1,117 research outputs found
Remarkable analytic relations among greybody parameters
In this paper we derive and discuss several implications of the analytic form
of a modified blackbody, also called greybody, which is widely used in
Astrophysics, and in particular in the study of star formation in the
far-infrared/sub-millimeter domain. The research in this area has been greatly
improved thanks to recent observations taken with the Herschel satellite, so
that it became important to clarify the sense of the greybody approximation, to
suggest possible further uses, and to delimi its intervals of validity. First,
we discuss the position of the greybody peak, making difference between the
optically thin and thick regimes. Second, we analyze the behavior of bolometric
quantities as a function of the different greybody parameters. The ratio
between the bolometric luminosity and the mass of a source, the ratio between
the so-called "sub-millimeter luminosity" and the bolometric one, and the
bolometric temperature are observables used to characterize the evolutionary
stage of a source, and it is of primary importance to have analytic equations
describing the dependence of such quantities on the greybody parameters. Here
we discuss all these aspects, providing analytic relations, illustrating
particular cases and providing graphical examples. Some equations reported here
are well-known in Astrophysics, but are often spread over different
publications. Some of them, instead, are brand new and represent a novelty in
Astrophysics literature. Finally we indicate an alternative way to obtain,
under some conditions, the greybody temperature and dust emissivity directly
from an observing spectral energy distribution, avoiding a best-fit procedure.Comment: accepted by MNRA
On the Decoding Complexity of Cyclic Codes Up to the BCH Bound
The standard algebraic decoding algorithm of cyclic codes up to the
BCH bound is very efficient and practical for relatively small while it
becomes unpractical for large as its computational complexity is .
Aim of this paper is to show how to make this algebraic decoding
computationally more efficient: in the case of binary codes, for example, the
complexity of the syndrome computation drops from to , and
that of the error location from to at most .Comment: accepted for publication in Proceedings ISIT 2011. IEEE copyrigh
Efficient evaluation of polynomials over finite fields
A method is described which allows to evaluate efficiently a polynomial in a
(possibly trivial) extension of the finite field of its coefficients. Its
complexity is shown to be lower than that of standard techniques when the
degree of the polynomial is large with respect to the base field. Applications
to the syndrome computation in the decoding of cyclic codes, Reed-Solomon codes
in particular, are highlighted.Comment: presented at AusCTW 201
The Rabin cryptosystem revisited
The Rabin public-key cryptosystem is revisited with a focus on the problem of
identifying the encrypted message unambiguously for any pair of primes. In
particular, a deterministic scheme using quartic reciprocity is described that
works for primes congruent 5 modulo 8, a case that was still open. Both
theoretical and practical solutions are presented. The Rabin signature is also
reconsidered and a deterministic padding mechanism is proposed.Comment: minor review + introduction of a deterministic scheme using quartic
reciprocity that works for primes congruent 5 modulo
Improvements on Cantor-Zassenhaus Factorization Algorithm
After revisiting Cantor-Zassenhaus polynomial factorization algorithm, we
describe a new simplified version of it, which requires less computational
cost. Moreover we show that it is able to find a factor of a fully splitting
polynomial of degree over with
attempts and over for odd with
attempts.Comment: extended and revised version; case s>1 adde
Learning Agile, Vision-based Drone Flight: from Simulation to Reality
We present our latest research in learning deep sensorimotor policies for
agile, vision-based quadrotor flight. We show methodologies for the successful
transfer of such policies from simulation to the real world. In addition, we
discuss the open research questions that still need to be answered to improve
the agility and robustness of autonomous drones toward human-pilot performance
Calibration of evolutionary diagnostics in high-mass star formation
The evolutionary classification of massive clumps that are candidate
progenitors of high-mass young stars and clusters relies on a variety of
independent diagnostics based on observables from the near-infrared to the
radio. A promising evolutionary indicator for massive and dense
cluster-progenitor clumps is the L/M ratio between the bolometric luminosity
and the mass of the clumps. With the aim of providing a quantitative
calibration for this indicator we used SEPIA/APEX to obtain CH3C2H(12-11)
observations, that is an excellent thermometer molecule probing densities >
10^5 cm^-3 , toward 51 dense clumps with M>1000 solar masses, and uniformly
spanning -2 < Log(L/M) < 2.3.
We identify three distinct ranges of L/M that can be associated to three
distinct phases of star formation in massive clumps. For L/M <1 no clump is
detected in CH3C2H , suggesting an inner envelope temperature below 30K. For 1<
L/M < 10 we detect 58% of the clumps, with a temperature between 30 and 35 K
independently from the exact value of L/M; such clumps are building up
luminosity due to the formation of stars, but no star is yet able to
significantly heat the inner clump regions. For L/M> 10 we detect all the
clumps, with a gas temperature rising with Log(L/M), marking the appearance of
a qualitatively different heating source within the clumps; such values are
found towards clumps with UCHII counterparts, suggesting that the quantitative
difference in T - L/M behaviour above L/M >10 is due to the first appearance of
ZAMS stars in the clumps.Comment: Astrophysical Journal Letters, Accepte
Deep Drone Racing: From Simulation to Reality with Domain Randomization
Dynamically changing environments, unreliable state estimation, and operation
under severe resource constraints are fundamental challenges that limit the
deployment of small autonomous drones. We address these challenges in the
context of autonomous, vision-based drone racing in dynamic environments. A
racing drone must traverse a track with possibly moving gates at high speed. We
enable this functionality by combining the performance of a state-of-the-art
planning and control system with the perceptual awareness of a convolutional
neural network (CNN). The resulting modular system is both platform- and
domain-independent: it is trained in simulation and deployed on a physical
quadrotor without any fine-tuning. The abundance of simulated data, generated
via domain randomization, makes our system robust to changes of illumination
and gate appearance. To the best of our knowledge, our approach is the first to
demonstrate zero-shot sim-to-real transfer on the task of agile drone flight.
We extensively test the precision and robustness of our system, both in
simulation and on a physical platform, and show significant improvements over
the state of the art.Comment: Accepted as a Regular Paper to the IEEE Transactions on Robotics
Journal. arXiv admin note: substantial text overlap with arXiv:1806.0854
Polynomial evaluation over finite fields: new algorithms and complexity bounds
An efficient evaluation method is described for polynomials in finite fields. Its complexity is shown to be lower than that of standard techniques, when the degree of the polynomial is large enough compared to the field characteristic. Specifically, if n is the degree of the polynomiaI, the asymptotic complexity is shown to be , versus O(n) of classical algorithms. Applications to the syndrome computation in the decoding of Reed-Solomon codes are highlighte
- …