5,774 research outputs found
Transits and Lensing by Compact Objects in the Kepler Field: Disrupted Stars Orbiting Blue Stragglers
Kepler's first major discoveries are two hot objects orbiting stars in its
field. These may be the cores of stars that have each been eroded or disrupted
by a companion star. The companion, which is the star monitored today, is
likely to have gained mass from its now-defunct partner, and can be considered
to be a blue straggler. KOI-81 is almost certainly the product of stable mass
transfer; KOI-74 may be as well, or it may be the first clear example of a blue
straggler created throughthree-body interactions.
We show that mass transfer binaries are common enough that Kepler should
discover ~1000 white dwarfs orbiting main sequence stars. Most, like KOI-74 and
KOI-81, will be discovered through transits, but many will be discovered
through a combination of gravitational lensing and transits, while lensing will
dominate for a subset. In fact, some events caused by white dwarfs will have
the appearance of "anti-transits" --i.e., short-lived enhancements in the
amount of light received from the monitored star. Lensing and other mass
measurements methods provide a way to distinguish white dwarf binaries from
planetary systems. This is important for the success of Kepler's primary
mission, in light of the fact that white dwarf radii are similar to the radii
of terrestrial planets, and that some white dwarfs will have orbital periods
that place them in the habitable zones of their stellar companions. By
identifying transiting and/or lensing white dwarfs, Kepler will conduct
pioneering studies of white dwarfs and of the end states of mass transfer. It
may also identify orbiting neutron stars or black holes. The calculations
inspired by the discovery of KOI-74 and KOI-81 have implications for
ground-based wide-field surveys as well as for future space-based surveys.Comment: 29 pages, 6 figures, 1 table; submitted to The Astrophysical Journa
Validation & Verification of an EDA automated synthesis tool
Reliability and correctness are two mandatory features for automated synthesis tools. To reach the goals several campaigns of Validation and Verification (V&V) are needed. The paper presents the extensive efforts set up to prove the correctness of a newly developed EDA automated synthesis tool. The target tool, MarciaTesta, is a multi-platform automatic generator of test programs for microprocessors' caches. Getting in input the selected March Test and some architectural details about the target cache memory, the tool automatically generates the assembly level program to be run as Software Based Self-Testing (SBST). The equivalence between the original March Test, the automatically generated Assembly program, and the intermediate C/C++ program have been proved resorting to sophisticated logging mechanisms. A set of proved libraries has been generated and extensively used during the tool development. A detailed analysis of the lessons learned is reporte
Location-Verification and Network Planning via Machine Learning Approaches
In-region location verification (IRLV) in wireless networks is the problem of
deciding if user equipment (UE) is transmitting from inside or outside a
specific physical region (e.g., a safe room). The decision process exploits the
features of the channel between the UE and a set of network access points
(APs). We propose a solution based on machine learning (ML) implemented by a
neural network (NN) trained with the channel features (in particular, noisy
attenuation values) collected by the APs for various positions both inside and
outside the specific region. The output is a decision on the UE position
(inside or outside the region). By seeing IRLV as an hypothesis testing
problem, we address the optimal positioning of the APs for minimizing either
the area under the curve (AUC) of the receiver operating characteristic (ROC)
or the cross entropy (CE) between the NN output and ground truth (available
during the training). In order to solve the minimization problem we propose a
twostage particle swarm optimization (PSO) algorithm. We show that for a long
training and a NN with enough neurons the proposed solution achieves the
performance of the Neyman-Pearson (N-P) lemma.Comment: Accepted for Workshop on Machine Learning for Communications, June 07
2019, Avignon, Franc
Modelling sustainable human development in a capability perspective
In this paper we model sustainable human development as intended in Sen's capability approach in a system dynamic framework. Our purpose is to verify the variations over time of some achieved functionings, due to structural dynamics and to variations of the institutional setting and instrumental freedoms (IF Vortex). The model is composed of two sections. The 'Left Side' one points out the 'demand' for functionings in an ideal world situation. The real world one, on the 'Right Side' indicates the 'supply' of functionings that the socio-economic system is able to provide individuals with. The general model, specifically tailored for Italy, can be simulated over desired time horizons: for each time period, we carry out a comparison between ideal world and real world functionings. On the basis of their distances, the model simulates some responses of decision makers. These responses, in turn influenced by institutions and instrumental freedoms, ultimately affect the dynamics of real world functionings, i.e. of sustainable human development.Functionings, Capabilities, Institutions, Instrumental Freedoms, Sustainable Human Development
An area-efficient 2-D convolution implementation on FPGA for space applications
The 2-D Convolution is an algorithm widely used in image and video processing. Although its computation is simple, its implementation requires a high computational power and an intensive use of memory. Field Programmable Gate Arrays (FPGA) architectures were proposed to accelerate calculations of 2-D Convolution and the use of buffers implemented on FPGAs are used to avoid direct memory access. In this paper we present an implementation of the 2-D Convolution algorithm on a FPGA architecture designed to support this operation in space applications. This proposed solution dramatically decreases the area needed keeping good performance, making it appropriate for embedded systems in critical space application
Topological Constraints in Eukaryotic Genomes and How They Can Be Exploited to Improve Spatial Models of Chromosomes
Several orders of magnitude typically separate the contour length of
eukaryotic chromosomes and the size of the nucleus where they are confined. The
ensuing topological constraints can slow down the relaxation dynamics of
genomic filaments to the point that mammalian chromosomes are never in
equilibrium over a cell's lifetime. In this opinion article, we revisit these
out-of-equilibrium effects and discuss how their inclusion in physical models
can enhance the spatial reconstructions of interphase eukaryotic genomes from
phenomenological constraints collected during interphase.Comment: 5 pages, 1 figure, opinion article, submitted for publicatio
Comparison between three glass fiber post cementation techniques
The aim of this experimental study was to compare the traditional cement systems with those of the latest generation, to assess if indeed these could represent of viable substitutes in the cementation of indirect restorations, and in the specific case of endodontic posts
On the evolution of elastic properties during laboratory stick-slip experiments spanning the transition from slow slip to dynamic rupture
The physical mechanisms governing slow earthquakes remain unknown, as does the
relationship between slow and regular earthquakes. To investigate the mechanism(s) of slow earthquakes
and related quasi-dynamic modes of fault slip we performed laboratory experiments on simulated fault
gouge in the double direct shear configuration. We reproduced the full spectrum of slip behavior, from slow
to fast stick slip, by altering the elastic stiffness of the loading apparatus (k) to match the critical rheologic
stiffness of fault gouge (kc). Our experiments show an evolution from stable sliding, when k>kc, to
quasi-dynamic transients when k ~ kc, to dynamic instabilities when k<kc. To evaluate the microphysical
processes of fault weakening we monitored variations of elastic properties. We find systematic changes in P
wave velocity (Vp) for laboratory seismic cycles. During the coseismic stress drop, seismic velocity drops
abruptly, consistent with observations on natural faults. In the preparatory phase preceding failure, we find
that accelerated fault creep causes a Vp reduction for the complete spectrum of slip behaviors. Our results
suggest that the mechanics of slow and fast ruptures share key features and that they can occur on same
faults, depending on frictional properties. In agreement with seismic surveys on tectonic faults our data show
that their state of stress can be monitored by Vp changes during the seismic cycle. The observed reduction in
Vp during the earthquake preparatory phase suggests that if similar mechanisms are confirmed in nature
high-resolution monitoring of fault zone properties may be a promising avenue for reliable detection of
earthquake precursors
- âŠ