Influence of Heat on Non-Ferrous Objects: Metallurgical Analysis in Fire Scene Investigations

NFPA 921 is a widely accepted standard to perform fire and arson analysis: it states that heat damage on items and components must be recognized to perform a more careful analysis of fire spread and to better define area and point of origin. With reference to metallic materials involved in a fire scene, NFPA 921 only indicate two useful parameters for temperature estimation, i.e. melting temperature and surface oxidation. However, the melting point of metals and alloys may define a wide range of temperatures (for example iron-based alloys normally melt between 1500 and 1600°C); in addition surface oxidation colors can only inform in a qualitative way. To better estimate the temperature range experienced by various items, much more information can be inferred from in-depth metallurgical analyses. Intergranular oxidation, recrystallization, second phase precipitations and incipient melting were some of the metallurgical features easily observable: if the investigator knows the approximate temperature of these microstructure modifications, a better estimate can be done of the “effective fire temperature” that the material might have reached. To this aim some components that can be found in fire a scene (aluminium airshaft, brass tap and copper gas pipe) were exposed to simulated fire conditions of known time durations and peak temperatures. The collected items were then examined by metallurgical techniques, identifying reference temperatures. The obtained results can give useful information to understand the fire scene.     

Starch Consolidation Casting of Cordierite Precursor Mixtures—Rheological Behavior and Green Body Properties

The rheology of suspensions and mechanical properties of green bodies with cordierite composition (raw materials 37 wt% kaolin, 41 wt% talc, 22 wt% alumina, resulting in 46.6 wt% SiO₂, 38.1 wt% Al₂O₃, 13.6 wt% MgO) and two types of starch (corn or potato) are investigated. Rotational viscometry of suspensions with solids loading 50, 60, and 70 wt% without starch showed that all tend to be shear‐thinning with a small degree of thixotropy. Suspensions with a total solids loading of 60 wt% with 25 wt% replaced by starch exhibited higher viscosity and thixotropy, but the viscometric behavior is almost identical for the two starch types (apparent viscosities 130–50 mPa ·s). Oscillatory rheometry shows that for suspensions with potato starch the onset temperature for gelatinization is 61°C–63°C, that is, lower than for corn starch (72°C–73°C). Maximum storage moduli and phase shift values after gelatinization are similar for both systems. The mechanical properties of green disks, measured via diametral compression tests, reveal clear differences between materials prepared with corn and potato starch, with the latter showing higher elastic modulus, higher strength, and higher deformation at fracture, obviously because of incompletely gelatinized starch granules in the green bodies prepared with corn starch .     

High glass transition temperature polyester coatings for the protection of stones

Copolymers of lactic acid with mandelic or salicylic acid were synthetized through ring‐opening polymerization (ROP) and tested as protective coatings for stones. Most notably, glass transition temperature (T_g), hydrophobicity, and UV barrier properties were increased, making these materials more suitable as protective coating for outdoor stones than poly(lactic acid). A T_g of 76°C was obtained for the alternating copolymer lactic acid/mandelic acid and it was considerably higher than the one of poly(lactic acid) with similar molecular weight (50–55°C). Furthermore, the introduction of a perfluorinated moiety as chain‐end group, using a perfluoro alcohol as initiator of the ROP process, allowed to increase the hydrophobicity and stability of the new coatings. These polymers showed a good protective efficiency when applied on marble stones and preliminary stability tests under solar light showed low degradation, good stability to photo‐oxidative conditions, and negligible color changes after an aging time of 1000 h. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42323.     

An efficient HARQ scheme for applications in multicast communication systems

This paper deals with the performance evaluation and optimization of an efficient hybrid automatic repeat request (HARQ) scheme suitable for applications delivered over lossy multicast communication channels. In particular, different from previously investigated strategies, this paper proposes a modified HARQ scheme based on the symbol combining principle (MHARQ‐SC) where multiple copies of a same packet are consecutively transmitted at each transmission opportunity. By considering as the performance metrics, the mean packet delivery delay, and the energy consumption per information packet, this paper presents suitable performance evaluation and optimization strategies tailored for multicast communications. For the sake of comparisons, it has been also analyzed, under the same operational conditions, the performance of different HARQ schemes optimized for multicast communications. Numerical results have been provided to validate the proposed performance evaluation and optimization approaches in the case of the MHARQ‐SC scheme. An important result devised here is that the reported analytical results clearly highlight the performance gain of the proposed strategy in comparison with all the other considered alternatives. Copyright © 2013 John Wiley & Sons, Ltd.     

One or infinite optimal city sizes? In search of an equilibrium size for cities

In this paper, the stylized assumption that one single “optimal” city size exists for all cities—achieved when marginal location costs equal marginal location benefits—is abandoned, as well as the opposite view that each city operates on its own cost and production curves, defining a specific optimal size. Instead, this work maintains the comparability among cities and demonstrates that urban specificities in functions performed, quality of life, industrial diversity and social conflicts shift up and down the benefits and costs linked to pure physical size, leading to different “equilibrium” sizes for cities. In order to achieve this result, a model of equilibrium urban size is set up, based on urban costs and urban benefits, merging elements suggested both by the traditional urban economics literature as well as by updated approaches considering also environmental quality, urban form and inter-urban cooperation networks. The model is then estimated on a sample of 59 European cities with data at FUA level. Empirical results allow the identification of city-specific “equilibrium” sizes. The error term, that is, the difference between actual urban population and the “equilibrium” one predicted by the model can be explained, beyond a measure of our ignorance, by good or bad governance, thereby suggesting future strategies for more efficient urban planning.     

Op Arch

Sitelessness and loss of place suggest the instability of boundaries that otherwise sustain the legibility of public institutions. Such conditions negate conventional affinities between architecture, ceremonial urban space, monuments, and monumental sculpture. Nowadays, the theoretical basis for a relationship between these actors is in flux. This article takes up several different contemporary conceptions of public space and the public thing and employs them in an interpretation of two recent projects: Maya Lin's Vietnam Veterans Memorial and Richard Serra's ill-fated Tilted Arc. These projects embody changing conditions in the dialogue between art, architecture, and the city.