A framework for avoiding steganography usage over HTTP

Steganographic techniques allow users to covertly transmit information, hiding the existence of the communication itself. These can be used in several scenarios ranging from evading censorship to discreetly extracting sensitive information from an organization. In this paper, we consider the problem of using steganography through a widely used network protocol (i.e. HTTP). We analyze the steganographic possibilities of HTTP, and propose an active warden model to hinder the usage of covert communication channels. Our framework is meant to be useful in many scenarios. It could be employed to ensure that malicious insiders are not able to use steganography to leak information outside an organization. Furthermore, our model could be used by web servers administrators to ensure that their services are not being abused, for example, as anonymous steganographic mailboxes. Our experiments show that steganographic contents can be successfully eliminated, but that dealing with high payload carriers such as large images may introduce notable delays in the communication process.     

Dynamic mechanical properties of polycarbonate and acrylonitrile–butadiene–styrene copolymer blends

Blends of polycarbonate (PC) and poly(acrylonitrile‐co‐butadiene‐co‐styrene) (ABS) with different compositions are characterized by means of dynamic mechanical measurements. The samples show phase separation. The shift in the temperatures of the main dynamic mechanical relaxation shown by the blend with respect to those of the pure components is attributed to the migration of oligomers present in the ABS toward the PC in the melt blending process. A comparison with other techniques (dielectric and calorimetric analysis) and the application of the Takayanagi three block model confirm this hypothesis. In all the studied blend compositions (ABS weight up to 28.6%) the PC appears as the matrix where a disperse phase of ABS is present. The scanning and transmission electron microscopy micrographs show that the size of the ABS particles increases when the proportion of ABS in the blend increases. The FTIR results indicate that the interaction between both components are nonpolar in nature and can be enhanced by the preparation procedure. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1507–1516, 2002     

Scalable,low complexity,and fast greedy scheduling heuristics for highly heterogeneous distributed computing systems

For heterogeneous distributed computing systems, important design issues are scalability and system optimization. Given such systems, it is crucial to develop low computational complexity algorithms to schedule tasks in a manner that exploits the heterogeneity of the resources and applications. In this paper, we report and evaluate three scalable, and fast scheduling heuristics for highly heterogeneous distributed computing systems. We conduct a comprehensive performance evaluation study using simulation. The benchmarking outlines the performance of the schedulers, representing scalability, makespan, flowtime, computational complexity, and memory utilization. The set of experimental results shows that our heuristics perform as good as the traditional approaches, for makespan and flowtime, while featuring lower complexity, lower running time, and lower used memory. The experimental results also detail the various scenarios under which certain algorithms excel and fail.     

Volatile Emissions Triggered by Multiple Herbivore Damage: Beet Armyworm and Whitefly Feeding on Cotton Plants

Plants are commonly attacked by more than one species of herbivore, potentially causing the induction of multiple, and possibly competing, plant defense systems. In the present paper, we determined the interaction between feeding by the phloem feeder silverleaf whitefly (SWF), Bemisia tabaci Gennadius (B-biotype = B. argentifolii Bellows and Perring), and the leaf-chewing beet armyworm (BAW), Spodoptera exigua Hübner, with regard to the induction of volatile compounds from cotton plants. Compared to undamaged control plants, infestation with SWF did not induce volatile emissions or affect the number and density of pigment glands that store volatile and nonvolatile terpenoid compounds, whereas infestation by BAW strongly induced plant volatile emission. When challenged by the two insect herbivores simultaneously, volatile emission was significantly less than for plants infested with only BAW. Our results suggest that tritrophic level interactions between cotton, BAW, and natural enemies of BAW, that are known to be mediated by plant volatile emissions, may be perturbed by simultaneous infestation by SWF. Possible mechanisms by which the presence of whiteflies may attenuate volatile emissions from caterpillar-damaged cotton plants are discussed.     

Mutation of herpesvirus thymidine kinase to generate ganciclovir-specific kinases for use in cancer gene therapies

Understanding the functional and mechanistic properties of themulti-substrate herpes simplex virus type-1 thymidine kinase(HSV-1 TK) remains critical to defining its role as a majorpharmacological target in herpesvirus and gene therapies forcancer. An inherent limitation of the activity of HSV-TK isthe >70-fold difference in the K_ms for phosphorylation ofthymidine over the pro-drug ganciclovir (GCV). To engineer anHSV-1 TK isoform that is specific for GCV as the preferred substrate,16 site-specific mutants were generated. The mutations wereconcentrated at conserved residues involved in nucleoside basebinding, Gln125 and near sites 3 and 4 involved in catalysisand substrate binding. The substrate preferences of each mutantenzyme were compared with wild-type HSV-1 TK. One mutant, termedQ7530 TK, had a lower K_m for GCV than thymidine. Expressionof the Q7530 TK in tumor cells indicated comparable metabolismto and improved sensitivity to GCV over wild-type HSV-1 TK,with minimal thymidine phosphorylation activity. A molecularmodeling simulation of the different HSV-1 TK active-sites wasdone for GCV and thymidine binding. It was concluded that mutationsat Gln125 and near site 4, especially at Ala168, were responsiblefor loss of deoxypyrimidine substrate binding.     

Morphology and thermomechanical properties of recycled PET–organoclay nanocomposites

Recycled PET/organoclay nanocomposites were prepared by melt intercalation process with several amounts (1, 3, and 5 wt %) of clay modified with quaternary ammonium salt (DELLITE 67G) dispersed in a recycled poly(ethylene terephthalate) (rPET) matrix. The resultant mechanical properties (modulus and yield strength) of the nanocomposites were found to be different from those of rPET. Wide angle X‐ray scattering (WAXS) and Transmission Electron Microscopy (TEM) measurements have shown that although complete exfoliation was not achieved, delaminated clay platelets could be observed. Thermal analysis did not show significant changes in the thermal properties from those of recycled PET. Mechanical testing showed that nanocomposite properties were superior to the recycled PET in terms of strength and elasticity modulus. This improvement was attributed to nanoscale effects and strong interaction between the rPET matrix and the clay interface, as revealed by WAXS and TEM. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1839–1844, 2007     

Addressing universal access in social networks: an inclusive search mechanism

Social network services (SNSs) have brought new possibilities and challenges to the design of software environments that respect people’s cultural differences. These systems may represent an opportunity for social and digital inclusion. However, search mechanisms in these systems impose serious barriers for people in the process of acquiring digital literacy. One of the barriers is the difficulty of using the adequate terms/keywords to perform content searches. This paper presents an approach to allow ordinary, non-technology proficient people to access the content of a network through the use of search parameters that make sense to them. The proposal is grounded on Semantic Web technologies (Web ontology) combined with Organizational Semiotics concepts and methods to identify the users’ profile and language. A case study was conducted with the search mechanism integrated into a SNS, and a preliminary evaluation reveals the advantages and drawbacks of the approach.     

Influence of processing on ethylene propylene block copolymers (II): Fracture behavior

The present work investigates the relationships between the microstructural state and fracture properties in commercial polypropylene‐based materials. In this case an isopolypropylene homopolymer and three ethylene propylene block copolymers (EPBC) with different ethylene content (EC) have been studied. A variety of morphologies were obtained by a combination of several processing methods (injection molding, injection molding‐annealing, and compression molding) and thickness. Fracture behavior of deeply double‐edged notched specimens was evaluated by scanning electron microscopy (SEM) and by the essential work of fracture (EWF) method, analyzing the influence of processing, thickness (t), EC, and orientation respect to melt flow direction (MD and TD). The testing direction and EC are the most relevant variables that affect the ability of the crack tip to deform plastically during the crack propagation, determining the final fracture behavior. The fracture parameters obtained with the EWF method, specific EWF, w_e, and plastic item, βw_p, have proved to be very sensitive to the processing induced morphology, finding interesting relationships between such morphologies (characterized by crystallinity index, orientation level, and skin/core ratio) and the fracture parameters of the plaques. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2714–2724, 2006     

Metabolic behavior in rats of a nonprotein microemulsion resembling low-density lipoprotein

A protein-free microemulsion (LDE) with a lipid composition resembling that of low-density lipoprotein (LDL) was used in metabolic studies in rats to compare LDE with the native lipoprotein. LDE labeled with radioactive lipids was injected into the bloodstream of male Wistar rats, and plasma kinetics of the labeled lipids were followed on plasma samples collected at regular intervals for 12 h after injection. The 24-h LDE uptake by different tissues was also measured in tissue samples excised after the animals had been sacrificed. We found that LDE plasma kinetics were similar to those described for native LDL [fractional clearance rate (FCR) of cholesteryl ester, 0.42±0.11 h⁻¹]. The major site for LDE uptake was the liver, and the tissue distribution of the LDE injected radioactivity was as one would expect for LDL. To test whether LDE was taken up by the specific LDL receptors, the LDE emulsion was injected into rats treated with 17α-ethinylestradiol, which is known to increase the activity of these receptors; as expected, removal of LDE from the bloodstream increased (FCR=0.90±0.35 h⁻¹). On the other hand, saturation of the receptors that remove remnants by prior infusion of massive amounts of lymph chylomicrons did not change LDE plasma kinetics. These results indicate that LDE is cleared from plasma by B,E receptors and not by the E receptors that remove remnants. Incorporation of free cholesterol into LDE increased LDE plasma clearance. Incubation studies also showed that LDE incorporates a variety of apolipoproteins, including apo E, a ligand for recognition of lipoproteins by specific receptors. Our data suggest that LDE can be a useful tool to test LDL metabolism and B,E receptor function.     

Oxygen and chlorine evolution on RuO2 + TiO2 + CeO2 + Nb2O5 mixed oxide electrodes

A systematic investigation was conducted on the mechanism and electrocatalytic properties of O₂ and Cl₂ evolution on mixed oxide electrodes of nominal composition: Ti/[Ru_(0.3)Ti_(0.6)Ce_(0.1−x)]O₂[Nb₂O₅]_(x) (0 ≤ x ≤ 0.1). For the oxygen evolution, a 30 mV Tafel slope is obtained in the presence of CeO₂, while in its absence a 40 mV coefficient is observed. The intrinsic electrocatalytic activity is mainly due to electronic factors, as result of the synergism between Ru and Ce oxides. For chlorine evolution, the Tafel slope (30 mV) is independent on oxide composition. The best global electrocatalytic activity for ClER was observed in the absence of Nb₂O₅ additive. Variation of the voltammetric charge throughout the experiments confirms high CeO₂ content compositions are fragile, due mainly to the porosity caused by CeO₂ presence. On the other hand, Nb₂O₅ addition decreases considerably this instability.