1,721,617 research outputs found
Repeatable classical one-time-pad crypto-system with quantum mechanics
Full text linkClassical one-time-pad key can only be used once. We show in this Letter that
with quantum mechanical information media classical one-time-pad key can be
repeatedly used. We propose a specific realization using single photons. The
reason why quantum mechanics can make the classical one-time-pad key repeatable
is that quantum states can not be cloned and eavesdropping can be detected by
the legitimate users. This represents a significant difference between
classical cryptography and quantum cryptography and provides a new tool in
designing quantum communication protocols and flexibility in practical
applications.
Note added: This work was submitted to PRL as LU9745 on 29 July 2004, and the
decision was returned on 11 November 2004, which advised us to resubmit to some
specialized journal, probably, PRA, after revision. We publish it here in
memory of Prof. Fu-Guo Deng (1975.11.12-2019.1.18), from Beijing Normal
University, who died on Jan 18, 2019 after two years heroic fight with
pancreatic cancer. In this work, we designed a protocol to repeatedly use a
classical one-time-pad key to transmit ciphertext using single photon states.
The essential idea was proposed in November 1982, by Charles H. Bennett, Gilles
Brassard, Seth Breidbart, which was rejected by Fifteenth Annual ACM Symposium
on Theory of Computing, and remained unpublished until 2014, when they
published the article, Quantum Cryptography II: How to re-use a one-time pad
safely even if P=NP, Natural Computing (2014) 13:453-458, DOI
10.1007/s11047-014-9453-6. We worked out this idea independently. This work has
not been published, and was in cooperated into quant-ph 0706.3791 (Kai Wen, Fu
Guo Deng, Gui Lu Long, Secure Reusable Base-String in Quantum Key
Distribution), and quant-ph 0711.1632 (Kai Wen, Fu-Guo Deng, Gui Lu Long,
Reusable Vernam Cipher with Quantum Media).Comment: Submitted to PRL in 2004. We designed a protocol to use repeatedly a
one-time-pad to transmit ciphertext using single photons. We publish it here
in memory of Prof. Fu-Guo Deng (1975.11.12-2019.1.18). Two related reference
numbers are corrected:quant-ph 0706.3791 & quant-ph 0711.163
Gamma-ray activity of Seyfert galaxies and constraints on hot accretion flows
No full textAims. We check how the Fermi/LAT data constrain the physics of hot accretion flows that are most likely present in low-luminosity AGNs.
Methods. Using a precise model of emission from hot flows, we studied the flow γ-ray emission resulting from proton-proton interactions. We explored the dependence of the γ-ray luminosity on the accretion rate, the black hole spin, the magnetic field strength, the electron heating efficiency, and the particle distribution. Then, we compared the hadronic γ-ray luminosities predicted by the model for several nearby Seyfert 1 galaxies with the results of our analysis of 6.4 years of Fermi/LAT observations of these AGNs.
Results. In agreement with previous studies, we find a significant γ-ray detection in NGC 6814. We were only able to derive upper limits for the remaining objects, although we report marginally significant (~3σ) signals at the positions of NGC 4151 and NGC 4258. The derived upper limits for the flux above 1 GeV allow us to constrain the proton acceleration efficiency in flows with heating of electrons dominated by Coulomb interactions, which case is favored by the X-ray spectral properties. In these flows, at most ~10% of the accretion power can be used for a relativistic acceleration of protons. Upper limits for the flux below 1 GeV can constrain the magnetic field strength and black hole spin value; we find these constraints for NGC 7213 and NGC 4151. We also note that the spectral component above ~4 GeV previously found in the Fermi/LAT data of Centaurus A may be due to hadronic emission from a flow within the above constraint. We rule out this origin of the γ-ray emission for NGC 6814. For models with a strong magnetohydrodynamic heating of electrons, the hadronic γ-ray fluxes are below the Fermi/LAT sensitivity even for the closest AGNs. In these models, nonthermal Compton radiation may dominate in the γ-ray range if electrons are efficiently accelerated and the acceleration index is hard; for the index ≃2, the LAT upper limits constrain the fraction of accretion power used for such an acceleration to at most ~5%. Finally, we note that the three Seyfert 2 galaxies with high starburst activity NGC 4595, NGC 1068, and Circinus show an interesting correlation of their γ-ray luminosities with properties of their active nuclei, and we discuss this in the context of the hot flow model
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Radiative efficiency of hot accretion flows
No full textOver the past few years, our understanding of hot accretion flows has been improved significantly by two findings: (i) only a small fraction of the accretion flow available at the outer boundary can finally fall on to the black hole, while most of it is lost in the outflow; (ii) electrons can directly receive a large fraction of the viscously dissipated energy in the accretion flow (i. e. delta similar to 0.1-0.5). The radiative efficiency of the hot accretion flow when these two findings are taken into account has not yet been systematically studied, and this is the subject of our paper. We consider two regimes of the hot accretion model: advection-dominated accretion flows that lie in the regime of the low accretion rate, less than or similar to 10 alpha L-2(Edd)/c(2), and the luminous hot accretion flows (LHAFs) that lie above this accretion rate. For the LHAFs, we assume that the accretion flow has a two-phase structure above a certain accretion rate, and we adopt a simplification in our calculation of the dynamics. Our results indicate that the radiative efficiency of hot accretion flow increases with the accretion rate and that it is greatly enhanced by the direct viscous heating to electrons, compared to the previous case of delta << 1. When the accretion rate is high, the radiative efficiency of the hot accretion flow is comparable to that of a standard thin disc. We present fitting formulae of radiative efficiency as a function of accretion rate for various values of delta
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