Charting of geoelectric potential signal dynamics via geometrical techniques and its possible relation to significant earthquakes in Western Greece

An exploratory data analysis (EDA) framework was developed in order to investigate the presence of possible correlations in the long-term geoelectric potential (LTGP) signal, prior to significant seismic events in Western Greece. Experimental data, which had been collected continuously within a 6-year period (1998–2003) at the earthquake signal-acquisition center of the University of Patras Seismological Laboratory (UPSL), were studied. The multidimensional scaling (MDS) technique was used to detect putative clustering tendencies in the ensemble of time-series (TS) segments that could indicate the existence of a possible correlation between the geoelectric signal structure and the impending seismic activity. The end result is a 2-dimensional point diagram with the geometry reflecting important signal characteristics, directly related with the underlying seismic events. In addition, the “appending technique”, a well-suited data analysis methodology was incorporated as a means of relating any other TS segment directly with the pre-computed, via the MDS, point diagram. Using the proposed EDA framework, we examined the presence of similar temporal patterns in the recorded geoelectric TS field, 10 days before the occurrence of the major earthquakes. The presented experimental results indicated clearly the validity of the introduced approach and, further, motivated the use of such advanced visualization schemes for charting precursor trends of significance seismicity.     

Adaptive Smooth Simulcast Protocol (ASSP) for Video Applications: Description and Performance Evaluation

In this paper, we present Adaptive Smooth Simulcast Protocol (ASSP) for simulcast transmission of multimedia data over best-effort networks. ASSP is a new multiple-rate protocol that implements a single rate TCP-friendly protocol as the underlying congestion control mechanism for each simulcast stream. The key attributes of ASSP are: (a) TCP-friendly behavior, (b) adaptive per-stream transmission rates, (c) adaptive scalability to large sets of receivers and (d) smooth transmission rates that are suitable for multimedia applications. We evaluate the performance of ASSP under an integrated simulation environment which combines the measurements of both network and video performance metrics. We also compare ASSP against other proposed solutions and the results demonstrate that the performance of ASSP is significantly better than the tested solutions. Finally, ASSP is a practical solution with very low implementation complexity for video transmission over best-effort networks.     

On the efficiency of user identification: a system-based approach

In the Internet era, users’ fundamental privacy and anonymity rights have received significant research and regulatory attention. This is not only a result of the exponential growth of data that users generate when accomplishing their daily task by means of computing devices with advanced capabilities, but also because of inherent data properties that allow them to be linked with a real or soft identity. Service providers exploit these facts for user monitoring and identification, albeit impacting users’ anonymity, based mainly on personal identifiable information or on sensors that generate unique data to provide personalized services. In this paper, we report on the feasibility of user identification using general system features like memory, CPU and network data, as provided by the underlying operating system. We provide a general framework based on supervised machine learning algorithms both for distinguishing users and informing them about their anonymity exposure. We conduct a series of experiments to collect trial datasets for users’ engagement on a shared computing platform. We evaluate various well-known classifiers in terms of their effectiveness in distinguishing users, and we perform a sensitivity analysis of their configuration setup to discover optimal settings under diverse conditions. Furthermore, we examine the bounds of sampling data to eliminate the chances of user identification and thus promote anonymity. Overall results show that under certain configurations users’ anonymity can be preserved, while in other cases users’ identification can be inferred with high accuracy, without relying on personal identifiable information.     

Performance evaluation of ad hoc routing protocols for military communications

Mobile ad hoc networks (MANETs) are of much interest to both the research community and the military because of the potential to establish a communication network in any situation that involves emergencies. Examples are search‐and‐rescue operations, military deployment in hostile environments, and several types of police operations. One critical open issue is how to route messages considering the characteristics of these networks. The nodes act as routers in an environment without a fixed infrastructure, the nodes are mobile, the wireless medium has its own limitations compared to wired networks, and existing routing protocols cannot be employed, at least without modifications. Over the last few years, a number of routing protocols have been proposed and enhanced to address the issue of routing in MANETs. It is not clear how those different protocols perform under different environments. One protocol may be the best in one network configuration but the worst in another. This article provides an analysis and performance evaluation of those protocols that may be suitable for military communications. The evaluation is conducted in two phases. In the first phase, we compare the protocols based on qualitative metrics to locate those that may fit our evaluation criteria. In the second phase, we evaluate the selected protocols from the first phase based on quantitative metrics in a mobility scenario that reflects tactical military movements. The results disclose that there is no routing protocol in the current stage without modifications that can provide efficient routing to any size of network, regardless of the number of nodes and the network load and mobility. Copyright © 2011 John Wiley & Sons, Ltd.     

ON THE DYNAMIC PROPERTIES OF THE EXTENSIVE VARIABLE CONTROL STRUCTURES

The purpose of this paper is to investigate the dynamic properties of controller structures synthesized using extensive thermodynamic variables of a process. Several state-space and frequency domain multivariable techniques, including INA, and Modal Interaction Analysis, are used in order to evaluate the dynamic properties of these control structures. These structures show zero steady state interaction and minimal dynamic interaction for all processes examined. Dynamic simulation of several application examples, including distillation columns and a network of two stirred tank heaters in series, shows that the loops in these structures can also be tuned with minimum effort. Comparison of the proposed structures, with the conventional parallel single-input single-output control structures, shows the advantages of the proposed method.     

Ethylene epoxidation on Ag catalysts supported on non-porous, microporous and mesoporous silicates

The ethylene epoxidation activity of Ag catalysts supported on non-porous SiO₂, microporous silicalite zeolite and mesoporous MCM-41 and HMS silicates was investigated in the present study in comparison to conventional low surface area -Al₂O₃ based catalysts. The MCM-41 and HMS based catalysts exhibited similar ethylene conversion activity and ethylene oxide (EO) selectivity with the SiO₂ and -Al₂O₃ based catalysts at relatively lower temperatures (up to 230 °C), whereas their activity and selectivity decreased significantly at higher temperatures (≥300 °C). The silicalite based catalyst was highly active for a wide temperature range, similar to the SiO₂ and -Al₂O₃ based catalysts, but it was the less selective amongst all catalysts tested. High loadings of Ag particles (up to ca. 40 wt.%) with medium crystallites size (20–55 nm) could be achieved on the mesoporous materials resulting in very active epoxidation catalysts. The HMS-type silicate with the 3D network of wormhole-like framework mesopores (with average diameter of 3.5 nm), in combination with a high-textural (interparticle) porosity, appeared to be the most promising mesoporous support.     

Soil wettability as determined from using low-field nuclear magnetic resonance

The molarity of ethanol droplet and water drop penetration time methods are commonly used to determine soil wettability because these tests are quick and easy to perform. However, these tests do not provide reproducible results on the same sample. Low-field nuclear magnetic resonance (NMR) is shown as an alternative tool to determine soil wettability. Addition of small amounts of water in dry wettable porous media produces predominant amplitude peaks at transverse relaxation times (T2) of 100 ms or less while addition of water in dry water-repellent porous media with the same pore structure produce predominant amplitude peaks at T2 values near 1000 ms. The geometric mean of T2 (T(2gm)) from water-repellent samples immediately after the addition of water is greater than 1000 ms, which is close to that of bulk water, while T(2gm) from wettable samples immediately after the addition of water is significantly less than 1000 ms. Measurements over time show that water-repellent samples eventually reach the same equilibrium end point as its corresponding wettable sample when continually exposed to water. This paper will show that NMR can be used to formulate a screening criterion for quickly determining wettability. The advantage of using NMR is that the results are reproducible provided the sample is prepared and analyzed in a systematic manner.