Antisolvent precipitation of hydrophobic functionalized multiwall carbon nanotubes in an aqueous environment

The possibility of antisolvent precipitation of hydrophobic, organic soluble functionalized carbon nanotubes (f-CNTs), where water acts as an antisolvent is presented. Octadecylamine functionalized multiwall carbon nanotubes (MWCNT-ODA) was used as the model compound and was found to form highly stable dispersions in different water/solvent systems, and the particle sizes ranged from 170 to 400 nm. Colloidal behavior was studied using dynamic light scattering and particle aggregation was found to increase with the addition of electrolytes, with tetrahydrofuran (THF) and ethanol showing the maximum effect. The aggregation behavior of the antisolvent precipitated system did not follow the conventional Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, which was different from what has been reported previously for hydrophilic, water soluble f-CNTs. Based on this study, it is evident that hydrophobic f-CNTs are potential water pollutants.     

Recognizing articulatory gestures from speech for robust speech recognition

Studies have shown that supplementary articulatory information can help to improve the recognition rate of automatic speech recognition systems. Unfortunately, articulatory information is not directly observable, necessitating its estimation from the speech signal. This study describes a system that recognizes articulatory gestures from speech, and uses the recognized gestures in a speech recognition system. Recognizing gestures for a given utterance involves recovering the set of underlying gestural activations and their associated dynamic parameters. This paper proposes a neural network architecture for recognizing articulatory gestures from speech and presents ways to incorporate articulatory gestures for a digit recognition task. The lack of natural speech database containing gestural information prompted us to use three stages of evaluation. First, the proposed gestural annotation architecture was tested on a synthetic speech dataset, which showed that the use of estimated tract-variable-time-functions improved gesture recognition performance. In the second stage, gesture-recognition models were applied to natural speech waveforms and word recognition experiments revealed that the recognized gestures can improve the noise-robustness of a word recognition system. In the final stage, a gesture-based Dynamic Bayesian Network was trained and the results indicate that incorporating gestural information can improve word recognition performance compared to acoustic-only systems.     

Effect of Nb and Cr incorporation on the structural and magnetic properties of rapidly quenched FeCoSiB microwires

Rapidly quenched microwires with a nominal composition of Fe₃₉Co₃₉Si₈B₁₄ (#A_O), Fe₃₇Co₃₇Nb₄Si₈B₁₄ (#A_N) and Fe₃₆Co₃₆Nb₄Cr₂Si₈B₁₄ (#A_NC) have been investigated. Devitrification of as-quenched microwires showed that crystallization temperatures increased with simultaneous incorporation of Nb and Cr as in #A_NC alloy. Addition of these elements also contributed to an increase in activation energy in #A_N and #A_NC alloys. Nb addition reduced the particle size, which became much finer in the case of the Cr-containing alloy. Although Nb addition did not have much effect on lowering the Curie temperature T_C of the amorphous phase, Cr substitution lowered T_C to 698 K from high values of 785 K and 787 K observed in the #A_O and #A_NC alloys, respectively. However, the Cr addition revealed a better Giant magneto-impedance (GMI) response compared to the other alloys. Such improved GMI properties in the Cr-containing alloy are attributed to lower values of the coercivity and magnetostriction in the alloy containing both Nb and Cr.     

Multiferroic properties of NiS nanoplates grown within Na-4 mica

Nanoplates of NiS with thickness 0.6 nm were grown within the crystal channels of Na-4 mica. The thickness of the nanoplates is confirmed by atomic force microscopy. The nanocomposites exhibited multiferroic (both ferromagnetic and ferroelectric) behavior at room temperature. Ferromagnetism was adduced to an increase of surface defects as a result of the two-dimensional configuration of the sample. Ferroelectric behavior was explained as arising due to a small distortion in the crystal structure of NiS grown within the Na-4 mica channels. This was substantiated by the refined values of lattice constants as determined by profile matching of X-ray data by a computer program. A magnetodielectric effect was also observed in this nanocomposite with a change of 0.77% in the dielectric constant for a magnetic field of 0.6 T.     

Two-potential theory of electric and magnetic charges via duality transformation

Dirac, Schwinger and Zwanziger theories of electric and magnetic charges are obtained via duality transformation. Analogous construction for three Euclidean dimensions, with magnetic charges interacting with electric currents, is also done. The role of Dirac strings as dislocations in the configurations of gauge potential is emphasized.     

Approximate controllability results for viscoelastic flows with infinitely many relaxation modes

We prove results on approximate controllability for linear viscoelastic flows, with a localized distributed control in the momentum balance equation. The constitutive law is a multimode Maxwell or Jeffreys model with an infinite number of relaxation modes.     

Dynamic admission and service rate control of a queue

This paper investigates a queueing system in which the controller can perform admission and service rate control. In particular, we examine a single-server queueing system with Poisson arrivals and exponentially distributed services with adjustable rates. At each decision epoch the controller may adjust the service rate. Also, the controller can reject incoming customers as they arrive. The objective is to minimize long-run average costs which include: a holding cost, which is a non-decreasing function of the number of jobs in the system; a service rate cost c(x), representing the cost per unit time for servicing jobs at rate x; and a rejection cost κ for rejecting a single job. From basic principles, we derive a simple, efficient algorithm for computing the optimal policy. Our algorithm also provides an easily computable bound on the optimality gap at every step. Finally, we demonstrate that, in the class of stationary policies, deterministic stationary policies are optimal for this problem.     

Regime switching volatility calibration by the Baum-Welch method

Regime switching volatility models provide a tractable method of modelling stochastic volatility. Currently the most popular method of regime switching calibration is the Hamilton filter. We propose using the Baum-Welch algorithm, an established technique from Engineering, to calibrate regime switching models instead. We demonstrate the Baum-Welch algorithm and discuss the significant advantages that it provides compared to the Hamilton filter. We provide computational results of calibrating and comparing the performance of the Baum-Welch and the Hamilton filter to S&P 500 and Nikkei 225 data, examining their performance in and out of sample.     

Nuclear magnetic resonance of paramagnetic metalloporphyrins

The present article reviews and discusses proton magnetic resonance studies on metalloporphyrins which provide good models for heme proteins in their physical and chemical properties. Emphasis is given on the discussion of the₁Hnmr work done in our laboratory.