10,615 research outputs found
IFLA Congress in Italy for the fourth time , Libraries create futures: building on cultural heritage : final programme, Milan, Italy, 23-27 August 2009
Welcome of the Chair of the Italian National Committee. IFLA Congress comes back to Italy for the fourth time: 1929, 1951, 1964, and now 2009. In June 1929, in the Marciana Library (Venice), Mr. Isak Collijn announced the name of the Library Federation, and the Italian librarian Vincenzo Fago read the Statute, dated "Florence, June 25, 1929": 1) The name of this organization shall be the International Federation of Library Associations. 2) The object of the Federation shall be to promote international library cooperation. One year after, in 1930, the Italian Library Association (AIB) was founded
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
Solid-State Effects on the Optical Excitation of Push-Pull Molecular J-Aggregates by First-Principles Simulations
J-aggregates are a class of low-dimensional molecular crystals which display
enhanced interaction with light. These systems show interesting optical
properties as an intense and narrow red-shifted absorption peak (J-band) with
respect to the spectrum of the corresponding monomer. The need to theoretically
investigate optical excitations in J-aggregates is twofold: a thorough
first-principles description is still missing and a renewed interest is rising
recently in understanding the nature of the J-band, in particular regarding the
collective mechanisms involved in its formation. In this work, we investigate
the electronic and optical properties of a J-aggregate molecular crystal made
of ordered arrangements of organic push-pull chromophores. By using a time
dependent density functional theory approach, we assess the role of the
molecular packing in the enhancement and red shift of the J-band along with the
effects of confinement in the optical absorption, when moving from bulk to
low-dimensional crystal structures. We simulate the optical absorption of
different configurations (i.e., monomer, dimers, a polymer chain, and a
monolayer sheet) extracted from the bulk crystal. By analyzing the induced
charge density associated with the J-band, we conclude that it is a
longitudinal excitation, delocalized along parallel linear chains and that its
overall red shift results from competing coupling mechanisms, some giving red
shift and others giving blue shift, which derive from both coupling between
transition densities and renormalization of the single-particle energy levels.Comment: This is the published version of the work, distributed under the
terms of the ACS AuthorChoice licence
https://pubs.acs.org/page/policy/authorchoice_termsofuse.htm
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 Coding Theoretic Study on MLL proof nets
Coding theory is very useful for real world applications. A notable example
is digital television. Basically, coding theory is to study a way of detecting
and/or correcting data that may be true or false. Moreover coding theory is an
area of mathematics, in which there is an interplay between many branches of
mathematics, e.g., abstract algebra, combinatorics, discrete geometry,
information theory, etc. In this paper we propose a novel approach for
analyzing proof nets of Multiplicative Linear Logic (MLL) by coding theory. We
define families of proof structures and introduce a metric space for each
family. In each family, 1. an MLL proof net is a true code element; 2. a proof
structure that is not an MLL proof net is a false (or corrupted) code element.
The definition of our metrics reflects the duality of the multiplicative
connectives elegantly. In this paper we show that in the framework one
error-detecting is possible but one error-correcting not. Our proof of the
impossibility of one error-correcting is interesting in the sense that a proof
theoretical property is proved using a graph theoretical argument. In addition,
we show that affine logic and MLL + MIX are not appropriate for this framework.
That explains why MLL is better than such similar logics.Comment: minor modification
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