729 research outputs found
Do Android Taint Analysis Tools Keep Their Promises?
In recent years, researchers have developed a number of tools to conduct
taint analysis of Android applications. While all the respective papers aim at
providing a thorough empirical evaluation, comparability is hindered by varying
or unclear evaluation targets. Sometimes, the apps used for evaluation are not
precisely described. In other cases, authors use an established benchmark but
cover it only partially. In yet other cases, the evaluations differ in terms of
the data leaks searched for, or lack a ground truth to compare against. All
those limitations make it impossible to truly compare the tools based on those
published evaluations.
We thus present ReproDroid, a framework allowing the accurate comparison of
Android taint analysis tools. ReproDroid supports researchers in inferring the
ground truth for data leaks in apps, in automatically applying tools to
benchmarks, and in evaluating the obtained results. We use ReproDroid to
comparatively evaluate on equal grounds the six prominent taint analysis tools
Amandroid, DIALDroid, DidFail, DroidSafe, FlowDroid and IccTA. The results are
largely positive although four tools violate some promises concerning features
and accuracy. Finally, we contribute to the area of unbiased benchmarking with
a new and improved version of the open test suite DroidBench
A Number-Theoretic Error-Correcting Code
In this paper we describe a new error-correcting code (ECC) inspired by the
Naccache-Stern cryptosystem. While by far less efficient than Turbo codes, the
proposed ECC happens to be more efficient than some established ECCs for
certain sets of parameters. The new ECC adds an appendix to the message. The
appendix is the modular product of small primes representing the message bits.
The receiver recomputes the product and detects transmission errors using
modular division and lattice reduction
CMB anisotropies due to cosmological magnetosonic waves
We study scalar mode perturbations (magnetosonic waves) induced by a helical
stochastic cosmological magnetic field and derive analytically the
corresponding cosmic microwave background (CMB) temperature and polarization
anisotropy angular power spectra. We show that the presence of a stochastic
magnetic field, or an homogeneous magnetic field, influences the acoustic
oscillation pattern of the CMB anisotropy power spectrum, effectively acting as
a reduction of the baryon fraction. We find that the scalar magnetic energy
density perturbation contribution to the CMB temperature anisotropy is small
compared to the contribution to the CMB -polarization anisotropy.Comment: 17 pages, references added, version accepted for publication in Phys.
Rev.
IGR J17544-2619: A new supergiant fast X-ray transient revealed by optical/infrared observations
One of the most recent discoveries of the INTEGRAL observatory is the
existence of a previously unknown population of X-ray sources in the inner arms
of the Galaxy. IGR J17544-2619, IGR J16465-4507 and XTE J1739-302 are among
these sources. Although the nature of these systems is still unexplained, the
investigations of the optical/NIR counterparts of the two last sources,
combined with high energy data, have provided evidence of them being highly
absorbed high mass X-ray binaries with blue supergiant secondaries and
displaying fast X-ray transient behaviour. In this work we present our
optical/NIR observations of IGR J17544-2619, aimed at identifying and
characterizing its counterpart. We show that the source is a high mass X-ray
binary at a distance of 2-4 kpc with a strongly absorbed O9Ib secondary, and
discuss the nature of the system.Comment: 7 pages, 4 figures. Accepted for publication in A&
Self-organization in a phonon laser
We make an adaptation of laser modelling equations to describe the behavior
of a phonon laser (saser). Our saser consists of an AlGaAs/GaAs double barrier
heterostructure designed to generate an intense beam of transversal acoustic
(TA) phonons. To study our system, we begin with a Hamiltonian that describes
the decay of primary longitudinal optical phonons (LO_1) into secondary (LO_2)
and TA (LO_1 -> LO_2 + TA) and its inverse process (recombination). Using this
Hamiltonian, a set of coupled equations of motion for the phonons is obtained.
We also consider the interaction between the phonons and its reservoirs. These
interactions are introduced in the equations of motion leading to a set of
coupled Langevin equations. In order to obtain an expression to describe our
saser we apply, in the Langevin equations, an adiabatic elimination of some
variables of the subsystem. Following the method above we obtain the value of
the injection threshold for the operation of our phonon laser. At this
threshold occurs a phase transition from a disordered to a coherent state. It
is shown that it is not necessary a big "optical" pumping to get a sasing
region.Comment: 4 figure
Stellar tracers of the Cygnus Arm. II: A young open cluster in Cam OB3
Cam OB3 is the only defined OB association believed to belong to the Outer
Galactic Arm or Cygnus Arm. Very few members have been observed and the
distance modulus to the association is not well known. We attempt a more
complete description of the population of Cam OB3 and a better determination of
its distance modulus. We present uvby photometry of the area surrounding the
O-type stars BD +56 864 and LS I +57 138, finding a clear sequence of
early-type stars that define an uncatalogued open cluster, which we call
Alicante 1. We also present spectroscopy of stars in this cluster and the
surrounding association. From the spectral types for 18 very likely members of
the association and UBV photometry found in the literature, we derive
individual reddenings, finding a extinction law close to standard and an
average distance modulus DM=13.0+-0.4. This value is in excellent agreement
with the distance modulus to the new cluster Alicante 1 found by fitting the
photometric sequence to the ZAMS. In spite of the presence of several O-type
stars, Alicante 1 is a very sparsely populated open cluster, with an almost
total absence of early B-type stars. Our results definitely confirm Cam OB3 to
be located on the Cygnus Arm and identify the first open cluster known to
belong to the association.Comment: Accepted for publication in Astronomy & Astrophysics. Tables 7 & 8 to
appear only in electronic forma
Single-molecule interfacial electron transfer dynamics manipulated by external electric current
Interfacial electron transfer (IET) dynamics in 1,1'-dioctadecyl-3, 3, 3',
3'-tetramethylindodicarbocyanine (DiD) dye molecules / indium tin oxide (ITO)
film system have been probed at the ensemble and single-molecule level by
recording the change of fluorescence emission intensity. By comparing the
difference of the external electric current (EEC) dependence of lifetime and
intensity for enambles and single molecules, it is shown that the
single-molecule probe can effcienly demonstrate the IET dynamics. The backward
electron transfer and electron transfer of ground state induce the single
molecules fluorescence quenching when an EEC is applied to ITO film.Comment: 6 pages, 6 figure
Nonequilibrium Electron Interactions in Metal Films
Ultrafast relaxation dynamics of an athermal electron distribution is
investigated in silver films using a femtosecond pump-probe technique with 18
fs pulses in off-resonant conditions. The results yield evidence for an
increase with time of the electron-gas energy loss rate to the lattice and of
the free electron damping during the early stages of the electron-gas
thermalization. These effects are attributed to transient alterations of the
electron average scattering processes due to the athermal nature of the
electron gas, in agreement with numerical simulations
The Stark effect in linear potentials
We examine the Stark effect (the second-order shift in the energy spectrum
due to an external constant force) for two 1-dimensional model quantum
mechanical systems described by linear potentials, the so-called quantum
bouncer (defined by V(z) = Fz for z>0 and V(z) infinite for z<0) and the
symmetric linear potential (given by V(z) = F|z|). We show how straightforward
use of the most obvious properties of the Airy function solutions and simple
Taylor expansions give closed form results for the Stark shifts in both
systems. These exact results are then compared to other approximation
techniques, such as perturbation theory and WKB methods. These expressions add
to the small number of closed-form descriptions available for the Stark effect
in model quantum mechanical systems.Comment: 15 pages. To appear in Eur. J. Phys. Needs Institute of Physics
(iopart) style file
Spectra from the shocked nebulae revealing turbulence near the Galactic Centre
The spectra emitted from clouds near the Galactic Centre are investigated
calculating the UV-optical-IR lines using the physical parameters and the
element abundances constrained by the fit of mid-IR observations. The
characteristic line ratios are compared with those observed in active galaxies.
We have found that the physical conditions in the nebulae near the GC are
different from those of starburst galaxies and AGN, namely, gas velocities and
densities as well as the photoionization fluxes are relatively low. The
geometrical thickness of the emitting nebulae is particularly small suggesting
that matter is strongly fragmented by instabilities leading to an underlying
shock-generated turbulence.Comment: 16 pages, 11 figures, 4 Tables. MNRAS, accepte
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