920 research outputs found
Structures and orientational transitions in thin films of tilted hexatic smectics
We present detailed systematic studies of structural transformations in thin
liquid crystal films with the smectic-C to hexatic phase transition. For the
first time all possible structures reported in the literature are observed for
one material (5 O.6) at the variation of temperature and thickness. In unusual
modulated structures the equilibrium period of stripes is twice with respect to
the domain size. We interpret these patterns in the frame work of
phenomenological Landau type theory, as equilibrium phenomena produced by a
natural geometric frustration in a system having spontaneous splay distortion.Comment: 7 pages, 6 figure
Diamagnetic energy measurement during the first operational phase at the Wendelstein 7-X stellarator
Key Rotation for Authenticated Encryption
A common requirement in practice is to periodically rotate the keys used to
encrypt stored data. Systems used by Amazon and Google do so using a hybrid
encryption technique which is eminently practical but has questionable
security in the face of key compromises and does not provide full key
rotation. Meanwhile, symmetric updatable encryption schemes (introduced by
Boneh et al. CRYPTO 2013) support full key rotation without performing
decryption: ciphertexts created under one key can be rotated to ciphertexts
created under a different key with the help of a re-encryption token. By
design, the tokens do not leak information about keys or plaintexts and so
can be given to storage providers without compromising security. But the
prior work of Boneh et al. addresses relatively weak confidentiality goals
and does not consider integrity at all. Moreover, as we show, a subtle issue
with their concrete scheme obviates a security proof even for confidentiality
against passive attacks.
This paper presents a systematic study of updatable Authenticated Encryption
(AE). We provide a set of security notions that strengthen those in prior
work. These notions enable us to tease out real-world security requirements
of different strengths and build schemes that satisfy them efficiently. We
show that the hybrid approach currently used in industry achieves relatively
weak forms of confidentiality and integrity, but can be modified at low cost
to meet our stronger confidentiality and integrity goals. This leads to a
practical scheme that has negligible overhead beyond conventional AE. We then
introduce re-encryption indistinguishability, a security notion that formally
captures the idea of fully refreshing keys upon rotation. We show how to
repair the scheme of Boneh et al., attaining our stronger confidentiality
notion. We also show how to extend the scheme to provide integrity, and we
prove that it meets our re- encryption indistinguishability notion. Finally,
we discuss how to instantiate our scheme efficiently using off-the-shelf
cryptographic components (AE, hashing, elliptic curves). We report on the
performance of a prototype implementation, showing that fully secure key
rotations can be performed at a throughput of approximately 116 kB/s
Topology of "white" stars in relativistic fragmentation of light nuclei
In the present paper, experimental observations of the multifragmentation
processes of light relativistic nuclei carried out by means of emulsions are
reviewed. Events of the type of "white" stars in which the dissociation of
relativistic nuclei is not accompanied by the production of mesons and the
target-nucleus fragments are considered.
A distinctive feature of the charge topology in the dissociation of the Ne,
Mg, Si, and S nuclei is an almost total suppression of the binary splitting of
nuclei to fragments with charges higher than 2. The growth of the nuclear
fragmentation degree is revealed in an increase in the multiplicity of singly
and doubly charged fragments with decreasing charge of the non-excited part of
the fragmenting nucleus.
The processes of dissociation of stable Li, Be, B, C, N, and O isotopes to
charged fragments were used to study special features of the formation of
systems consisting of the lightest , d, and t nuclei. Clustering in
form of the He nucleus can be detected in "white" stars via the
dissociation of neutron-deficient Be, B, C, and N isotopes.Comment: 20 pages, 3 figures, 9 tables, conference: Conference on Physics of
Fundamental Interactions, Moscow, Russia, 1-5 Mar 2004.(Author's translation
Consumer credit information systems: A critical review of the literature. Too little attention paid by lawyers?
This paper reviews the existing literature on consumer credit reporting, the most extensively used instrument to overcome information asymmetry and adverse selection problems in credit markets. Despite the copious literature in economics and some research in regulatory policy, the legal community has paid almost no attention to the legal framework of consumer credit information systems, especially within the context of the European Union. Studies on the topic, however, seem particularly relevant in view of the establishment of a single market for consumer credit. This article ultimately calls for further legal research to address consumer protection concerns and inform future legislation
Insights into the catalytic production of hydrogen from propane in the presence of oxygen: cooperative presence of vanadium and gold catalysts
[EN] H-2 and propylene can be obtained from propane and oxygen in defect using appropriate catalysts. Meanwhile propylene is formed from propane via oxidative or non-oxidative dehydrogenation, molecular hydrogen can be obtained from several reactions such as propane dehydrogenation, coke formation and water gas shift. It has been observed that a gold catalyst hardly activates propane and no H-2 was detected, whereas using vanadium oxide a relatively high concentration of propylene and H-2 was obtained. Interestingly, the simultaneous use of vanadium oxide and gold has meant a higher hydrogen production, higher in a 40% than that of the catalyst containing only vanadium oxide. This performance has been. related to the capacity of gold to activate CO in the water gas shift reaction. (C) 2015 Elsevier B.V. All rights reserved.The authors would like to acknowledge the DGICYT in Spain (CTQ2012-37925-C03-1, CTQ2012-37925-C03-2 and CTQ2012-37984-C02-01) for financial support We also thank the University of Valencia and SCSIE-UV for assistance. J.M. Lopez would also like to thank Spanish MICINN and CSIC for funding his Ramon y Cajal contract (RYC-2009-04483).Garcia, T.; Lopez, JM.; López Nieto, JM.; Sanchis, R.; Dejoz, A.; Vazquez, MI.; Solsona, B. (2015). Insights into the catalytic production of hydrogen from propane in the presence of oxygen: cooperative presence of vanadium and gold catalysts. Fuel Processing Technology. 134:290-296. https://doi.org/10.1016/j.fuproc.2015.02.012S29029613
NA61/SHINE facility at the CERN SPS: beams and detector system
NA61/SHINE (SPS Heavy Ion and Neutrino Experiment) is a multi-purpose
experimental facility to study hadron production in hadron-proton,
hadron-nucleus and nucleus-nucleus collisions at the CERN Super Proton
Synchrotron. It recorded the first physics data with hadron beams in 2009 and
with ion beams (secondary 7Be beams) in 2011.
NA61/SHINE has greatly profited from the long development of the CERN proton
and ion sources and the accelerator chain as well as the H2 beamline of the
CERN North Area. The latter has recently been modified to also serve as a
fragment separator as needed to produce the Be beams for NA61/SHINE. Numerous
components of the NA61/SHINE set-up were inherited from its predecessors, in
particular, the last one, the NA49 experiment. Important new detectors and
upgrades of the legacy equipment were introduced by the NA61/SHINE
Collaboration.
This paper describes the state of the NA61/SHINE facility - the beams and the
detector system - before the CERN Long Shutdown I, which started in March 2013
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