Synthesis of polyurethane cationomers with anil groups: intramolecular proton transfer in salicylideneanil structures

Three new o‐hydroxy Schiff bases, 2‐chloromethyl‐N‐(2‐hydroxybenzilidene)aniline, 3‐(11‐bromoundecanoyloxymethyl)‐N‐(2‐hydroxybenzilidene)aniline and 4‐chloromethylphenyl (carbamoyloxymethyl‐2‐hydroxybenzylidene)aniline, used as quaternization agents for a polyetherurethane precursor based on poly(tetramethylene oxide) diol of 2000 g mol^?1 average molar mass (PTMO), 2,4‐toluene diisocyanate and N‐methyldiethanolamine (1:3:2 molar ratio), have been synthesized in order to obtain polymeric films with fluorescent properties. The structure and the photochromic mechanism of the salicylideneanil units were investigated. The excited state intramolecular proton‐transfer process (ESIPT) with the cis‐ and trans‐keto isomers formation as intermediate compounds and the formation of a keto tautomer were evidenced by a large Stokes shifted emission (100 nm). Copyright © 2005 Society of Chemical Industry     

Log file analysis for disengagement detection in e-Learning environments

Most e-Learning systems store data about the learner’s actions in log files, which give us detailed information about learner behaviour. Data mining and machine learning techniques can give meaning to these data and provide valuable information for learning improvement. One area that is of particular importance in the design of e-Learning systems is learner motivation as it is a key factor in the quality of learning and in the prevention of attrition. One aspect of motivation is engagement, a necessary condition for effective learning. Using data mining techniques for log file analysis, our research investigates the possibility of predicting users’ level of engagement, with a focus on disengaged learners. As demonstrated previously across two different e-Learning systems, HTML-Tutor and iHelp, disengagement can be predicted by monitoring the learners’ actions (e.g. reading pages and taking test/quizzes). In this paper we present the findings of three studies that refine this prediction approach. Results from the first study show that two additional reading speed attributes can increase the accuracy of prediction. The second study suggests that distinguishing between two different patterns of disengagement (spending a long time on a page/test and browsing quickly through pages/tests) may improve prediction in some cases. The third study demonstrates the influence of exploratory behaviour on prediction, as most users at the first login familiarize themselves with the system before starting to learn.     

Mechanisms for activity spread in a neural field model

Field models of continuous neural networks incorporate nonlocal connectivities as well as finite axonal propagation velocities and lead therefore to delayed integral equations. For special choices of the synaptic footprint it is possible to reduce the integral model to a system of partial differential equations. One example is that of the inhomogeneous damped wave equation in one space dimension derived by Jirsa and Haken for exponential synaptic footprint. We show that this equation can be put into the form of a conservation law with nonlinear source, and explore numerically this representation. We find two mechanisms for the spread of the activity from an initially excited region.     

Polydimethylsiloxane/silica composites incorporating pyrite powders for actuation elements

BACKGROUND: Among polymers, elastomers can achieve very large deformations and deliver relatively high forces when an electric field is applied to them. In addition, a number of active components, such as carbon black, multi‐walled nanotubes or metallic powders, can be used to obtain increased effects. One elastomer used as a host for these active fillers is polydimethylsiloxane. RESULTS: Pyrite powders were physically incorporated in a polymeric matrix consisting of interconnected polydimethylsiloxane/silica networks. The mixtures were processed as films by casting on a Teflon substrate before crosslinking. The films thus formed were investigated from the point of view of their mechanical behaviour and were tested as active elements in an actuation system. CONCLUSION: Electromechanical tests of the polymeric membranes under investigation revealed a very good behaviour for applications in nano‐ and micro‐actuation. Some of the prepared films showed significant displacements at reasonable voltages (i.e. 56 000 nm at 460 V or 1000 nm at 6 V). Sensitivities between 2.608 and 333.33 nm V^?1 were obtained in inverse dependence on the Young's modulus values. Copyright © 2009 Society of Chemical Industry     

Evaluation of waste embankment slope stability: Valea Manastirii,Gorj, Romania

One of the largest mining waste deposits in Romania is in the Montru valley where coal has been exploited for many years. The waste embankment is 60 m high and covers an area of 6 km² . In March 2000 a large landslip occurred with lateral movement in the order of 30 to 50 m which resulted in the blocking of the River Montru. The slip surface extended downwards into the Pliocene deposits beneath the river floor. The paper describes the investigations undertaken to assess the short and long term stabilty of the waste embankment.      

Electrochemically modulated liquid-liquid extraction of ions

The development of ion extraction methods under electrochemical control via electrochemistry at the interface between two immiscible electrolyte solutions is discussed. A hydrodynamic flow injection system was used for the potentiostatic extraction of non-redox-active species from a flowing aqueous phase into a stationary organogel phase. The ions tetraethylammonium, 4-octylbenzenesulfonate (4-OBSA-), and p-toluenesulfonate (p-TSA-) were studied as model analytes. The extraction study comprised examination of the influence of extraction potentials, aqueous-phase flow rate, and target species concentration. The extraction process can be monitored in situ by means of the ion-transfer current, which has opposing signs for anions and cations. Hydrodynamic voltammograms were obtained from these experiments. The selective extraction of 4-OBSA-, from its mixture with p-TSA-, as well as coextraction of both anions is shown. The results demonstrate the utility of electrochemical modulation for the controlled extraction of ions from an aqueous phase into an organogel electrolyte phase. This offers potential benefits for various analytical processes including sample preparation and cleanup.     

Three- and four-photon absorption of a multiphoton absorbing fluorescent probe

High-order multiphoton excitation processes are becoming a reality for fluorescence imaging and phototherapy treatment because they afford minimization of scattered light losses and a reduction of unwanted linear absorption in the living organism transparency window, making them less susceptible to photodamage, while improving the irradiation penetration depth and spatial resolution. We report the four-photon-excited fluorescence emission of (7-benzothiazol-2-yl-9,-didecylfluoren-2-yl)diphenylamine in hexane and its four-photon absorption cross section sigma4' = 8.1 x 10(-109) cm8 s3 photon(-3) for the transition S0 --> S1 when excited at 1600 nm with a tunable optical parametric generator (OPG) pumped by picosecond laser pulses. When pumped at 1200 nm, three-photon absorption was observed, corresponding to the same transition.     

Improving Wireless Sensor Network Lifetime through Power Aware Organization

A critical aspect of applications with wireless sensor networks is network lifetime. Battery-powered sensors are usable as long as they can communicate captured data to a processing node. Sensing and communications consume energy, therefore judicious power management and scheduling can effectively extend operational time. To monitor a set of targets with known locations when ground access in the monitored area is prohibited, one solution is to deploy the sensors remotely, from an aircraft. The loss of precise sensor placement would then be compensated by a large sensor population density in the drop zone, that would improve the probability of target coverage. The data collected from the sensors is sent to a central node for processing. In this paper we propose an efficient method to extend the sensor network operational time by organizing the sensors into a maximal number of disjoint set covers that are activated successively. Only the sensors from the current active set are responsible for monitoring all targets and for transmitting the collected data, while nodes from all other sets are in a low-energy sleep mode. In this paper we address the maximum disjoint set covers problem and we design a heuristic that computes the sets. Theoretical analysis and performance evaluation results are presented to verify our approach.Mihaela Cardei is an Assistant Professor in the Department of Computer Science and Engineering at the Florida Atlantic University. Her research interests are in the areas of wireless networking, wireless sensor networks, algorithm and protocol design in communication networks and resource management. Mihaela Cardei received her M.S. and Ph.D. in Computer Science from the University of Minnesota in 1999 and 2003 respectively. Her Ph.D. adviser was Dr. Ding-Zhu Du. During her graduate studies, she worked with Honeywell Laboratories on the Real Time Adaptive Resource Management DARPA project. She is also a recipient of the University of Minnesota Graduate School Doctoral Dissertation Fellowship for 2002–2003.Ding-Zhu Du received his M.S. degree in 1982 from Institute of Applied Mathematics, Chinese Academy of Sciences under the supervision of Minyi Yue, and his Ph.D. degree in 1985 from the University of California at Santa Barbara under the supervision of Ronald V. Book. He worked at Mathematical Sciences Research Institute, Berkeley in 1985–86, at MIT in 1986–87, and at Princeton University in 1990–91. Currently, he is a professor at Department of Computer Science, University of Minnesota and also a research professor at Institute of Applied Mathematics, Chinese Academy of Sciences. His research interests include combinatorial optimization, communication networks, and theory of computation. He has published more than 140 journal papers and 30 books. Currently, he is the editor-in-chief of Journal of Combinatorial Optimization and book series on Network Theory and Applications. He is also in editorial boards of eight journals.     

Thermal stability of copolymer acrylamide–maleic anhydride

The thermal degradation of copolymer acrylamide–maleic anhydride prepared in various solvents (benzene, dioxane, methylethyl ketone) and different monomer ratios was investigated. The techniques of thermogravimetry (TG and DTG) and differential scanning calorimetry (DSC) were used. The IR spectra of degraded copolymers are discussed.     

Improved Method for Creating Time-Domain Unsteady Aerodynamic Models

Multidisciplinary aeroservoelastic interactions are studied by the combination of knowledge acquired in two main disciplines: aeroelasticity and servocontrols. In aeroelasticity, the doublet lattice method is used to calculate the unsteady aerodynamic forces for a range of reduced frequencies and Mach numbers on a business aircraft in the subsonic flight regime by use of NASTRAN software. For aeroservoelasticity studies, there is the need to conceive methods for these unsteady aerodynamic forces conversions from frequency into Laplace domain. A new method different from classical methods is presented, in which Chebyshev polynomials theories and their orthogonality properties are applied. In this paper, a comparison between flutter results expressed in terms of flutter speeds and frequencies obtained with our method with flutter results obtained with classical Padé and least squares methods is presented for a business aircraft at one Mach number and a range of reduced frequencies. It has been found that results obtained with our method are better in terms of average error than results obtained with the two classical methods here presented.