9,853 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
Null Branes in Curved Backgrounds
We consider null bosonic p-branes in curved space-times. Some exact solutions
of the classical equations of motion and of the constraints for the null
membrane in general stationary, axially symmetrical, four dimensional, gravity
background are found.Comment: 19 pages, LaTeX, no figures. Extended version. To appear in Phys.
Rev.
Strain-mediated metal-insulator transition in epitaxial ultra-thin films of NdNiO3
We have synthesized epitaxial NdNiO ultra-thin films in a
layer-by-layer growth mode under tensile and compressive strain on SrTiO
(001) and LaAlO (001), respectively. A combination of X-ray diffraction,
temperature dependent resistivity, and soft X-ray absorption spectroscopy has
been applied to elucidate electronic and structural properties of the samples.
In contrast to the bulk NdNiO, the metal-insulator transition under
compressive strain is found to be completely quenched, while the transition
remains under the tensile strain albeit modified from the bulk behavior.Comment: 4 pages, 4 figure
Large-scale multielectrode recording and stimulation of neural activity
Large circuits of neurons are employed by the brain to encode and process information. How this encoding and processing is carried out is one of the central questions in neuroscience. Since individual neurons communicate with each other through electrical signals (action potentials), the recording of neural activity with arrays of extracellular electrodes is uniquely suited for the investigation of this question. Such recordings provide the combination of the best spatial (individual neurons) and temporal (individual action-potentials) resolutions compared to other large-scale imaging methods. Electrical stimulation of neural activity in turn has two very important applications: it enhances our understanding of neural circuits by allowing active interactions with them, and it is a basis for a large variety of neural prosthetic devices. Until recently, the state-of-the-art in neural activity recording systems consisted of several dozen electrodes with inter-electrode spacing ranging from tens to hundreds of microns. Using silicon microstrip detector expertise acquired in the field of high-energy physics, we created a unique neural activity readout and stimulation framework that consists of high-density electrode arrays, multi-channel custom-designed integrated circuits, a data acquisition system, and data-processing software. Using this framework we developed a number of neural readout and stimulation systems: (1) a 512-electrode system for recording the simultaneous activity of as many as hundreds of neurons, (2) a 61-electrode system for electrical stimulation and readout of neural activity in retinas and brain-tissue slices, and (3) a system with telemetry capabilities for recording neural activity in the intact brain of awake, naturally behaving animals. We will report on these systems, their various applications to the field of neurobiology, and novel scientific results obtained with some of them. We will also outline future directions
An extended scheme for fitting X-ray data with accretion disk spectra in the strong gravity regime
Accreting black holes are believed to emit X-rays which then mediate
information about strong gravity in the vicinity of the emission region. We
report on a set of new routines for the Xspec package for analysing X-ray
spectra of black-hole accretion disks. The new computational tool significantly
extends the capabilities of the currently available fitting procedures that
include the effects of strong gravity, and allows one to systematically explore
the constraints on more model parameters than previously possible (for example
black-hole angular momentum). Moreover, axial symmetry of the disk intrinsic
emissivity is not assumed, although it can be imposed to speed up the
computations. The new routines can be used also as a stand-alone and flexible
code with the capability of handling time-resolved spectra in the regime of
strong gravity. We have used the new code to analyse the mean X-ray spectrum
from the long XMM--Newton 2001 campaign of the Seyfert 1 galaxy MCG--6-30-15.
Consistent with previous findings, we obtained a good fit to the broad Fe K
line profile for a radial line intrinsic emissivity law in the disk which is
not a simple power law, and for near maximal value of black hole angular
momentum. However, equally good fits can be obtained also for small values of
the black hole angular momentum. The code has been developed with the aim of
allowing precise modelling of relativistic effects. Although we find that
current data cannot constrain the parameters of black-hole/accretion disk
system well, the approach allows, for a given source or situation, detailed
investigations of what features of the data future studies should be focused on
in order to achieve the goal of uniquely isolating the parameters of such
systems.Comment: Accepted for publication in ApJ S
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