2,906 research outputs found
Conditional linearizability criteria for a system of third-order ordinary differential equations
We provide linearizability criteria for a class of systems of third-order
ordinary differential equations (ODEs) that is cubically semi-linear in the
first derivative, by differentiating a system of second-order quadratically
semi-linear ODEs and using the original system to replace the second
derivative. The procedure developed splits into two cases, those where the
coefficients are constant and those where they are variables. Both cases are
discussed and examples given
Mesoscale magnetism at the grain boundaries in colossal magnetoresistive films
We report the discovery of mesoscale regions with distinctive magnetic
properties in epitaxial LaSrMnO films which exhibit
tunneling-like magnetoresistance across grain boundaries. By using
temperature-dependent magnetic force microscopy we observe that the mesoscale
regions are formed near the grain boundaries and have a different Curie
temperature (up to 20 K {\it higher}) than the grain interiors. Our images
provide direct evidence for previous speculations that the grain boundaries in
thin films are not magnetically and electronically sharp interfaces. The size
of the mesoscale regions varies with temperature and nature of the underlying
defect.Comment: 4 pages of text, 4 figure
Remarks on Renormalization of Black Hole Entropy
We elaborate the renormalization process of entropy of a nonextremal and an
extremal Reissner-Nordstr\"{o}m black hole by using the Pauli-Villars
regularization method, in which the regulator fields obey either the
Bose-Einstein or Fermi-Dirac distribution depending on their spin-statistics.
The black hole entropy involves only two renormalization constants. We also
discuss the entropy and temperature of the extremal black hole.Comment: 14 pages, revtex, no figure
Characterization of a Plain Broadband Textile PIFA
Bandwidth characteristic of a wearable antenna is one of the major factors in determining its usability on the human body. In this work, a planar inverted-F antenna (PIFA) structure is proposed to achieve a large bandwidth to avoid serious antenna reflection coefficient detuning when placed in proximity of the body. The proposed structure is designed based on a simple structure, in order to provide practicality in application and maintain fabrication simplicity. Two different types of conductive textiles, namely Pure Copper Polyester Taffeta Fabric (PCPTF) and ShieldIt, are used in order to proof its concept, in comparison with a metallic antenna made from copper foil. The design is spaced and fabricated using a 6 mm thick fleece fabric. To cater for potential fabrication and material measurement inaccuracies, both antennas' performance are also investigated and analyzed with varying physical and material parameters. From this investigation, it is found that the proposed structure's extended bandwidth enabled the antenna to function with satisfactory on-body reflection coefficients, despite unavoidable gain and efficiency reduction
Renormalized Thermodynamic Entropy of Black Holes in Higher Dimensions
We study the ultraviolet divergent structures of the matter (scalar) field in
a higher D-dimensional Reissner-Nordstr\"{o}m black hole and compute the matter
field contribution to the Bekenstein-Hawking entropy by using the Pauli-Villars
regularization method. We find that the matter field contribution to the black
hole entropy does not, in general, yield the correct renormalization of the
gravitational coupling constants. In particular we show that the matter field
contribution in odd dimensions does not give the term proportional to the area
of the black hole event horizon.Comment: Final Revision Form as to be published in Physical Review D, ReVTeX,
No Figure
Electromagnetic fields in a 3D cavity and in a waveguide with oscillating walls
We consider classical and quantum electromagnetic fields in a
three-dimensional (3D) cavity and in a waveguide with oscillating boundaries of
the frequency . The photons created by the parametric resonance are
distributed in the wave number space around along the axis of the
oscillation. When classical waves propagate along the waveguide in the one
direction, we observe the amplification of the original waves and another wave
generation in the opposite direction by the oscillation of side walls. This can
be understood as the classical counterpart of the photon production. In the
case of two opposite walls oscillating with the same frequency but with a phase
difference, the interferences are shown to occur due to the phase difference in
the photon numbers and in the intensity of the generated waves.Comment: 8 pages revTeX including 1 eps fi
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