4,827 research outputs found
More than a job: An exploration of student employee and professional staff perceptions of the relationship between on-campus employment and student development
The purpose of this sequential exploratory mixed methods study is to explore the relationship between on-campus employment and student development through examining student employees\u27 and professional staffs\u27 perceptions. While certain impacts (i.e., retention and grade point average) of on-campus employment have been researched, the impact this experience has on student development is understudied. Furthermore, the formation of a dueling narrative (the inclusion of both student and professional perceptions) is even less present in research. By analyzing the perceptions held by both populations, these findings compare what student employees are truly gaining from their employment experience versus what professional staff believe student employees are gaining. Findings from the quantitative and qualitative data suggest student employees and professional staff share similar perceptions in many domains, such as transferable skill acquisition and the role professionals play in student development. However, findings also imply there are domains student employees and professional staff do not hold similar perceptions, such as leadership development and the inclusion of student voices in the planning and facilitation of student development opportunities
The School Improvement Partnership Programme: Using Collaboration and Enquiry to tackle Educational Inequity
No abstract available
On the efficiency of the Blandford-Znajek mechanism for low angular momentum relativistic accretion
Blandford-Znajek (BZ) mechanism has usually been studied in the literature
for accretion with considerably high angular momentum leading either to the
formation of a cold Keplerian disc, or a hot and geometrically thick
sub-Keplerian flow as described within the framework of ADAF/RIAF. However, in
nearby elliptical galaxies, as well as for our own Galactic centre, accretion
with very low angular momentum is prevalent. Such quasi-spherical strongly
sub-Keplerian accretion has complex dynamical features and can accommodate
stationary shocks. In this letter, we present our calculation for the maximum
efficiency obtainable through the BZ mechanism for complete general
relativistic weakly rotating axisymmetric flow in the Kerr metric. Both shocked
and shock free flow has been studied in detail for rotating and counter
rotating accretion. Such study has never been done in the literature before. We
find that the energy extraction efficiency is low, about 0.1%, and increases by
a factor 15 if the ram pressure is included. Such an efficiency is still much
higher than the radiative efficiency of such optically thin flows. For BZ
mechanism, shocked flow produces higher efficiency than the shock free
solutions and retrograde flow provides a slightly larger value of the
efficiency than that for the prograde flow.Comment: Substantially revised final version to appear in MNRAS Letters. Three
colour figure
A Note on the Slim Accretion Disk Model
We show that when the gravitational force is correctly calculated in dealing
with the vertical hydrostatic equilibrium of black hole accretion disks, the
relationship that is valid for geometrically thin disks, i.e., constant, where is the sound speed, is the Keplerian
angular velocity, and is the half-thickness of the disk, does not hold for
slim disks. More importantly, by adopting the correct vertical gravitational
force in studies of thermal equilibrium solutions, we find that there exists a
maximally possible accretion rate for each radius in the outer region of
optically thick accretion flows, so that only the inner region of these flows
can possibly take the form of slim disks, and strong outflows from the outer
region are required to reduce the accretion rate in order for slim disks to be
realized.Comment: 14 pages, 5 figures, accepted by Ap
Baryon Loading of AGN Jets Mediated by Neutrons
Plasmas of geometrically thick, black hole (BH) accretion flows in active
galactic nuclei (AGNs) are generally collisionless for protons, and involve
magnetic field turbulence. Under such conditions a fraction of protons can be
accelerated stochastically and create relativistic neutrons via nuclear
collisions. These neutrons can freely escape from the accretion flow and decay
into protons in dilute polar region above the rotating BH to form relativistic
jets. We calculate geometric efficiencies of the neutron energy and mass
injections into the polar region, and show that this process can deposit
luminosity as high as L_j ~ 2e-3 dot{M} c^2 and mass loading dot{M}_j ~ 6e-4
dot{M} for the case of the BH mass M ~ 1e8 M_sun, where dot{M} is mass
accretion rate. The terminal Lorentz factors of the jets are Gamma ~ 3, and
they may explain the AGN jets having low luminosities. For higher luminosity
jets, which can be produced by additional energy inputs such as Poynting flux,
the neutron decay still can be a dominant mass loading process, leading to
e.g., Gamma ~ 50 for L_{j,tot} ~ 3e-2 dot{M}c^2.Comment: 7 pages, 6 figures; accepted for publication in Ap
GRB 110328A/Swift J164449.3+573451: The Tidal Obliteration of a Deeply Plunging Star?
We examine the tidal disruption event scenario to explain Sw 1644+57, a
powerful and persistent X-ray source which suddenly became active as GRB
110328A. The precise localization at the center of a z=0.35 galaxy argues for
activity of the central engine as the underlying cause. We look at the
suggestion by Bloom et al of the possibility of a tidal disruption event (TDE).
We argue that Sw 1644+57 cannot be explained by the traditional TDE model in
which the periastron distance is close to the tidal disruption radius - three
independent lines of argument indicate the orbit must be deeply plunging or
else the powerful jet we are observing could not be produced. These arguments
stem from (i) comparing the early X-ray light curve to the expected theoretical
fallback rate, (ii) looking at the time of transition to disk-dominated decay,
and (iii) considering the TDE rate. Due to the extreme excess in the tidal
force above that which would be required minimally to disrupt the star in a
deeply plunging orbit at periastron, we suggest this scenario might be referred
to more descriptively as a TOE (tidal obliteration event) rather than a TDE.Comment: 7 pages, 2 figures, accepted by the Astrophysical Journal, major
revisions since vers. [1]; corrupted file in vers. [2] replace
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