Thermo acoustic and spectral investigations of charge transfer interaction between aromatic amine and ketones

Ultrasonic velocity (u), density (ρ) and coefficient of viscosity (η) were measured for ternary mixtures containing aniline (ANI) as common component and acetophenone (ACP), 4-chloroactophenone (ClACP) and 4-methylacetophenone (MACP) as other components in n-hexane medium in the concentration range 0.025-0.2 M. The measurements were made at four different temperatures, namely, 293, 298, 303 and 308 K and at atmospheric pressure. The experimental results have been used to calculate various acoustical parameters and excess parameters. The trend in these parameters with concentration establishes that (i) strong intermolecular interactions exist in these mixtures and (ii) formation of charge transfer complexes through hydrogen bonding between primary amine and aromatic ketones. The formation of complexes has also been confirmed by optical spectroscopy at 303 K. The formation constants of the charge transfer complexes determined using Benesi-Hildebrand equation (spectroscopic method) are comparable with those obtained using Kannappan equation (ultrasonic method). It is observed that the stability of the complexes is influenced by the structure of the component molecules. In order to assess the thermodynamic stability of the complexes, free energy of formation (ΔG), enthalpy of formation (ΔH) and entropy changes (ΔS) are computed.     

Practical packet combining for use with cooperative and non-cooperative ARQ schemes in resource-constrained wireless sensor networks

An improved implementation of a post-detection packet combining scheme, which is especially applicable to low power, resource-constrained sensor networks, is developed and practically implemented on popular off-the-shelf wireless motes. The algorithm can be used as part of protocols such as cooperative communications and hybrid-ARQ schemes which have been shown to be of major benefit for wireless communications. Using the packet combining implementation developed in this paper more than an 85% reduction in energy costs are possible over previous, similar approaches. Both simulated and practical experiments are developed in which packet combining is shown to offer up to approximately 2.5 dB reduction in the required Signal-to-Noise Ratio (SNR) for a desired Packet Error Rate (PER). This is a welcome result as complex schemes, such as maximal-ratio combining, are not implementable on many of the resource constrained devices under consideration.     

Theoretic analysis of unique localization for wireless sensor networks

Node self-localization has become an essential requirement for realistic applications over wireless sensor networks (WSNs). Although many distributed localization algorithms have been proposed, fundamental theoretic analysis of unique localization is still in its early stage of development. This paper aims at a synthetic and homogeneous survey of the theoretical basis on WSN localization problem carried out thus far. Specifically, subsequent to establishing a technological context of relevant terms, we construct a graph and then a formation for each WSN to present current state-of-the-art by analyzing possible conditions for unique localization, as well as corresponding verification algorithms, by drawing on the powerful results from rigidity theory, distance geometry, geometric constraints in CAD, and combinatorial theory. We show that the unique localization problem is well understood in two-dimension, however, only partial analogous results are available in three-dimension.     

MrFair: Misbehavior-resistant fair scheduling in wireless mesh networks

It is a critical issue to ensure that nodes and/or flows have fair access to the network bandwidth in wireless mesh networks (WMNs). However, current WMNs based on IEEE 802.11 exhibit severe unfairness. Several scheduling schemes have been proposed to ensure fairness in WMNs. Unfortunately, all of them implicitly trust nodes in the network, and thus are vulnerable to the misbehavior of nodes participating in scheduling. In this paper, we address the threats to fair scheduling in WMNs resulting from node misbehavior and present a generic verification framework to detect such misbehavior. Moreover, we develop two verification schemes based on this framework for distributed and centralized authentication environments, respectively. We validate our approach by extending an existing fair scheduling scheme and evaluating it through simulation. The results show that our approach improves misbehavior detection with light performance overhead.     

EMLTrust: An enhanced Machine Learning based Reputation System for MANETs

Many mission critical networks including MANETs for military communications and disaster relief communications rely on node cooperation. If malicious nodes gain access to such networks they can easily launch attacks, such as spreading viruses or spam, or attacking known vulnerabilities. One way to defend against malicious nodes is to use Reputation Systems (RS) that try to predict future behavior of nodes by observing their past behavior. In this paper, we propose a Machine Learning (ML) based RS that defends against many patterns of attacks. We specifically consider the proposed RS in the context of MANETs.After introducing a basic RS, we propose further enhancements to it to improve its performance and to deal with some of the more challenging aspects of MANETs. For instance, we consider digital signature based mechanisms that do not require trusted third parties, or servers that are always online. Another enhancement uses an algorithm called Fading Memories that allows us to look back at longer histories using fewer features. Finally, we introduce a new technique, called Dynamic Thresholds, to improve accuracies even further. We compare the performance of our RS with another RS found in the literature, called TrustGuard, and perform detailed evaluations against a variety of attacks. The results show that our RS significantly outperforms TrustGuard, even when the proportion of malicious nodes in the network is high. We also show that our scheme has very low bandwidth and computation overhead. In contrast to existing RSs designed to detect specific attacks, ML based RSs can be retrained to detect new attack patterns as well.     

Distributed detection of mobile malicious node attacks in wireless sensor networks

In wireless sensor networks, sensor nodes are usually fixed to their locations after deployment. However, an attacker who compromises a subset of the nodes does not need to abide by the same limitation. If the attacker moves his compromised nodes to multiple locations in the network, such as by employing simple robotic platforms or moving the nodes by hand, he can evade schemes that attempt to use location to find the source of attacks. In performing DDoS and false data injection attacks, he takes advantage of diversifying the attack paths with mobile malicious nodes to prevent network-level defenses. For attacks that disrupt or undermine network protocols like routing and clustering, moving the misbehaving nodes prevents them from being easily identified and blocked. Thus, mobile malicious node attacks are very dangerous and need to be detected as soon as possible to minimize the damage they can cause. In this paper, we are the first to identify the problem of mobile malicious node attacks, and we describe the limitations of various naive measures that might be used to stop them. To overcome these limitations, we propose a scheme for distributed detection of mobile malicious node attacks in static sensor networks. The key idea of this scheme is to apply sequential hypothesis testing to discover nodes that are silent for unusually many time periods—such nodes are likely to be moving—and block them from communicating. By performing all detection and blocking locally, we keep energy consumption overhead to a minimum and keep the cost of false positives low. Through analysis and simulation, we show that our proposed scheme achieves fast, effective, and robust mobile malicious node detection capability with reasonable overhead.     

Quantitative analysis of the hidden terminal problem in preamble sampling WSNs

Collisions in preamble sampling WSNs cause a high waste of resources due to the mandatory transmission of a long preamble before every message. Moreover, when hidden terminals are present, collisions are even more noticeable since the vulnerability time is proportional to the long preamble duration. This effect reduces considerably the network performance as both the number of collisions and the resources spent in them are significant. The effects of hidden nodes in preamble sampling WSNs, in different case scenarios and under variable offered loads, are analyzed in this work. Results show that the impact of hidden terminals in the network performance is non-negligible, specially at medium to high loads. These results should be considered by MAC protocol designers in order to devise mechanisms to mitigate the hidden terminal problem.     

Certified reference materials for analytical mercury speciation in biological and environmental matrices: Do they meet user needs?; a review

The usefulness of a certified reference material (CRM) for analytical method validation and quality control purposes is attributed mainly to its key properties, namely homogeneity and stability. However, it is also advisable to select suitable CRMs in terms of representativeness. To assess the representativeness of a CRM for analytical mercury speciation, a number of aspects must be considered in regard to the routine samples analyzed: the origin of the matrix, the type of mercury species and the level of concentration.     

Photostability of sunscreens

Sunscreens were originally designed to include mainly UVB-filters. Because of the deeper penetration of UVA light, causing photoaging and DNA damage, there has been a shift towards broad spectrum sunscreens. These broad spectrum sunscreens now include both UVA- and UVB-filters and other ingredients which possess antioxidant activity. Although sunscreens are regulated in most countries, photostability testing is not mandatory. Because of the ability of sunscreen ingredients to absorb UV-light and the complexity of most of these formulations, which may include more than one UV-filter, antioxidants and other formulation excipients, it is important that their photostability in combination is determined.