302 research outputs found
On the low detection efficiency of disk water megamasers in Seyfert 2 AGN
Disk megamasers are a unique tool to study active galactic nuclei (AGN)
sub-pc environment, and precisely measure some of their fundamental parameters.
While the majority of disk megamasers are hosted in heavily obscured (i.e.,
Seyfert 2, Sy2) AGN, the converse is not true, and disk megamasers are very
rarely found even in obscured AGN. The very low detection rate of such systems
in Sy2 AGN could be due to the geometry of the maser beaming, which requires a
strict edge-on condition. We explore some other fundamental factors which could
play a role in a volume-limited survey of disk megamasers in Sy2 galaxies, most
importantly the radio luminosity.Comment: 2 pages, 2 figures. To appear in the Proceedings IAU Symposium No.
336, 2017 "Astrophysical Masers: Unlocking the Mysteries of the Universe
A History of Until
Until is a notoriously difficult temporal operator as it is both existential
and universal at the same time: A until B holds at the current time instant w
iff either B holds at w or there exists a time instant w' in the future at
which B holds and such that A holds in all the time instants between the
current one and w'. This "ambivalent" nature poses a significant challenge when
attempting to give deduction rules for until. In this paper, in contrast, we
make explicit this duality of until to provide well-behaved natural deduction
rules for linear-time logics by introducing a new temporal operator that allows
us to formalize the "history" of until, i.e., the "internal" universal
quantification over the time instants between the current one and w'. This
approach provides the basis for formalizing deduction systems for temporal
logics endowed with the until operator. For concreteness, we give here a
labeled natural deduction system for a linear-time logic endowed with the new
operator and show that, via a proper translation, such a system is also sound
and complete with respect to the linear temporal logic LTL with until.Comment: 24 pages, full version of paper at Methods for Modalities 2009
(M4M-6
Towards A Theory Of Quantum Computability
We propose a definition of quantum computable functions as mappings between
superpositions of natural numbers to probability distributions of natural
numbers. Each function is obtained as a limit of an infinite computation of a
quantum Turing machine. The class of quantum computable functions is
recursively enumerable, thus opening the door to a quantum computability theory
which may follow some of the classical developments
Quantum Turing Machines Computations and Measurements
Contrary to the classical case, the relation between quantum programming
languages and quantum Turing Machines (QTM) has not being fully investigated.
In particular, there are features of QTMs that have not been exploited, a
notable example being the intrinsic infinite nature of any quantum computation.
In this paper we propose a definition of QTM, which extends and unifies the
notions of Deutsch and Bernstein and Vazirani. In particular, we allow both
arbitrary quantum input, and meaningful superpositions of computations, where
some of them are "terminated" with an "output", while others are not. For some
infinite computations an "output" is obtained as a limit of finite portions of
the computation. We propose a natural and robust observation protocol for our
QTMs, that does not modify the probability of the possible outcomes of the
machines. Finally, we use QTMs to define a class of quantum computable
functions---any such function is a mapping from a general quantum state to a
probability distribution of natural numbers. We expect that our class of
functions, when restricted to classical input-output, will be not different
from the set of the recursive functions.Comment: arXiv admin note: substantial text overlap with arXiv:1504.02817 To
appear on MDPI Applied Sciences, 202
A Logic for Quantum Register Measurements
We know that quantum logics are the most prominent logical systems associated to the lattices of closed Hilbert subspaces. However, what happen if, following a quantum computing perspective, we want to associate a logic to the process of quantum registers measurements? This paper gives an answer to this question, and, quite surprisingly, shows that such a logic is nothing else that the standard propositional intuitionistic logic
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