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151.
Anonymous database search protocols allow users to query a database anonymously. This can be achieved by letting the users form a peer-to-peer community and post queries on behalf of each other. In this article we discuss an application of combinatorial configurations (also known as regular and uniform partial linear spaces) to a protocol for anonymous database search, as defining the key-distribution within the user community that implements the protocol. The degree of anonymity that can be provided by the protocol is determined by properties of the neighborhoods and the closed neighborhoods of the points in the combinatorial configuration that is used. Combinatorial configurations with unique neighborhoods or unique closed neighborhoods are described and we show how to attack the protocol if such configurations are used. We apply k-anonymity arguments and present the combinatorial configurations with k-anonymous neighborhoods and with k-anonymous closed neighborhoods. The transversal designs and the linear spaces are presented as optimal configurations among the configurations with k-anonymous neighborhoods and k-anonymous closed neighborhoods, respectively. 相似文献
152.
The goal of this study was to optimize and validate a combined spin- and gradient-echo (SAGE) sequence for dynamic susceptibility-contrast magnetic resonance imaging to obtain hemodynamic parameters in a preclinical setting. The SAGE EPI sequence was applied in phantoms and in vivo rat brain (normal, tumor, and stroke tissue). Partial and full Fourier encoding schemes were implemented and characterized. Maps of cerebral blood volume (CBV), cerebral blood flow (CBF), mean transit time (MTT), vessel size index (VSI), volume transfer constant (Ktrans), and volume fraction of the extravascular extracellular space (ve) were obtained. Partial Fourier encoding provided shortened echo times with acceptable signal-to-noise ratio and temporal stability, thus enabling reliable characterization of T2, T2? and T1 in both phantoms and rat brain. The hemodynamic parameters CBV, CBF, and MTT for gradient-echo and spin-echo contrast were determined in tumor and stroke; VSI, Ktrans, and ve were also computed in tumor tissue. The SAGE EPI sequence allows the acquisition of multiple gradient- and spin-echoes, from which measures of perfusion, permeability, and vessel size can be obtained in a preclinical setting. Partial Fourier encoding can be used to minimize SAGE echo times and reliably quantify dynamic T2 and T2? changes. This acquisition provides a more comprehensive assessment of hemodynamic status in brain tissue with vascular and perfusion abnormalities. 相似文献
153.
D. U. Gubser W. W. Fuller T. O. Poehler J. Stokes D. O. Cowan M. Lee 《Molecular Crystals and Liquid Crystals》2013,570(1):581-590
We report measurements of the ac magnetic susceptibility and dc resistive superconducting transitions in the organic superconductor (TMTSF)2C104. Inductive measurements show complete diamagnetic shielding below a broad transition and initial flux penetration at very low fields [Hc1(0) < 1 Oe]. The resistive transition is also broad, but occurs at a significantly higher temperature than the inductive transition, Tc = 1.0 K and 0.65 K respectively. Resistance measurements also show evidence of a phase transition in the vicinity of 24 K. Magnetic field induced transitions, measured both inductively and resistively, show marked anistropy both in magnitude and in breadth of the transition. Results suggest that (TMTSF)2C104 is a quasi ID or 2D superconductor at high temperatures and high magnetic fields and an anisotropic bulk superconductor at low temperatures and fields. Associated thermoelectric power measurements suggest that spin density waves coexist with the superconducting state. 相似文献
154.
The Laplace transform route to the calculation of the rate of radiationless processes is illustrated for the 1 B 2u state of benzene. Although available spectral data are not enough to allow a calculation in detail, some general features are illustrated including the basis of the energy gap law. A treatment is given of the variation in radiationless decay rates for different levels of a spectral progression. 相似文献
155.
Phase transitions for systems with diperiodic symmetry are discussed. Direct group-theoretical methods are employed to obtain a list of possible commensurate lower-symmetry phases (subgroups) which are induced by a single order parameter. The lower-symmetry phases for all 80 diperiodic space groups are given, along with specific details of the group-subgroup relationships. Results for the 17 two-dimensional space groups are also contained in our list. The renormalization-group Hamiltonian densities for the diperiodics are calculated. The 12 densities listed constitute the complete set of densities which may arise in the diperiodic space groups. Critical properties for the diperiodics can thus be obtained from analysis of these densities. 相似文献
156.
Tim Stokes 《代数通讯》2013,41(9):3979-4007
A D-semigroup S is a semigroup equipped with an operation D satisfying laws asserting that for a ∈ S, D(a) is the smallest e in some set of idempotents U ? S for which ea = a. D-semigroups correspond to left-reduced U-semiabundant semigroups. The basic properties and many examples of D-semigroups are given. Also considered are D-rings, whose multiplicative semigroup is a D-semigroup. Rickart *-rings provide important examples, and the most general D-rings for which the elements of the form D(a) constitute a lattice under the same meet and join operations as for Rickart *-rings are described. 相似文献
157.
158.
For use in determining the stability of outcomes in non-cooperative games, an improved definition of simultaneous sanctioning is devised. Conditions such as ‘procrastination’, ‘staying power’ and ‘fear of dire consequences’, which may invoke stability by simultaneous sanctioning in games, are described. 相似文献
159.
Perturbation analysis of an energy-balance model: time constants oflow-current cascade arcs in argon
Seebacher P.J. Stokes A.D. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1995,23(2):171-176
A time-constant formula is derived from a perturbation analysis of an equilibrium energy-balance equation of arc plasmas. The formula gives the time constant associated with changes in arc quantities when the arc current is perturbed from its steady-state. The current perturbation is assumed to be very small and the mathematical approach assumes that the arc behavior is linear. This paper investigates how well a linear model describes the small-signal behavior of the arc. The derived formula gives an insight into which are properties are responsible for the dynamic behavior of the arc about its steady-state operating point. Application of the method has been illustrated with arcs in argon. Results calculated with the formula are compared to time-constants deduced from equilibrium model predictions of the decay in the electric field when the current is stepped 相似文献
160.
Stephen Stokes 《Radiation measurements》1994,23(2-3)
The timing of 110°C thermoluminescence (TL) and optically stimulated luminescence (OSL) sensitivity changes is explored using a natural (aeolian) quartz sample from Australia that was previously found to exhibit marked dose-dependent sensitivity change. The changes occur asynchronously; the 110°C TL sensitivity changes after dosing plus pre-heating, whereas the OSL sensitivity changes (proportionately with dose) after optical bleaching. Although the magnitude and saturation characteristics of the sensitivity changes are found to be similar, their non-synchronicity negates a direct link between the phenomena. Implications of these results for dating procedures are discussed. In particular, the results indicate that a single aliquot additive dose procedure similar to that developed for coarse-grained potassium feldspar should be possible for some quartz samples. 相似文献