A game‐theoretic model for users' participation in ephemeral social vehicular networks

Ephemeral social vehicular networks allow for short‐lived communications between occupants. While such transient interactions may provide important usage benefits such as traffic warnings, the reality of short‐lived interactions also poses challenges for deciding to participate in such social networks. In this paper, we develop a game‐theoretic model to understand the role of occupants' incentives to contribute to these ephemeral social networks. We rigorously study the properties of the model and resulting equilibrium outcomes. A further key objective of our work is to evaluate the robustness of our model to different notions of intrinsic motivation for network participation. As a baseline case, we assume that users are homogeneous regarding their motivation. Next, we investigate the impact of different motivational distributions and explore their impact on users' behaviors in a comprehensive simulation setup. We identify the circumstances under which ephemeral social networks are viable and can successfully sustain an increased level of network participation.     

Multi-objective cooperative medium access control protocols in wireless Ad-Hoc networks

Wireless Networks - Relay-based cooperative communications have been emerging as a novel paradigm in many wireless protocols. The IEEE 802.11 medium access control (MAC) protocols have attracted...     

Regioselective Palladium(0)‐Catalyzed Cross‐Coupling Reactions and Metal‐Halide Exchange Reactions of Tetrabromothiophene: Optimization,Scope and Limitations

The Suzuki reaction of tetrabromothiophene with arylboronic acids provides a regioselective approach to various 5‐aryl‐2,3,4‐tribromothiophenes, symmetrical 2,5‐diaryl‐3,4‐dibromothiophenes, and tetraarylthiophenes. Unsymmetrical 2,5‐diaryl‐3,4‐dibromothiophenes are prepared by Suzuki reaction of 5‐aryl‐2,3,4‐tribromothiophenes. Tetraarylthiophenes containing two different types of aryl groups are obtained by Suzuki reactions of 2,5‐diaryl‐3,4‐dibromothiophenes. During the optimization of the conditions of each individual reaction, the solvent, the catalyst and the temperature play an important role. In several cases, classical conditions [use of tetrakis(triphenylphosphane)palladium(0), Pd(PPh₃)₄, as the catalyst] gave excellent yields. The yields of those transformations which failed or proceeded sluggishly could be significantly improved by application of a new biarylmonophosphine ligand developed by Buchwald and co‐workers. Regioselective metal‐halide exchange reactions of tetrabromothiophene provide a convenient approach to various 2,5‐disubstituted 3,4‐dibromothiophenes. 5‐Alkyl‐2‐trimethylsilyl‐3,4‐dibromothiophenes could be prepared in one pot by sequential addition of trimethylchlorosilane and alkyl bromides. The reaction of tetrabromothiophene with methyl chloroformate and subsequent Suzuki reactions afforded 3,4‐diaryl‐2,5‐bis(methoxycarbonyl)thiophenes.     

Antioxidant activity of mulberry fruit extracts

Phenolic compounds were extracted from the fruits of Morus nigra and Morus alba using methanol and acetone. The sugar-free extracts (SFEs) were prepared using Amberlite XAD-16 column chromatography. All of the SFEs exhibited antioxidant potential as determined by ABTS (0.75-1.25 mmol Trolox/g), DPPH (2,2-diphenyl-1-picrylhydrazyl) (EC(50) from 48 μg/mL to 79 μg/mL), and reducing power assays. However, a stronger activity was noted for the SFEs obtained from Morus nigra fruits. These extracts also possessed the highest contents of total phenolics: 164 mg/g (methanolic SFE) and 173 mg/g (acetonic SFE). The presence of phenolic acids and flavonoids in the extracts was confirmed using HPLC method and chlorogenic acid and rutin were found as the dominant phenolic constituents in the SFEs.     

GTHBAC: A Generalized Temporal History Based Access Control Model

Time plays a crucial role in access control for new computing environments, which is not supported in traditional access control models. In this paper, we propose a Generalized Temporal History Based Access Control (GTHBAC) model, aimed at integrating history-based constraints along with a generic access control model. GTHBAC enhances the specification of user-defined authorization rules by constraining time interval and temporal expression over users’ history of accesses. Due to different application needs, GTHBAC uses two different time schemes, i.e., real time and logical time, in its authorization rules. A formal semantics for temporal authorizations is provided, and conflicting situations are also investigated and resolved in the model. To represent the applicability of the proposed model, an architecture for an access control system based on the model is proposed, and a case of employing the model in specifying and enforcing access control policies in a banking system is studied. The operators of GTHBAC are also compared with Linear Time Temporal Logic (LTL) operators to show the expressive power of the model.     

Investigation of iron ore particle size and shape on green pellet quality

ABSTRACT

Particle size and shape of iron ore concentrate are effective parameters in the production of quality green pellets. In this research, the effect of particle morphology on green pellet quality was studied. It was concluded that pellet quality improved with increasing specific surface area. Drop number and green compression strength of pellets ground by HPGR were found to be superior over those ground in the ball mill. The chief reasons were related to particle shape and the fraction of fine particles. Smaller particle size results in a higher order of bonding between particles and therefore the formation of a stronger system. Also, the rougher and less circular shape of particles resulted in higher strength. According to the breakage model in the particle-moisture system, pellet failure occurs because of crack propagation in the solid–liquid interface. The effects of roughness on capillary force and wettability have been explained mathematically. In addition, the effects of roughness and aspect ratio on breakage path and increase of required energy for pellet failure have been modelled.     

Dielectric properties of CaCu3Ti4O12 improved by chromium/lanthanum co-doping

The dielectric properties of Cr + La co-doped CaCu₃Ti₄O₁₂ ceramics prepared by a solid-state reaction method were evaluated and compared to Cr-doped, La-doped, and parent CaCu₃Ti₄O₁₂ (CCTO). Their structure and grain size were evaluated by X-ray diffraction and scanning electron microscopy, respectively. No secondary phase was detected based on the XRD analysis. The results show that, the room temperature dielectric loss of the co-doped samples is reduced to 43% compared to CCTO and their dielectric permittivity is higher than the un-doped, Cr-doped, and La-doped samples at frequencies over 325 kHz, 30 kHz, and 12 Hz, respectively. Furthermore, the temperature stability of the co-doped sample is significantly more convenient than that of CCTO, and its dielectric loss is three times lower. The results also indicated that the co-doping method is effective in reducing the dielectric loss, still maintaining the high dielectric permittivity.     

The value of information in stochastic maximum flow problems

In this paper, we study the maximum flow problem in stochastic networks with random arc failures. We present the concept of expected value of a given flow and seek a flow whose expected value is maximum. We also introduce the concept of expected capacity of a given cut. While the expected capacity of a cut can be computed in polynomial time, we show that it is NP-hard to compute the expected value of a flow.