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21.
In the Horn theory based approach for cryptographic protocol analysis, cryptographic protocols and (Dolev?CYao) intruders are modeled by Horn theories and security analysis boils down to solving the derivation problem for Horn theories. This approach and the tools based on this approach, including ProVerif, have been very successful in the automatic analysis of cryptographic protocols. However, dealing with the algebraic properties of operators, such as the exclusive OR (XOR), which are frequently used in cryptographic protocols has been problematic. In particular, ProVerif cannot deal with XOR. In this paper, we show how to reduce the derivation problem for Horn theories with XOR to the XOR-free case. Our reduction works for an expressive class of Horn theories. A large class of intruder capabilities and protocols that employ the XOR operator can be modeled by these theories. Our reduction allows us to carry out protocol analysis using tools, such as ProVerif, that cannot deal with XOR, but are very efficient in the XOR-free case. We implemented our reduction and, in combination with ProVerif, used it for the fully automatic analysis of several protocols that employ the XOR operator. Among others, our analysis revealed a new attack on an IBM security module. 相似文献
22.
Henrique Moniz Nuno Ferreira Neves Miguel Correia Paulo Ver��ssimo 《Distributed Computing》2011,24(3-4):165-175
Wireless ad-hoc networks are being increasingly used in diverse contexts, ranging from casual meetings to disaster recovery operations. A promising approach is to model these networks as distributed systems prone to dynamic communication failures. This captures transitory disconnections in communication due to phenomena like interference and collisions, and permits an efficient use of the wireless broadcasting medium. This model, however, is bound by the impossibility result of Santoro and Widmayer, which states that, even with strong synchrony assumptions, there is no deterministic solution to any non-trivial form of agreement if n ? 1 or more messages can be lost per communication round in a system with n processes. In this paper we propose a novel way to circumvent this impossibility result by employing randomization. We present a consensus protocol that ensures safety in the presence of an unrestricted number of omission faults, and guarantees progress in rounds where such faults are bounded by ${f \,{\leq}\,\lceil \frac{n}{2} \rceil (n\,{-}\,k)\,{+}\,k\,{-}\,2}$ , where k is the number of processes required to decide, eventually assuring termination with probability 1. 相似文献
23.
J��r?me Schmid Jos�� A. Iglesias?Guiti��n Enrico Gobbetti Nadia Magnenat-Thalmann 《The Visual computer》2011,27(2):85-95
Despite the ability of current GPU processors to treat heavy parallel computation tasks, its use for solving medical image
segmentation problems is still not fully exploited and remains challenging. A lot of difficulties may arise related to, for
example, the different image modalities, noise and artifacts of source images, or the shape and appearance variability of
the structures to segment. Motivated by practical problems of image segmentation in the medical field, we present in this
paper a GPU framework based on explicit discrete deformable models, implemented over the NVidia CUDA architecture, aimed for
the segmentation of volumetric images. The framework supports the segmentation in parallel of different volumetric structures
as well as interaction during the segmentation process and real-time visualization of the intermediate results. Promising
results in terms of accuracy and speed on a real segmentation experiment have demonstrated the usability of the system. 相似文献
24.
Mario A. S. Lizi��r Marcelo F. Siqueira Joel Daniels II Claudio T. Silva L. Gustavo Nonato 《The Visual computer》2011,27(10):887-903
This paper describes a novel template-based meshing approach for generating good quality quadrilateral meshes from 2D digital
images. This approach builds upon an existing image-based mesh generation technique called Imeshp, which enables us to create a segmented triangle mesh from an image without the need for an image segmentation step. Our
approach generates a quadrilateral mesh using an indirect scheme, which converts the segmented triangle mesh created by the
initial steps of the Imesh technique into a quadrilateral one. The triangle-to-quadrilateral conversion makes use of template meshes of triangles. To
ensure good element quality, the conversion step is followed by a smoothing step, which is based on a new optimization-based
procedure. We show several examples of meshes generated by our approach, and present a thorough experimental evaluation of
the quality of the meshes given as examples. 相似文献
25.
Zolt��n Kir��ly 《Algorithmica》2011,60(1):3-20
We first consider the problem of finding a maximum size stable matching if incomplete lists and ties are both allowed, but ties are on one side only. For this problem we give a simple, linear time 3/2-approximation algorithm, improving on the best known approximation factor 5/3 of Irving and Manlove (J. Comb. Optim., doi:10.1007/s10878-007-9133-x, 2007). Next, we show how this extends to the Hospitals/Residents problem with the same ratio if the residents have strict orders. We also give a simple linear time algorithm for the general problem with approximation factor 5/3, improving the best known 15/8-approximation algorithm of Iwama, Miyazaki and Yamauchi (SODA ??07: Proceedings of the Eighteenth Annual ACM-SIAM Symposium on Discrete Algorithms, pp.?288?C297, 2007). For the cases considered in this paper it is NP-hard to approximate within a factor of 21/19 by the result of Halldórsson et?al. (ACM Transactions on Algorithms 3(3):30, 2007). Our algorithms not only give better approximation ratios than the cited ones, but are much simpler and run significantly faster. Also we may drop a restriction used in (J. Comb. Optim., doi:10.1007/s10878-007-9133-x, 2007) and the analysis is substantially more moderate. Preliminary versions of this paper appeared in (Király, Egres Technical Report TR-2008-04, www.cs.elte.hu/egres/, 2008; Király in Proceedings of MATCH-UP 2008: Matching Under Preferences??Algorithms and Complexity, Satellite Workshop of ICALP, July 6, 2008, Reykjavík, Iceland, pp.?36?C45, 2008; Király in ESA 2008, Lecture Notes in Computer Science, vol.?5193, pp.?623?C634, 2008). For the related results obtained thenceforth see Sect.?5. 相似文献
26.
Jaakko Marttila Markus All��n Mikko Valkama 《Circuits, Systems, and Signal Processing》2011,30(4):775-797
This article discusses the applicability of quadrature ΣΔ modulator (QΣΔM) based analog-to-digital (A/D) conversion in cognitive
radio (CR) receivers. First, unavoidable in-phase/quadrature (I/Q) mismatch effects, limiting the dynamic range, are analyzed
in closed-form in the case of a first-order modulator. In addition, using the derived analytical converter model, it is shown
that notching the signal transfer function (STF) of the modulator at the mirror frequencies of the desired signals will effectively
cancel the I/Q imbalance induced mirror-frequency interference in case of the modulator feedback mismatch. In practice, such
STF design is easy to implement within the existing converter circuitry, as will be demonstrated in this article. The latter
part of the article proposes a novel complex multiband QΣΔM scheme, particularly aimed for the CR receivers. This multiband
scheme allows parallel reception of scattered frequency chunks in the CR context and is stemming from the additional degrees
of freedom in noise transfer function (NTF) design, provided by the QΣΔM principle. Here multiple noise shaping notches on
distinct frequencies are effectively realized through proper design of complex NTF. The modulator structure also allows flexible
reconfigurability of the notches with straightforward parameterization of the modulator transfer functions. When combined
with the above mirror-frequency rejecting STF design, the concept is demonstrated and proved effective and robust against
I/Q imbalances using practical radio signal simulations in realistic received signal conditions. 相似文献
27.
Guadalupe Aparicio Gallego Vanessa Medina Villaamil Enrique Grande Isabel Santamarina Ca��nzos Lu��s M. Ant��n Aparicio 《International journal of molecular sciences》2012,13(10):12710-12733
Historically, cell-signaling pathways have been studied as the compilation of isolated elements into a unique cascade that transmits extracellular stimuli to the tumor cell nucleus. Today, growing evidence supports the fact that intracellular drivers of tumor progression do not flow in a single linear pathway, but disseminate into multiple intracellular pathways. An improved understanding of the complexity of cancer depends on the elucidation of the underlying regulatory networks at the cellular and intercellular levels and in their temporal dimension. The high complexity of the intracellular cascades causes the complete inhibition of the growth of one tumor cell to be very unlikely, except in cases in which the so-called “oncogene addiction” is known to be a clear trigger for tumor catastrophe, such as in the case of gastrointestinal stromal tumors or chronic myeloid leukemia. In other words, the separation and isolation of the driver from the passengers is required to improve accuracy in cancer treatment. This review will summarize the signaling pathway crossroads that govern renal cell carcinoma proliferation and the emerging understanding of how these pathways facilitate tumor escape. We outline the available evidence supporting the putative links between different signaling pathways and how they may influence tumor proliferation, differentiation, apoptosis, angiogenesis, metabolism and invasiveness. The conclusion is that tumor cells may generate their own crossroads/crosstalk among signaling pathways, thereby reducing their dependence on stimulation of their physiologic pathways. 相似文献
28.
29.
We present a framework to segment cultural and natural features, given 3D aerial scans of a large urban area, and (optionally) registered ground level scans of the same area. This system provides a primary step to achieve the ultimate goal of detecting every object from a large number of varied categories, from antenna to power plants. Our framework first identifies local patches of the ground surface and roofs of buildings. This is accomplished by tensor voting that infers surface orientation from neighboring regions as well as local 3D points. We then group adjacent planar surfaces with consistent pose to find surface segments and classify them as either the terrain or roofs of buildings. The same approach is also applied to delineate vertical faces of buildings, as well as free-standing vertical structures such as fences. The inferred large structures are then used as geometric context to segment linear structures, such as power lines, and structures attached to walls and roofs from remaining unclassified 3D points in the scene. We demonstrate our system on real LIDAR datasets acquired from typical urban regions with areas of a few square kilometers each, and provide a quantitative analysis of performance using externally provided ground truth. 相似文献
30.
Mar��a-Pilar S��enz-Navajas Federico Echavarri Vicente Ferreira Purificaci��n Fern��ndez-Zurbano 《European Food Research and Technology》2011,232(5):877-887
Anthocyanins play a crucial role in wine color. Thus, their analysis results essential for evaluating their contribution to perceived color in wines, attribute directly linked to quality judgements. In this context, this study was aimed at: (1) defining the color space of a relative large number of commercial oaked Spanish red wines and (2) establishing a linkage between wine coloring, anthocyanic composition, and quality perception of this set of wines. Therefore, CIELab parameters (a 10*, b 10*, L 10*), monomeric anthocyanin contents analyzed by HPLC with ultraviolet and mass detection, and polymeric pigment content estimated by a protein precipitation assay combined with bisulfite bleaching were evaluated in a total of 58 wine samples. Principal component analysis was performed on color variables, and their correlations were discussed. The results have evidenced the important role played by the pyranoanthocyanic compounds since they seem to be the main contributors to the red color of these aged wines, and they have been demonstrated not to increase their yellow nuances. On the other hand, results highlight that, regardless of the time of aging, wines presenting more red (higher values for a 10* and for low molecular weighted anthocyanins) and lower yellow nuances (lower values for b 10* and T) as well as a darker color (lower in L 10* and higher in CI) are in general evaluated with higher quality scores by wine experts. 相似文献