1,263 research outputs found
Mechanical properties and the electronic structure of transition of metal alloys
This interdiscipline research program was undertaken in an effort to investigate the relationship between the mechanical strength of Mo based alloys with their electronic structure. Electronic properties of these alloys were examined through optical studies, and the classical solid solution strengthening mechanisms were considered, based on size and molecular differences to determine if these mechanisms could explain the hardness data
Feedback in the Antennae Galaxies (NGC 4038/9): I. High-Resolution Infrared Spectroscopy of Winds from Super Star Clusters
We present high-resolution (R ~ 24,600) near-IR spectroscopy of the youngest
super star clusters (SSCs) in the prototypical starburst merger, the Antennae
Galaxies. These SSCs are young (3-7 Myr old) and massive (10^5 - 10^7 M_sun for
a Kroupa IMF) and their spectra are characterized by broad, extended Br-gamma
emission, so we refer to them as emission-line clusters (ELCs) to distinguish
them from older SSCs. The Brgamma lines of most ELCs have supersonic widths
(60-110 km/s FWHM) and non-Gaussian wings whose velocities exceed the clusters'
escape velocities. This high-velocity unbound gas is flowing out in winds that
are powered by the clusters' massive O and W-R stars over the course of at
least several crossing times. The large sizes of some ELCs relative to those of
older SSCs may be due to expansion caused by these outflows; many of the ELCs
may not survive as bound stellar systems, but rather dissipate rapidly into the
field population. The observed tendency of older ELCs to be more compact than
young ones is consistent with the preferential survival of the most
concentrated clusters at a given age.Comment: Accepted to Ap
Performing under pressure: Quiet eye training improves surgical knot-tying performance
Background: We examined the effectiveness of traditional technical training (TT) and quiet eye training (QET) on the performance of one-handed square knot tying in first-year surgery residents under normal and high anxiety conditions.
Methods: Twenty surgery residents were assigned randomly to the two groups and completed pretest, training, and simple and complex retention tests under conditions of high and low anxiety. The TT group received traditional instruction on improving hand movements; the QET group received feedback on their gaze behaviors. Participants wore an eye tracker that recorded simultaneously their gaze and hand movements. Dependent variables were: knot tying performance (%), quiet eye duration (%), number of fixations, and total movement time (s).
Results: Both groups improved their knot tying performance (p 0.05). The QET group also demonstrated more efficient gaze and hand movements post training.
Conclusions: These data demonstrate the effectiveness of training gaze behaviors, not only to improve the effectiveness and efficiency of performance, but also to mediate any negative effects of anxiety on performance. These findings may have important implications for medical educators and practitioners, as well as surgeons who may be (re)training or learning new procedures
Quiet eye training improves surgical knot tying more than traditional technical training: A randomized controlled study
Background We examined the effectiveness of technical training (TT) and quiet eye training (QE) on the performance of one-handed square knot tying in surgical residents. Methods Twenty surgical residents were randomly assigned to the 2 groups and completed pretest, training, retention, and transfer tests. Participants wore a mobile eye tracker that simultaneously recorded their gaze and hand movements. Dependent variables were knot tying performance (%), QE duration (%), number of fixations, total movement time (s), and hand movement phase time (s). Results The QE training group had significantly higher performance scores, a longer QE duration, fewer fixations, faster total knot tying times, and faster movement phase times compared with the TT group. The QE group maintained performance in the transfer test, whereas the TT group significantly decreased performance from retention to transfer. Conclusions QE training significantly improved learning, retention, and transfer of surgical knot tying compared with a traditional technical approach. Both performance effectiveness (performance outcome) and movement efficiency (hand movement times) were improved using QE modeling, instruction, and feedback. © 2014 Elsevier Inc. All rights reserved
Electronic Chart of the Future: The Hampton Roads Project
ECDIS is evolving from a two-dimensional static display of chart-related data to a decision support system capable of providing real-time or forecast information. While there may not be consensus on how this will occur, it is clear that to do this, ENC data and the shipboard display environment must incorporate both depth and time in an intuitively understandable way. Currently, we have the ability to conduct high-density hydrographic surveys capable of producing ENCs with decimeter contour intervals or depth areas. Yet, our existing systems and specifications do not provide for a full utilization of this capability. Ideally, a mariner should be able to benefit from detailed hydrographic data, coupled with both forecast and real-time water levels, and presented in a variety of perspectives. With this information mariners will be able to plan and carry out transits with the benefit of precisely determined and easily perceived underkeel, overhead, and lateral clearances. This paper describes a Hampton Roads Demonstration Project to investigate the challenges and opportunities of developing the “Electronic Chart of the Future.” In particular, a three-phase demonstration project is being planned: 1. Compile test datasets from existing and new hydrographic surveys using advanced data processing and compilation procedures developed at the University of New Hampshire’s Center for Coastal and Ocean Mapping/Joint Hydrographic Center (CCOM/JHC); 2. Investigate innovative approaches being developed at the CCOM/JHC to produce an interactive time- and tide-aware navigation display, and to evaluate such a display on commercial and/or government vessels; 3. Integrate real-time/forecast water depth information and port information services transmitted via an AIS communications broadcast
Adaptive Optics for Astronomy
Adaptive Optics is a prime example of how progress in observational astronomy
can be driven by technological developments. At many observatories it is now
considered to be part of a standard instrumentation suite, enabling
ground-based telescopes to reach the diffraction limit and thus providing
spatial resolution superior to that achievable from space with current or
planned satellites. In this review we consider adaptive optics from the
astrophysical perspective. We show that adaptive optics has led to important
advances in our understanding of a multitude of astrophysical processes, and
describe how the requirements from science applications are now driving the
development of the next generation of novel adaptive optics techniques.Comment: to appear in ARA&A vol 50, 201
Detection of the Galaxy Lensing the Doubly-imaged Quasar SBS 1520+530
H band observations with a spatial resolution of 0.15" carried out with the
Canada-France-Hawaii Telescope adaptive optics system show a galaxy between the
components of the double BAL quasar SBS 1520+530, thereby confirming this
system as a gravitational lens. The galaxy is located 0.40" from the fainter of
the two QSO images and is offset 0.12" from the line joining them. The H
magnitude of the lensing galaxy is ~1 mag fainter than expected from the
velocity dispersion derived for the lensing galaxy were it at z = 0.71 or z =
0.81, the redshifts of the two absorption line systems.Comment: 11 pages latex including one table and 2 postscript figures.
Corrected typo. Accepted by AJ. Also available at
http://www.hia.nrc.ca/science/preprint/preprint.htm
The Disks of Galaxies with Seyfert and Starburst Nuclei: II. Near-Infrared Structural Properties
We have derived the near-infrared structural components of a sample of
Seyfert and starburst (SBN) host galaxies by fitting the images of Hunt et al.
(1997,ApJS,108,229) with a new two-dimensional decomposition algorithm. An
analysis of the fitted parameters shows that Seyfert 1 and SBN bulges resemble
normal early-type bulges in structure and color, with (J-K)^c_b about 0.1 mag
redder than disk (J-K)^c_d. Seyfert 2 bulges, instead, are bluer than normal
with (J-K)^c_b ~ (J-K)^c_d. Seyfert disks (especially Type 1), but not those of
SBNs, are abnormally bright (in surface brightness), significantly more so than
even the brightest normal disks. Seyfert disks are also compact, but similar to
those in normal early-type spirals. For a given mass, Seyferts and especially
SBNs are abnormally rich in neutral hydrogen, and there is strong, albeit
indirect, evidence for lower mass-to-light (M/L) ratios in Seyfert and SBN
disks, but for normal M/Ls in their bulges. In Seyferts and SBNs, HI mass
fractions and M/L ratios are anticorrelated, and we attribute the high gas mass
fractions and low M/Ls in SBNs and several Seyferts to ongoing star formation.
Such abundant gas in Seyferts would be expected to inhibit bar formation, which
may explain why active galaxies are not always barred.Comment: 25 pgs (two-column, single-spaced) including 8 incorporated figures
and 2 tables (aas2pp4, amssym, epsfig). Accepted for publication in Ap
The Potential-Density Phase Shift Method for Determining the Corotation Radii in Spiral and Barred Galaxies
We have developed a new method for determining the corotation radii of
density waves in disk galaxies, which makes use of the radial distribution of
an azimuthal phase shift between the potential and density wave patterns. The
approach originated from improved theoretical understandings of the relation
between the morphology and kinematics of galaxies, and on the dynamical
interaction between density waves and the basic-state disk stars which results
in the secular evolution of disk galaxies. In this paper, we present the
rationales behind the method, and the first application of it to several
representative barred and grand-design spiral galaxies, using near-infrared
images to trace the mass distributions, as well as to calculate the potential
distributions used in the phase shift calculations. We compare our results with
those from other existing methods for locating the corotations, and show that
the new method both confirms the previously-established trends of bar-length
dependence on galaxy morphological types, as well as provides new insights into
the possible extent of bars in disk galaxies. Application of the method to a
larger sample and the preliminary analysis of which show that the phase shift
method is likely to be a generally-applicable, accurate, and essentially
model-independent method for determining the pattern speeds and corotation
radii of single or nested density wave patterns in galaxies. Other implications
of this work are: most of the nearby bright disk galaxies appear to possess
quasi-stationary spiral modes; that these density wave modes and the associated
basic state of the galactic disk slowly transform over time; and that
self-consistent N-particle systems contain physics not revealed by the passive
orbit analysis approaches.Comment: 48 pages, 16 figures. Accepted for publication in the Astronomical
Journa
The Influence of Bars on Nuclear Activity
We test ideas on fueling of galactic nuclei by bar-driven inflow by comparing
the detection rate and intensity of nuclear H II regions and AGNs among barred
and unbarred galaxies in a sample of over 300 spirals selected from our recent
optical spectroscopic survey of nearby galaxies. Among late-type spirals
(Sc-Sm), but not early-type (S0/a-Sbc), we observe in the barred group a very
marginal increase in the detection rate of H II nuclei and a corresponding
decrease in the incidence of AGNs. The minor differences in the detection
rates, however, are statistically insignificant, most likely stemming from
selection effects and not from a genuine influence from the bar. The presence
of a bar seems to have no noticeable impact on the likelihood of a galaxy to
host either nuclear star formation or an AGN. The nuclei of early-type barred
spirals do exhibit measurably higher star-formation rates than their unbarred
counterparts, as indicated by either the luminosity or the equivalent width of
H-alpha emission. By contrast, late-type spirals do not show such an effect.
Bars have a negligible effect on the strength of the AGNs in our sample,
regardless of the Hubble type of the host galaxy. This result confirms similar
conclusions reached by other studies based on much smaller samples.Comment: To appear in the Astrophysical Journal. LaTex, 31 pages including 6
postscript figures and 3 tables. AAStex macros include
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