11,886 research outputs found
Acousto-optic signal processors for transmission and reception of phased-array antenna signals
Novel acousto-optic processors for control and signal processing in phased-array antennas are presented. These processors can operate in both the antenna transmit and receive modes. An experimental acousto-optic processor is demonstrated in the laboratory. This optical technique replaces all the phase-shifting devices required in electronically controlled phased-array antennas
Instruments of RT-2 Experiment onboard CORONAS-PHOTON and their test and evaluation III: Coded Aperture Mask and Fresnel Zone Plates in RT-2/CZT Payload
Imaging in hard X-rays of any astrophysical source with high angular
resolution is a challenging job. Shadow-casting technique is one of the most
viable options for imaging in hard X-rays. We have used two different types of
shadow-casters, namely, Coded Aperture Mask (CAM) and Fresnel Zone Plate (FZP)
pair and two types of pixellated solid-state detectors, namely, CZT and CMOS in
RT-2/CZT payload, the hard X-ray imaging instrument onboard the CORONAS-PHOTON
satellite. In this paper, we present the results of simulations with different
combinations of coders (CAM & FZP) and detectors that are employed in the
RT-2/CZT payload. We discuss the possibility of detecting transient Solar
flares with good angular resolution for various combinations. Simulated results
are compared with laboratory experiments to verify the consistency of the
designed configuration.Comment: 27 pages, 16 figures, Accepted for publication in Experimental
Astronomy (in press
Comparative study of different scattering geometries for the proposed Indian X-ray polarization measurement experiment using Geant4
Polarization measurements in X-rays can provide unique opportunity to study
the behavior of matter and radiation under extreme magnetic fields and extreme
gravitational fields. Unfortunately, over past two decades, when X-ray
astronomy witnessed multiple order of magnitude improvement in temporal,
spatial and spectral sensitivities, there is no (or very little) progress in
the field of polarization measurements of astrophysical X-rays. Recently, a
proposal has been submitted to ISRO for a dedicated small satellite based
experiment to carry out X-ray polarization measurement, which aims to provide
the first X-ray polarization measurements since 1976. This experiment will be
based on the well known principle of polarization measurement by Thomson
scattering and employs the baseline design of a central low Z scatterer
surrounded by X-ray detectors to measure the angular intensity distribution of
the scattered X-rays. The sensitivity of such experiment is determined by the
collecting area, scattering and detection efficiency, X-ray detector
background, and the modulation factor. Therefore, it is necessary to carefully
select the scattering geometry which can provide the highest modulation factor
and thus highest sensitivity within the specified experimental constraints. The
effective way to determine optimum scattering geometry is by studying various
possible scattering geometries by means of Monte Carlo simulations. Here we
present results of our detailed comparative study based on Geant4 simulations
of five different scattering geometries which can be considered within the
weight and size constraints of the proposed small satellite based X-ray
polarization measurement experiment.Comment: 14 pages, 6 figures, accepted for publication in "Nuclear Inst. and
Methods in Physics Research, A
Adversarial Detection of Flash Malware: Limitations and Open Issues
During the past four years, Flash malware has become one of the most
insidious threats to detect, with almost 600 critical vulnerabilities targeting
Adobe Flash disclosed in the wild. Research has shown that machine learning can
be successfully used to detect Flash malware by leveraging static analysis to
extract information from the structure of the file or its bytecode. However,
the robustness of Flash malware detectors against well-crafted evasion attempts
- also known as adversarial examples - has never been investigated. In this
paper, we propose a security evaluation of a novel, representative Flash
detector that embeds a combination of the prominent, static features employed
by state-of-the-art tools. In particular, we discuss how to craft adversarial
Flash malware examples, showing that it suffices to manipulate the
corresponding source malware samples slightly to evade detection. We then
empirically demonstrate that popular defense techniques proposed to mitigate
evasion attempts, including re-training on adversarial examples, may not always
be sufficient to ensure robustness. We argue that this occurs when the feature
vectors extracted from adversarial examples become indistinguishable from those
of benign data, meaning that the given feature representation is intrinsically
vulnerable. In this respect, we are the first to formally define and
quantitatively characterize this vulnerability, highlighting when an attack can
be countered by solely improving the security of the learning algorithm, or
when it requires also considering additional features. We conclude the paper by
suggesting alternative research directions to improve the security of
learning-based Flash malware detectors
A methodology for the generation of efficient error detection mechanisms
A dependable software system must contain error detection mechanisms and error recovery mechanisms. Software components for the detection of errors are typically designed based on a system specification or the experience of software engineers, with their efficiency typically being measured using fault injection and metrics such as coverage and latency. In this paper, we introduce a methodology for the design of highly efficient error detection mechanisms. The proposed methodology combines fault injection analysis and data mining techniques in order to generate predicates for efficient error detection mechanisms. The results presented demonstrate the viability of the methodology as an approach for the development of efficient error detection mechanisms, as the predicates generated yield a true positive rate of almost 100% and a false positive rate very close to 0% for the detection of failure-inducing states. The main advantage of the proposed methodology over current state-of-the-art approaches is that efficient detectors are obtained by design, rather than by using specification-based detector design or the experience of software engineers
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