2,176 research outputs found
Quantum Optical Communication in the presence of strong attenuation noise
No full textIs quantum communication possible over an optical fibre with transmissivity
? The answer is well known to be negative if the environment
with which the incoming signal interacts is initialised in a thermal state.
However, in [PRL 125:110504, 2020] the quantum capacity was found to be always
bounded away from zero for all , a phenomenon dubbed "die-hard
quantum communication" (D-HQCOM), provided that the initial environment state
can be chosen appropriately (depending on ). Here we show an even
stronger version of D-HQCOM in the context of entanglement-assisted classical
communication: entanglement assistance and control of the environment enable
communication with performance at least equal to that of the ideal case of
absence of noise, even if is arbitrarily small. These two phenomena
of D-HQCOM have technological potential provided that we are able to control
the environment. How can we achieve this? Our second main result answers this
question. Here we provide a fully consistent protocol to activate the phenomena
of D-HQCOM without directly accessing the environment state. This is done by
sending over the channel "trigger signals", i.e. signals which do not encode
information, prior to the actual communication, with the goal of modifying the
environment in an advantageous way. This is possible thanks to the memory
effects which arise when the sender feeds signals separated by a sufficiently
short temporal interval. Our results may offer a concrete scheme to communicate
across arbitrarily long optical fibres, without using quantum repeaters. As a
by-product of our analysis, we derive a simple Kraus representation of the
thermal attenuator exploiting the associated Lindblad master equation.Comment: 38 pages, 12 figures. The present paper serves as the companion to
the paper [F. A. Mele, L. Lami, and V. Giovannetti. Restoring quantum
communication efficiency over high loss optical fibres. Preprint
arXiv:2204.13128, 2022], by providing proofs of the results stated there and
additional developments. In v3 minor typos have been fixe
Una scuola accademica di arte sacra nella Torino di don Bosco, in Kermes n.118
No full textAn accademic sacred art school in the don Bosco in the city of Torino, between XIX and XX century. Multispectral and stylistic anlysi
Political cycles in income from privatization: The case of Albania
No full textThe phenomenon of manipulation of the economy by the incumbent for electoral purpose is called Political Business Cycles (PBC). Using policy control economic instruments, such as fiscal and monetary instruments, governments may manipulate the economy to gain electoral advantage by producing growth and decreasing unemployment before elections. Earlier research on PBC in Albania found clear evidence of fiscal expansion before elections. In addition to increased income from taxes and borrowing, another source of financing the increased fiscal expansion in transition countries may be income from privatization, which is also the object of the analysis of this paper. In our analysis we apply standard econometric approach, used widely for research related to PBC. We test if income from privatization increases before elections. We find statistically significant increase of income from privatization before general (parliamentary) elections, which may lead us to conclude that one of the reasons may be to finance increased expenditures before elections. Another motivation, behind this behavior of the incumbent, may be rent - seeking. These results are of particular interest, as it is for the first time that income from privatization is analyzed in conjunction with PBC. --Albania,Political Business Cycle,Privatization
Aspetti della terapia nel Corpus Hippocraticum
No full textAtti del «IX Colloque International Hippocratique» (Pisa 25-29 settembre 1996), a cura di I. Garofalo, A. L., D. Manetti, A. Roselli, Accademia toscana di Scienze e Lettere «La Colombaria», vol. 183, Leo S. Olschki, Firenz
La questione ucraina fra '800 e '900
No full textIl libro è stato concepito per fornire un quadro dell''evolversi delle vicende ucraine fra il Medioevo e la Prima guerra mondiale, tenendo conto del fatto che in Italia non esisteva un lavoro d''insieme sulla storia ucraina, benché l''Ucraina fosse indipendente dal 1991. Il lavoro si concentra sul periodo a cavallo fra ''800 e ''900, quando si afferma la "questione nazionale" ucraina nel contesto dell''Impero russo e dell''Impero asburgico. Si sono analizzate le dinamiche politiche, economiche e sociali proprie di tutti i territori ucraini che ricadevano sotto la sovranità dei due imperi. Particolare attenzione è stata riservata allo sviluppo dei movimenti politici e culturali ucraini, specialmente nel periodo fra la Prima guerra mondiale e la nascita dell''URSS, cercando di analizzare le ragioni interne ed internazionali per le quali il progetto di una Ucraina unita ed indipendente non riuscì allora a realizzarsi. Il libro è corredato da un''ampia bibliografia che, per venire incontro al pubblico italiano, dà conto soprattutto delle fonti e dei titoli disponibili in lingue occidentali, ma anche, più limitatamente, in ucraino, polacco e russo, che possono servire come base per ulteriori approfondimenti
Entanglement–breaking indices
No full textWe study a set of new functionals (called entanglement--breaking indices)
which characterize how many local iterations of a given (local) quantum channel
are needed in order to completely destroy the entanglement between the system
of interest over which the transformation is defined and an external ancilla.
The possibility of contrasting the noisy effects introduced by the channel
iterations via the action of intermediate (\it filtering) transformations is
analyzed. We provide some examples in which our functionals can be exactly
calculated. The differences between unitary and non-unitary filtering
operations are analyzed showing that, at least for systems of dimension
larger than or equal to 3, the non-unitary choice is preferable (the gap
between the performances of the two cases being divergent in some cases). For
(qubit case) on the contrary no evidences of the presence of such gap is
revealed: we conjecture that for this special case unitary filtering
transformations are optimal. The scenario in which more general filtering
protocols are allowed is also discussed in some detail. The case of a
depolarizing noise acting on a two--qubit system is exactly solved in a general
case
Using species-habitat networks to inform agricultural landscape management for spiders
No full textLand-use intensification is a major threat to arthropods across agricultural landscapes. To mitigate these negative effects through appropriate landscape management, it is necessary to understand how entire species communities respond to land-use at the landscape scale. We performed a whole-landscape sampling of spiders in 300 habitat patches across 15 landscapes and built species-habitat networks to evaluate the impact of compositional and configurational simplification on network modularity and habitat specialisation. Within each landscape mosaic, spiders showed a high degree of habitat selectivity, i.e. patches of the same habitat type tended to cluster into modules that rarely interacted with each other. Although spiders are expected to disperse between habitat patches more often when landscapes are fragmented, their high modularity and habitat selectivity were not influenced by edge density. However, modularity was the highest at intermediate cover of semi-natural habitats, probably due to the simultaneous presence of multiple habitats with sufficient area to support the associated specialist species. Despite the high habitat selectivity, perennial crops and meadows seemed to play a central role in connecting different habitat modules across the landscapes. On the contrary, forest and hedgerows hosted very distinct species communities that did not occur outside woody habitats. Encouraging the spill-over of spiders from semi-natural habitats to crops to enhance biological control might be more effective for the better-connected permanent crops, while for annual crops it would be more effective to improve local field quality for crop specialists or to introduce open semi-natural habitats such as meadows
Electronic Circular Dichroism in Exciton-Coupled Dimers: Vibronic Spectra from a General All-Coordinates Quantum-Dynamical Approach
No full textWe present a computational approach of general applicability to simulate the vibronic line shapes of absorption and electronic circular dichroism (ECD) spectra in rigid exciton-coupled dimers based on a time-dependent expression of the spectra and quantum dynamical calculations. We adopt a diabatic model of interacting states localized on the monomers whose electronic potential energy surfaces are described within harmonic approximation, including the effect of displacements, frequency changes, and normal-mode mixings. Spectra that fully account for the effect of all nuclear degrees of freedom of the system are obtained through a hierarchical representation of the Hamiltonian in blocks, defined so that few blocks accurately describe the short-time dynamics of the system. With this approach, on the ground of time-dependent density functional theory calculations, we simulate the absorption and ECD spectra of a covalent compound representing a "dimer" of anthracene, in the spectral region of the 1La monomer transition, obtaining results in good agreement with the experiment
Ritratto del poeta, Alessandro Lami
No full textAlessandro Lami is the author of a text surely known by those who deal with Lombard art history of the sixteenth century (his Discorso intorno alla scoltura e pittura, published in Cremona, Cristoforo Draconi, 1584, which is actually the praise of the painter Bernardino Campi, excluded by Giorgio Vasari’s Vite). But he is also a poet, the author, in his youth, of a long poem about the most illustrious Cremonese of all times (Sogno non meno piacevole che morale, Cremona, Draconi, 1572) and, in his late age, of a collection of Rime spirituali (Pavia, per gli heredi di Girolamo Bartoli, 1598). His biographical outlines (e.g. dates of birth and death) as well as the main facts of his life, have always been unknown to scholars. To establish some fundamental turning points in his life (thanks both to unpublished archival documentation and to ancient and modern sources) may be useful to better understand his effective role in the career of Bernardino Campi, one of the most important painters in Milan in the mid-16th century.Alessandro Lami è autore di un testo ben noto a chi si occupa di storia dell’arte lombarda del Cinquecento (il Discorso intorno alla scoltura e pittura, pubblicato a Cremona, per i tipi di Cristoforo Draconi, nel 1584, che è in realtà l’elogio del pittore Bernardino Campi, escluso dalle Vite di Giorgio Vasari), ma è anche un poeta, autore, in gioventù, di un lungo elogio dei cremonesi illustri in ottava rima (Sogno non meno piacevole che morale, Cremona, Draconi, 1572) e, in tarda età, di una raccolta di Rime spirituali (Pavia, per gli heredi di Girolamo Bartoli, 1598). I suoi contorni biografici, così come i principali fatti della sua vita, sono da sempre ignoti agli studiosi, come dimostra l’oscillazione degli estremi anagrafici nella letteratura specialistica. Stabilire alcuni punti fondamentali della sua vita, sulla scorta di documentazione d’archivio inedita e di un confronto con le fonti antiche e moderne, sarà utile anche per comprendere il suo ruolo effettivo nel percorso di Bernardino Campi, uno dei pittori più importanti nella Milano della metà del XVI secolo
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