Selective decomposition of isopropanol using as prepared and oxidized graphite nanofibers

Three types of as prepared and treated graphite nanofibers (GNFs) were used as catalysts in the decomposition of isopropanol to propene and acetone in the presence of oxygen to evaluate the surface chemistry of the fibers. As prepared herringbone fibers were found to produce higher selectivity for propene compared to the as prepared platelet and ribbon fibers at all temperatures explored. Herringbone fibers that had undergone oxidative treatment with nitric acid, phosphoric acid, ruthenium tetroxide or potassium permanganate were also evaluated at a 290 °C. Effects of oxidation treatments on fiber structure were evaluated using a host of analytical techniques including BET, SEM/EDS, TGA, XPS, and fluorescence labeling of surface species. Selectivity for acetone dehydrogenation product or propene dehydration product could be achieved by the appropriate surface treatment. Nitric acid was the mildest treatment and the treated fibers showed minimal changes. (Potassium permanganate was a harsh treatment that almost completely degraded fiber structure, creating amorphous carbon.) Phosphoric acid treated fibers were found to produce very high conversions and almost pure selectivity for propene. Ruthenium tetroxide did not appear to have a large affect on fiber morphology; however, selectivity for acetone was much higher when GNFs were treated with ruthenium tetroxide.     

Spatial-structure differences between urban and regional systems

The total population and the overall average density are derived for a single city, in which the spatial structure conforms approximately to the negative exponential function. It is then shown that across the cities of an urban system, the areal extent of a city is positively related to its average density and also to its population. Consideration is next given to a system of regions and again to the manner in which areal extent is related to average density and population across regions. In this setting, however, the relationships are usually different from those found within an urban system.     

Seismic damage and fragility analysis of structures with tuned mass dampers based on plastic energy

The effectiveness of using a tuned mass damper (TMD) to improve a structure's ability to dissipate earthquake input energy is investigated through the use of seismic fragility curves. The nonlinear material behaviour of the structure is captured using the force analogy method, the backbone for analytically quantifying plastic energy dissipation in the structure. Numerical analysis was performed to study the global response and local energy dissipation of a six‐storey moment‐resisting steel frame with and without a TMD installed for 100 simulated non‐stationary Gaussian earthquake ground motions. The effectiveness of the TMD, based on reduction of seismic responses and enhancement of the seismic fragility, is considered at structural performance levels for immediate occupancy and life safety as identified in FEMA 440. An ‘equivalent monotonic plastic strain’ approach—a local measure of structural damage—is used to correlate the seismic fragilities at different global performance levels based on storey drift. Results illustrate that a TMD can enhance the structure's ability to dissipate energy at low levels of earthquake shaking, while less effective during moderate to strong earthquakes, which can cause a significant period shift associated with major structural damage. This ‘de‐tuning’ effect suggests that an extremely sizable TMD is not effective in reducing damage of a structure. Published in 2010 by John Wiley & Sons, Ltd.     

Two-server password-only authenticated key exchange

Typical protocols for password-based authentication assume a single server that stores all the information (e.g., the password) necessary to authenticate a user. An inherent limitation of this approach, assuming low-entropy passwords are used, is that the user?s password is exposed if this server is ever compromised. To address this issue, it has been suggested to share a user?s password information among multiple servers, and to have these servers cooperate (possibly in a threshold manner) when the user wants to authenticate. We show here a two-server version of the password-only key-exchange protocol of Katz, Ostrovsky, and Yung (the KOY protocol). Our work gives the first secure two-server protocol for the password-only setting (in which the user need remember only a password, and not the servers? public keys), and is the first two-server protocol (in any setting) with a proof of security in the standard model. Our work thus fills a gap left by the work of MacKenzie et al. (2006) [31] and Di Raimondo and Gennaro (2006) [16]. As an additional benefit of our work, we show modifications that improve the efficiency of the original KOY protocol.