Verifying a signature architecture: a comparative case study

We report on a case study in applying different formal methods to model and verify an architecture for administrating digital signatures. The architecture comprises several concurrently executing systems that authenticate users and generate and store digital signatures by passing security relevant data through a tightly controlled interface. The architecture is interesting from a formal-methods perspective as it involves complex operations on data as well as process coordination and hence is a candidate for both data-oriented and process-oriented formal methods. We have built and verified two models of the signature architecture using two representative formal methods. In the first, we specify a data model of the architecture in Z that we extend to a trace model and interactively verify by theorem proving. In the second, we model the architecture as a system of communicating processes that we verify by finite-state model checking. We provide a detailed comparison of these two different approaches to formalization (infinite state with rich data types versus finite state) and verification (theorem proving versus model checking). Contrary to common belief, our case study suggests that Z is well suited for temporal reasoning about process models with complex operations on data. Moreover, our comparison highlights the advantages of proving theorems about such models and provides evidence that, in the hands of an experienced user, theorem proving may be neither substantially more time-consuming nor more complex than model checking.     

The rate of antimony elimination from molten copper by the use of Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> slag

The rate of Sb elimination from molten copper by the use of Na₂CO₃ slag was measured at 1523 K. The results obtained under the present experimental conditions show that Sb in molten copper is eliminated in a tri-valent or a penta-valent form, depending on the oxygen concentration at the slag-metal interface, and its elimination rate increases with increasing initial oxygen concentration in molten copper. The overall elimination rate of Sb is affected by the stirring condition of the molten copper, which indicates a rate control by mass transfer in that phase. The mass-transfer coefficients of Sb and oxygen in molten copper at 1523 K without external stirring were determined, respectively, to be

A low-cost municipal sewage treatment system with a combination of UASB and the "fourth-generation" downflow hanging sponge reactors.

This paper presents an evaluation of the process performance of a pilot-scale "fourth generation" downflow hanging sponge (DHS) post-treatment system combined with a UASB pretreatment unit treating municipal wastewater. After the successful operation of the second- and third-generation DHS reactors, the fourth-generation DHS reactor was developed to overcome a few shortcomings of its predecessors. This reactor was designed to further enhance the treatment efficiency and simplify the construction process in real scale, especially for the application in developing countries. Configuration of the reactor was modified to enhance the dissolution of air into the wastewater and to avert the possible clogging of the reactor especially during sudden washout from the UASB reactor. The whole system was operated at a total hydraulic retention time (HRT) of 8 h (UASB: 6 h and DHS: 2 h) for a period of over 600 days. The combined system was able to remove 96% of unfiltered BOD with only 9 mg/L remaining in the final effluent. Likewise, F. coli were removed by 3.45 log with the final count of 10(3) to 10(4) MPN/100 ml. Nutrient removal by the system was also satisfactory.     

Simultaneous stratospheric gas and aerosol retrievals from broadband infrared occultation measurements

The inversion method for simultaneous gas (O3, NO2, HNO3, N2O, CH4, H2O, CFC-11, CFC-12, N2O5, and ClONO2) and aerosol retrievals from broadband continuous IR spectra of occultation measurements is described. Both gas and aerosol physical modeling with consideration of the multicomponent character of aerosol and polar stratospheric clouds (PSCs) are used to minimize the difference between measured and modeled transmittance spectra under smoothness constraints imposed on particle-size distributions for each PSC component and positive constraints on all gas and aerosol parameters. The method is tested by numerical simulations in which synthetic occultation measurements inherent to the improved limb atmospheric spectrometer are used. The study reveals that the method has significant advantages over other approaches based on offset or gas-window-channel aerosol correction for accurate gas retrievals and provides additional information on the particle-size composition, volume density, and chemical component character of PSCs.     

Effect of crystalline quality of diamond film to the propagation loss of surface acoustic wave devices

Diamond films with various crystal qualities were grown by chemical vapor deposition on silicon wafers. Their crystallinity was characterized by Raman scattering and electron backscattering diffraction. By fabricating a device structure for surface acoustic wave (SAW) using these diamond films, the propagation loss was measured at 1.8 GHz and compared with the crystallinity. It was found that the propagation loss was lowered in relatively degraded films having small crystallites, a narrow distribution in the diamond crystallite size, and preferential grain orientation. This experiment clarifies diamond film characteristics required for high-frequency applications in SAW filters.     

The structural color in the polymer blend of poly(methyl methacrylate) and polystyrene

Morphologic and optical studies were performed on the coloring of poly(methyl methacrylate) (PMMA) and polystyrene (PS) opal sheet. It was concluded that the origin of color is the polymer structure itself. There exist three structures in the colored polymer blend: small PS spheres are dispersed in the PMMA matrix, and each PS sphere contains smaller PMMA spheres within it. The dimension of the smaller PMMA spheres is of the same order as the wavelength of visible or near-infrared light. The coloring measured by a spectrometer is well interpreted by the equation of structural color derived by Clewell qualitatively.     

Estimation of intrinsic birefringence of poly(ethylene terephthalate) crystal

The intrinsic birefringence of poly(ethylene terephthalate) crystal has been estimated by means of the Orito method using experimental data and using theoretical calculation. The experimental estimation was performed on the basis of the assumption of a two-phase model consisting of crystalline and amorphous phases and the additivity of birefringence contributions — that total birefringence is equal to the sum of the orientation contributions from crystalline and amorphous phases, and of form birefringence. The value experimentally extrapolated by the Orito method is approx. 0.24. On the other hand, the theoretical calculation was carried out in the usual way using the values of bond polarizabilities according to Bunn and the atomic arrangements within the crystal according to Daubeny et al. The calculated value is 0.251. The difference between two results is also discussed.