2,504 research outputs found
An intelligent, free-flying robot
The ground based demonstration of the extensive extravehicular activity (EVA) Retriever, a voice-supervised, intelligent, free flying robot, is designed to evaluate the capability to retrieve objects (astronauts, equipment, and tools) which have accidentally separated from the Space Station. The major objective of the EVA Retriever Project is to design, develop, and evaluate an integrated robotic hardware and on-board software system which autonomously: (1) performs system activation and check-out; (2) searches for and acquires the target; (3) plans and executes a rendezvous while continuously tracking the target; (4) avoids stationary and moving obstacles; (5) reaches for and grapples the target; (6) returns to transfer the object; and (7) returns to base
How does breakup influence the total fusion of Li at the Coulomb barrier?
Total (complete + incomplete) fusion excitation functions of Li on
Co and Bi targets around the Coulomb barrier are obtained using
a new continuum discretized coupled channel (CDCC) method of calculating
fusion. The relative importance of breakup and bound-state structure effects on
total fusion is particularly investigated. The effect of breakup on fusion can
be observed in the total fusion excitation function. The breakup enhances the
total fusion at energies just around the barrier, whereas it hardly affects the
total fusion at energies well above the barrier. The difference between the
experimental total fusion cross sections for Li on Co is notably
caused by breakup, but this is not the case for the Bi target.Comment: 9 pages, 9 figures, Submitted to Phys. Rev.
Expanding the parameters of academia
This paper draws on qualitative data gathered from two studies funded by the UK Leadership Foundation for Higher Education to examine the expansion of academic identities in higher education. It builds on Whitchurchâs earlier work, which focused primarily on professional staff, to suggest that the emergence of broadly based projects such as widening participation, learning support and community partnership is also impacting on academic identities. Thus, academic as well as professional staff are increasingly likely to work in multi-professional teams across a variety of constituencies, as well as with external partners, and the binary distinction between âacademicâ and ânon-academicâ roles and activities is no longer clear-cut. Moreover, there is evidence from the studies of an intentionality about deviations from mainstream academic career routes among respondents who could have gone either way. Consideration is therefore given to factors that influence individuals to work in more project-oriented areas, as well as to variables that affect ways in which these roles and identities develop. Finally, three models of academically oriented project activity are identified, and the implications of an expansion of academic identities are reviewed
Tests of Transfer Reaction Determinations of Astrophysical S-Factors
The reaction has been used to determine
asymptotic normalization coefficients for transitions to the ground and first
excited states of . The coefficients provide the normalization for
the tails of the overlap functions for and allow us
to calculate the S-factors for at astrophysical
energies. The calculated S-factors are compared to measurements and found to be
in very good agreement. This provides the first test of this indirect method to
determine astrophysical direct capture rates using transfer reactions. In
addition, our results yield S(0) for capture to the ground and first excited
states in , without the uncertainty associated with extrapolation from
higher energies.Comment: 6 pages, 2 figure
Weighing Super-Massive Black Holes with Narrow Fe K Line
It has been suggested that the narrow cores of the Fe K emission
lines in Active Galactic Nuclei (AGNs) are likely produced in the torus, the
inner radius of which can be measured by observing the lag time between the
and band flux variations. In this paper we compare the virial products of
the infrared time lags and the narrow Fe K widths for 10 type 1 AGNs
with the black hole masses from other techniques. We find the narrow Fe
K line width is in average 2.6 times broader than
expected assuming an isotropic velocity distribution of the torus at the
distance measured by the infrared lags. We propose the thick disk model of the
torus could explain the observed larger line width. Another possibility is the
contamination by emission from the broad line region or the outer accretion
disk. Alternatively, the narrow iron line might originate from the inner most
part of the obscuring torus within the sublimation radius, while the infrared
emission from outer cooler part. We note the correlation between the black hole
masses based on this new technique and those based on other known techniques is
statistically insignificant. We argue that this could be attributed to the
small sample size and the very large uncertainties in the measurements of iron
K line widths. The next generation of X-ray observatories could help verify the
origin of the narrow iron K line and the reliability of this new
technique.Comment: 12 pages, 2 figures, 2 tables, Science China G, in pres
Multiple electromagnetic electron positron pair production in relativistic heavy ion collisions
We calculate the cross sections for the production of one and more
electron-positron pairs due to the strong electromagnetic fields in
relativistic heavy ion collisions. Using the generating functional of fermions
in an external field we derive the N-pair amplitude. Neglecting the
antisymmetrisation in the final state we find that the total probability to
produce N pairs is a Poisson distribution. We calculate total cross sections
for the production of one pair in lowest order and also include higher-order
corrections from the Poisson distribution up to third order. Furthermore we
calculate cross sections for the production of up to five pairs including
corrections from the Poisson distribution.Comment: 13 pages REVTeX, 4 Postscript figures, This and related papers may
also be obtained from http://www.phys.washington.edu/~hencken
Mapping the Growth and Demographics of Managerial and Professional Staff in Higher Education
This chapter presents a descriptive analysis of the growth of managerial and professional staff from Fall 1993 to Fall 2011 across institution types and sectors, and a detailed snapshot of the demographic composition of these staff in Fall 2016. Our results indicate tremendous growth in the population of nonâfaculty staff over time, and reveal key patterns in staff employment by gender and race/ethnicity.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154664/1/he20352.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154664/2/he20352_am.pd
Optical model potentials involving loosely bound p-shell nuclei around 10 MeV/A
We present the results of a search for optical model potentials for use in
the description of elastic scattering and transfer reactions involving stable
and radioactive p-shell nuclei. This was done in connection with our program to
use transfer reactions to obtain data for nuclear astrophysics, in particular
for the determination of the astrophysical S_17 factor for 7Be(p,\gamma)8B
using two (7Be,8B) proton transfer reactions. Elastic scattering was measured
using 7Li, 10B, 13C and 14N projectiles on 9Be and 13C targets at or about
E/A=10 MeV/nucleon. Woods-Saxon type optical model potentials were extracted
and are compared with potentials obtained from a microscopic double folding
model. We use these results to find optical model potentials for unstable
nuclei with emphasis on the reliability of the description they provide for
peripheral proton transfer reactions. We discuss the uncertainty introduced by
the procedure in the prediction of the DWBA cross sections for the (7Be,8B)
reactions used in extracting the astrophysical factor S_17(0).Comment: 16 pages, LaTEX file, 9 figures (PostScript files
Exact scaling of pair production in the high-energy limit of heavy-ion collisions
The two-center Dirac equation for an electron in the external electromagnetic
field of two colliding heavy ions in the limit in which the ions are moving at
the speed of light is exactly solved and nonperturbative amplitudes for free
electron-positron pair production are obtained. We find the condition for the
applicability of this solution for large but finite collision energy, and use
it to explain recent experimental results. The observed scaling of positron
yields as the square of the projectile and target charges is a result of an
exact cancellation of a nonperturbative charge dependence and holds as well for
large coupling. Other observables would be sensitive to nonperturbative phases.Comment: 4 pages, Revtex, no figures, submitted to PR
- âŠ