1,058 research outputs found
Indentation of an elastic arch on a frictional substrate: Pinning, unfolding and snapping
We investigate the morphology and mechanics of a naturally curved elastic
arch loaded at its center and frictionally supported at both ends on a flat,
rigid substrate. Through systematic numerical simulations, we classify the
observed behaviors of the arch into three distinct types of configurations in
terms of the arch geometry and the coefficient of static friction with the
substrate. A linear theory is developed based on a planar elastica model
combined with Amontons-Coulomb's frictional law, which quantitatively explains
the numerically constructed phase diagram. The snapping transition of a loaded
arch in a sufficiently large indentation regime, which involves a discontinuous
force jump, is numerically observed. The proposed model problem allows a fully
analytical investigation and demonstrates a rich variety of mechanical
behaviors owing to the interplay between elasticity, geometry, and friction.
This study provides a basis for understanding more common but complex systems,
such as a cylindrical shell subjected to a concentrated load and simultaneously
supported by frictional contact with surrounding objects
Weakened Random Oracle Models with Target Prefix
Weakened random oracle models (WROMs) are variants of the random oracle model
(ROM). The WROMs have the random oracle and the additional oracle which breaks
some property of a hash function. Analyzing the security of cryptographic
schemes in WROMs, we can specify the property of a hash function on which the
security of cryptographic schemes depends. Liskov (SAC 2006) proposed WROMs and
later Numayama et al. (PKC 2008) formalized them as CT-ROM, SPT-ROM, and
FPT-ROM. In each model, there is the additional oracle to break collision
resistance, second preimage resistance, preimage resistance respectively. Tan
and Wong (ACISP 2012) proposed the generalized FPT-ROM (GFPT-ROM) which
intended to capture the chosen prefix collision attack suggested by Stevens et
al. (EUROCRYPT 2007). In this paper, in order to analyze the security of
cryptographic schemes more precisely, we formalize GFPT-ROM and propose
additional three WROMs which capture the chosen prefix collision attack and its
variants. In particular, we focus on signature schemes such as RSA-FDH, its
variants, and DSA, in order to understand essential roles of WROMs in their
security proofs
Adjustment of oxygen reserve index (ORi™) to avoid excessive hyperoxia during general anesthesia
博士(医学)福島県立医科大
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