54,468 research outputs found
Global aspects of accelerating and rotating black hole space-times
The complete family of exact solutions representing accelerating and rotating
black holes with possible electromagnetic charges and a NUT parameter is known
in terms of a modified Plebanski-Demianski metric. This demonstrates the
singularity and horizon structure of the sources but not that the complete
space-time describes two causally separated black holes. To demonstrate this
property, the metric is first cast in the Weyl-Lewis-Papapetrou form. After
extending this up to the acceleration horizon, it is then transformed to the
boost-rotation-symmetric form in which the global properties of the solution
are manifest. The physical interpretation of these solutions is thus clarified.Comment: 15 pages, 1 figure. To appear in Class. Quantum Gra
The C-metric as a colliding plane wave space-time
It is explicitly shown that part of the C-metric space-time inside the black
hole horizon may be interpreted as the interaction region of two colliding
plane waves with aligned linear polarization, provided the rotational
coordinate is replaced by a linear one. This is a one-parameter generalization
of the degenerate Ferrari-Ibanez solution in which the focussing singularity is
a Cauchy horizon rather than a curvature singularity.Comment: 6 pages. To appear in Classical and Quantum Gravit
Radiation generated by accelerating and rotating charged black holes in (anti-)de Sitter space
Asymptotic behaviour of gravitational and electromagnetic fields of exact
type D solutions from the large Plebanski-Demianski family of black hole
spacetimes is analyzed. The amplitude and directional structure of radiation is
evaluated in cases when the cosmological constant is non-vanishing, so that the
conformal infinities have either de Sitter-like or anti-de Sitter-like
character. In particular, explicit relations between the parameters that
characterize the sources (that is their mass, electric and magnetic charges,
NUT parameter, rotational parameter, and acceleration) and properties of the
radiation generated by them are presented. The results further elucidate the
physical interpretation of these solutions and may help to understand radiative
characteristics of more general spacetimes than those that are asymptotically
flat.Comment: 24 pages, 18 figures. To appear in Classical and Quantum Gravit
Interpreting the C-metric
The basic properties of the C-metric are well known. It describes a pair of
causally separated black holes which accelerate in opposite directions under
the action of forces represented by conical singularities. However, these
properties can be demonstrated much more transparently by making use of
recently developed coordinate systems for which the metric functions have a
simple factor structure. These enable us to obtain explicit
Kruskal-Szekeres-type extensions through the horizons and construct
two-dimensional conformal Penrose diagrams. We then combine these into a
three-dimensional picture which illustrates the global causal structure of the
space-time outside the black hole horizons. Using both the weak field limit and
some invariant quantities, we give a direct physical interpretation of the
parameters which appear in the new form of the metric. For completeness,
relations to other familiar coordinate systems are also discussed.Comment: 22 pages, 14 figures (low-resolution figures; for the version with
high-resolution figures see http://utf.mff.cuni.cz/~krtous/papers/ or
http://www-staff.lboro.ac.uk/~majbg/
Modelling and control of the flame temperature distribution using probability density function shaping
This paper presents three control algorithms for the output probability density function (PDF) control of the 2D and 3D flame distribution systems. For the 2D flame distribution systems, control methods for both static and dynamic flame systems are presented, where at first the temperature distribution of the gas jet flames along the cross-section is approximated. Then the flame energy distribution (FED) is obtained as the output to be controlled by using a B-spline expansion technique. The general static output PDF control algorithm is used in the 2D static flame system, where the dynamic system consists of a static temperature model of gas jet flames and a second-order actuator. This leads to a second-order closed-loop system, where a singular state space model is used to describe the dynamics with the weights of the B-spline functions as the state variables. Finally, a predictive control algorithm is designed for such an output PDF system. For the 3D flame distribution systems, all the temperature values of the flames are firstly mapped into one temperature plane, and the shape of the temperature distribution on this plane can then be controlled by the 3D flame control method proposed in this paper. Three cases are studied for the proposed control methods and desired simulation results have been obtained
Spinning String and Giant Graviton in Electric/Magnetic Field Deformed
We apply the transformation of mixing azimuthal and internal coordinate or
mixing time and internal coordinate to the 11D M-theory with a stack of
M2-branes M2-branes, then, through the mechanism of Kaluza-Klein
reduction and a series of the T duality we obtain the corresponding background
of a stack of D1-branes D5-branes which, in the near-horizon limit,
becomes the magnetic or electric Melvin field deformed . We find the giant graviton solution in the deformed spacetime and see
that the configuration whose angular momentum is within a finite region could
has a fixed size and become more stable than the point-like graviton, in
contrast to the undeformed giant graviton which only exists when its angular
momentum is a specific value and could have arbitrary size. We discuss in
detail the properties of how the electric/magnetic Melvin field will affect the
size of the giant gravitons. We also adopt an ansatz to find the classical
string solutions which are rotating in the deformed with an angular
momentum in the rotation plane. The spinning string and giant graviton
solutions we obtained show that the external magnetic/electric flux will
increase the solution energy. Therefore, from the AdS/CFT point of view, the
corrections of the anomalous dimensions of operators in the dual field theory
will be positive. Finally, we also see that the spinning string and giant
graviton in the near-horizon spacetime of Melvin field deformed D5-branes
background have the similar properties as those in the deformed .Comment: Latex 21 pages, slightly detail calculation
Colossal negative magnetoresistance in dilute fluorinated graphene
Adatoms offer an effective route to modify and engineer the properties of
graphene. In this work, we create dilute fluorinated graphene using a clean,
controlled and reversible approach. At low carrier densities, the system is
strongly localized and exhibits an unexpected, colossal negative
magnetoresistance. The zero-field resistance is reduced by a factor of 40 at
the highest field of 9 T and shows no sign of saturation. Unusual "staircase"
field dependence is observed below 5 K. The magnetoresistance is highly
anisotropic. We discuss possible origins, considering quantum interference
effects and adatom-induced magnetism in graphene.Comment: 21 pages, 4 figures, including supplementary informatio
- …