13,484 research outputs found
Fiber optic wavelength division multiplexing: Principles and applications in telecommunications and spectroscopy
Design and fabrication tradeoffs of wavelength division multiplexers are discussed and performance parameters are given. The same multiplexer construction based on prism gratings has been used in spectroscopic applications, in the wavelength region from 450 to 1600 nm. For shorter wavelengths down to 200 nm, a similar instrument based on longer fibers (500 to 1000 micrometer) has been constructed and tested with both a fiber array and a photodiode detector array at the output
Simulated three-component granular segregation in a rotating drum
Discrete particle simulations are used to model segregation in granular
mixtures of three different particle species in a horizontal rotating drum.
Axial band formation is observed, with medium-size particles tending to be
located between alternating bands of big and small particles. Partial radial
segregation also appears; it precedes the axial segregation and is
characterized by an inner core region richer in small particles. Axial bands
are seen to merge during the long simulation runs, leading to a coarsening of
the band pattern; the relocation of particles involved in one such merging
event is examined. Overall, the behavior is similar to experiment and
represents a generalization of what occurs in the simpler two-component
mixture.Comment: 7 pages, 11 figures (low resolution color figures only; originals at
author's website http://www.ph.biu.ac.il/~rapaport/research/granular.html)
[revised version contains extra figures
PCA of PCA: Principal Component Analysis of Partial Covering Absorption in NGC 1365
We analyse 400 ks of XMM-Newton data on the active galactic nucleus NGC 1365
using principal component analysis (PCA) to identify model independent spectral
components. We find two significant components and demonstrate that they are
qualitatively different from those found in MCG?6-30-15 using the same method.
As the variability in NGC 1365 is known to be due to changes in the parameters
of a partial covering neutral absorber, this shows that the same mechanism
cannot be the driver of variability in MCG-6-30-15. By examining intervals
where the spectrum shows relatively low absorption we separate the effects of
intrinsic source variability, including signatures of relativistic reflection,
from variations in the intervening absorption. We simulate the principal
components produced by different physical variations, and show that PCA
provides a clear distinction between absorption and reflection as the drivers
of variability in AGN spectra. The simulations are shown to reproduce the PCA
spectra of both NGC 1365 and MCG-6-30-15, and further demonstrate that the
dominant cause of spectral variability in these two sources requires a
qualitatively different mechanism.Comment: 8 pages, 10 figures. Accepted for publication in MNRA
Searching for the Donor Stars of ULX Pulsars
We report on our search for the optical counterparts of two ultraluminous
X-ray pulsars with known orbital periods, M82 X-2 and NGC 5907 X-1, in new and
archival HST observations, in an effort to characterize the donor stars in
these systems. We detect five near-infrared sources consistent with the
position of M82 X-2 that are too bright to be single stars. We also detect
seven sources in the WFC3/UVIS F336W image whose photometry matches that of
10-15 M stars turning off the main sequence. Such stars have densities
consistent with the properties of the donor star of M82 X-2 as inferred from
X-ray timing analysis, although it is also possible that the donor is a lower
mass star below our detection limit or that there is a significant contribution
from the accretion disc to the optical emission. We detect three candidate
counterparts to NGC 5907 X-1 in the near-infrared. All of these are too bright
to be the donor star of the ULX, which based on its orbital period is a red
giant. The high background at the location of NGC 5907 X-1 precludes us from
detecting this expected donor star. The recently discovered NGC 5907 ULX-2 also
falls within the field of view of the near-infrared imaging; we detect four
sources in the error circle, with photometry that matches AGB stars. The star
suggested to be the counterpart of NGC 5907 ULX-2 by Pintore et al. (2018)
falls outside our 2- error circle.Comment: 10 pages, 3 figures, accepted for publication in Ap
BROADENING STUDENTSā PERCEPTIONS OF CONFLICT: THE CHALLENGE OF METAPHORICAL CHANGE
This qualitative investigation examined the semester long effects of a critical transformative pedagogy on studentsā metaphorical understandings of conflict interaction. The study included five university conflict management seminars taught over a four year period. Findings revealed that (a) while most students entered the course with predominantly negative and oppositional perceptions of conflict, the use of a critical transformative pedagogy did indeed (b) help support new metaphorical understandings of conflict interaction and (c) supported instances of personal empowerment and expanded self-knowledge. Implications and suggestions for future research are considered
āYour fears are appreciated hereā: Exploring a humanistic approach to public speaking instruction
Communication teachers have long been concerned with the development of studentsā oral communication competencies. Regrettably, public speaking remains one of the most feared communicative contexts. Though there has been extensive interest in cognitive/behavioral strategies for alleviating communication apprehension, there has been surprisingly little descriptive pedagogical research conducted on the subject within actual classroom settings. This qualitative case study examines the way one communication teacher dealt with issues of student reticence and fear in her introductory public speaking courses through the use of humanistic, student-centered principles. Findings reveal that her pedagogy emphasized (a) the expression of feelings and emotions, (b) prizing the whole student, and (c) intrinsic motivational learning. Implications for communication instruction and pedagogical research are considered
Complexity, Knowledge and Structure: A Systemic Understanding of Organizational Learning
Organizations are among the most socially complex institutions within modern culture. As corporations face the challenges of technological change and globalization, it becomes essential that they find new ways and forms of fostering knowledge sharing and creativity. Challenging the age-old belief that employees should ādominated and directed,ā complexity theory challenges the classic machine metaphor of organizational structure with a view that conceptualizes them as nonlinear systems that fluctuate between conditions of stability and chaos. This model offers new and exciting opportunities for exploring the dynamics of organizational learning. Toward this end, this paper examines the systemic features of organizations with a particular focus on knowledge generation
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