11,247 research outputs found
Easy 4G/LTE IMSI Catchers for Non-Programmers
IMSI Catchers are tracking devices that break the privacy of the subscribers
of mobile access networks, with disruptive effects to both the communication
services and the trust and credibility of mobile network operators. Recently,
we verified that IMSI Catcher attacks are really practical for the
state-of-the-art 4G/LTE mobile systems too. Our IMSI Catcher device acquires
subscription identities (IMSIs) within an area or location within a few seconds
of operation and then denies access of subscribers to the commercial network.
Moreover, we demonstrate that these attack devices can be easily built and
operated using readily available tools and equipment, and without any
programming. We describe our experiments and procedures that are based on
commercially available hardware and unmodified open source software
Reflected Iron Line From a Source Above a Kerr Black Hole Accretion Disc
In this paper we present a fully relativistic approach to modelling both the
continuum emission and the reflected fluorescent iron line from a primary X-ray
source near a Kerr black hole. The X-ray source is located above an accretion
disc orbiting around the black hole. The source is assumed to be a static point
source located on an arbitrary position above the disc, on or off the axis of
rotation. We carry out Monte Carlo simulations in order to estimate the iron
line spectrum as well as its equivalent width. Because of the gravitational
lensing effect, an enhancement of the iron line is expected when the primary
source is located close to the central black hole. We find that for a source
located on the axis of rotation the enhancement is relatively modest. An
observer at inclination 30 degrees would measure an equivalent width of ~300eV
in the extreme case of a maximally rotating black hole and a source located at
height 1.5 gravitational radius from the centre. This corresponds to an
equivalent width enhancement factor of about 2 compared to the classical value
where no lensing effect comes into play. However, when allowing the source to
be located off the axis of rotation, much stronger enhancement can be obtained.
In the extreme case of a maximally rotating black hole and a source located
just above the approaching side of the disc, an observer at inclination 30d
egrees could measure an equivalent width as high as ~1.5 keV (i.e. ~10 times
the classical value). We also find that observers located at high inclination
angles observe a stronger line than observers at low inclination angles.Comment: 11 pages, 13 figures. Submitted to Monthly Notices of the Royal
Astronomical Society (MNRAS
Negative Refraction in Ferromagnet/Superconductor Superlattices
Negative refraction, which reverses many fundamental aspects of classical
optics, can be obtained in systems with negative magnetic permeability and
negative dielectric permittivity. This Letter documents an experimental
realization of negative refraction at millimeter waves, finite magnetic fields
and cryogenic temperatures utilizing a multilayer stack of ferromagnetic and
superconducting thin films. In the present case the superconducting
YBa_2Cu_3O_7 layers provide negative permittivity while negative permeability
is achieved via ferromagnetic (La:Sr)MnO_3 layers for frequencies and magnetic
fields close to the ferromagnetic resonance. In these superlattices the
refractive index can be switched between positive and negative regions using
external magnetic field as tuning parameter.Comment: 4 Pages, 3 Figures, Phys. Rev. Lett., accepte
Non-commutative connections of the second kind
A connection-like objects, termed {\em hom-connections} are defined in the
realm of non-commutative geometry. The definition is based on the use of
homomorphisms rather than tensor products. It is shown that hom-connections
arise naturally from (strong) connections in non-commutative principal bundles.
The induction procedure of hom-connections via a map of differential graded
algebras or a differentiable bimodule is described. The curvature for a
hom-connection is defined, and it is shown that flat hom-connections give rise
to a chain complex.Comment: 13 pages, LaTe
Star product formula of theta functions
As a noncommutative generalization of the addition formula of theta
functions, we construct a class of theta functions which are closed with
respect to the Moyal star product of a fixed noncommutative parameter. These
theta functions can be regarded as bases of the space of holomorphic
homomorphisms between holomorphic line bundles over noncommutative complex
tori.Comment: 12 page
NA48/2 final results on charged semileptonic kaon decays and , NA48 measurements of the form factors from decays
Measured ratios of decay rates for and are presented, based on decays collected in a dedicated run in 2003 by the NA48/2 experiment at CERN. The results obtained are and . Using the PDG average for the normalisation mode, both values are found to be larger than the current values given by the Particle Data Book [1] and lead to a larger magnitude of the element in the CabibboKobayashi-Maskawa (CKM) matrix than previously accepted. When combined with the latest Particle Data Book value of [1], the result is in agreement with unitarity of the CKM matrix. In addition, a new measured value of is compared to the semi-empirical predictions based on the latest form factor measurements. The form factors have been measured from a sample of decays in a dedicated run in 1999 by the NA48 experiment at CERN. Studying the Dalitz plot density, using the linear form factor approximation, a measurement was made of and . Measurements were also made using the quadratic parameterisation, the pole parameterisation and the dispersive parameterisation. The results of all parameterisations will be presented
Why is the nuclear symmetry energy so uncertain at supra-saturation densities?
Within the interacting Fermi gas model for isospin asymmetric nuclear matter,
effects of the in-medium three-body interaction and the two-body short-range
tensor force due to the meson exchange as well as the short-range
nucleon correlation on the high-density behavior of the nuclear symmetry energy
are demonstrated respectively in a transparent way. Possible physics origins of
the extremely uncertain nuclear symmetry energy at supra-saturation densities
are discussed.Comment: Added discussions and revised format. Version to appear in Phys. Rev.
C (2010
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