382 research outputs found
Entropy in the RST Model
The RST Model is given boundary term and Z-field so that it is well-posed and
local. The Euclidean method is described for general theory and used to
calculate the RST intrinsic entropy. The evolution of this entropy for the
shockwave solutions is found and obeys a second law.Comment: 10 pages, minor revisions, published version in Late
The use of an e-learning constructivist solution in workplace learning
We wished to investigate whether an e-learning approach which uses constructivist principles can be successfully applied to train employees in a highly specialised skill thought to require expert individuals and extensive prolonged training. The approach involved the development of an e-learning package which included simulations and interactivity, then experimental testing in a case study workplace environment with the collection of both quantitative and qualitative data to assess the effectiveness of the package. Our study shows that this e-learning strategy improved the skills of the inexperienced
operator significantly. We therefore propose that such programmes could be used as a work based training aid and used as a model system for the training of employees in complex skilled tasks in the workplace. This research demonstrates that the e-learning can be applied outside the traditional learning environment to train unskilled employees to undertake complex practical tasks which traditionally would involve prohibitively expensive instruction. This work also illustrates that simulations and interactivity are powerful tools in the design of successful e-learning packages in preparing learners for real world practical situations. Finally this study shows that workplace learners can be better served by elearning environments rather than conventional training as they allow asynchronous learning and private study which are valued by employees who have other demands on their time and are more comfortable receiving tuition privately Relevance to industry: E-learning using constructivist principles, and incorporating simulations and interactivity can be used successfully in the training of highly specialised and skilled tasks required in the
modern workplace
Entropic N-bound and Maximal Mass Conjecture Violations in Four Dimensional Taub-Bolt(NUT)-dS Spacetimes
We show that the class of four-dimensional Taub-Bolt(NUT) spacetimes with
positive cosmological constant for some values of NUT charges are stable and
have entropies that are greater than that of de Sitter spacetime, in violation
of the entropic N-bound conjecture. We also show that the maximal mass
conjecture, which states "any asymptotically dS spacetime with mass greater
than dS has a cosmological singularity", can be violated as well. Our
calculation of conserved mass and entropy is based on an extension of the path
integral formulation to asymptotically de Sitter spacetimes.Comment: 37 pages, 22 figures, 3 tables, few typos corrected, version to
appear in Nucl. Phys.
Decay of flux vacua to nothing
We construct instanton solutions describing the decay of flux
compactifications of a gauge theory by generalizing the Kaluza-Klein
bubble of nothing. The surface of the bubble is described by a smooth
magnetically charged solitonic brane whose asymptotic flux is precisely that
responsible for stabilizing the 4d compactification. We describe several
instances of bubble geometries for the various vacua occurring in a
Einstein-Maxwell theory namely, AdS_4 x S^2, R^{1,3} x S^2, and dS_4 x S^2.
Unlike conventional solutions, the bubbles of nothing introduced here occur
where a {\em two}-sphere compactification manifold homogeneously degenerates.Comment: 31 pages, 15 figure
Aspects of Magnetic Field Configurations in Planar Nonlinear Electrodynamics
In the framework of three-dimensional Born-Infeld Electrodynamics, we pursue
an investigation of the consequences of the space-time dimensionality on the
existence of magnetostatic fields generated by electric charges at rest in an
inertial frame, which are present in its four-dimensional version. Our analysis
reveals interesting features of the model. In fact, a magnetostatic field
associated with an electric charge at rest does not appear in this case.
Interestingly, the addition of the topological term (Chern-Simons) to
Born-Infeld Electrodynamics yields the appearance of the magnetostatic field.
We also contemplate the fields associated to the would-be-magnetic monopole in
three dimensions.Comment: 8 page
-Strands
A -strand is a map for a Lie
group that follows from Hamilton's principle for a certain class of
-invariant Lagrangians. The SO(3)-strand is the -strand version of the
rigid body equation and it may be regarded physically as a continuous spin
chain. Here, -strand dynamics for ellipsoidal rotations is derived as
an Euler-Poincar\'e system for a certain class of variations and recast as a
Lie-Poisson system for coadjoint flow with the same Hamiltonian structure as
for a perfect complex fluid. For a special Hamiltonian, the -strand is
mapped into a completely integrable generalization of the classical chiral
model for the SO(3)-strand. Analogous results are obtained for the
-strand. The -strand is the -strand version of the
Bloch-Iserles ordinary differential equation, whose solutions exhibit dynamical
sorting. Numerical solutions show nonlinear interactions of coherent wave-like
solutions in both cases. -strand equations on the
diffeomorphism group are also introduced and shown
to admit solutions with singular support (e.g., peakons).Comment: 35 pages, 5 figures, 3rd version. To appear in J Nonlin Sc
Saddle point solutions in Yang-Mills-dilaton theory
The coupling of a dilaton to the -Yang-Mills field leads to
interesting non-perturbative static spherically symmetric solutions which are
studied by mixed analitical and numerical methods. In the abelian sector of the
theory there are finite-energy magnetic and electric monopole solutions which
saturate the Bogomol'nyi bound. In the nonabelian sector there exist a
countable family of globally regular solutions which are purely magnetic but
have zero Yang-Mills magnetic charge. Their discrete spectrum of energies is
bounded from above by the energy of the abelian magnetic monopole with unit
magnetic charge. The stability analysis demonstrates that the solutions are
saddle points of the energy functional with increasing number of unstable
modes. The existence and instability of these solutions are "explained" by the
Morse-theory argument recently proposed by Sudarsky and Wald.Comment: 11 page
Open Cosmic Strings in Black Hole Space-Times
We construct open cosmic string solutions in Schwarzschild black hole and
non-dilatonic black p-brane backgrounds. These strings can be thought to
stretch between two D-branes or between a D-brane and the horizon in curved
space-time. We study small fluctuations around these solutions and discuss
their basic properties.Comment: 11 pages, REVTex, 5 figures, a reference adde
Tension term, interchange symmetry, and the analogy of energy and tension laws of the AdS soliton solution
In this paper, we reconsider the energy and tension laws of the Ricci flat
black hole by taking the contribution of the tension term into account. After
this considering and inspired by the interchange symmetry between the Ricci
flat black hole and the AdS soliton solution which arises from the double
analytic continuation of the time and compact spatial direction, we find out
the analogy of the energy and tension laws of the AdS soliton solution.
Moreover, we also investigate the energy and tension laws of the boosted Ricci
flat black hole, and discuss the boosted AdS soliton solution. However,
although there is the same interchange symmetry between the boosted Ricci flat
black hole and boosted AdS soliton, the analogy of laws of the boosted AdS
soliton solution may be of no sense for the existence of the closed timelike
curves and conical singularity. In spite of that, the conserved charges such as
the energy and momentum of the boosted AdS soliton are well-defined, and an
interesting result is that its energy is lower than that of the static AdS
soliton. On the other hand, note that although the laws obtained above are the
same as those of the asymptotically flat case, the underlying deduced contents
are different. Thus, our results could also be considered as a simple
generalization to the asymptotically AdS case. Moreover, during the
calculation, we find that there may be a new way to define the gravitational
tension which can come from the quasi-local stress tensor of the counter-term
method.Comment: V4: 15 pages, no figure, version to appear in JHE
Ricci flat rotating black branes with a conformally invariant Maxwell source
We consider Einstein gravity coupled to an gauge field for which the
density is given by a power of the Maxwell Lagrangian. In -dimensions the
action of Maxwell field is shown to enjoy the conformal invariance if the power
is chosen as . We present a class of charge rotating solutions in
Einstein-conformally invariant Maxwell gravity in the presence of a
cosmological constant. These solutions may be interpreted as black brane
solutions with inner and outer event horizons or an extreme black brane
depending on the value of the mass parameter. Since we are considering power of
the Maxwell density, the black brane solutions exist only for dimensions which
are multiples of four. We compute conserved and thermodynamics quantities of
the black brane solutions and show that the expression of the electric field
does not depend on the dimension. Also, we obtain a Smarr-type formula and show
that these conserved and thermodynamic quantities of black branes satisfy the
first law of thermodynamics. Finally, we study the phase behavior of the
rotating black branes and show that there is no Hawking--Page phase transition
in spite of conformally invariant Maxwell field.Comment: 13 pages, one figur
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