Fast distributed multi-hop relative time synchronization protocol and estimators for wireless sensor networks

The challenging problem of time synchronization in wireless sensor networks is considered in this paper, where a new distributed protocol is proposed for both local and multi-hop synchronization. The receiver-to-receiver paradigm is used, which has the advantage of reducing the time-critical-path and thus improving the accuracy compared to common sender-to-receiver protocols. The protocol is fully distributed and does not rely on any fixed reference. The role of the reference is divided amongst all nodes, while timestamp exchange is integrated with synchronization signals (beacons). This enables fast acquisition of timestamps that are used as samples to estimate relative synchronization parameters. An appropriate model is used to derive maximum likelihood estimators (MLE) and the Cramer-Rao lower bounds (CRLB) for both the offset-only, and the joint offset/skew estimation. The model permits to directly estimating relative parameters without using or referring to a reference’ clock. The proposed protocol is extended to multi-hop environment, where local synchronization is performed proactively and the resulted estimates are transferred to the intermediate/end-point nodes on-demand, i.e. as soon as a multi-hop communication that needs synchronization is initiated. On-demand synchronization is targeted for multi-hop synchronization instead of the always-on global synchronization model, which avoids periodic and continuous propagation of synchronization signals beyond a single-hop. Extension of local MLE estimators is proposed to derive relative multi-hop estimators. The protocol is compared by simulation to some state-of-the-art protocols, and results show much faster convergence of the proposed protocol. The difference has been on the order of more than twice compared to CS-MNS, more than ten times compared to RBS, and more than twenty times compared to TPSN. Results also show scalability of the proposed protocol concerning the multi-hop synchronization. The error does not exceed few microseconds for as much as 10 hops in R4Syn, while in CS-MNS, and TPSN, it reaches few tens of microseconds. Implementation and tests of the protocol on real sensor motes confirm microsecond level precision even in multi-hop scenarios, and high stability (long lifetime) of the skew/offset model.     

“Metakaolin‐Slag‐Clinker Blends.” The Role of Na+ or K+ as Alkaline Activators of Theses Ternary Blends

This article reports on research into the use of solid alkalis (Na₂CO₃ and K₂CO₃) as activators to obtain hybrid cement (cement whose hydration generates a mix of C–A–S–H and (N,C)–A–S–H gels) from a blend of 20% clínker + 40% blast furnace slag + 40% metakaolin. More specifically, the study aimed to determine the effect of activator dosage (5 and 8 wt%) and type of alkaline cation (Na⁺ or K⁺) on the 2‐ and 28‐d mechanical strength of the end materials. The findings showed that the highest mechanical strength values were obtained with 5% Na₂CO₃. According to the XRD, NMR, and SEM/EDX analyses conducted on the reaction products, the alkalinity and solubilized chemical species generated by adding 5% Na₂CO₃ to the system yielded a mix of (N,C)–A–S–H and C–A–S–H cementitious gels as the main reaction products. The secondary reaction products included metastable (3CaO·Al₂O₃·CaCO₃·11H₂O‐type) carboaluminates that evolved into the calcite or vaterite forms of calcium carbonate. When K₂CO₃ was used (instead of Na₂CO₃), a (3CaO·Al₂O₃·0.5Ca(OH)₂·0.5CaCO₃·11H₂O‐type) hemicarboaluminate also formed. The study also revealed that Na⁺ favors coagulation/precipitation more effectively than K⁺, generating gels with a wider range of Qⁿ species.     

Effects of repeated-dose isradipine on the abuse liability of cocaine.

Despite preclinical studies suggesting that isradipine may antagonize the abuse liability of cocaine, pretreatment with sustained-release isradipine did not reduce euphoric mood in cocaine-using volunteers. This double-blind, within-subject, crossover laboratory study determined whether maximal dose-loading with isradipine could antagonize effects of cocaine in 12 cocaine-dependent research volunteers administered intravenous cocaine doses (0, 0.325, and 0.65 mg/kg) on different days after 5 days of treatment with isradipine or placebo. Isradipine dose was 30 mg sustained release nightly plus 15 mg immediate release 2 hr before cocaine infusion. Cocaine produced dose-related increases in cocaine's subjective effects and a behavioral measure of reinforcement. Isradipine enhanced, rather than antagonized, subjective effects, indicating that isradipine does not antagonize cocaine's abuse liability in dependent research volunteers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Experimental study of pollution effect on the behavior of high voltage insulators under alternative current

In this paper, the impact of the conductivity and the distribution of pollution on the behavior of the high voltage insulator cap and pin 1512L, artificially polluted is described. An experimental model in form of a disc is proposed. This experimental model reproduces the real model which is the 1512L insulator. Besides, a comparative study is presented. For this comparative study, different solutions are adopted to s`imulate the pollution (containing NaCl+ distilled water) that has different conductivities for a discontinuous distribution of the pollution on the insulator under an AC voltage. Furthermore, the influence of the pollution on the flashover voltage and the leakage current is studied. Finally, the behavior of real and experimental model of the insulator is investigated.     

Numerical and analytical investigation of the size-dependency of the FPZ length in concrete

The main objective of this paper is to study the size effect on the fracture characteristics in concrete structures. The numerical investigation is based on a mesoscale modeling approach. Analytically, two size effect laws are investigated: the classical Ba?ant SEL and a new size effect law based on the enrichment of the stress field on the crack tip. The mesoscopic approach is used to study the evolution of the tangential stress along the crack path in order to investigate the fracture process zone variation during the cracking process. In addition, different analytical governing equations are used to evaluate the size-dependency of the FPZ length.     

Characterization of dynamic behaviour of the continuous phase in liquid fluidized bed

The dynamic behaviour of the continuous phase in liquid solid fluidized bed is characterized through velocity measurements by laser anemometry at the top of the bed. The experiments were conducted using glass particles of 2, 4 and 8 mm diameter fluidized by water. The root mean square (RMS) of axial velocity fluctuations presents a maximum value at porosity around 0.7 and increases with particle diameter. When compared to the fixed bed situation, we observe an enhancement of the agitation probably due to the added mass effect which plays the role of a turbulence promoter. The spectra analysis of the velocity time series has revealed a specific spectral dynamic of liquid fluidized bed for the higher frequency range which does neither follow strictly the Kolmogorov law nor a Brownian process power law. A time frequency-scale decomposition combined to an autocorrelation analysis of velocity signal was pertinent to capture the impact of porosity waves and cooperative movements of particles on the liquid phase dynamic, and to characterize these coherent structures by low frequency scales (below 1 Hz). The results compare well with the available data obtained directly from void propagation studies by light transmission techniques. Moreover, the high frequency scales have been found random and linked to the small scale movements of the particles. We have shown, when possible, the similarity of behaviour between the liquid and the dispersed phase dynamics through the comparison of some characteristics.     

Graphene oxide reinforced chitosan/polyvinylpyrrolidone polymer bio‐nanocomposites

Bio‐nanocomposite films based on chitosan/polyvinylpyrrolidone (CS/PVP) and graphene oxide (GO) were processed using the casting/evaporation technique. It has been found that the three components of bio‐nanocomposites can be easily mixed in controlled conditions enabling the formation of thick films with high quality, smooth surface and good flexibility. Structural and morphological characterizations showed that the GO sheets are well dispersed in the CS/PVP blend forming strong interfacial interactions that provide an enhanced load transfer between polymer chains and GO sheets thus improving their properties. It has been found that the water resistance of the CS/PVP blend is improved, and the hydrolytic degradation is limited by addition of 0.75 and 2 wt % GO. The modulus, strength, elongation and toughness of the bio‐nanocomposites are together increased. Herein, the steps to form new bio‐nanocomposite films have been described, taking the advantage of the combination of CS, PVP and GO to design the aforementioned bio‐nanocomposite films, which allow to have extraordinary properties that would have promising applications as eventual packaging materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41042.     

Antioxidant capacity and phenol content of selected Algerian medicinal plants

Extracts from the bark of Fraxinus angustifolia as well as the leaves of Pistacia lentiscus and Clematis flammula have been investigated for their reducing power, inhibition of linoleic acid peroxidation and scavenging capacity on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and H₂O₂ using in vitro spectrophotometric methods. The results indicate that the best overall antioxidant capacity was shown by extracts of Pistacia lentiscus, followed by Fraxinus angustifolia and Clematis flammula.