the companion was observed with NPOI over the full 7-year orbit.
Our aim was to determine the dynamical mass of a supergiant that, due to the
physical separation of more than 10 AU between the components, cannot have
undergone mass exchange with the companion. The interferometric observations
allow measuring the relative positions of the binary components and their
relative brightness. The data collected over the full orbital period allows all
seven orbital elements to be determined. In addition to the interferometric
observations, we analyzed archival spectra obtained at the Calar Alto, Haute
Provence, Cerro Armazones, and La Silla observatories, as well as new spectra
obtained at the VLT on Cerro Paranal. In the high-resolution spectra we
identified a few lines that can be associated exclusively to one or the other
component for the measurement of the radial velocities of both. The combination
of astrometry and spectroscopy then yields the stellar masses and the distance
to the binary star. The resulting masses for components Aa of 14.0 solar masses
and Ab of 7.4 solar masses are low compared to theoretical expectations, with a
distance of 294 pc which is smaller than a photometric distance estimate of 387
pc based on the spectral type B0III of the B component. If the latter (because
it is also consistent with the distance to the Orion OB1 association) is
adopted, the mass of the secondary component Ab of 14 solar masses would agree
with classifying a star of type B0.5IV. It is fainter than the primary by about
2.2 magnitudes in the visual. The primary mass is then determined to be 33
solar masses
Expanding Representations for Historical Content in Literacy
In spite of the need for literacy educators to possess an understanding of the history of the field, such historical perspectives are often absent in current programs, even at the graduate level. Fortunately, embedding history in programs and courses can be done in a variety of meaningful, engaging, and simple ways. In this article we present and describe several approaches for instructors who want to embed or even expand history into current literacy courses. We organize these approaches into three areas: Inquiry-based learning, dramatic structures, and humanistic approaches
The Development and Validation of a Comprehensive List of Primary Sources in College Reading Instruction
It may be argued that a field only comes of age when its professional membership is able to gain insight into the present and begin to predict the future through the organized studying and the collective valuing of the field\u27s past. As we enter the 1990\u27s, it is time for the field of college reading and learning assistance to achieve a broader perspective that more fully incorporates the field\u27s rich and varied past. To achieve this end, collectively we should endeavor to understand our professional roots through chronicling, interpreting, and evaluating the fundamental ideas, the pedagogical achievements, and the research contributions of our colleagues, both past and present
A Parametric Finite-Element Model for Evaluating Segmented Mirrors with Discrete, Edgewise Connectivity
Since future astrophysics missions require space telescopes with apertures of at least 10 meters, there is a need for on-orbit assembly methods that decouple the size of the primary mirror from the choice of launch vehicle. One option is to connect the segments edgewise using mechanisms analogous to damped springs. To evaluate the feasibility of this approach, a parametric ANSYS model that calculates the mode shapes, natural frequencies, and disturbance response of such a mirror, as well as of the equivalent monolithic mirror, has been developed. This model constructs a mirror using rings of hexagonal segments that are either connected continuously along the edges (to form a monolith) or at discrete locations corresponding to the mechanism locations (to form a segmented mirror). As an example, this paper presents the case of a mirror whose segments are connected edgewise by mechanisms analogous to a set of four collocated single-degree-of-freedom damped springs. The results of a set of parameter studies suggest that such mechanisms can be used to create a 15-m segmented mirror that behaves similarly to a monolith, although fully predicting the segmented mirror performance would require incorporating measured mechanism properties into the model. Keywords: segmented mirror, edgewise connectivity, space telescop
General relativistic gravitational field of a rigidly rotating disk of dust: Solution in terms of ultraelliptic functions
In a recent paper we presented analytic expressions for the axis potential,
the disk metric, and the surface mass density of the global solution to
Einstein's field equations describing a rigidly rotating disk of dust. Here we
add the complete solution in terms of ultraelliptic functions and quadratures.Comment: 5 pages, published in 1995 [Phys. Rev. Lett. 75 (1995) 3046
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