12,105 research outputs found
Integrating security in a group oriented distributed system
A distributed security architecture is proposed for incorporation into group oriented distributed systems, and in particular, into the Isis distributed programming toolkit. The primary goal of the architecture is to make common group oriented abstractions robust in hostile settings, in order to facilitate the construction of high performance distributed applications that can tolerate both component failures and malicious attacks. These abstractions include process groups and causal group multicast. Moreover, a delegation and access control scheme is proposed for use in group oriented systems. The focus is the security architecture; particular cryptosystems and key exchange protocols are not emphasized
Origin of the anapole condition as revealed by a simple expansion beyond the toroidal multipole
Toroidal multipoles are a topic of increasing interest in the nanophotonics
and metamaterials communities. In this paper, we separate out the toroidal
multipole components of multipole expansions in polar coordinates (two- and
three-dimensional) by expanding the Bessel or spherical Bessel functions. We
discuss the formation of the lowest order of magnetic anapoles from the
interaction between the magnetic toroidal dipole and the magnetic dipole. Our
method also reveals that there are higher order current configurations other
than the electric toroidal multipole that have the same radiation
characteristics as the pure electric dipole. Furthermore, we find that the
anapole condition requires that there is a perfect cancellation of all higher
order current configurations
Short Interests in Real Estate Investment Trusts
We examine short interests in equity real estate investment trusts (REITs) between 1994 and 2001. Our results show that only high levels (the 90th percentile) of short interest are associated with significant negative REIT returns as the bearish content of short interest may have been mitigated by the favorable risk characteristics of real estate securities. In addition, the significant negative relationship between short interest and REIT returns applies only to REITs with poor performance. The result implies that the bearish sentiment of short interest could also be mitigated by good REIT managers in a real estate market that is informationally inefficient. The results of a logistic regression model further show that the short selling of REIT shares can be explained by firm-specific factors such as operating efficiency, fundamental value, and liquidity. Given that short interest is not indiscriminately associated with negative REIT returns and that the short positions are firm-specific, the results are consistent with implications that short interests in REITs represent attempts to make short-term profits rather than general bearishness regarding real estate investments.short interest, real estate investment trusts (REITs)
HFR Code: A Flexible Replication Scheme for Cloud Storage Systems
Fractional repetition (FR) codes are a family of repair-efficient storage
codes that provide exact and uncoded node repair at the minimum bandwidth
regenerating point. The advantageous repair properties are achieved by a
tailor-made two-layer encoding scheme which concatenates an outer
maximum-distance-separable (MDS) code and an inner repetition code. In this
paper, we generalize the application of FR codes and propose heterogeneous
fractional repetition (HFR) code, which is adaptable to the scenario where the
repetition degrees of coded packets are different. We provide explicit code
constructions by utilizing group divisible designs, which allow the design of
HFR codes over a large range of parameters. The constructed codes achieve the
system storage capacity under random access repair and have multiple repair
alternatives for node failures. Further, we take advantage of the systematic
feature of MDS codes and present a novel design framework of HFR codes, in
which storage nodes can be wisely partitioned into clusters such that data
reconstruction time can be reduced when contacting nodes in the same cluster.Comment: Accepted for publication in IET Communications, Jul. 201
Absolutely Continuous Representations and a Kaplansky Density Theorem for Free Semigroup Algebras
We introduce notions of absolutely continuous functionals and representations
on the non-commutative disk algebra . Absolutely continuous functionals
are used to help identify the type L part of the free semigroup algebra
associated to a -extendible representation . A -extendible
representation of is ``regular'' if the absolutely continuous part
coincides with the type L part. All known examples are regular. Absolutely
continuous functionals are intimately related to maps which intertwine a given
-extendible representation with the left regular representation. A simple
application of these ideas extends reflexivity and hyper-reflexivity results.
Moreover the use of absolute continuity is a crucial device for establishing a
density theorem which states that the unit ball of is weak-
dense in the unit ball of the associated free semigroup algebra if and only if
is regular. We provide some explicit constructions related to the
density theorem for specific representations. A notion of singular functionals
is also defined, and every functional decomposes in a canonical way into the
sum of its absolutely continuous and singular parts.Comment: 26 pages, prepared with LATeX2e, submitted to Journal of Functional
Analysi
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