5,218 research outputs found
Understanding and controlling the ingress of driven rain through exposed, solid wall masonry structures
Long term performance of historic buildings can be affected by many environmental factors, some of which become more apparent as the competence of the fabric deteriorates. Many tall historic buildings suffer from water ingress when exposed to driving rain conditions, particularly church towers in the south west of England. It is important to recognise that leakage can occur not only through flaws in the roof of a building but also through significant thicknesses of solid masonry. Identification of the most appropriate intervention requires an understanding of the way in which water might enter the structure and the assessment of potential repair options. While the full work schedule used an integrated assessment involving laboratory, field and archival work to assess the repairs which might be undertaken on these solid wall structures, this paper focuses on the laboratory work done to inform the writing of a Technical Advice Note on the effects of wind driven rain and moisture movement in historic structures (English Heritage, 2012). The laboratory work showed that grouting and rendering was effective at reducing water penetration without retarding drying rates, but that use of internal plastering also had a very beneficial effect
Interest-Based Access Control for Content Centric Networks (extended version)
Content-Centric Networking (CCN) is an emerging network architecture designed
to overcome limitations of the current IP-based Internet. One of the
fundamental tenets of CCN is that data, or content, is a named and addressable
entity in the network. Consumers request content by issuing interest messages
with the desired content name. These interests are forwarded by routers to
producers, and the resulting content object is returned and optionally cached
at each router along the path. In-network caching makes it difficult to enforce
access control policies on sensitive content outside of the producer since
routers only use interest information for forwarding decisions. To that end, we
propose an Interest-Based Access Control (IBAC) scheme that enables access
control enforcement using only information contained in interest messages,
i.e., by making sensitive content names unpredictable to unauthorized parties.
Our IBAC scheme supports both hash- and encryption-based name obfuscation. We
address the problem of interest replay attacks by formulating a mutual trust
framework between producers and consumers that enables routers to perform
authorization checks when satisfying interests from their cache. We assess the
computational, storage, and bandwidth overhead of each IBAC variant. Our design
is flexible and allows producers to arbitrarily specify and enforce any type of
access control on content, without having to deal with the problems of content
encryption and key distribution. This is the first comprehensive design for CCN
access control using only information contained in interest messages.Comment: 11 pages, 2 figure
Large substitution boxes with efficient combinational implementations
At a fundamental level, the security of symmetric key cryptosystems ties back to Claude Shannon\u27s properties of confusion and diffusion. Confusion can be defined as the complexity of the relationship between the secret key and ciphertext, and diffusion can be defined as the degree to which the influence of a single input plaintext bit is spread throughout the resulting ciphertext. In constructions of symmetric key cryptographic primitives, confusion and diffusion are commonly realized with the application of nonlinear and linear operations, respectively. The Substitution-Permutation Network design is one such popular construction adopted by the Advanced Encryption Standard, among other block ciphers, which employs substitution boxes, or S-boxes, for nonlinear behavior. As a result, much research has been devoted to improving the cryptographic strength and implementation efficiency of S-boxes so as to prohibit cryptanalysis attacks that exploit weak constructions and enable fast and area-efficient hardware implementations on a variety of platforms. To date, most published and standardized S-boxes are bijective functions on elements of 4 or 8 bits. In this work, we explore the cryptographic properties and implementations of 8 and 16 bit S-boxes. We study the strength of these S-boxes in the context of Boolean functions and investigate area-optimized combinational hardware implementations. We then present a variety of new 8 and 16 bit S-boxes that have ideal cryptographic properties and enable low-area combinational implementations
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Improved Log(gf) Values for Lines of Ti I and Abundance Determinations in the Photospheres of the Sun and Metal-Poor Star HD 84937 (Accurate Transition Probabilities for Ti I)
New atomic transition probability measurements for 948 lines of Ti I are reported. Branching fractions from Fourier transform spectra and from spectra recorded using a 3 m echelle spectrometer are combined with published radiative lifetimes from laser-induced fluorescence measurements to determine these transition probabilities. Generally good agreement is found in comparisons to the NIST Atomic Spectra Database. The new Ti I data are applied to re-determine the Ti abundance in the photospheres of the Sun and metal-poor star HD 84937 using many lines covering a range of wavelength and excitation potential to explore possible non-local thermal equilibrium effects. The variation of relative Ti/Fe abundance with metallicity in metal-poor stars observed in earlier studies is supported in this study.NSF AST-1211055, AST-0908978, AST-1211585NSF REU grant AST-1004881ESO Science Archive Facility 073.D-0024, 266.D-5655NASA NAS 5-26555Astronom
In vitro characterization of cadmium and zinc uptake via the gastrointestinal tract of rainbow trout (Oncorhynchus mykiss): interactive effects and the influence of calcium
An in vitro gut sac technique was employed to study whether Cd and Zn uptake mechanisms in the
gastro-intestinal tract of the rainbow trout are similar to those at the gills, where both metals are taken
up via the Ca transport pathway. Metal accumulation in surface mucus, in the mucosal epithelium, and
transport into the blood space were assayed using radiolabelled Cd or Zn concentrations of 50 mol L−1
in the luminal (internal) saline. Elevated luminal Ca (10 or 100 mmol L−1 versus 1 mmol L−1) reduced Cd
uptake into all three phases by approximately 60% in the stomach, but had no effect in the anterior,
mid, or posterior intestine. This finding is in accordance with recent in vivo evidence that Ca is taken
up mainly via the stomach, and that high [Ca] diets inhibit Cd accumulation from the food specifically
in this section of the tract. In contrast, 10 mmol L−1 luminal Ca had no effect on Zn transport in any
section, whereas 100 mmol L−1 Ca stimulated Zn uptake, by approximately threefold, into all three phases
in the stomach only. There was no influence of elevated luminal Zn (10 mmol L−1) on Cd uptake in the
stomach or anterior intestine, or of high Cd (10 mmol L−1) on Zn uptake in these sections. However, high
[Zn] stimulated Cd transport into the blood space but inhibited accumulation in the mucosal epithelium
and/or mucus-binding in the mid and posterior intestine, whereas high [Cd] exerted a reciprocal effect
in the mid-intestine only. We conclude that Cd uptake occurs via an important Ca-sensitive mechanism
in the stomach which is different from that at the gills, while Cd transport mechanisms in the intestine
are not directly Ca-sensitive. Zn uptake does not appear to involve Ca uptake pathways, in contrast to the
gills. These results are discussed in the context of other possible Cd and Zn transport pathways, and the
emerging role of the stomach as an organ of divalent metal uptake.Natural Sciences and Engineering Research Council of Canada CRD Program, the International Lead
Zinc Research Organization, the International Zinc Association, the
Nickel Producers Environmental Research Association, the International Copper Association, the Copper Development Association,
Teck-Cominco, Xstrata (Noranda-Falconbridge), and Inc
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