246,229 research outputs found
Computation-Communication Trade-offs and Sensor Selection in Real-time Estimation for Processing Networks
Recent advances in electronics are enabling substantial processing to be
performed at each node (robots, sensors) of a networked system. Local
processing enables data compression and may mitigate measurement noise, but it
is still slower compared to a central computer (it entails a larger
computational delay). However, while nodes can process the data in parallel,
the centralized computational is sequential in nature. On the other hand, if a
node sends raw data to a central computer for processing, it incurs
communication delay. This leads to a fundamental communication-computation
trade-off, where each node has to decide on the optimal amount of preprocessing
in order to maximize the network performance. We consider a network in charge
of estimating the state of a dynamical system and provide three contributions.
First, we provide a rigorous problem formulation for optimal real-time
estimation in processing networks in the presence of delays. Second, we show
that, in the case of a homogeneous network (where all sensors have the same
computation) that monitors a continuous-time scalar linear system, the optimal
amount of local preprocessing maximizing the network estimation performance can
be computed analytically. Third, we consider the realistic case of a
heterogeneous network monitoring a discrete-time multi-variate linear system
and provide algorithms to decide on suitable preprocessing at each node, and to
select a sensor subset when computational constraints make using all sensors
suboptimal. Numerical simulations show that selecting the sensors is crucial.
Moreover, we show that if the nodes apply the preprocessing policy suggested by
our algorithms, they can largely improve the network estimation performance.Comment: 15 pages, 16 figures. Accepted journal versio
Tunable zero and first sounds in ultracold Fermi gases with Rabi coupling
We consider a weakly-interacting fermionic gas of alkali-metal atoms
characterized by two hyper- fine states which are Rabi coupled. By using a
Hartree approximation for the repulsive interaction we determine the
zero-temperature equation of state of this Fermi gas in D spatial dimensions (D
= 1, 2, 3). Then, adopting the Landau-Vlasov equation and hydrodynamic
equations, we investi- gate the speed of first sound and zero sound. We show
that the two sounds, which occur respectively in collisional and collisionless
regimes, crucially depend on the interplay between interaction strength and
Rabi coupling. Finally, we discuss for some experimentally relevant cases the
effect of a trapping harmonic potential on the density profiles of the
fermionic system.Comment: Accepted in Journal of Statistical Mechanic
Safe Recursion on Notation into a Light Logic by Levels
We embed Safe Recursion on Notation (SRN) into Light Affine Logic by Levels
(LALL), derived from the logic L4. LALL is an intuitionistic deductive system,
with a polynomial time cut elimination strategy.
The embedding allows to represent every term t of SRN as a family of proof
nets |t|^l in LALL. Every proof net |t|^l in the family simulates t on
arguments whose bit length is bounded by the integer l. The embedding is based
on two crucial features. One is the recursive type in LALL that encodes Scott
binary numerals, i.e. Scott words, as proof nets. Scott words represent the
arguments of t in place of the more standard Church binary numerals. Also, the
embedding exploits the "fuzzy" borders of paragraph boxes that LALL inherits
from L4 to "freely" duplicate the arguments, especially the safe ones, of t.
Finally, the type of |t|^l depends on the number of composition and recursion
schemes used to define t, namely the structural complexity of t. Moreover, the
size of |t|^l is a polynomial in l, whose degree depends on the structural
complexity of t.
So, this work makes closer both the predicative recursive theoretic
principles SRN relies on, and the proof theoretic one, called /stratification/,
at the base of Light Linear Logic
Quantum bright solitons in a quasi-one-dimensional optical lattice
We study a quasi-one-dimensional attractive Bose gas confined in an optical
lattice with a superimposed harmonic potential by analyzing the effective
one-dimensional Bose-Hubbard Hamiltonian of the system. In order to have a
reliable description of the ground-state, that we call quantum bright soliton,
we use the Density-Matrix-Renormalization-Group (DMRG) technique. By comparing
DMRG results with mean-field (MF) ones we find that beyond-mean-field effects
become relevant by increasing the attraction between bosons or by decreasing
the frequency of the harmonic confinement. In particular we discover that,
contrary to the MF predictions based on the discrete nonlinear Schr\"odinger
equation, quantum bright solitons are not self-trapped. We also use the
time-evolving-block-decimation (TEBD) method to investigate dynamical
properties of bright solitons when the frequency of the harmonic potential is
suddenly increased. This quantum quench induces a breathing mode whose period
crucially depends on the final strength of the super-imposed harmonic
confinement
Economic Factors of Vulnerability Trade and Exploitation
Cybercrime markets support the development and diffusion of new attack
technologies, vulnerability exploits, and malware. Whereas the revenue streams
of cyber attackers have been studied multiple times in the literature, no
quantitative account currently exists on the economics of attack acquisition
and deployment. Yet, this understanding is critical to characterize the
production of (traded) exploits, the economy that drives it, and its effects on
the overall attack scenario. In this paper we provide an empirical
investigation of the economics of vulnerability exploitation, and the effects
of market factors on likelihood of exploit. Our data is collected
first-handedly from a prominent Russian cybercrime market where the trading of
the most active attack tools reported by the security industry happens. Our
findings reveal that exploits in the underground are priced similarly or above
vulnerabilities in legitimate bug-hunting programs, and that the refresh cycle
of exploits is slower than currently often assumed. On the other hand,
cybercriminals are becoming faster at introducing selected vulnerabilities, and
the market is in clear expansion both in terms of players, traded exploits, and
exploit pricing. We then evaluate the effects of these market variables on
likelihood of attack realization, and find strong evidence of the correlation
between market activity and exploit deployment. We discuss implications on
vulnerability metrics, economics, and exploit measurement.Comment: 17 pages, 11 figures, 14 table
A comparison of four different methods to estimate population size of Alpine marmot (Marmota marmota)
Obtaining reliable information on animal abundance in mountainous landscapes is challenging. Highly heterogeneous habitats tend to reduce detection probabilities, and the three-dimensional, rugged nature of the terrain poses severe limits to the fulfilment of a number of assumptions underlying several statistical methods. In this study, we aimed to compare the performance of 4 different methods to estimate population size of Alpine marmot (Marmota marmota), a highly social semifossorial rodent widely distributed on the European Alps. Between May and August 2015, in a study area within the Stelvio National Park (Italy) we conducted 8 sessions of capture-mark-recapture, 6 sessions of mark-resight from vantage points, 8 sessions of line distance sampling along 4 transects, and 2 sessions using double-observer methods from vantage points. The minimum number of animals alive, obtained during the mark-resight surveys, was n=54 individuals. Capture-mark-recapture models estimated a population size of n=56 individuals [95% CI (45,87)]; similar, but more precise estimates were obtained with the mark-resight approach {Bowden’s estimator: n=62 [95% CI (54,71)]; Poisson log-normal estimator: n=62 [95% CI (55,69)]}. Line distance sampling and double-observer methods were severely biased low {Line distance sampling: n=24 individuals [95% CI (19,31)]; Independent double-observer: n=24 [95% CI (22, 35)]; Dependent double-observer: n=15 [95% CI (15,20)]}. Our results suggest that the probabilistic approach based on marked individuals yielded fairly robust estimates of population size. The underestimates obtained using distance sampling and double-observer methods were likely due to the violation of some underlying assumptions. While the topography of the mountainous landscape makes it difficult to randomize the sampling scheme, the semifossorial behaviour of the target species is likely to lower the detection probabilities and violate the assumption of perfect detection on the transect
Rich, Sturmian, and trapezoidal words
In this paper we explore various interconnections between rich words,
Sturmian words, and trapezoidal words. Rich words, first introduced in
arXiv:0801.1656 by the second and third authors together with J. Justin and S.
Widmer, constitute a new class of finite and infinite words characterized by
having the maximal number of palindromic factors. Every finite Sturmian word is
rich, but not conversely. Trapezoidal words were first introduced by the first
author in studying the behavior of the subword complexity of finite Sturmian
words. Unfortunately this property does not characterize finite Sturmian words.
In this note we show that the only trapezoidal palindromes are Sturmian. More
generally we show that Sturmian palindromes can be characterized either in
terms of their subword complexity (the trapezoidal property) or in terms of
their palindromic complexity. We also obtain a similar characterization of rich
palindromes in terms of a relation between palindromic complexity and subword
complexity.Comment: 7 page
Quantum Programming Made Easy
We present IQu, namely a quantum programming language that extends Reynold's
Idealized Algol, the paradigmatic core of Algol-like languages. IQu combines
imperative programming with high-order features, mediated by a simple type
theory. IQu mildly merges its quantum features with the classical programming
style that we can experiment through Idealized Algol, the aim being to ease a
transition towards the quantum programming world. The proposed extension is
done along two main directions. First, IQu makes the access to quantum
co-processors by means of quantum stores. Second, IQu includes some support for
the direct manipulation of quantum circuits, in accordance with recent trends
in the development of quantum programming languages. Finally, we show that IQu
is quite effective in expressing well-known quantum algorithms.Comment: In Proceedings Linearity-TLLA 2018, arXiv:1904.0615
Enumeration and Structure of Trapezoidal Words
Trapezoidal words are words having at most distinct factors of length
for every . They therefore encompass finite Sturmian words. We give
combinatorial characterizations of trapezoidal words and exhibit a formula for
their enumeration. We then separate trapezoidal words into two disjoint
classes: open and closed. A trapezoidal word is closed if it has a factor that
occurs only as a prefix and as a suffix; otherwise it is open. We investigate
open and closed trapezoidal words, in relation with their special factors. We
prove that Sturmian palindromes are closed trapezoidal words and that a closed
trapezoidal word is a Sturmian palindrome if and only if its longest repeated
prefix is a palindrome. We also define a new class of words, \emph{semicentral
words}, and show that they are characterized by the property that they can be
written as , for a central word and two different letters .
Finally, we investigate the prefixes of the Fibonacci word with respect to the
property of being open or closed trapezoidal words, and show that the sequence
of open and closed prefixes of the Fibonacci word follows the Fibonacci
sequence.Comment: Accepted for publication in Theoretical Computer Scienc
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