Taxonomy of trust relationships in authorization domains for cloud computing

Cloud computing is revealing a new scenario where different cloud customers need to collaborate to meet client demands. The cloud stack must be able to support this situation by enabling collaborative agreements between cloud customers. However, these collaborations entail new security risks since participating entities should trust each other to share a set of resources. The management of trust relationships in the cloud is gaining importance as a key element to establish a secure environment where entities are given full control in the definition of which particular services or resources they are willing to share. Entities can cooperate at different levels of trust, according to their willingness of sharing information. This paper analyses these collaboration agreements defining a taxonomy of different levels of trust relationships among customers for the cloud. Privacy concerns, assumed risk, as well as easiness in the definition of the trust relationships have been taken into account. A set of different trust relationships have been identified and modeled, enabling entities to control the information they share with others in the cloud. The proposed model has been validated with a prototypical implementation. Likewise, some examples to illustrate the application of these trust models to common cloud collaboration scenarios are provided.     

Effect of Forging on Microstructure,Texture, and Uniaxial Properties of Cast AZ31B Alloy

The effect of open-die hot forging on cast AZ31B magnesium alloy was investigated in terms of the evolution of microstructure, texture, and mechanical properties. A refined microstructure with strong basal texture was developed in forged material. A significant increase in tensile yield and ultimate strengths by 143 and 23%, respectively, was determined as well. When tested in compression at room temperature, the forged alloy displayed significant in-plane asymmetry and unchanged yield strength compared to the cast alloy owing to the activation of \(\left\{ {10\bar{1}2} \right\}\left\langle {10\bar{1}1} \right\rangle\) extension twins in both the cast and forged conditions. However, the ultimate compressive strength for the forged material increased by 22 percent compared to the as-cast material. Microstructure and texture analysis of the fracture samples confirmed that the deformation of the forged samples was dominated by slip during tension and twin in compression. In comparison, both slip and twin were observed in the cast samples for similar testing conditions. The increase in strength of forging was attributed to the refinement of grains and the formation of strong basal texture, which activated the non-basal slip on the prismatic and pyramidal slip systems instead of extension twin.     

Normal Adhesive Force-Displacement Curves of Living Geckos

In this paper, we report experimental measurements of normal adhesive force versus body displacement for living Tokay geckos (Gekko gecko) adhered to Poly(methyl meth acrylate) (PMMA) or glass surfaces. We have measured the normal adhesive force needed for reaching the gecko detachment. Atomic force and scanning electron microscopies are used to characterize the surfaces and feet topologies. The measured safety factors (maximum adhesive force divided by the body weight) are 10.23 on PMMA surfaces or 9.13 on glass surfaces. We have observed minor and reversible damage of the gecko feet caused by our tests, as well as the self-renewal of the gecko adhesive abilities after the moult.     

Influence of CYP1A2 and NAT2 Metabolic Phenotypes on Smokers' Urinary Mutagenicity

The influence of the metabolic phenotypes NAT2 and CYP1A2 on urinary mutagenicity of 118 smokers was studied. Mutagenicity of urine samples was determined by Ames test (preincubation plate incorporation assay on YG1024 Salmonella typhimurium strain with S9 mix). Urinary nicotine plus its metabolites were determined to check cigarette smoke intake. The N -acetyltransferase (NAT2) and cytochrome P450 1A2 (CYP1A2) phenotypes were measured by the molar ratio of urinary caffeine metabolites, determined by HPLC analysis. Urinary mutagenicity was significantly higher in smokers CYP1A2 extensive (EM) than in CYP1A2 poor metabolizers (PM) (Mann-Whitney U test, p = 0.020). Linear multiple regression analysis shows that an increase in urinary mutagenicity levels was significantly related to cigarette smoke intake and to CYP1A2 N -hydroxylation activity ( t = 5.06, p < 0.001, and t = 2.33, p = 0.021), but not to NAT2 acetylation phenotype. In conclusion, phenotypic differences in metabolic activation of tobacco smoke mutagens are able to modulate the presence of mutagens in urine of cigarette smokers and, consequently, the potential genotoxic risk.     

Ischemic and Ozone Oxidative Preconditioning in the Protection Against Hepatic Ischemic-Reperfusion Injury

It has been demonstrated that ozone, probably through a mechanism of oxidative preconditioning (OP), protected the liver against the damage mediated by reactive oxygen species. Taking into account that iscehmic preconditioning (IschP) is also a protective mechanism, a comparative study between both preconditioning settings was performed in order to study the effectiveness of both protective procedures. Rats were randomly divided into 4 groups: 1- control, sham operated (anesthesia and laparotomy plus surgical manipulation); 2- I/R (ischemia for 90?min followed by 90?min reperfusion); 3- Ischp+I/R, as group 2 but submitted to a previous ischemic preconditioning (ischemia 10?min and reperfusion 10?min); 4- OzoneOP+I/R, as group 2 but submitted to a pervious oxidative preconditioning with 15 sessions, daily, of ozone by rectal administration (dose of 1?mg/kg). The comparison between both preconditionings showed no biochemical differences for the parameters evaluated. Nevertheless, the histological study demonstrated that the protective effect produced by the OzoneOP is superior to that achieved with the IschP.     

Hot‐wire parallel technique: A new method for simultaneous determination of thermal properties of polymers

The hot‐wire parallel technique standardized for determining the thermal conductivity of ceramic materials was employed in the determination of the thermal properties of polymers. For these materials, additional care must be taken considering the low melting point of polymers, when compared with that for ceramic materials. Samples can be prepared either in the shape of bricks or in the shape of half‐cylinders. The thermal conductivity and the specific heat were simultaneously determined from the same experimental thermal transient, and the thermal diffusivity is derived from these properties. Five different polymers with different structures at room temperature were selected, and measurements were carried out from room temperature to approximately the maximum service operating temperature. A nonlinear least‐squares fitting method was employed in the calculations, so that all the experimental points obtained are considered in the thermal properties' calculations. The apparatus used in this work is fully automatic. The reproducibility is very good with respect to the thermal conductivity, even with a defective experimental arrangement with respect to the theoretical model. However, deviations from the theoretical model have a severe influence on the specific heat values and, consequently, on the thermal diffusivity. Experimental results were compared with those available in the literature, showing the applicability of this technique for the determination of thermal properties of polymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1779–1786, 2002     

Concentration effect of <Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide on viscoelastic properties of hydrosoluble thermo-thickening copolymers

In this work, we described the preparation of hydrosolubles thermosensitive copolymers obtained via free radical polymerization in aqueous media. The reactions were carried out under different molar ratio of acrylamide and N-isopropylacrylamide (NIPAM) and are considered [80]/[20], [60]/[40], [50]/[50], [40]/[60] and [20]/[80], respectively. The initial concentration of monomer mixture was kept at 3% (weight) based on the water volume. The polymerizations were performed at 70 °C under mechanical agitation during 7 h and the molar ratio between monomer and initiator (4,4′-azobis cyano pentanoic acid) was kept at 0.07%. The copolymers were characterized and results demonstrated that the monomer concentrations were closed to previously feed to the reaction. The turbidity point rises according to the quantity of poly(acrylamide), PAM, incorporated into the copolymers (composition value). Also, it was observed that the molecular weight of each copolymer decreases when the amount of NIPAM increases. On the other hand, the viscosity of all copolymers growth compared to the increase in the temperature from 25 to 70 °C is observed. Notwithstanding, in the case of copolymer with highest NIPAM concentration (CP5), the viscosity decreases in the temperature range from 60 to 70 °C.     

Linear segmented polyurethanes: I. A kinetics study

This work investigates the two‐step polymerization between methylene diphenyl diisocyanate (MDI), two different poly(tetramethylene oxide) macrodiols, and 1,4‐butanediol (BD) as chain extender. At the end of the prepolymerization, the reaction mixture contains MDI in excess and a prepolymer with isocyanate end group. Then, BD and a solvent (tetrahydrofuran) were added to start the finishing stage under nominal stoichiometric equilibrium. The reaction was analyzed by Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance (¹H‐NMR), and size exclusion chromatography. ¹H‐NMR was employed to follow global concentrations of unreacted isocyanate end groups and internal urethane groups. This information enabled to estimate the following “effective” rate constants: k₁ = 1.07 × 10^?3 L mol^?1 s^?1 for the prepolymerization; and k₂ = 1.94 × 10^?4 L mol^?1 s^?1 for the finishing stage. These values are subject to errors caused by biases introduced in the recipe, in the measurements, in the reaction conditions, in the quality of reagents, and in the reaction mechanism assumptions. Such errors also explain the dispersion of the published rate constants values. The ¹H‐NMR measurements also enabled to estimate the evolution (with extent of reaction) of the number‐average number of structural units along the prepolymerization and finishing stages; and such estimates reasonably verify Flory's classical expressions. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45747.     

TiO2 nanotubes manufactured by anodization of Ti thin films for on-chip Li-ion 2D microbatteries

The use of self-organized TiO₂ nanotube arrays electrochemically grown onto Si is investigated for the fabrication of an alternative electrode dedicated to on-chip Li-ion 2D microbatteries. Discharge/charge curves and cycling performance are studied in lithium-anode electrochemical test cells for both amorphous and crystalline titania nanotubes. At 5 μA cm⁻² amorphous TiO₂ nanotube layers onto Si deliver a maximum areal capacity of 89 μAh cm⁻² in the first reversible discharge and 56 μAh cm⁻² over 50 cycles. We demonstrate that these nanostructured thin film electrodes showing such electrochemical performances are compatible with IC technology.