866 research outputs found

### Electronic information resource use: Implications for teaching and library staff

Traditionally, guidance from teaching staff to students on the use of information sources has taken the form of reading lists containing a mix of books and journal articles, and the assumption is that information specialists within the library will provide whatever additional help is needed to access these resources. Given the rapidly increasing availability of electronic sources of information, and changes in the learning and teaching environment, such an approach can no longer be regarded as appropriate. This paper addresses the issue of the best way of helping students make effective use of electronic information resources, thereby developing their informationâgathering skills. Reference is made to the lessons learned from undertaking a small action research project in this field. Consideration is also given to a number of broader, more contextual issues, such as the ongoing shift towards more independent learning by students and changing relationships between teaching staff and information specialists. We conclude that more research is urgently needed if ways are to be found of ensuring that students maximize the potential of electronic information resources, and argue that there should be greater collaboration between teaching staff and information specialists, and that their roles and responsibilities in providing appropriate support and in assessing the informationâgathering skills of students need to be redefined

### Hadamard Renormalisation of the Stress Energy Tensor on the Horizons of a Spherically Symmetric Black Hole Space-Time

We consider a quantum field which is in a Hartle-Hawking state propagating in
a general spherically symmetric black hole space-time. We make use of uniform
approximations to the radial equation to calculate the components of the stress
tensor, renormalized using the Hadamard form of the Green's function, on the
horizons of this space-time. We then specialize these results to the case of
the `lukewarm' Reissner-Nordstrom-de Sitter black hole and derive some
conditions on the stress tensor for the regularity of the Hartle-Hawking state.Comment: 18 pages, minor changes to introduction and conclusions, typos
correcte

### Transport Equation Approach to Calculations of Hadamard Green functions and non-coincident DeWitt coefficients

Building on an insight due to Avramidi, we provide a system of transport
equations for determining key fundamental bi-tensors, including derivatives of
the world-function, \sigma(x,x'), the square root of the Van Vleck determinant,
\Delta^{1/2}(x,x'), and the tail-term, V(x,x'), appearing in the Hadamard form
of the Green function. These bi-tensors are central to a broad range of
problems from radiation reaction to quantum field theory in curved spacetime
and quantum gravity. Their transport equations may be used either in a
semi-recursive approach to determining their covariant Taylor series
expansions, or as the basis of numerical calculations. To illustrate the power
of the semi-recursive approach, we present an implementation in
\textsl{Mathematica} which computes very high order covariant series expansions
of these objects. Using this code, a moderate laptop can, for example,
calculate the coincidence limit a_7(x,x) and V(x,x') to order (\sigma^a)^{20}
in a matter of minutes. Results may be output in either a compact notation or
in xTensor form. In a second application of the approach, we present a scheme
for numerically integrating the transport equations as a system of coupled
ordinary differential equations. As an example application of the scheme, we
integrate along null geodesics to solve for V(x,x') in Nariai and Schwarzschild
spacetimes.Comment: 32 pages, 5 figures. Final published version with correction to Eq.
(3.24

### Quantum field theory on the Bertotti-Robinson space-time

We consider the problem of quantum field theory on the Bertotti-Robinson
space-time, which arises naturally as the near horizon geometry of an extremal
Reissner-Nordstrom black hole but can also arise in certain near-horizon limits
of non-extremal Reissner Nordstrom space-time. The various vacuum states have
been considered in the context of $AdS_{2}$ black holes by Spradlin and
Strominger who showed that the Poincare vacuum, the Global vacuum and the
Hartle-Hawking vacuum are all equivalent, while the Boulware vacuum and the
Schwarzschild vacuum are equivalent. We verify this by explicitly computing the
Green's functions in closed form for a massless scalar field corresponding to
each of these vacua. Obtaining a closed form for the Green's function
corresponding to the Boulware vacuum is non-trivial, we present it here for the
first time by deriving a new summation formula for associated Legendre
functions that allows us to perform the mode-sum. Having obtained the
propagator for the Boulware vacuum, which is a zero-temperature Green's
function, we can then consider the case of a scalar field at an arbitrary
temperature by an infinite image imaginary-time sum, which yields the
Hartle-Hawking propagator upon setting the temperature to the Hawking
temperature. Finally, we compute the renormalized stress-energy tensor for a
massless scalar field in the various quantum vacua.Comment: 15 pages, to be published in PR

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